18 March 2008

More on pets and human infections

Another snippet from the International Conference on Emerging Infectious Diseases in Atlanta — again, not about staph, but about the unique role that pets may play in disease transmission:

In the exhibit hall that houses the "posters" (which are just what they sound like: broad swaths of shiny paper printed with graphical presentations of research), there is an intriguing report from West Virgina and the CDC about a novel infection in a cat. The infection is very serious: Corynebacterium diphtheriae, the bacillus that causes diphtheria (the "D" in the childhood DPT vaccine). Diphtheria seldom occurs in the United States — five or fewer cases per year — which is a good thing since it is a horrible disease that causes a membrane to grow across the throat and cut off breathing. It occurs so seldom because humans are the sole host for the disease, and when vaccination renders humans inaccessible territory, diphtheria fades away.

Well, make that: Humans were thought to be the sole host. The report at ICEID describes a pet cat (by the picture, a charming tortoiseshell) who came into a West Virginia veterinary hospital with a very severe ear infection. The infection turned out to be caused by C. diphtheriae that was present not only in that cat, but in a second household cat as well — but not in the cats' two human household members, nor in the eight vet personnel who had been exposed to the cats. Four isolates from the two cats had identical genetic fingerprints, but did not match any C. diphtheria isolates ever analyzed by the CDC.

And this means... what, exactly? It's not not clear how significant a development it is — "More research needed," the CDC says — but it's not good. A disease that was thought to exist only in humans, and thus could be chased out of humans if the percentage of vaccination is high enough, might instead be sustained in humans' environment by another species. And that species just happens to be a very common animal that shares our space very intimately. (Reports that my cats sleep on my pillow are merely vicious rumors. Anyway, it's only during the day.)

If vaccination coverage of the population were perfect, this would not matter: We would be protected anyway. But it's not.

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