Picornaviridae

 

  

 

Image:www.lasvacunas.org/enfermedades/poliomielitis.asp

Image: www.qub.ac.uk/afs/vs/vsd6e.html

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Created by Emily Flynn ~ Created February 4, 2004, Last Modified March 14, 2004 ~ contact: eflynn@stanford.edu

 

 

 

 
This viral webpage was created for a Stanford University course:

 

 

Follow the “Student Web Pages” link to view webpages from:

 
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For more general information:

 

 

 

Contents of this webpage:

 

  • Introduction to Picornaviridae

             Epidemiology

             Incubation & Pathogenesis

             Clinical Presentation

             Treatment & Prevention

             Epidemiology

             Incubation & Pathogenesis

             Clinical Presentation

                   Treatment & Prevention

 

 

Introduction

 

Though picornaviruses are named for their small (“pico” + “RNA” = picorna) size, they include a large and diverse array of viruses – over 200 serotypes.  These viruses can be traced all the way back to Ancient Egyptian records of polio epidemics, but are still around and cause a menagerie of diseases today, from polio to hepatitis A to the “common cold.”

 

Į    Picornaviruses contain positive sense, single-stranded RNA that is approximately 7-8 kilobases long. 

 

Į    The genome is monopartite  and polyadenylated at the 3’ end, but has a VPg protein at the 5’ end in place of a cap. 

 

Į    The viral RNA is infectious and replication takes place in the cytoplasm. 

 

Į    The virus has an IRES (Internal Ribosomal Entry Site) which distinguishes it from many other RNA viruses. 

 

Į    The virus is naked with an icosahedral capsid. 

 

Į    The triangulation number is 3, while the capsid has four unique proteins: VP1, 2, 3, and 4.

 

Į    The capsid is one of the smallest of all viruses with a diameter of only 27-30nm.

 

Į    Translation and cleavage of viral polypeptides produces eleven distinct proteins.

 

 

 

 

There are four picornavirus genera that cause human disease:

 

Į   Enteroviruses

Į   Rhinoviruses

Į   Hepatovirus

Į   Parechoviruses

 

 

Į    Enteroviruses (more than 60 known serotypes):

 

Š      Poliovirus 1-3

Š      Coxsackie A1-24

Š      Coxsackie B1-5

Š      ECHOvirus 1-7, 9, 11-21, 24-27, 29-33

Š      Enterovirus 68-71

Š      Viluisk human encephalomyelitis virus

 

v    Enteroviruses are transmitted through the fecal-oral route and are highly communicable.  Generally, viral shedding persists long after symptoms cease so that transmission occurs frequently, particularly in schools, childcare centers, and with close contact.  Enteroviruses cause a wide variety of syndromes that range in severity from mild and non-neurologic to neurologic, paralytic, and fatal:

 

Š      Assorted enteroviral exanthems (rashes)

Š      Acute hemorrhagic conjunctivitis (AHC)

Š      Hand, foot, and mouth disease

Š      Poliomyelitis

Š      Encephalitis

Š      Summer colds

Š      Herpangina

Š      Myocarditis

Š      Pericarditis

Š      Meningitis

Š      Pleurodynia

Š      Myalgia

 

For more information on poliomyelitis, see the Polio Viral Profile below.

 

Į    Rhinoviruses (more than 100 known serotypes):

 

v    Rhinoviruses are transmitted through the respiratory route and replicate in the nose (“rhino”).  The many serotypes are divided into “major” and “minor” groups and all cause a similar syndrome – the “common cold.”  The large number of serotypes allows many rhinovirus infections to occur in one person over time, since immunity only develops for one serotype and each newly acquired rhinovirus causes a new “cold.”  About half of all colds can be attributed to rhinoviruses, particularly those that occur in the winter.

 

Į    Hepatovirus (one serotype):

 

v    Hepatovirus is the lone virus in its own genus.  The virus is transmitted through the fecal-oral route, which is manifested most often by ingestion of contaminated food or water.  The resulting disease is hepatitis A.  For more information, see the Hepatitis A Viral Profile below.

 

Į    Parechovirus (two serotypes):

 

v    Parechoviruses are limited to two serotypes of human parechovirus, formerly known as echovirus 22 and 23.  These viruses are closely related to the ECHOvirus group, a name that refers to Enteric Cytopathic Human Orphan virus.  Neither the ECHOviruses nor the Parechoviruses are now considered orphan viruses, but the name remains unchanged.

 

Sources:

 

  1. D. M. Knipe, P. M. Howley, D. E. Griffin, R. A. Lamb, M. A. Martin, B. Roizman and S. E. Straus, Eds .  Fields Virology, Fourth Edition, Volumes 1 and 2.  Lippincott Williams and Wilkins, Philadelphia (2001)

 

  1. Ryan, Kenneth, and Ray, C. George, Sherris Medical Microbiology, 4th Edition, McGraw-Hill, 2004, pp 541.

 

 

 

 

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Polio Virus Profile

 

 

Poliomyelitis (commonly known as “polio”) is an infectious disease caused by polioviruses 1, 2, and 3 in the enterovirus genus of the picornaviridae viral family.  From a public health standpoint, it is the most important of the enteroviruses.  Like all enteroviruses, poliovirus is transmitted through the fecal-oral route, either directly from person-to-person or indirectly through contaminated water sources.  It is characterized by permanent paralysis due to spinal nerve damage and muscular wasting, particularly in young children who are most commonly affected.

