TRICHINOSIS

* The presence of T. pseudospiralis in a muscle biopsy (provided by http://www.Medscape.com/)

 

TRICHINOSIS is a disease that is present around most parts of the world, from North America and Europe, to Japan, China and tropical Africa. Some regions that are not really affected are Puerto Rico and Australia. Highlighting the incidences of transmission through uncooked portions of meat, specifically pork, Trichinosis impacts the realm of food and culture for its specific regions. Let’s see how the disease has unfolded over the years:

What’s in a name?

Trichinosis’ primary agent is Trichinella spiralis, which is a tissue nematode immediately infecting the epithelium of the small intestine. It has four other species:


T. nativa–Occurs in Artic and Sub-Artic zones; high pathogenicity, high resistance to freezing

T. nelsoni–Occurs in tropical Africa; intermediate in pathogenicity

T. britovi–Occurs in temperate Paleoartic region, very low pathogenicity

T. pseudospiralis–Cosmopolitan, does not encyst, infections to birds, pathogenicity in humans not well characterized


History of Discovering Trichinosis:

In 1835, two men by the name of Sir Richard Owen and Sir James Paget were working in the laboratory in London. Sir Paget was just a first-year medical student at the time, and was under the direction of Sir Owen during an autopsy. Both of the gentlemen observed the mass of worms that lined the diaphragm of the cadaver. With his scientific excitement, Sir Paget decide to collect some of this tissue to observe the worms a bit more closely. However, without alerting his student, Sir Owen, decided to report to the zoological society in London about the findings of this new parasite, providing its present day name. What is interesting is that the day after the discovery, Sir Paget decided to write to his brother about the new scientific observation. If this was not the case, the discovery of Trichinosis would be credited to only Sir Owens.

Transmission, Vector, and Reservoir:

Trichinosis begins its infection with the larvae of T. spiralis. There is the direct transmission with the current host to the other by ingesting this larvae. The targets for this parasite are usually in bears, rats and also in pigs, who are fed garbage that has not been properly treated or the remains from the slaughterhouse. When the host involve humans, the cause of infection is due to the consumption of pork, specifically that is uncooked. Here is an overview of Trichinella and the most common hosts:

 

Species Name

Common Hosts

Distribution

T. spiralis

Worldwide

Pigs, rats, horses, bears, foxes

T. nativa

Arctic, subarctic

Bears, horses

T. britovi

Temperate, subarctic

Boar, horses, foxes

T. pseudospiralis

Arctic Tasmania

Birds, omnivorous

T. nelsoni

Southern Africa

Hyenas

 

Tropical Africa

Lions, panthers

* SOURCE: Mandell's Principles and Practice of Infectious Diseases, 5th ed.

Incubation Period and Clinical Reflections:

The incubation period of T. spiralis last between 1 to 2 weeks. The first week after ingesting the parasite, the human host may experience nausea, diarrhea, and abdominal pains. More clinical signs continue to develop, ranging from the second week up to 2 months after ingestion, giving the larvae the opportunity to circulate and infect more of the tissues within the body. These signs include fever, myalgia, which is muscle pain, conjuctival hemorrhage and periorbital edema.

The larvae has the capability of surviving within its host for years. After this two-month period, clinical signs ranging up to 2 years of ingestion include calcification of the skeletal muscle that the larvae attack within their hosts. This calcification prolongs the life span of the larvae, and at this point, may cause signs such as myocardial failure and a deterioration of neurological function.

*SOURCE: Larvae in the muscle.  http://www.biosci.ohiostate.edu/~parasite/trichinella.html

Morphology:

One ingestion occurs, the larvae are liberated from the enveloping cyst walls. This is due the acidity of digestion with pepsin, allowing the larvae to move into the small intestine. From this point, the larvae attack the villi found on the epithelial cells and continue to develop into adult worms after about 30 hours.

