Cowpox

Cowpox
Classification and external resources
ICD-10	B08.0
ICD-9	051.01
MeSH	D015605

Cowpox (vaccina) pustules on a cow's udder.

Cowpox virus
Virus classification
Group:	Group I (dsDNA)
Order:	Unassigned
Family:	Poxviridae
Subfamily:	Chordopoxvirinae
Genus:	Orthopoxvirus
Type species
Vaccinia virus
Species
Cowpox virus

Cowpox is a skin disease caused by a virus known as the Cowpox virus. The pox is related to the vaccinia virus and got its name from the distribution of the disease when dairymaids touched the udders of infected cows.^[1] The ailment manifests itself in the form of red blisters and is transmitted by touch from infected animals to humans. Cowpox is similar to but much milder than the highly contagious and sometimes deadly smallpox disease.^[1] It resembles mild smallpox, and was the basis of the first smallpox vaccines. When the patient recovers from cowpox, the person is immune to smallpox.

The cowpox virus was used to perform the first successful vaccination against a disease, smallpox, which is caused by the related Variola virus. Therefore, the word "vaccination" — first used by Edward Jenner (an English physician) in 1796 —^[2] has the Latin root vaccinus meaning of or from cows.^[3] World Health Organization in 1980 announced that smallpox was the first disease that had been eradicated world wide by a program of vaccination.^[3] Despite the eradication of smallpox in the past century, other orthopoxviruses, such as monkeypox virus, vaccinia virus in Brazil, and cowpox virus (CPXV) in Europe, still infect humans. CPXV has been restricted to the Old World with wild rodents as its natural reservoir.^[4] Human CPXV infections are commonly described in relation to contact with diseased domestic cats, sometimes directly from rats or domesticated house mice. Human infections usually remain localized and self-limiting but can become fatal in immunosuppressed patients.

Origin

In the years 1770 till 1790 at least six people who had contact with a cow had tested independently the possibility of using the cowpox vaccine as an immunization for smallpox in humans for the first time; among them the English farmer Benjamin Jesty, in Dorset, in 1774 and the German teacher Peter Plett in 1791.^[5] Jesty inoculated his wife and two young sons and thus spared them probable death by smallpox which was raging in the area in which they lived. His patients who had contracted and recovered from the similar but milder cowpox (mainly milkmaids), seemed to be immune not only to further cases of cowpox, but also to smallpox. By scratching the fluid from cowpox lesions into the skin of healthy individuals, he was able to immunize those people against smallpox. It was reported that farmers and people working regularly with cows and horses were often spared during smallpox outbreaks. More and more an investigation conducted towards 1790 by the British Army showed that horse-mounted troops were less infected by smallpox than infantry, and this due to a major exposure to the similar horse pox virus (Variola equina). By the early 19th century, more than 100,000 persons in Great Britain had been vaccinated. The arm-to-arm method was also used to distribute Jenner's vaccine throughout the Spanish Empire. Spanish king Charles IV's daughter had been stricken with smallpox in 1798, and after she recovered, he arranged for the rest of his family to be vaccinated. In 1803, the king, convinced of the benefits of the vaccine, ordered his personal physician Francis Xavier de Balmis, to deliver it to the Spanish dominions in North and South America. To maintain the vaccine in an available state during the voyage, the physician recruited from the orphanages of Spain twenty-two young boys, age three to nine years, who have never had cowpox or smallpox before. During the trip across the Atlantic, de Balmis vaccinated the orphans in a living chain. Two children were vaccinated immediately before departure, and when cowpox pustules had appeared on their arms, material from these lesions was used to vaccinate two more children.^[6]

Jesty did not publicise his findings, however, credit was assumed by Dr. Jenner who performed his first inoculation, twenty-two years later and publicised his findings. It is said that Jenner made this discovery by himself possibly with out knowing previous accounts twenty years earlier. Although Jesty could have been the first to discover it, Jenner let everyone know and understand it, thus taking credit for it.

