Sexual transmission of cowpox
Well, the title stretches this case study a bit, but it is all about drawing the reader in. I came across this story via the ever enlightening Morbidity Mortality Weekly Report, published by the Center for Disease Control and Prevention. The latest issue describes a local outbreak of vaccinia (cowpox) infections during June 2012. The first patient was admitted to a private hospital, reporting painful skin lesions. Superficially, the lesions resembled those of cowpox, and the patient reported sexual contact with someone who had been vaccinated with this virus, suggesting a route of transmission. The San Diego Public Health Laboratory then detected non-smallpox Orthopoxvirus by polymerase chain reaction (PCR) analysis to confirm the diagnosis. The patient was then treated with vaccinia immune globulin intravenous (VIGIV), a form of serum therapy, or passive immune protection against the infection. The lesions resolved without complications.
A second patient also reported skin lesions a few days later, and follow up of the case indicated that this individual’s only link to the case was sexual contact with the previous patient. This was a tertiary transmission event, from the initial vaccinated individual, to the first patient, then to the second patient. Again, vaccinia infection was verified by the Public Health lab, and treatment with VIGIV resulted in full resolution. Patient Zero was a civilian who had received the smallpox vaccine as part of the Department of Defense vaccination program. Epidemiological investigation indicated that he had only been in contact with the first patient. All patients were monitored to ensure no further transmission had occurred, particularly to at risk individuals, such as those with immunocompromised status, pregnant women, or people with chronic eczema.
Vaccinia infection has historically been widely administrated, and was the key component in the eradication of smallpox globally. Routine vaccination of the US public ended in the late 1960’s, and the last cases of smallpox were in the mid-1970’s. Currently, viable smallpox virus is only found in freezers at the CDC, and at Vektor labs in Russia. Risk of smallpox infection in human populations is therefore only due to a purposeful bioterrorism event, and as such only at risk first responders receive the smallpox vaccine. The utility of vaccinia as a method of protection against smallpox is several fold; first, infection with the cowpox virus provides excellent protection against subsequent infection by smallpox, due to the similarity of viral surface antigens. Second, vaccinia is very poorly transmissible from person to person. According to a review article in the Journal of the American Medical Association, mass vaccination programs have resulted in a reinfection rate among the general public at a rate of under 0.1%. Furthermore, complications due to reinfection are strongly associated with some other underlying medical issue in the patient.
The CDC report notes that secondary infection of vaccinia has been reported in a number of cases, including non-intimate situations. Tertiary transmission has also been reported through household contact, as well as from mother to child via breastfeeding, however this is the first documented case of sexual transmission through a community.
Bonus time! Vaccinia virus is an example of a live virus. Although you cannot get smallpox from this vaccine (because smallpox virus is not the same as vaccinia virus), this case study pretty concretely demonstrates that infection due to vaccinia can result in a transmissible disease. For a bonus point, in the comment thread list another vaccine that has been demonstrated as a possible side effect to produce an active disease in the recipient. Standard rules apply: no repeats, and you need to include a citation link.
For the purposes of this bonus opportunity, I am banning any citation sources that I would question their veracity. A good place to look for information might be the CDC website or Pubmed. If your citation link is Jenny McCarthy’s website, I will deduct a point from your final course grade in anger.