The number of larvae released depends on the species and the hosts involved. The female is able to release up to 500 larvae (.08mm in size) in a two week period and then she is excreted along with the wastes of the host. The new larvae circulate throughout the body and attack the skeletal muscles of the host for survival. Three weeks later, the parasites have grown up to ten times the original length and our now capable of infecting new hosts. Time also allows them to produce calcium remains within the muscles to produce the cyst walls, prolonging their life span for several ears.

Adult male worms are 1.5 by .05 mm in size, while the females ,on average, are 3.5 by .06 mm in size

* SOURCE: http://www.biosci.ohio-state.edu/~parasite/trichinella.html

Diagnostic Tests:  

Scientists usually review the history of particularly the meat consumption one to five weeks ago of the patient. The focus is with pork and ground meats that may have been contaminated with pork in the process. One of the first signs is the elevated levels of eosinophilia within the host. After 12 days of infection, the levels of eosinophilia rises between five and ten percent, while the numbers change from 30 to 50% after a two week period.

Immunological tests also provide scientists with results of a positive test after two weeks as well. Tests known as ELISA and counterimmunoelectrophoresis can detect the antibodies after 12 days. Another examination is known as bentonite flocculation and it displays a positive reading after three weeks of infection and remains in that state during the two to three month recovery period. The best format in diagnosis is performing tissue biopsies.

Management and Therapy:

The treatment for trichinosis is not excellent, but there are some options to pursue. Different options include corticosteroids for the more seriously ill patients which alleviate the inflammatory pain experienced, thiabendazole (orally every day for about one week), flubendazole, and albendazole. Albendazole has been know to work just as effectively as thiabendazole, and is better to use in terms of any side effects of the patient.

Epidemiology:

Trichinosis is prevalent within most regions around the world. Around the beginning of the twentieth century, it was estimated that 1 out of 6 persons specifically in the United States was infected with T. spiralis, for example. By the 1970s, the ratio reduced to one out of 25, particularly for adults under the age of 45. Up to the early 1990s, he number of US cases of T. spiralis dropped from about 200 to 30 cases.

The infection is known to be enzootic, which means that it affects animals, especially carnivores and scavengers. Adult worms are attracted to the mucous layer of the small intestine. The larvae that initiates a chain reaction of infection is not only found in pork, but it also includes other animals such as bears and walrus meat from North America, as well as horsemeat.

 Public Health and Prevention Strategies:

Legislature has required that pigs should be fed with treated garbage, that which is cooked. The proper way to prevent the spread of trichinosis is properly cooking pork and other meat before consumption. The USDA recommends heating it to more than 137 degrees F, and storing at low temperatures of -15 degrees Celsius in the refrigerator to about -37 degrees Celsius for freezing. One should be careful about methods such as salting or smoking, because it does not ensure that it will kill the larvae.

Useful Web Links:

http://www.cdc.gov/ncidod/dpd/parasites/tricinosis/default.htm

http://www.nwtwildlife.rwed.gov.nt.ca/Publications/diseasepamphletweb/trichinosis.htm


References:

"AAP 2000 Red Book: Report of the committee of Infectious Diseases." American Academy of Pediatrics. 25th ed. P. 587-588.

Balows, Albert, Leslie Collier and Max Sussman. (Eds.). (1998). Microbiology and Microbial Infections. Ninth edition. London: Hodder Headline Group.

Catty, David. The Immunology of Nematode Infections Trichinosis in Guinea-Pigs as a Model. Switzerland: Buchdruckerei Benteli AG, 1969.

Gould, Sylvester E. Trichinosis. Springfield: Charles C. Thomas, 1945.

John, David T, Wojciech Krotoski, and Edward Markell. (Eds.). (1999). Medical Parasitology. Philidelphia: W.B. Saunders Company.

Kate, Michael. (1989). Parasitic Diseases (2nd ed.). New York: Springer-Verlag.

Mandell Principles and Practice of Infectious Diseases. 5th ed. New York: Churchill Livingstone, Inc., 2000.

 http://www.biosci.ohio-state.edu/~parasite/trichinella.html