 

 

Polio EPIDEMIOLOGY

 

Poliovirus has been a primary subject of medical research and public health intervention for most of the 20th century, as it continues to devastate communities worldwide.  Though the summer epidemics of the 1940s and 1950s caused panic and widespread paralysis in the United States and Western Europe, polio has since become more of a concern in less developed countries.  Since it can be transmitted both indirectly though contaminated food and water and directly from person-to-person, polio prevalence is highest in countries with poor sanitation and among children who generally have poor hygiene practices.  Indeed, two thirds of cases occur in children under age 9 and nearly all cases occur in less developed countries.  As development improves sanitary conditions in these countries, polio incidence drops significantly.  As children are not exposed to the virus during childhood, adults may become infected when exposed at an older age.  These adult cases carry a much higher risk of paralytic poliomyelitis, which is a serious concern that accompanies the positive trends in polio reduction.

 

Currently, there are only a handful countries in which polio is endemic (countries which have not successfully eliminated the virus).  India, Pakistan, and Nigeria have 98 percent of polio cases in the world, with particular regions most affected: Uttar Pradesh and Bihar in India, North West Frontier Province in Pakistan, and Kano in Nigeria.  Egypt, Niger, and Afganistan are also endemic.  At the time of the World Health Assembly in 1988, there were more than 125 countries with significant poliovirus prevalence which paralyzed more than 1000 children every day.  At the end of 2003, reports indicated that there were only 677 cases during the whole year – a reduction of 99 percent from 1988.  This reduction is due to improvements in sanitary conditions in combination with widespread vaccination efforts.  By 1993, wild poliovirus was eliminated from the Western Hemisphere and many parts of the world:

 

 

 

 

Images: WHO Polio Eradication: http://www.polioeradication.org/vaccines/polioeradication/all/global/default.asp

 

 

 

Polio INCUBATION & PATHOGENESIS

 

Poliovirus enters the body orally and makes its way to the upper gastrointestinal tract where it replicates in the epithelial and lymphoid tissues.  The incubation period between infection and clinical presentation may last anywhere from 4-35 days, though it usually lasts 7-14 days.  Once the virus reaches the gastrointestinal tract, it can spread to other locations in the body, including the central nervous system.  Poliovirus’ unique ability to cross the blood-brain barrier allows it to travel to the peripheral spinal nerves – the axons and perineural sheaths.  Anterior motor neurons are particularly vulnerable to infection.  Viral infection induces an inflammatory response that can cause extensive neural destruction.  This destruction is irreparable and often leads to paralysis and muscular wasting.  After clinical symptoms cease, the virus may persist in the body for up to four weeks.

 

 

Polio CLINICAL PRESENTATION

 

Though polio infection can be devastating in its paralytic form, 9 out of 10 infections are actually asymptomatic or have symptoms that are too mild to be noticed.  There are three types of disease caused by poliovirus:

 

Š      Abortive poliomyelitis: a non-specific febrile illness that lasts for 2-3 days without central nervous system involvement; has complete recovery.

 

Š      Aseptic meningitis: a non-paralytic poliomyelitis that includes irritation of the meninges (back pain, neck stiffness), in addition to signs of abortive poliomyelitis, has complete recovery.

 

Š      Paralytic poliomyelitis: a rare disease that occurs in less than 2% of infections; it often begins with minor illness that appears to improve but then results in asymmetric flacid paralysis.  In the most severe cases, all four limbs may be paralyzed or the brainstem may be damaged with cranial nerve paralysis and respiratory muscle damage.  Recovery may begin within a few days and can last six months, at which point the remaining paralysis is permanent.

 

The disease of greatest concern is paralytic poliomyelitis, since it can be permanently debilitating.  Generally, acute flaccid (floppy) paralysis of the legs is more common than the arms.  In some cases, more extensive paralysis results and can reach muscles of the trunk and result in quadriplegia.  Bulbar polio is the most severe form of paralysis that reaches the brainstem and can impair breathing, speaking, and swallowing capacity.  Death by asphyxiation is possible in such severe cases.

 

Post-polio syndrome (PPS) is a condition that occurs in 25-40 percent of polio survivors from 30-40 years after initial polio disease.  Muscles that were damaged in the initial infection may become weaker and symptoms such as fatigue, joint pain and in some cases forms of scoliosis may occur.  Some patients may even develop symptoms that resemble Lou Gehrig’s disease (amyotropic lateral sclerosis – ALS).  Post-polio syndrome is not usually life-threatening and does not involve infectious virus.

 

Source: The Pink Book, 8th Edition, pp 90.

