Monday, April 10, 2006

Cats and other carnivores

With every piece of reassurance there comes a catch. Consider the claim that you can't get bird flu from poultry that has been properly cooked. What about raw poultry?

Eating raw poultry or drinking poultry blood is uncommon, although it is done in some cuisines. But many animals -- carnivores that prey on small animals like birds -- do eat poultry raw. And some, like cats and dogs, live closely with humans. They also seem to be competent hosts for the virus.

Some scientists have been concerned about this and last week they laid out those concerns in the scientific journal, Nature.
A scientist with the UN's Food and Agriculture Organization is setting up a study aimed at trying to determine if cats are playing a role in the spread of the H5N1 avian flu virus, looking at Indonesia where a perplexing pattern of human cases has raised questions about how the disease is transmitting.

Dr. Peter Roeder and Indonesian colleagues will be looking for infected cats in areas with H5N1 outbreaks in poultry. Indonesia is the current hot zone of H5N1 infection, reporting 30 cases — including 23 deaths — since last July.

Experts have been watching the country closely, puzzled by the tenuous and at times seemingly non-existent links between some human cases and infected poultry. Elsewhere investigations have almost always traced human infections back to contact with sick or dead birds.

“The worry is in quite a significant number of human cases in Indonesia that there is no apparent connection between the people and poultry,” Dr. Roeder, an animal health officer with the FAO, said in an interview from Beirut, where he was attending a conference.

“Now is it possible that cats could be an intermediary between the two? I'm not wanting to propose that they are, but what I'm saying is I think this raises the question.”

Dr. Roeder and some scientists from Erasmus Medical Centre in Rotterdam explored just that issue in a commentary published Wednesday in the journal Nature.

They argued that given the growing number of reports of dying cats in areas with H5N1 outbreaks, and the fact that laboratory experiments have shown cats can become infected and spread the virus cat to cat, it would be imprudent to rule out feline involvement in the spread of virus.

“It's really rather preliminary stuff, although it's been a very consistent story, everywhere we've started asking,” Dr. Roeder said.

“As the moment, we have no evidence that they're playing a role in the transmission of infection within poultry flocks, between poultry flocks or between infected chickens and people. But the potential is obviously there.” (Helen Branswell, Canadian Press via The Globe and Mail)
What we know is that cats (and apparently dogs) can become infected. That cats can pass it to each other when caged together. That some cats get sick and die and others don't. And we believe cats shed less virus than birds.

What we don't know is more important. We don't know if small carnivores are significant vectors of the disease under natural conditions. That is why Roeder's Indonesian experiments are important. Dr. Andrew Jerimijenko has already reported that a kitten he swabbed in Indonesia was infected and word is virus was similar to the human strains in Indonesia as opposed to the bird strains. We await further information on this animal which is being investigated by scientists associated with the US Navy Laboratory in Indonesia. It's time they released the data.

In addition we don't know what other wild carnivores are also competent hosts for H5N1 in the wild. Last month a stone marten, a weasel-like carnivore, was found to have died from H5N1 in northern Germany. How many other animals are at risk as the wild bird population becomes infected? Cats and other carnivores may now be dead-end hosts because they do not readily transmit the disease. This seems to be true of humans at the moment. But as more and more mammals become infected, any change in the virus that allows it to to be transmitted more efficiently will be under selective pressure to emerge.

It's time for systematic surveys for evidence of viral infection in non-bird species in those areas where the bird population is infected, beginning with animals that prey on birds. This is an urgent need, made more urgent by the explosive spread of the virus to ever new environments.