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This is a tale of cuteness and folly; it’s about a furry animal, a potentially lethal virus, a man with two jobs, and a sinister intruder. The animal is the prairie dog; not a dog but a rodent, a short-tailed squirrel, that lives in burrows on the North American prairies; so cute that it is traded as a pet. The virus is the monkeypox virus, a member of the orthopoxvirus genus; it was first recognised as a cause of disease in captive primates in 1958 and the first cases of human monkeypox were reported from the Democratic Republic of Congo (then Zaire) in 1970. (The man and the sinister intruder? They will appear; I solicit your patience.)
Human monkeypox has occurred sporadically since 1970, but not outside Africa—until now. Between late May and late June 2003 (
; see also perspective article, ibid: 324–7) there were 72 confirmed or suspected cases in the USA. The first was a 3 year old girl in Wisconsin. Over the next 2 or 3 weeks there were 10 other cases in the state, all related to prairie dogs and a meat inspector. This meat inspector had a second job; he bought and sold exotic and unusual animals, including prairie dogs. Between mid-April and mid-May he bought 39 prairie dogs from a distributor in Illinois and in early May he took a sick giant Gambian rat recently arrived from Ghana (gentle and sensitive reader, I share your thoughts) from this distributor to a veterinary surgeon in Wisconsin. Many of the prairie dogs, though they were said never to have been in direct contact with the rat, subsequently became ill and not a few died. By the end of the first week in June eleven people in Wisconsin had developed confirmed (8) or suspected (3) monkeypox. They were: the meat inspector/animal dealer and his wife, the 3 year old girl and her parents who had bought two of the prairie dogs, two members of another household with two more of the prairie dogs, two people who worked in the two pet shops that sold the prairie dogs, and two vets who had each treated a sick prairie dog. Two patients had been bitten or scratched by a sick prairie dog and three had had minor open skin wounds from other causes when they were in contact with one of the animals. All eleven patients complained of headache and had monkeypox skin lesions (local nodular swellings around bites and scratches, a papular rash that became vesiculopustular, or both). Skin lesions at various stages of evolution were seen together and lesions might involve any part of the skin, the inside of the mouth, and the conjunctivae. The median time to crusting of all lesions was 12 days. Nine had fever, sweats, and chills and some had cough, lymphadenopathy, sore throat, and a variety of other signs and symptoms. All recovered. (Case fatality rates of up to 22% have been reported in Africa.) Monkeypox virus was isolated from seven patients and one prairie dog and its identity confirmed by detailed DNA studies. No information is given about the way in which it spread to infect another 61 people. There were no more cases after June 22.
Serological surveys in Africa have pointed to rodents and primates as carriers of monkeypox. A large shipment of six different species of African rodent arrived in the United States from Ghana on April 9, 2003. There are two types of monkeypox virus, West African and Congolese, and gene sequencing put the virus in this outbreak in the West African camp. Ghana is in West Africa.
The import of rodents from Africa into the USA has now been banned, as has the sale, distribution, transport, or release of prairie dogs or of six named African rodent species (Gambian giant pouched rats, brush-tailed porcupines, striped mice, tree squirrels, rope squirrels, and dormice). (How many other countries import these beasts? Could your children’s new but already loved pet rabbit be at risk?)
Could the virus have infected American wildlife and could it become established in North America? Nobody knows. But the next time you trip over a brush-tailed porcupine by the shores of Lake Michigan, look out. And never introduce Floppy the bunny to a giant Gambian rat, pouched or not pouched.