8 February 2007 Cats can become infected with the highly lethal H5N1 bird flu virus but there is no scientific evidence at present to suggest that there has been sustained transmission in cats or from cats to humans, and they should not be killed as a control option, the United Nations Food and Agriculture Organization (FAO) said today.
As a precaution, FAO recommended that in areas where H5N1 has been found in poultry or wild birds, cats should be separated from infected birds until the danger has passed. On commercial poultry premises cats should even be kept indoors. But it advised against killing cats because there is nothing to suggest they are transmitting the virus in a sustained way.
Moreover, removing them could lead to a surge in rodents such as rats, which are an agricultural pest and often transmit diseases to humans. Ever since the first human case of H5N1, linked to widespread poultry outbreaks in Viet Nam and Thailand, was reported in January 2004, UN health officials have warned that the virus could evolve into a human pandemic if it mutates into a form which could transmit easily between people.
Unconfirmed reports that H5N1 has been detected in a high prevalence in cats in Indonesia have caused some alarm. The scavenging cats were sampled in the vicinity of poultry markets in Java and Sumatra where outbreaks of bird flu had recently occurred.
This is not the first time that cats have been infected as previous incidents in Thailand, Iraq, Russia, the European Union and Turkey show. Cats can become infected by feeding on sick domestic or wild birds; they can develop severe to fatal disease and excrete the virus from the respiratory and digestive tracts.
“This raises some concern not only because cats could act as intermediary hosts in the spread of the H5N1 virus between species but also because growth in cats might help the H5N1 virus to adapt into a more highly infectious strain that could spark an influenza pandemic,” FAO Assistant Director-General Alexander Müller said.
But findings reported from Indonesia in January suggested that about 80 per cent of cats in outbreak areas have not been infected. “This is rather encouraging because it indicates that cats are unlikely to constitute a reservoir of virus infection. Cats are more likely to be a dead-end host for the H5N1 virus,” FAO Animal Health Officer Peter Roeder said.
But they should be closely monitored. “Any unusual mortality in cats should spark a suspicion of H5N1. Infection in cats could be an early warning signal for the virus. The observation of cats should therefore become part of surveillance systems in affected areas,” Mr. Roeder added.
FAO will start field studies in areas in Java where the H5N1 virus is prevalent and where cats have died to investigate their role in disease transmission. This research will be extended to other parts of Indonesia and elsewhere.
“We also need experimental studies to better understand the biology of H5N1 infection in cats, including most importantly the duration of virus shedding by infected animals,” Mr. Roeder said.
There have so far been 272 confirmed human cases worldwide, 166 of them fatal, the vast majority in South-East Asia. Indonesia has recorded the highest death toll – 63 out of 81 cases. UN health officials have been on constant alert to detect any mutation that could make the disease more easily transmissible in humans.
The so-called Spanish flu pandemic of 1918-1920 is estimated to have killed from 20 million to 40 million people worldwide. More than 200 million birds have died worldwide from either the virus or preventive culling in the current outbreak.