Cowpox is a rare viral skin infection caused by the cowpox virus which is a member of the Orthopoxvirus family and a close relative of the now eradicated smallpox virus, which was responsible for the deaths of between 200 - 300 million people in the 20th century.
Cowpox gets its name from the dairymaids who often catch the infection from the udders of cows they milked, however, despite its name, the natural hosts of the virus are in fact rodents. Humans, cats, dogs, horses, rodents, cattle and many other mammals can all become infected with the cowpox virus. The most common mode of transmission to humans is now via domestic cats. Our beloved felines shouldn't take all the blame for human infection, though, there was an outbreak of cowpox which occurred between pet rats and humans in France in 2009.
In 1796 British physician Edward Jenner took some fluid from the vesicle on the hand of a milkmaid named Sarah Nelmes infected with cowpox and inoculated it into two small cuts on the skin of an eight-year-old boy named James Phipps. The boy was later exposed to smallpox on multiple occasions but never came down with the deadly disease.
Cowpox is found in Europe and some parts of the former Soviet Union although most cases are in the United Kingdom. The first reported case of cowpox in cats was in 1977.
How do cats become infected with cowpox?
The most common mode of infection is inoculation through a bite of an infected rodent during hunting. Rural cats have a higher prevalence than those in cities and towns. There is an increased incidence of cowpox in summer and autumn. The virus enters the skin via the wound and replicates locally, creating the characteristic singular lesion at the site of inoculation.
What are the symptoms of cowpox in cats?
The incubation period of cowpox is between 9 to 10 days.
- Symptoms typically present as a small single macule (a flat red lesion) as localised viral replication occurs, this is usually on the cat's head, neck or forelimb. Over time this gradually increases in size developing into an inflamed lesion which over time becomes raised (papular) before finally ulcerating. At this stage, the infection may be spread from the head to the legs during grooming. It is not uncommon for the ulcer to develop a secondary bacterial infection or become abscessed. Singular lesions typically heal within 4 - 5 weeks.
- Lesions are usually the only symptom to occur in healthy cats, however, during the viremic period, some cats may display symptoms such as fever, localised swollen lymph nodes, loss of appetite and malaise. Respiratory infections such as pneumonia may also develop, which can be fatal. More severe symptoms are most commonly found in cats who are very young or immunocompromised, such as those with feline immunodeficiency virus or feline leukemia virus and may be fatal.
- In some cases, a few days after the viremic phase, widespread secondary lesions may develop as small red spots which over time develop into papules and ulcers. These scab over before completely drying out and disappearing within 6 - 8 weeks.
How is cowpox diagnosed?
Your veterinarian will perform a physical examination of your cat and obtain a medical history from you. A presumptive diagnosis may be made by visible signs, although a biopsy and microscopic examination from a lesion can confirm diagnosis.
Polymerase chain reaction (PCR) can also be used to diagnose cowpox. This test involves amplifying a few copies of a piece of viral DNA which produces millions of copies of a DNA sequence. Some veterinary practices may have in-house PCR testing kits for cowpox with results obtained in a few hours.
How is cowpox treated?
In most cases, cowpox is a self-limiting infection. There is no specific treatment for cowpox and is generally supportive. This may include:
- Antiseptics may be used to clean lesions in an effort to prevent bacterial infection taking hold.
- Antibiotics may be prescribed to treat secondary infection of lesions.
- The use of corticosteroids must be avoided in cats with cowpox as these will make the condition worse.
Can I catch cowpox from my cat?
Yes, cowpox is zoonotic, meaning it can be transmitted from infected animals to humans. Lesions usually develop on the hands or face.
If your cat has been diagnosed with cowpox proper precautions must be taken including only handling your cat while you are wearing rubber gloves and always wash your hands.
Immunocompromised people should avoid all contact with infected cats and seek advice from their doctor.