Cowpox is an infectious disease of cows’ udders that resembles a mild form of smallpox when contracted by humans through touch. Cowpox is a skin infection and visually manifests in cows by pustules or ulcers on the teats. It formed the basis of early smallpox vaccines.
It was first observed in cattle but is more commonly found in felines. Cowpox is notable in that when transmitted to a healthy human host, it produced smallpox immunity, leading to early smallpox vaccines.
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Pioneers of Vaccination
Benjamin Jesty (1736-1816), an English farmer from Devon, was one of the first to realize that people who contracted cowpox were also immune to smallpox. Cases of cowpox were common among milkmaids, who would often catch the disease when it entered their system through cuts or other breaks in the skin while milking diseased cows.
When there was a smallpox breakout in Jesty’s local town, he discovered the connection when he saw that these milkmaids were immune not only to smallpox but also from succumbing to cowpox again. He removed fluid from the pustules on the teats of infected cows and applied this to the skin of his wife and two sons, hoping to “vaccinate” them against smallpox.
In 1796, an English medical practitioner called Edward Jenner (1749-1823) first coined “vaccination” from the Latin for cow, Vacca. Jenner also provided the first description of cowpox in 1798 and created and administered the first modern smallpox pox.
While Jesty is primarily considered to be the first to use cowpox as an inoculation attempt, he was no scientist. Jenner has achieved recognition as the master of the science behind the smallpox vaccination.
An interesting theory is that he used an extinct or rare equine orthopoxvirus resembling the Vaccinia virus in his experiments.
Symptoms and Timelines
Human cases of cowpox have tell-tale signs of pusy lesions on the hands and face. These lesions then become ulcers and eventually scab before healing on their own. The virus incubation period is about 8 to 12 days, while it takes 3 months from contraction to complete healing.
The typical stages of infection are:
| Day 1 to 6 | The site of infection appears as a macule or an inflamed flat spot on the skin. |
| Day 7 to 12 | The macule turns into a papule (an abscess or inflamed raised spot on the skin) and becomes a vesicle, blister, or cyst. |
| Day 13 to 20 | The cyst fills with blood and pus and becomes ulcerated. You may notice the presence of other cowpox lesions in the same area. |
| Weeks 3–6 | The ulcer becomes a deep-seated, crusty black eschar, surrounded by swollen red skin. |
| Weeks 6–12 | The eschar dries and sloughs off. The skin lesion heals, often leaving a scar. |
Other general symptoms of cowpox are fever, lethargy, vomiting, and a sore throat.
Swollen and painful lymph nodes can also occur. Eye afflictions like conjunctivitis, periorbital swelling, and corneal involvement may result from cases of cowpox. Ocular cowpox may have grave consequences and shares some similarities to anthrax.
It is helpful to test serum anti-IgM antibodies for Bartonella henselae (the cause of “cat scratch disease”) and Francisella tularensis (the cause of the sometimes-lethal tularemia, transmitted by ticks and small rodents) to rule out cowpox.
To avoid confusion and confirm cowpox DNA, you should use a polymerase chain reaction (PCR) test.
History and Background
The words vaccine and vaccination derive from the phrase Vaccinia. Vaccinia is a virus whose origins are unclear, although it is possibly a variola and cowpox hybrid. Its genetic makeup is different from the modern-day cowpox virus. This difference could be because the variola virus was allowed to contaminate early vaccine cultures. This hybrid still grants smallpox immunity, however.
There is no recorded evidence of human-to-human transmission of the virus. However, cowpox is a zoonotic skin disease, meaning that humans can be infected from an animal.
Human infection follows after direct contact with an infected animal, usually a rodent or cat, and appears as red blisters on the hands, fingers, or face.
No specific treatment or antiviral therapy exists, but this is often not an issue as cowpox is self-limiting and will disappear in time without treatment. It has no long-lasting or harmful effects as long as the patient is not immunosuppressed.
Human cowpox is relatively rare worldwide and is most common in Europe. Cowpox virus (CPXV) is part of the Orthopoxvirus genus within the Poxvirus family.
The cowpox virus is one of four orthopox viruses. One of the other three is variola, a virus variant that causes smallpox.
Natural Reservoirs
In the 1980s, scientists realized that rats and domestic cats were also carriers of the virus and that they, not cattle, were responsible for most cowpox infections in humans. However, rodents are a cowpox’s natural reservoir.
A natural reservoir is an organism where an infectious pathogen lives or depends on for its spread. Natural reservoirs do generally not harm their hosts.
Although not confirmed as the definitive cause of all cowpox virus variants, the natural reservoirs of cowpox in Britain and Eurasia are bank voles and wood mice in Great Britain and great gerbils in Eurasia (Kurth A, Wibbelt G, Gerber HP, Petschaelis A, Pauli G, Nitsche A (April 2008).
There is marked seasonality for human cases in Great Britain. These cases occur mainly from July to October when woodland rodents are most common and active.
However, the virological characteristics of Cowpox viruses, their geographic range, and the symptoms and features of the resulting illness in humans are very different from the ones caused by the monkeypox virus or other pox viruses.
Human and animal cowpox recognition started before Edward Jenner’s smallpox inoculation experiments. However, he does mention the “cowpox virus” as an agent to prevent smallpox,
The risk of severe illness from cowpox virus infection is similar to Vaccinia virus, i.e., potential ill health from smallpox vaccinations. Eczema or atopic dermatitis, immune system deficiency, and disseminated cowpox virus infection may result in death in a few cases.
It is still unclear whether smallpox vaccination can protect again cowpox virus infection, but any resistance would be nominal. Public health focus on cowpox virus infections increases awareness among rural healthcare providers and veterinary practitioners.
Research Results
Between 2008 and 2011, there were reports of about 40 cases of human cowpox in Germany and France. Reports confirmed that young pet rats were responsible for the infections.
Scientists found a unique hemagglutinin gene sequence in various samples of the cowpox virus, indicating the source of infection was the same.
At an animal clinic in Germany in 2015, vets found four out of five cats with cowpox demonstrated common hemagglutinin sequences. The consensus was that the cats had acquired the disease in the same clinic.
In reinvestigating the outbreaks, laboratory staff used next-generation sequencing as epidemiological data could not confirm all the cases adequately.
An Emerging Infectious Disease
There is an increasing number of cases of human cowpox affecting young people in Europe.
This phenomenon demonstrates that the absence of smallpox vaccination since 1977 may reduce people’s resistance to the cowpox virus. Combined with the rise of small domestic animals, proven natural reservoirs for cowpox, the virus might now be considered an emerging infectious disease (emerg infect dis).
This hazard increases concerns about public health and the efficacy of vaccines and antiviral medicines.
