Cowpox
Cowpox is a rare zoonotic disease caused by the cowpox virus, a double-stranded DNA virus related to the variola virus, which causes smallpox. It primarily affects humans through direct contact with infected animals, particularly pet cats, though it can also be found in cattle and various mammalian reservoirs such as wild rodents and zoo animals. The disease manifests as a skin rash that develops into pustular blisters, which ulcerate and can leave scars, but typically does not cause long-term health issues. While rare, cowpox has been reported mostly in the United Kingdom and parts of Asia, with no cases documented in the United States.
Historically significant, cowpox was instrumental in the development of the smallpox vaccine by Edward Jenner in 1796, as milkmaids who had contracted cowpox were found to be immune to smallpox. Although supportive treatment is usually sufficient due to the mild nature of the illness, immunocompromised individuals are at higher risk for severe complications. Diagnosis can be challenging due to its rarity, often leading to misdiagnosis. Preventative measures mostly involve avoiding contact with potential sources of infection, particularly in areas where cowpox is more common.
Cowpox
- ANATOMY OR SYSTEM AFFECTED: Skin
Definition
Cowpox is an extremely rare zoonotic disease in humans, acquired from direct contact with an infected cow or other mammalian hosts. It is a skin disease that results in a rash and ulceration but no long-term effects. Edward Jenner, observing that milkmaids who had had cowpox never were infected with smallpox, used biological material from a cowpox lesion as the basis of the first successful vaccination in 1796.
Causes
Cowpox is caused by infection with cowpox virus, a double-stranded deoxyribonucleic acid (DNA) virus of the Poxviridae family and related to variola virus, the agent of smallpox. Because the two viruses have similar antigenic sites, antibodies produced against the cowpox virus provide immunity to smallpox. In modern times, inoculation with the related vaccinia virus is used as the smallpox vaccination agent, providing cross-immunity to cowpox. Although found in cattle, from which it derives its name, the cowpox virus has many mammalian reservoirs, including wild rodents such as mice and voles, and cats. Pet cats are the most likely source of infections in humans. The virus also has been found in zoo animals, particularly feline species and elephants. Cowpox is found primarily in the United Kingdom and the former western states of the Soviet Union and adjacent areas of north and central Asia. Even at that, there are only a few cases reported each year worldwide. There have never been any reported cases in the United States.
Risk Factors
Infection can occur only through a break in the skin in direct contact with a cowpox lesion, especially from cats. Immunocompromised and eczematous persons are at higher risk of infection. Only one reported case of systemic involvement and death has been reported, and this occurred in an immunocompromised person.
Symptoms
At the site of infection, which is usually the hands, the normal symptoms are a rash followed by a pustular blister that then ulcerates, scabs over, and leaves a scar. The rash and infection do not spread. Normally, only one lesion is found. Swollen nodes, slight fever, chills, loss of appetite, headache, and muscle aching may occur. Scientists believe the ocular version of cowpox, though rare, could be significantly more serious than simple cowpox lesions and lead to complications with skin necrosis around the eyes and eyelids.
Screening and Diagnosis
Because cowpox is so rare, a physician will often misdiagnose the condition as bullous impetigo and treat it with antibiotics, which are ineffective. A patient history of contact with cats, and subsequent scratches, may help in diagnosis. Polymerase chain reaction (PCR) analysis can be used to identify the virus, but this would normally not be done.
Treatment and Therapy
Generally, treatment is only supportive, as the disease is mild. Poxvirus infections can be treated with cidofovir or vaccinia immunoglobulin in immunocompromised persons.
Prevention and Outcomes
Because of its rarity, cowpox prevention techniques are not needed. If traveling in countries with endemic infections, one should avoid contact with cats.
Bibliography
Bruneau, Ryan C., Loubna Tazi, and Stefan Rothenburg. "Cowpox Viruses: A Zoo Full of Viral Diversity and Lurking Threats." Biomolecules, vol. 13, no. 2, 8 Feb. 2023, p. 325, doi: 10.3390/biom13020325. Accessed 2. Feb. 2025.
Essbauer, Sandra, Martin Pfeffer, and Hermann Meyer. “Zoonotic Poxviruses.” Veterinary Microbiology 140 (2010): 229-236.
Fenner, Frank. “Adventures with Poxviruses of Vertebrates.” FEMS Microbiology Reviews 24 (2000): 123-133.
Knorr, Corinna W., et al. “Effects of Cidofovir Treatment on Cytokine Induction in Murine Models of Cowpox and Vaccinia Virus Infection.” Antiviral Research 72 (2006): 125-133.
Krankowska, Dagny C., et al. “Cowpox: How Dangerous Could It Be For Humans? Case Report." International Journal of Infectious Diseases, vol. 104, 2021, pp. 239-241. NIH: National Library of Medicine PubMed, pubmed.ncbi.nlm.nih.gov/33359672/. Accessed 2 Feb. 2025.
Rusnock, Andrea. “Catching Smallpox: The Early Spread of Smallpox Vaccination, 1798-1810.” Bulletin of the History of Medicine 83 (2009): 17-36.