Cowpox is a viral disease that normally affects the udders and teats of cows. On rare occasions, it may be transmitted to humans and produce a characteristic red skin rash and abnormally enlarged lymph nodes (lymphadenopathy). Cowpox is caused by the vaccinia virus and has been known to cause systemic reactions (generalized vaccinia) in some people who have been recently vaccinated against cowpox.
Cowpox produces immunity to smallpox and, beginning in the 19th century, the virus for cowpox was used to develop the vaccines used against smallpox. Because of the widespread vaccination, smallpox was wiped out worldwide but has now come under study again because of concern that it might be used as an agent of biological terrorism. .
The symptoms of cowpox in humans include a characteristic skin rash that consists of numerous raised blisters (vesicles) which typically appear on the face, arms, and legs. These red inflamed blisters may bleed or ulcerate. Some people with Cowpox may also have abnormally swollen lymph nodes (lymphadenopathy).
If a person whose immune system is not functioning properly (immunosuppressed) contracts the cowpox virus, a more severe form of the infection may occur. This is especially true for those people with agammaglobulinemia or chronic lymphocytic leukemia. This severe form of the infection is known as Vaccinia Necrosum or progressive vaccinia and is characterized by progressive decay (necrosis) of the tissue around the vaccination site where the cowpox virus was injected. Other symptoms usually include the eruption of skin lesions in other areas of the body. The complications of Vaccinia Necrosum may be life-threatening.
People who have severe widespread red skin lesions (eczema or dermatitis) may also experience a generalized vaccinia when vaccinated with the cowpox virus or if they have direct contact with someone who has recently been vaccinated.
A mild form of generalized vaccinia occurs after vaccination with the cowpox virus in some people with normal immune systems. A raised blistered skin rash develops seven to 12 days after vaccination. No other symptoms are associated with this form of generalized vaccinia and the rash resolves on its own.
Some people who have been vaccinated with cowpox may also get bacterial infection of the skin blisters. In rare cases the brain may become inflamed (postinfectious encephalitis) causing headache, fever, neck pain, nausea, vomiting, seizures, and/or paralysis. Other complications may include acute inflammation of the heart muscle (myocarditis) and/or the fibrous sac that surrounds the heart (pericarditis). Affected individuals may also experience swollen and painful joints (arthritis).
Cowpox is a rare viral disease caused by vaccinia virus. The virus can be transmitted from the udders and teats of infected cows. Diary farmers guard against this virus by cleaning the cow's udders before milking, and the pasteurization of milk before it is sold to the public. It can also result from vaccination against smallpox or from direct contact with a skin lesion from a recently vaccinated person.
Cowpox affects males and females in equal numbers. It is very rare in industrialized countries due to sanitation measures.
In recent years, cowpox resulting from small pox vaccination has become very rare because the extinction of smallpox has rendered this vaccination unnecessary. It is no longer routine or required for overseas travel. However, the vaccinia virus is being considered as a vector for immunization against other types of infectious agents. A more widespread use of this virus may increase the prevalence of its adverse reactions, so scientists are hesitant to experiment with the virus on humans.
Symptoms of the following disorders can be similar to those of cowpox. Comparisons may be useful for a differential diagnosis:
Smallpox is an infectious disease caused by the virus variola. The disease was declared extinct in 1980, although the virus is retained in a few laboratories for experimental purposes. Smallpox is a more severe and disfiguring disease than cowpox. The symptoms include a feeling of ill health, headache, backache, and high fever. A skin rash develops on the face followed by the widespread appearance of fluid-filled blisters. The cowpox virus is used to vaccinate people against smallpox.
There is no specific treatment for cowpox. Lotions or creams may alleviate some discomfort and help to protect against secondary infection of skin lesions. Bed rest will help to speed recovery.
Some people with cowpox with Progressive Vaccinia may be given the drug Vaccinia Immune Globulin (VIG). This drug is a solution of immunoglobulins prepared from the serum of persons recently immunized with vaccinia virus. VIG may be used to treat some complications of smallpox vaccination (i.e., eczema vaccinatum, vaccinia necrosum, ocular vaccinia, generalized vaccinia). VIG is of no benefit in the treatment of people with acute inflammation of the membranes that surround the brain which occurs because of vaccination (postvaccinal encephalitis). Other complications of cowpox are treated symptomatically.
Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.
For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:
Fauci AS, Braunwald E, Isselbacher KJ, et al. Eds. Harrison's Principles of Internal Medicine. 14th ed.McGraw-Hill Companies. New York, NY; 1998:1096.
Neff JM. Vaccinia Virus (Cowpox). In: Mandell GL, Bennett JE, Dolan R. Eds. Mandell, Douglas and Bennett's Principles and Practice of Infectious Diseases. 4th ed. Churchill Livingstone Inc. New York, NY; 1995:1325-28.
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