 

 

 

 

Polio TREATMENT AND PREVENTION

 

 

 

Image: http://www.unicef.org/immunization/index.html

 

 

            Treatment for poliovirus infection is non-specific and targets alleviation of symptoms only, since no effective antiviral treatment is currently available.  One anti-picornal drug, pleconaril, is currently being studied and has been delayed in clinical trials (see “Drug Profile” section for more information).  In symptomatic cases, moist heat and physical therapy can help to stimulate and relax muscles to improve patient comfort.  When paralysis occurs, it is almost always permanent, since motor nerve damage cannot be repaired.  There are cases such as that of runner Wilma Rudolf in which wasted muscles might be strengthened with additional stimulation, but recovery is extremely rare.  Most paralytic patients lose function of one or more limbs and often use crutches to assist with walking and daily tasks.

 

Prevention of poliovirus infection is possible with improvements in sanitary conditions and with immunization.  Because poliovirus is often transmitted through water sources, efforts to improve sewage treatment and to ensure a clean water supply have had very positive effects in reducing polio prevalence in less developed countries, along with reductions in many other illnesses.  However, more intervention is required since the virus can also be transmitted from person-to-person and can then spread rapidly where there is no immunity.

 

            Prevention of polio through immunization has been proven to be tremendously successful in reducing polio incidence for the past 40 years.  Development of the inactivated Salk vaccine in 1955 and the live attenuated Sabin vaccine in 1963 dramatically changed the face of the polio panic that engulfed the United States in the preceding decades.  While both vaccines are effective in preventing most poliovirus infections, they differ in some characteristics:

 

Š      The Salk Vaccine

o      Known as “IPV,” inactivated

o      Contains all 3 viral serotypes

o      Given in 3 subcutaneous injections

o      Has no serious side effects

o      Induces antibody response in 98 percent of recipients

o      Standard childhood vaccine in the United States and most developed countries

 

Š      The Sabin Vaccine

o      Known as “OPV,” live attenuated

o      Contains all 3 viral serotypes

o      Given in 3 oral doses

o      Induces antibody response in 95 percent of recipients

o      Boosters required to maintain antibody levels

o      Small risk of vaccine-associated paralytic poliomyelitis (VAPP) in 1 out of every 2.4 million doses, higher risk with immunodeficiency

o      Can lead to herd immunization

o      No longer used in the United States since 1999

o      Used frequently in less developed countries, easier to administer because it does not require injection by needle.

 

Vaccine-associated paralytic poliomyelitis (VAPP) is a concern with administration of the Sabin vaccine and has motivated many countries (including the United States) to use only the Salk vaccine.  This paralytic disease occurs when the live attenuated virus in OPV reverts or mutates to a more neurotropic form and causes permanent neural damage.  VAPP cases comprised the great majority of polio cases in the United States for many years:

 

            Global polio eradication efforts have been largely successful in eliminating wild poliovirus from most countries and even continents.  In 1988, the World Health Organization set a goal to eradicate polio from the world by 2000 in cooperation with The Global Polio Eradication Initiative (GPEI), Rotary International, the U.S. Centers for Disease Control, UNICEF, and over 200 national governments.  It has been one of the world’s largest public health initiatives and has immunized over 2 billion children and has cost US$ 3 billion since it began.

 

 

Source: The Pink Book, 8th Edition, pp 98.

 

 

Sources:

 

  1. End of Polio Campaign: http://www.endofpolio.org/home.html

 

  1. National Institute of Neurological Disorders and Stroke: Post-Polio Syndrome Fact Sheet.  http://www.ninds.nih.gov/health_and_medical/pubs/post-polio.htm

 

  1. Ryan, Kenneth, and Ray, C. George, Sherris Medical Microbiology, 4th Edition, McGraw-Hill, 2004, pp 532.

 

  1. The Pink Book, 8th Edition.  Poliomyelitis.  Pp 88-100. 

 

  1. WHO: Polio Eradication, Background: The Disease and Virus. http://www.polioeradication.org/all/background/disease.asp

 

  1. WHO: “Now more than ever: Stop Polio Forever,” Global Status and Progress. http://www.polioeradication.org/vaccines/polioeradication/all/news/20040115bpress.htm

 

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Hepatitis A Viral Profile

 

 

The hepatitis A virus occupies its own Hepatovirus genus of the Picornaviridae viral family.  It is one of two hepatitis viruses that is transmitted through the fecal-oral route and most often travels from person-to-person through contaminated water or food.  Though its symptoms are usually mild and self-limited, this virus infects over 90 percent of the population in many less developed countries where clean water and sanitation are lacking, and is therefore a major public health concern.

 

 

Hepatitis A EPIDEMIOLOGY

 

Hepatitis A is a disease that affects both adults and children worldwide.  It occurs most frequently in less developed countries or countries in transition where water and sanitation systems are often contaminated.  In such countries, it affects communities of lower socio-economic status where people may live in more crowded conditions and without access to clean water sources.  More than 90 percent of the population may show evidence of previous infection, and is therefore immune to further infection.  In these countries, most hepatitis A infection occurs during childhood and is usually asymptomatic.  International travelers are at increased risk, since they often are not immune, and vaccination is recommended.

 

Hepatitis A causes disease in more developed countries as well, particularly under crowded conditions, as in child-care centers, residential living centers, and residential hospitals.  Outbreaks may occur, but are difficult to trace to specific sources.  In the United States, as many as 35,000 people have been infected in outbreaks, sometimes linked to contaminated shellfish or vegetables exposed to contaminated water.  Only about one third of the population has immunity due to previous infections.   Transmission can also occur directly from person-to-person through close contact.  Men who have sex with men, drug users, people with chronic liver disease, and people with clotting factor disorders are at increased risk.  With improving sanitation and wide vaccination initiatives, hepatitis A incidence has been decreasing since the 1970s.

