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. 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. . 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 — has the Latin root vaccinus meaning of or from cows. World Health Organization in 1980 announced that smallpox was the first disease that had been eradicated world wide by a program of vaccination.. 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 . 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.
In the years 1770 till 1790 at least six people 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. 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.
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