Saturday, May 20, 2006

Cats, pigeons, Indonesia

There has been much talk about the possibility of domestic cats being infected with H5N1 and some cases have been described (see posts here, here and here). Cats eating infected birds is suspected as the source of infection in some of these cases.

Cats, both feral and domestic, are common inhabitants of urban environments. So are pigeons. We've been told we don't have to worry about pigeons and bird flu. But this paper (which got by me when it appeared in Emerging Infectious Diseases in April) tells a somewhat different story.
In early February 2004, during the outbreak of HPAI (H5N1) in Thailand, a carcass of a 2-year-old male cat (Felis catus) was taken in an icebox 6 hours postmortem to the Faculty of Veterinary Medicine at Kasetsart University, Nakornpathom, Thailand. The cat's owner volunteered the information that the cat had eaten a pigeon (Columba levia) carcass 5 days before illness onset. The owner reported that the cat had a temperature of 41°C, was panting, and appeared to be depressed. Furthermore, the cat had convulsions and ataxia and died 2 days after onset of illness. The cat was given a single dose of 75 mg aspirin 1 day before it died; however, its body temperature remained elevated. Many dead pigeons were found in the area where the cat lived.
H5N1 was isolated from the cat and from dead pigeons in the area. The genetic sequences of the viruses matched closely and resembled the sequences of the H5N1 circulating simultaneously in poultry and large zoo cats (tigers, leopards) in early 2004 in southeast Asia. Horizontal transmission ("cat to cat") has been described elsewhere but so far no one has shown any cases of cat to human. In April Dr. Peter Roeder, a Food and Agriculture Organization scientist working with Indonesian colleagues, was reported setting up a study to see if cats were playing a role in the Indonesian outbreak but we don't know if that study is happening or not. The Indonesians have a history of foot dragging. Earlier, the former NAMRU2 epidemiologist Dr. Andrew Jeremijenko had swabbed a kitten in Indonesia and isolated an H5N1 that was a close match for a virus isolated from a human.

It seems not a day goes by that this virus doesn't confront us with something new and unsettling.

Addendum: Several commenters have questioned the use of aspirin for the cat in this report, believing that aspirin is deadly for cats. Cats lack the enzyme glucuronyl transferase which is involved in the metabolism of aspirin but they tolerate appropriate doses of aspirin well and it is used routinely in veterinary medicine for arthritis or as a blood thinner. A common dose is a quarter of a buffered adult aspirin once every three days for arthritis. The literature says that 10 mg to 25 mg per kilogram every two or three days is safe.

Note that acetaminophen (Tylenol) and ibuprofen (Advil, Motrin) are extremely toxic to cats and will kill them. This may be the source of the idea that aspirin, too, is deadly. The dosage of 75 mg in this report seems excessive and may have contributed to the cat's demise, but the animal was also infected with H5N1 which was the main issue. [NB: Disregard this last comment. 75 mg would be about right for a 3 kg cat and it is about 1/4 of an adult aspirin tab. Thus the cat's relatives shouldn't sue the owner for malpractice.]