 

 

Hepatitis A Cases in the United States:

Source: http://www.cdc.gov/ncidod/diseases/hepatitis/a/vax/index.htm

 

 

 

Hepatitis A INCUBATION & PATHOGENESIS

     
            Once the virus enters the body, it begins to replicate in the enteric mucosa, then in the intestine, and eventually in the liver during the viremic phase.  Once in the liver, the virus infiltrates lymphoid cells and causes necrosis of parenchymal cells depending on the severity of infection.  This liver infection is responsible for many of the symptoms of infection.  Patients are most contagious one or two weeks before symptoms appear, during which time virus can also be detected in fecal samples.

 

 

Hepatitis A CLINICAL PRESENTATION

 

Hepatitis A infection causes clinical symptoms in about half of infected adults.  It is more than five times more likely to be symptomatic in adults than children, so most children have asymptomatic infection.  Presentation of clinical symptoms begins quickly after incubation with fever, nausea, diarrhea, loss of appetite, and abdominal pain.  Some with acute infection present with jaundice within 2-3 days of clinical onset, due to elevated serum bilirubin and aminotransferase levels resulting from liver swelling and damage.  Jaundice is a common sign of most hepatitides.  This liver malfunction causes stools to be reddish and urine to be dark before jaundice becomes evident in the skin.  Clinical disease may last days or sometimes weeks, but 99 percent of cases are self-limiting and leave no lasting damage.  Fewer than one sixth of people have relapse of mild symptoms over a period of 6-9 months.  In very rare cases (0.01%), severe liver necrosis may occur, which can lead to fulminant disease that can also cause death. 

 

 

Hepatitis A TREATMENT AND PREVENTION

 

Treatment of acute hepatitis A is non-specific and targets alleviation of symptoms only.  Nutritious foods and adequate rest are recommended until symptoms improve, which they almost always do without intervention. 

           

Prevention of hepatitis A infection is possible with both behavioral interventions and with immunization.  Avoiding exposure to water and food that may be contaminated whenever possible is the most direct approach to avoid infection.  In less developed countries, improvements in sanitation and access to clean water sources have reduced hepatitis A infection rates significantly.  Travelers to these countries are advised to avoid drinking tap water and foods (especially vegetables) that have been peeled or rinsed in unpurified water.

 

Effective vaccines against hepatitis A virus have been available for many years and are in widespread use in the United States.  The inactivated, formalin-killed vaccine is almost 100 percent effective in inducing long-lasting immunity.  Live attenuated vaccines are not nearly as effective.  Hepatitis A vaccination is common, though not universal, and is highly recommended for international travelers to endemic areas.  Passive immunization is also widely available and consists of immune serum globulin (ISG) collected from a large group of donors.  It can be effective (80-90%) in preventing hepatitis A infection when administered to people with determined exposure before the appearance of clinical symptoms.  This can also be given to travelers who need vaccination right before travel, with short-term notice.  Overall, vaccine immunization is preferred over passive ISG immunization.

 

            Though an effective hepatitis A vaccine is available, universal immunization may not be the most cost-effective method to reduce disease burden.  Because hepatitis A causes a mild disease that is severe only in extremely rare cases, health programs in less developed countries may not find immunization campaigns necessary.  With limited financial resources, their money may be better spent on prevention efforts for more severe diseases such as polio, tuberculosis, measles, and malaria, which cause much higher fatality and have a larger socio-economic impact.

 

 

Sources:

 

  1. MMWR: Recommendations and Reports: Recommendations of the Advisory Committee on Immunization Practices (ACIP) and the American Academy of Family Physicians (AAFP).  February 8, 2002 / 51(RR02);1-36.  http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5102a1.htm

 

  1. National Center for Infectious Diseases, CDC: Hepatitis A Fact Sheet.  http://www.cdc.gov/ncidod/diseases/hepatitis/a/fact.htm

 

  1. Ryan, Kenneth, and Ray, C. George, Sherris Medical Microbiology, 4th Edition, McGraw-Hill, 2004, pp 541.

 

  1. World Health Organization: Water-borne Diseases.  http://www.who.int/water_sanitation_health/diseases/hepatitis/en/

 

 

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Research Updates

 

 

 

On Recombinant Polioviruses:

 

Į   Rapid RT-PCR amplification of full-length poliovirus genomes allows rapid discrimination between wild-type and recombinant vaccine-derived polioviruses.Boot HJ, Schepp RM, van Nunen FJ, Kimman TG.  J Virol Methods. 2004 Mar 1;116(1):35-43. Laboratory of Vaccine-preventable Diseases, National Institute for Public Health and the Environment (RIVM), PO Box 1, 3720 BA Bilthoven, The Netherlands. hein.boot@rivm.nl

 

