Cowpox
A Microbial Biorealm page on the genus Cowpox
Classification
Higher order taxa
Poxiviridae;Chordopoxvirinae;Orthopoxvirus
Species
Cowpox
Description and significance
Cowpox is an zoonotic viral disease from the Poxiviridae family and stems from the Orthopoxvirus genus. It causes postular lesions on teats and udders of female cows. Cowpox is transmitted to humans who may milk the infected cow. Cowpox is related to the variola virus (smallpox) which is exclusive to humans with a mortality rate of 40 % when infected [5].
The pathogen is easily transferred in areas of high population, poverty , poor malnutrition and sanitation which create favorable conditions, as with any other virus. Smallpox was one of the first vaccines made and was generated through cowpox[8]. During the 16th century Edward Jenner investigated claims that farmers or milkmaids that came in contact with cowpox did not develop smallpox. He used the cowpox virus to create his own vaccine. After much rejection, his research and theory were accepted[6].
Today the World Health Organization is heavily dedicated to continue eradicating smallpox. This year alone it cost 1 billion to save lives of millions of people. In the U.S alone, it is nearly eradicated [2]. Ironic that a mild, discomforting ulcer on the mammary gland of cows could cause such horrific lesions, on the body, hands and face of humans. However, it was through this poxvirus that we are able to demonstrate that transmission is a direct mechanism for protection [8].
Genome structure
Cowpox is a linear double stranded DNA virus. It is comprised of 222,499 nucleotides. The virus codes only 223 proteins, and has no structural RNAs, or pseudo genes. Its genome content only makes up about 33% and while its codes about 91%. As of April 16, 2002 the cowpox genome was completed through the combined efforts of Duke University Medical Center and Molecular Genetics and Microbiology USA, Durham [9].
Cell structure and metabolism
Cowpox is an enveloped virus approximated 350-250 nm in size. The genome of the virus lies in the center along with its enzymes and other structural proteins. These enzymes include a transcriptional complex that can synthesize, cap, methylate, and polyadenlylate early mRNAs [2]. Cowpox replicates in the cytoplasm. It is aided by DNA and RNA polymerase the virus codes. It replicates in female cows and can be transferred to humans. The virus has an early and late phase during replication which takes 15-20 hours to complete [8].
The golgi membrane gives cowpox an extra lipid envelope which contains its unique glycoproteins. One of these glycoproteins is vCCI. VCCI is made up of two parallel beta-sheets with short alpha helices and loops. It is thought that this unique protein binds to CC-chemokines receptors, and reduce inflammation within the host. Inflammation is our body’s natural way to combat infection. While white blood cells are being recruited to the infected area our temperature rises creating unfavorable conditions for the virus. With the vCCI globular protein manipulating inflammation, it gives the virus more time to replicate and continue infecting the host.[1]
Ecology
Our idea of cowpox before the 1970s is that cowpox created the smallpox outbreak. Now we are unable to find the source of cowpox because smallpox has nearly been eradicated. Studies have shown that cowpox may have originated from the rodents Clethriomonomys Glaraeolus or Apodemus Sylvaticus that both exhibit the cowpox virus [4]. After numerous testing and data it was found that these two host species significantly transmitted infection to other susceptible individuals. However, the study proved that they were not able to transmit the virus interspecifically (they were independent hosts)[7].
Pathology
Cowpox causes skin lesions much like that of small pox [3]. However, the epithelial lining is much thicker and necrosis of the cells is less rapid. Mesoderm tissue is also involved. Cowpox has two unique inclusion bodies (irregular type B and type A) which allow it to replicate more efficiently inside the host [8].
Current Research
Cowpox unlike smallpox is not prevalent. Its is only found in parts of Europe and the former Soviet Union. Current research includes veterinary medicine where they believe cowpox may be infecting domestic cats. The chemokine inhibitor vCCI identified in cowpox is also being studied to see the role it has in disrupting our immune response (in regards to inflammation)[1].The presence of the virus in the blood has been studied to make sure that it does not create a similar severe infection like smallpox. Scientists found cowpox was detectible in whole blood but not in the serum after infection indicating it was significantly different form smallpox ( which lasts longer)[7].
Smallpox is nearly eliminated because there is no animal reservoir while studies have linked cowpox origination in rodents. Some reports have connected cowpox to bioterrorism, since it is possible to be found in animals [2]. Animals use our air, soil, water and with all of them potentially infected with the virus organizations could use it to threaten our lives. However, much remains to be seen and researched!
References
1.Dasgupta A., Hammarland E.,Slifka A., Fruh K. 2007,Cowpox Virus Evades CTL recognition and Inhibit’s the Intracellular Transport of MHC Class I Molecules.The Journal of Immunology.v.178,p.1654-1661.
2. Ryan P.C. May -June 2008., Zoonoses Likely to Be used in BioTerroism.Los Angeles County Department of Public Health Reports.v,123, p.276-281.
3. Carfi A., Smith C.A., Smolak P.J., McGrew J.,Wiley D.C.1999,Structure of a soluable secreted chemokine inhibitor vCCI (p35) from cowpox virus. Proceedings of the National Academy of Science. v.96.12379-12383.
4. Nitsche A. Kuruth A.Pauli G.2007.Viremia in human Cowpox virus infection. The Journal of Clinical Virology.v.40,p. 160-162.
5. Feuerstein-Kadgien B. Korn K.,Images in Clinical Medicine. The New England Journal of Medicine.v.348,p.415.
6. Smith G.L. 1989.Carrier of Vaccine Antigens.p.32-38.Vaccination Strategies of Tropical Diseases.CRC Press.320 pages
7. Jones T.C, Hunt R.D, King N.W,.1997. Diseases caused by viruses.p204-205 . Veterinary Pathology.Blackwell Publishing.1392 pages
8. Shchelkunov S.N., Marennikova S.S., Moyer R.W.2005. Cowpox Virus.p.206-210.Orthopoxviruses Pathogenic for Humans.Springer.425 pages.
9. www.ncbi.nlm.nih.gov
Edited by Kerriann Virgo student of Emily Lilly at University of Massachusetts Dartmouth.
