Be up to
date on your knowledge of Poxviridae! Here are some interesting findings
from the past year.
|Since the mid-1990s, the
United States government had supported an international effort to eradicate
every last trace of variola virus, the causative agent of smallpox. There
was a tentative plan to destroy all known stocks of variola virus by June
1999. However, in April of 1999, President Clinton signed a memo calling for
a preservation of variola virus in the five WHO-approved high-security labs.
Only Russia and the United States are currently known to possess cultures of
variola. However, some experts allege that not all variola stocks have been
|According to a White House
security official, the decision to preserve the live virus was for its use
in developing new anti-viral drugs and testing improved smallpox vaccines.
What do you think? Should small-pox be preserved? We’d love to hear what
you think. Email us at email@example.com
Reference: Marshall, E.
"President Revokes Plan to Destroy Smallpox" Science 30 Apr
|In June 1999, a working group
from the Center for Civilian Biodefense Studies at the School of Public
Health, John Hopkins University issued a comprehensive report on
recommendations for measures to be taken by medical and public health
officials following use of smallpox as a biological weapon. The research
group consisted of 21 representatives from major medical centers, research,
government, military, public health, and emergency management institutions
and agencies. The report issued included specific recommendations regarding
smallpox vaccination, therapy, postexposure infection control, hospital
epidemiology, and home care. In the event of an actual release of smallpox
virus and subsequent outbreaks, early detection, isolation of infected
individuals, surveillance of contacts, and an effective vaccination program
will be absolutely vital to successful epidemiological control of smallpox.
For a more detailed version of the group’s report, please see reference
Reference: Henderson, DA et al.
"Smallpox as a Biological Weapon: Medical and Public Health
Management" Journal of the American Medical Association. 9 Jun
1999 281 (22): 2127-37.
|The replication kinetics of
tanapoxvirus were understood this year by growth of tanapox virus in owl
monkey kidney cells. Virus replication revealed production of cytopathic
effect, characterized by densely packed rounded cells with granular,
vacuolated cytoplasm. An important feature of tanapoxvirus multiplication is
that most of the mature progeny is retained inside the cell. The results of
this study suggest that tanapoxvirus, in terms of replication kinetics, is
very similar to other poxviruses. However, the virus is much slower in
replication than vaccinia virus. For more details of this study, please see
Reference: Mediratta, S. and K.
Essani "The replication cycle of tanapox virus in owl monkey kidney
cells" Canadian Journal of Microbiology. Jan 1999 45 (1): 92-96.
|The development of vaccines
for various pathogens using vaccinia virus as a vector has recently sparked
significant interest. Cancer research is one such field that has looked into
the possibility of using vaccinia virus in the development of vaccination
strategies that would give rise to strong tumor-specific responses in cancer
patients. One strategy, discovered this year, consisted of using a
well-defined human melanoma tumor system to check the possibility of
translating the immunological potency of synthetic tumor antigenic peptide
analogues into recombinant vaccinia viruses carrying constructs with
appropriate nucleotide substitutions. The results of this study indicated
that use of these constructs directed the expression of modified melanoma
tumor antigens, which then led to improved antigen recognition, and thus, to
enhanced immunogenicity. Recombinant vaccinia viruses containing mutated
sequences may lead to new strategies for the induction of strong tumor
specific responses in cancer patients.|
Reference: Valmori, D. et al
"Induction of potent antitumor CTL responses by recombinant vaccinia
encoding a melan-A peptide analogue" Journal of Immunology. 15 Jan
2000 164(2): 1125-31.
|Poxviruses are known
to encode several cytokine response modifying (Crm) proteins. The Crm
proteins possess sequence homology to several human proteins important in
immunity. This homology and the conservation of Crm proteins among poxvirus
strains suggests an immunomodulatory function that provides a survival
advantage to the virus. It was recently discovered that cowpox virus encodes
several tumor necrosis factor (TNF) receptors. The researcher of this study
have suggested that understanding the role that these TNF receptors play in
altering host immune reponses may lead to the development of specific
Reference: Cunnion, K.M.
"Tumor necrosis factor receptors encoded by poxviruses." Molecular
Genetics and Metabolism Aug 1999 67 (4): 278-82.
|In recent years,
vaccinia virus and other poxviruses have been found to express a collection
of proteins that can block parts of the host immune response. A recent study
found several types of these proteins that bind to interleukin-1, type 1
interferons, and chemokines and are secreted from cells infected with
vaccinia virus. The study of immune modulation by proteins such as these can
shed light on the understanding of viral pathogenesis and interaction with
the immune system. This can in turn have potential application in the
treatment of immunological disorders caused by infectious agents.|
Refernce: Smith, G.L.,
J.A. Symons, A. Alcami "Immune modulation by proteins secreted from cells
infected by vaccinia virus." Archives of Virology Supplementum,
1999 15: 111-29.
|A chemokine cell
receptor, MC 148, encoded by human molluscum contagiosum virus was recently
found to block the action of I-309 chemokine on CCR 8. This resulted in
interference with monocyte invasion and dendrite cell function. The
discovery of the function of MC148 protein could be a useful tool for better
understanding the role that CCR 8 plays in the immune system. This study
reinforces the idea that by understanding more about the function of viral
proteins, we can learn more about how the immune system functions.|
B.H. et al. "A highly selective CC chemokine receptor encoded by the
poxvirus molluscum contagiosum." Journal of Experimental Medicine3
Jan 2000 191(1): 171-80.
orthopoxvirus strains isolated from human subjects, cats, a dog, and an
elephant were studied in 1999 in Germany. A detailed comparison of these
strains demonstrated a close relationship between all of them and confirmed
that they were all cowpox viruses. Some differences were detected and this
was significant for their epidemiological value. This study helps us better
understand the host range of cowpox, despite its misleading name.|
Reference: Meyer, H., C.
Schay, H. Mahnel, and M. Pfeffer. "Characterization of orthopox virus
isolated from man and animals inGermany." Archives of Virology
1999 144 (3): 491-501.
pneumonia was observed in a domestic cat which had no clinical history of
severe respiratory distress. Electronmicroscopy and immunohistology revealed
infection by cowpox virus from the genus Orthpoxvirus. This confirms
reports of zoonosis of cowpox virus from infected cats, which seems to be
the leading cause of human infection with cowpox.|
Reference: Hinrichs, U.,
H. Van de Poel, and T.S. Van den Ingh "Necrotizing pneumonia in a cat
caused by an orthopoxvirus." Journal of Comparative Pathology
Aug 1999 121 (2): 191-6.
|A recent study found
that the A-type inclusion bodies characteristic of poxviral infections are
generated by endoribonucleolytic cleavage at a specific site in the primary
transcript. The 3’ end of late mRNAs of the ati gene are responsible for
encoding these inclusion bodies. For more detailed information on the
sequencing of these mRNAs please see reference below.|
Reference: Howard, S.T.,
C.A Ray, D.D. Patel, J.B. Antczak, and D.J. Pickup "A 43-nucleotide cis-acting
element governs the site-specific formation of the 3' end of a poxvirus late
mRNA." Virology 1 Mar 1999 225(1): 190-204.