This Dutch study sought to develop a full-length reverse transcriptase-PCR that would allow for characterization and amplification of wild-type and recombinant vaccine-derived poliovirus genomes.  Differentiation between wild-type and recombinant vaccine-derived polioviruses is useful in determining the causative source of poliomyelitis in people who fall ill but have no clear, identifiable risk for infection.  Vaccine-induced poliomyelitis has long been a concern of public health officials adopting universal vaccination programs using the live attenuated oral poliovirus vaccine, since vaccine-induced conditions like Guillan-Barre Syndrome have occurred at low but significant rates.  This project used SuperScript II (RT) and expand (PCR) to develop a full-length reverse transcriptase that then allowed researchers to examine the full-length genomes of all polioviruses – wild-type, vaccine, and recombinant vaccine-derived.  Endonuclease nuclease analysis was then used to differentiate recombinant from non-recombinant viruses.  Upon close examination, there appeared to be preservation of the quasi-species nature of the recombinant vaccine-derived virus.  This method proved successful and can now be used by epidemiologists and public health officials during local polio outbreaks to determine the source of viral emergence, particularly as the wild-type becomes more rare with vaccination campaigns and as possible vaccine-derived strains become more common.

 

 

 

On the poliovirus non-coding region:

 

Į    Cell-dependent role for the poliovirus 3' noncoding region in positive-strand RNA synthesis. Brown DM, Kauder SE, Cornell CT, Jang GM, Racaniello VR, Semler BL. J Virol. 2004 Feb;78(3):1344-51. Department of Microbiology and Molecular Genetics, College of Medicine, University of California, Irvine, California 92697, USA.

 

This study is a continuation of a previous study that successfully isolated a mutant poliovirus which lacked an entire RNA 3’ noncoding region in its genome.  That study then used the mutant strain to infect HeLa cells and observed that viral replication was only minorly affected, despite the significant genomic mutation in the original mutant.  This study applied the mutant poliovirus to a different set of cells, namely the neuroblastoma cell line (SK-N-SH cells).  It found that while replication defects were minor in HeLa cells, defects were major in SK-N-SH cells.  Major defects greatly impaired mutant viral replication in these cells.  Researchers subsequently suspected that the deleted 3’ noncoding region must have resulted in a defect in the positive RNA strand.  Thus, the defects in SK-N-SH cells were not due to major errors in protein processing or translation.  In order to test for neurovirulence of this mutant strain, the study went further to examine its effects in transgenic laboratory mice.  Comparing the wild-type poliovirus with the mutant strain, the study found that in order to paralyze 50% of the mice, the mutant virus would have to be innoculated in a quantity 1000 times that of the wild-type poliovirus.  This outcome suggests that the 3’ noncoding region is indeed involved in RNA synthesis.  It also implies that cell type factors also play a role in determining severity of disease outcome.  The finding gives insight into the potential for reduced poliovirus disease with mutation and removal of certain genomic regions.  Studies of this type help us to better understand the mutation and recombination patterns of picornaviruses and the outcomes of the diseases they cause.

 

On Hepatitis A immunogenicity and antibodies:

 

Į    Effect of maternal antibody on immunogenicity of hepatitis A vaccine in infants*1 G. William Letson MD , Craig N. Shapiro MD , Deborah Kuehn RN/CNP, MSN , Charlotte Gardea RN , Thomas K. Welty MD , David S. Krause MD , Stephen B. Lambert MS and Harold S. Margolis MD.  The Journal of Pediatrics, Volume 144, Issue 3 , March 2004, Pages 327-332.

 

This study sought to determine the effect of maternal antibodies on hepatitis A immunogenicity in newborn infants.  Two groups of infants were studied.  Group 1 was comprised of infants born to mothers who did not have antibodies to hepatitis A. Groups 2 and 3 were comprised of infants born to mothers who did have antibodies to hepatitis A.  The infants in group 1 were given the hepatitis A vaccine at 2, 4, and 6 months of age.  The remaining infants were randomly divided into group 2, where infants received the hepatitis A vaccine at 2, 4, and 6 months of age, and group 3, where infants received the hepatitis B vaccine on the same schedule.  Group 3 later received the hepatitis A vaccine at 8 and 10 months of age.  Infants were tested for HAV antibodies at 15 months.  Results showed that 100% of infants in group 1 had HAV antibodies, while 93% in group 2 and 92% in group 1 had HAV antibodies.  Despite the presence of antibodies, the geometric mean concentration of antibodies in group 1 was significantly higher than in either group 2 or group 3 (GMC of 231 mIU/mL in group 1, 85 mIU/mL in group 2, 84 mIU/mL in group 3, P<.001, group 1 vs. group 3).  This suggests that while most infants in all groups had antibodies, the infants in group 1 had many more antibodies and thus, better protection from HAV.  The study concluded that infants who had passive immunity to hepatitis A passed down from their mothers at birth had fewer anti-hepatitis A antibodies even after immunization.  Active immunity in infants immunized without presence of maternal antibodies proved more effective in building an immune response.

 

 

 

On Coxsackie B virus and RNA recombination:

 

Į    RNA Recombination Plays a Major Role in Genomic Change during Circulation of Coxsackie B Viruses. Oberste MS, Penaranda S, Pallansch MA. J Virol. 2004 Mar;78(6):2948-55.  Respiratory and Enteric Viruses Branch, Division of Viral and Rickettsial Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia 30333.