The virus is found in Europe, and mainly in the UK. Human cases today are very rare and most often contracted from domestic cats. The virus is not commonly found in cows; the reservoir hosts for the virus are woodland rodents, particularly voles. It is from these rodents that domestic cats contract the virus. Symptoms in cats include lesions on the face, neck, forelimbs, and paws, and less commonly upper respiratory tract infection.^[7] Symptoms of infection with cowpox virus in humans are localized, pustular lesions generally found on the hands and limited to the site of introduction. The incubation period is nine to ten days. The virus is prevalent in late summer and autumn.

Kinepox

Kinepox is an alternate term for the smallpox vaccine used in early 19th century America. Popularized by Jenner in the late 1790s, kinepox was a far safer method for inoculating people against smallpox than the previous method, variolation, which had a 3% fatality rate.

In a famous letter to Meriwether Lewis in 1803, Thomas Jefferson instructed the Lewis and Clark expedition to "carry with you some matter of the kine-pox; inform those of them with whom you may be, of its efficacy as a preservative from the smallpox; & encourage them in the use of it..."^[8] Jefferson had developed an interest in protecting Native Americans from smallpox having been aware of epidemics along the Missouri River during the previous century. One year prior to his special instructions to Lewis, Jefferson had persuaded a visiting delegation of North American Indian Chieftains to be vaccinated with kinepox during the winter of 1801-2. Unfortunately, Lewis never got the opportunity to use kinepox during the pair's expedition as it had become inadvertently inactive — a common occurrence in a time before vaccines were stabilized with preservatives like glycerol or kept at refrigeration temperatures.

Historical use

In The Cow-Pock—or—the Wonderful Effects of the New Inoculation! (1802), James Gillray caricatured recipients of the vaccine developing cow-like appendages.

Cowpox was the original vaccine of sorts for smallpox. After infection with the disease, the body (usually) gains the ability of recognizing the similar smallpox virus from its antigens and so is able to fight the smallpox disease much more efficiently. The vaccinia virus now used for smallpox vaccination is sufficiently different from the cowpox virus found in the wild as to be considered a separate virus.^[9] The virus contains one hundred and eighty-six thousand base pairs of DNA, which contains the information for about one hundred and eighty-seven genes. This makes smallpox one of the most complicated viruses known. Some one hundred of these genes give instructions for key parts of the human immune system, giving a clue as to why smallpox is so lethal.^[10]

Prevention

As cowpox virus was tested to invent a smallpox vaccine, prevention against cowpox is by vaccination against smallpox.

References

1. ^ ^{a b} Vanessa Ngan, "Viral and Skin Infections", 2009
2. ^ Thomas Cooper Library, University of South Carolina: "Edward Jenner and the Discovery of Vaccination", exhibition, 1996
3. ^ ^{a b} Cellular and Molecular Immunology K. Abbas Fifth Edition
4. ^ "Rat-to-Elephant-to-Human Trasmission of Cowpox Virus". EID Journal 14 (4): 670–671. 2008. 
5. ^ Plett PC (2006). "[Peter Plett and other discoverers of cowpox vaccination before Edward Jenner]" (in German). Sudhoffs Arch 90 (2): 219–32. PMID 17338405. 
6. ^ Jonathan B. Tucker "Scourge" 2001 pp. 31
7. ^ Mansell, Joanne K.;Rees, Christine A. (2005). "Cutaneous manifestations of viral disease". In August, John R. (ed.). Consultations in Feline Internal Medicine Vol. 5. Elsevier Saunders. ISBN 0-7216-0423-4. 
8. ^ "Jefferson's Instructions to Lewis and Clark (1803)". http://www.library.csi.cuny.edu/dept/history/lavender/jefflett.html. Retrieved 2007-08-10. 
9. ^ Yuan, Jenifer The Small Pox Story
10. ^ Pete, Moore "Killer Germs"2001

Sources

• Peck, David R. (2002). Or Perish in the Attempt: Wilderness Medicine in the Lewis & Clark Expedition. Farcountry Press. ISBN 1-56037-226-5.