 

This recent study chose to focus on the role of RNA recombination in the evolution of coxsackie B viruses (CVB), a group that is not often the subject of research attention.  Using the six main clinical isolates of CVB, the group sequenced four genomic intervals for multiple isolates of each: the polymerase (3D, 491 nt), the 5’-nontranslated region (5’-NTR, 350 nt), and two capsid intervals (VP4-VP2, 416 nt, and VP1, approximately 320 nt).  Based on the results of this sequencing, the group was able to create phylogenetic trees for each region and each isolate.  An observation was made that “the partial VP1 sequences of each CVB serotype were monophyletic with respect to serotype, as were the VP4-VP2 sequences, in agreement with previously published studies.”  Not all trees were consistently congruent, as some incongruency between regions of VP2 and VP1 led researchers to believe that there must be some degree of recombination between serotypes (not hard to believe).  There was also indication that recombination had occurred between other regions, namely the 5’-NTR and the capsid and the 3D and the capsid.  Overall, most isolates seemed to be recombination products when compared to the prototypical serotype strains.  The conclusion of this observational study is that genetic recombination is quite common among coxsackie B viruses.  Common recombination is a trait of many enterovirus serotypes that helps to explain why enteroviruses are so diverse and so common and why preventive or reactionary treatment proves so difficult for drug development.

 

 

 

On Rhinoviruses and bronchial epithelial cells:

 

Į    Rhinovirus increases human beta-defensin-2 and -3 mRNA expression in cultured bronchial epithelial cells.  Duits LA, Nibbering PH, van Strijen E, Vos JB, Mannesse-Lazeroms SP, van Sterkenburg MA, Hiemstra PS. FEMS Immunol Med Microbiol. 2003 Aug 18;38(1):59-64. Department of Infectious Diseases, Leiden University Medical Center, P.O. Box 9600, 2300 RC, Leiden, The Netherlands.

 

This study examined the role of human beta-defensin (hBD) expression in airway epithelial cells under conditions of the common cold.  HBDs are antimicrobial peptides that participate in the inflammatory and immune responses to infection.  They have been shown to be mediated by pro-inflammatory mediators and micro-organisms.  The study looked at cultured primary bronchial epithelial cells (PBEC) in patients with the common cold rhinovirus RV16, which is also associated with exacerbation of asthma.  While RV16 did not affect hBD-1 mRNA expression, it did appear to induce hBD-2 and hBD-3 mRNA expression in PBEC.  The study concluded that “viral replication appeared essential for rhinovirus-induced beta-defensin mRNA expression, since UV-inactivated rhinovirus did not increase expression of hBD-2 and hBD-3 mRNA.” Polyinosinic polycytidylic acid, a synthetic dsRNA, was also investigated.  It appeared to affect mRNA expression of hBDs in the PBEC in a similar was as RV16.  Overall, the study showed that hBD-2 and hBD-3 mRNA expression increases in PBER in the presence of RV16 infection.  In other words, in the presence of rhinoviral infection, the immune and inflammatory response is increased, which leads to resolution of the viral infection without external interference.  This finding may lead towards development of better treatment of viral exacerbations of asthma and of the common cold.

 

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Drug Profile

 

 

Picovir™ (pleconaril)

 

Though there are many drugs commonly used to treat the various symptoms of picornaviruses, there are few drugs currently available to treat actual picornaviral infections.  Pleconaril (brand name PicovirTM) is one of those few antivirals that is closest to being marketed and seems to work well.  It contains active, antipicornal molecular inhibitors of rhinoviruses and enteroviruses.  Rhinoviruses and enteroviruses each contain many dozens of viral serotypes that commonly infect people in all parts of the world and can cause mild, moderate, or severe disease in a great variety of body systems.  They cause many diseases, including the common cold, viral meningitis, pharyngitis, bronchitis, pneumonia, infectious asthma, pericarditis, herpangina, acute hemorrhagic conjunctivitis, paralytic diseases, and more.  These diseases affect millions of people in the United States alone and are a widespread concern.

 

Pleconaril was developed and patented by the pharmaceutical company ViroPharma.  The drug was designed after close study of picornavirus structure, which led to the observation that capsid and envelope structure are highly conserved among rhinoviruses and enteroviruses.  The drug was designed to function by integrating into hydrophobic pockets in the virion and disrupting viral replication.  Developers used x-ray crystallography to demonstrate the process.  Metabolic processes were accounted for in order to create an orally-administered drug that would survive metabolic breakdown and take effect in full force.  Because it is lipophilic, Pleconaril is able to cross the blood-brain barrier to treat diseases such as viral meningitis, which can be quite serious and even fatal.

 

ViroPharma’s laboratory studies showed that pleconaril inhibits replication of 96% of picornaviral replication of enteroviruses and rhinoviruses in human samples over a short period of time (usually within 2 days).  Samples were selected from a diverse patient group that included a wide range of viral diseases from acute, mild infections to chronic and fatal diseases.  In laboratory mouse studies, mice were given oral doses of pleconaril after induced enteroviral infection and infection consistently improved.  In subsequent clinical studies, the drug was shown to be safe and effective in treating the common cold (its most common intended use)

 

ViroPharma is attempting to market its PicovirTM as a cure-all for the common cold.  If sold as an antiviral nasal spray or a tablet, the marketing potential of the drug is quite high.  Despite its high efficacy, Pleconaril was not approved by the FDA in early 2002.  The FDA expressed concern about the drug’s safety due to potential interactions with common drugs such as birth control pills, in which case birth control efficacy was reduced.  If the drug is approved, it will likely be sold on a very large scale, since rhinoviruses and enteroviruses are so common in the general population.  This potential for widespread use has raised FDA concern about the indirect creation of potentially drug-resistant viruses.  The drug is currently in clinical trials to examine its efficacy and safety for many serotypes of enteroviruses and rhinoviruses.  Of particular interest are trials of Pleconaril used to treat enteroviral CNS infection in newborns, a group that can be seriously affected by enteroviral meningitis and enteroviral sepsis syndrome.

 

 

For more information:

 

Š      A 2003 clinical trial of Pleconaril to treat infant enteroviral meningitis:

 

Double blind placebo-controlled trial of pleconaril in infants with enterovirus meningitis. Abzug MJ, Cloud G, Bradley J, Sanchez PJ, Romero J, Powell D, Lepow M, Mani C, Capparelli EV, Blount S, Lakeman F, Whitley RJ, Kimberlin DW; National Institute of Allergy and Infectious Diseases Collaborative Antiviral Study Group. Pediatr Infect Dis J. 2003 Apr;22(4):335-41.

 

Abstract:

 

BACKGROUND: Enterovirus (EV) meningitis is common in infants and may have neurologic complications. Treatment of older children and adults with pleconaril has been associated with reduced severity and duration of symptoms. This study evaluated the pharmacokinetics, safety and efficacy of pleconaril in infants with EV meningitis. METHODS: Infants < or =12 months old with suspected EV meningitis were randomized 2:1 to receive pleconaril, 5 mg/kg/dose orally three times a day or placebo for 7 days. Evaluations included pharmacokinetic determinations, safety laboratory testing, serial culture and PCR assays and clinical evaluations. RESULTS: Of 21 evaluable subjects 20 were confirmed with EV infection (12 pleconaril, 8 placebo). Among pleconaril-treated subjects 26 of 29 peak and trough pleconaril levels exceeded the 90% inhibitory concentration for EVs. A median 3.5-fold drug accumulation occurred between Days 2 and 7. Pleconaril was well-tolerated, although twice as many adverse events occurred per subject in the pleconaril group. Serial cultures from the oropharynx, rectum and serum had low yield (< or =50%) and positivity generally persisted for <4 days in both groups. Serial PCR assays of culture-negative oropharyngeal and rectal specimens had high positivity rates (generally > or =50%) persisting through Day 14. No significant differences in duration of positivity by culture or PCR, hospitalization or symptoms were detected between groups. CONCLUSIONS: The dose of pleconaril studied provided sufficient plasma levels and was well-tolerated; however, drug accumulation was evident. The low yields of serial viral cultures, relatively short and benign clinical courses and the small number of subjects enrolled precluded demonstration of efficacy. If this medication is to be prescribed in infants, surveillance for toxicity related to drug accumulation will be necessary.

 

 

Sources:

 

  1. FDA Approval Meeting Report: http://www.fda.gov/ohrms/dockets/ac/02/slides/3847s1_01_viropharma/

 

  1. NIH ClinicalTrials.gov: http://www.clinicaltrials.gov/show/NCT00031512

 

  1. ViroPharma Picovir Information: http://www.viropharma.com/Pipeline/Pleconaril.htm

 

 

 

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Pathogen Cards

 

 

Mumps virus

 

                          

 

Power: XXX highly contagious, but not usually life-threatening.

 

Description: Mumps is caused by the mumps virus, a member of the Paramyxoviridae family.   It contains single-stranded RNA and has helical morphology.  This highly infectious virus is transmitted through the respiratory route and causes painful enlargement of one or both parotid salivary glands, typically in children.

 

 

Offenses:

o      Attacks: Mumps virus is transmitted very easily from person to person through oropharyngeal secretions.  Children are the primary susceptible group.  Mumps is characterized by visible swelling of the parotid salivary glands that results after initial infection of the respiratory tract.  In most cases, the virus passes into the bloodstream and spreads to glandular and nervous tissue throughout the body, possibly including the meninges, thyroid, pancreas, ovaries, testes, and kidneys.  Mild fever and pain is common in persons with symptoms.

o      Outcome: Mumps usually resolves without long-lasting effects.  Nerve damage due to gland and organ swelling is possible in serious cases and can lead to long term nerve damage or potential deafness in children.

o      Speed: Mumps infection comes in four stages: incubation, prodrome, swelling, and reduction in swelling.  The incubation period lasts about 2-3 weeks after exposure, at which point the virus enters the bloodstream.  The viremic phase lasts 3-5 days.

 

 

Defenses:

o      Vaccine: The Mumps vaccine is given in a live attenuated trivalent vaccine along with vaccines for measles and rubella (MMR).  Universal childhood vaccination is recommended in two doses, the first at 15 months and the second at 5 years.  More than 90% of recipients have lifelong immunity.

o      Behavioral: Avoidance of persons known to have mumps virus infection may be somewhat effective, but respiratory transmission is difficult to prevent through behavior alone.

o      Treatment: There is no commonly used treatment for mumps virus infection, though treatment for symptoms of fever and pain is common.

 

 

Game Action: Skip ahead, chances are you’ll be fine once the swelling goes down.

 

 

One-liner: Bumpy Mumpy Grumps.

 

Source: Fields’ Virology, pp 1255.

 

 

 

Rubella virus

                           

 

Power: XXX highly contagious, but not usually life-threatening.  It can be very dangerous as a teratogen.

 

Description: Rubella, also known as “German measles,” is caused by the rubella virus, a member of the Rubivirus genus of the Togaviridae family.  It contains single-stranded RNA and has an idosahedral morphology.  This virus is transmitted through the respiratory route and causes a maculopapular rash, typically in children.  Rubella can also act as a teratogen and cause Congenital Rubella Syndrome in infants.

 

 

Offenses:

o      Attacks: Rubella virus is transmitted easily from person to person through oropharyngeal secretions.  Children and pregnant women are the primary susceptible groups.  Rubella is characterized by the appearance of pink macules on the face in about half of all cases.  Facial rash spreads to the trunk and limbs, then fades within two days.  Lymph node enlargement is common, as is fever and mild muscle and joint pain.  Women may experience polyarthritis and may transmit the virus to an unborn fetus. 

o      Outcome: Rubella virus infection typically resolves without any long-lasting effects.  In rare cases, complications such as thrombocytopenic purpura and postinfectious encephalopathy may occur.  In infants with Congenital Rubella Syndrome, the virus may cause long-term damage to many organs and body systems, including the eyes, ears, heart, and nervous system.

o      Speed: Rubella infection comes in three phases: incubation, prodrome, and development of rash.  The incubation period lasts 16-18 days after exposure, or 12-23 days at the most.  The infectious period is from 7 days before onset of rash to 7 days after.

 

 

Defenses:

o      Vaccine: The Rubella vaccine is given in a live attenuated trivalent vaccine along with vaccines for measles and mumps (MMR).  Universal childhood vaccination is recommended in two doses, the first at 15 months and the second at 5 years.  More than 90% of recipients have lifelong immunity.  Women who may become pregnant are particularly encouraged to be vaccinated.

o      Behavioral: Avoidance of persons known to have rubella virus infection may be somewhat effective, but respiratory transmission is difficult to prevent through behavior alone.

o      Treatment: There is no commonly used treatment for rubella virus infection, though treatment for symptoms of fever and pain is common.

 

 

Game Action: Better hope you’re not pregnant because this could be BAD…lose one turn.

 

 

One-liner: MMR: protect your baby, it’s well worth the poke.

 

Source: Field’s Virology pp 2011-2045

 

 

West Nile virus

                                    

 

Power: XXX symptomatic infection is unlikely, but rare, severe encephalitis or meningitis can be fatal.

 

Description: West Nile is caused by the West Nile virus, a member of the Flaviviridae family. It contains single-stranded RNA and has icosahedral morphology.  This virus is commonly found in Africa, the Middle East, and West Asia, but has arrived in North America and Europe in recent years.  It is an arbovirus that infects humans, birds, horses, and other mammals, and is transmitted by mosquitos from host to host.  While often asymptomatic in humans, West Nile fever, West Nile encephalitis, and West Nile meningitis can result from serious infection.

 

 

  Offenses:

o      Attacks: West Nile virus is transmitted to humans primarily through the bite of an infected mosquito that acquires the virus from infected birds.  In rare cases the virus has been transmitted through donor blood and organ transplants from persons unknown to be infected.  Only about 20% of those infected will be symptomatic and experience mild fever, headache, muscle and joint pain, eye aches, swollen lymph nodes, nausea, vomiting, or rash on the trunk.  Only 1% of those infected will experience severe muscle weakness, encephalitis, meningitis, disorientation, paralysis, and potentially coma.

o      Outcome: In people with weakened immune systems, including the elderly, West Nile encephalitis and meningitis can be fatal.  In asymptomatic and mild cases, outcome is normal.

o      Speed: West Nile virus has an incubation period of 3-15 days, after which symptoms may appear.

 

 

  Defenses:

o      Vaccine: There is no vaccine for West Nile virus.

o      Behavioral: Prevention of mosquito bites is the only way to prevent viral infection.  Insect repellents, bed nets, clothing spray, and protective clothing can reduce the risk of mosquito bites during temperate months.  Pest control and local management of water in which mosquitos may breed are methods of controlling the mosquito population in a community.

o      Treatment: There is no commonly used treatment for West Nile virus infection, though treatment for symptoms of fever and pain is common.

 

 

Game Action: ZZZAP! You’ve been bitten by an infected mosquito…lose one turn.

 

 

One-liner: “Birds, mosquitos, and humans…OH MY!”

 

Source: Department of Health and Family Services: West Nile Virus Infection

(West Nile Encephalitis, West Nile Fever)

http://www.dhfs.state.wi.us/healthtips/BCD/WestNile.htm