Harvard Public Health Review: Spring 2006

Harvard Public Health Review
Spring 2006

HSPH Update: Avian Flu

Avian Flu in Africa

What does an outbreak in resource-poor Nigeria mean? Perhaps faster evolution to a virus that can spread efficiently among humans, says veteran infectious disease expert and AIDS researcher Max Essex.

In early January 2006, the African continent saw its first reported outbreak of A/H5N1, the pathogenic strain of avian flu that is now spreading quickly in birds around the globe. The virus hit a large commercial egg farm in Kaduna State, in northern Nigeria. In less than a month, the virus had killed more than 40,000 chickens. Soon after, it was detected in the countries of Niger to the north, and Cameroon to the south.

What might the discovery of the deadly virus in Africa portend? To find out, the Harvard Public Health Review spoke with the Harvard School of Public Health's Max Essex, the John LaPorte Given Professor of Infectious Diseases in the Department of Immunology and Infectious Diseases. For 20 years, Essex's team has been conducting research on the virology, immunobiology, and molecular epidemiology of hepatitis viruses and HIVs in laboratories in Boston and at several sites in Africa, especially Senegal, Tanzania, and Botswana. As someone very familiar with the public-health problems in resource-poor Africa, Essex has deep concerns about stemming this new disease on the continent.

Here are his thoughts.

On the magnitude of the problem
That AH5N1 has now been found in Africa is particularly frightening. I would think it would be appropriate for the U.S. government and the other European Economic Community players to declare some kind of emergency program to do more comprehensive sentinel surveillance in Africa and see what's happening beyond the commercial farms in which AH5N1 has been found. And that means mobilizing funds as well as people.

In the U.S. and Western Europe, very few chickens are kept in people's yards. In Asia, Thailand, Vietnam, and China, the number is quite a bit higher; in Africa, it's even higher. In most villages in Africa, people have 5 to 30 chickens running around, a few sheep or goats, and a pig or two. It's extremely likely that AH5N1 is already present in a lot of those chickens, at least in the regions of West Africa around Nigeria and Cameroon. And the infection of those privately kept chickens is probably even more important than the infection of the 40,000-chicken commercial flock, because they're the ones with access to the people. In almost all the cases in Thailand, Vietnam, China, and Turkey, transmissions to people have occurred when they've had a lot of interaction with the chickens--killing them and being sprayed with their blood. Larger commercial organizations do that with machines. Villagers do that by hand, so they're at greater risk for becoming infected.

On diagnosing flu in humans
In Africa, diagnosing that a villager has died from avian flu would be a lot harder than in Turkey, Thailand, and China, for example, because there are fewer medical experts and so, fewer chances that AH5N1 would be suspected and investigated as a cause of death. And so I would not in any sense rule out that people have already been infected with the virus in Africa--even dozens of them. I think that's a very likely possibility.

On surveillance efforts in Africa
Surveillance of AH5N1 is poorer to begin with in Africa than in Asia--both clinical surveillance, because there are not as many medical experts, and molecular epidemiologic surveillance, because there are not as many people who can do lab workups or serology monitoring. Indeed, if what happened in Turkey or Thailand regarding transmission to humans has already happened in Nigeria, I don't think anyone can possibly have noticed at the world-surveillance epidemiological level. In Asia, a lot more is known about the movement of the virus in the avian populations and the number of people getting occasional infections from chickens.

On a virus capable of efficient human-to-human transmission
If the number of infections is soon to be higher in Africa than in Asia, the chance of recombination events--which could lead to a virus that could transmit efficiently from human to human--is also higher. Yet even if that happens and many more people die, they are a lot less likely to be noticed than in other countries.

In my opinion, the chance that any epidemic could get a head start in the human population is higher in Africa than other places in the world because there is less infrastructure to detect what's going on. There are higher rates of human illness to begin with in Africa, and you would not be able to distinguish avian flu from HIV/AIDS and many other illnesses unless diagnostic tests and experts were available.

New HIV viruses have emerged much faster in Africa than in any other parts of the world. There are now at least four different HIVs in Africa, each of which has infected millions of people. Many more are rapidly emerging as new chimeric HIVs--illustrating exactly what can happen to bird flu AH5N1 to make it more transmissible between people.

On what can be done
The World Health Organization has sent out representatives to do surveillance in the geographical areas with proximity to the affected commercial flocks, and to ask questions about whether chickens are dying on family compounds around there. But how many people can be mobilized by WHO, and how much effort can be extended to sample these family household chickens? The virus is likely in a lot of areas--not just in Nigeria, but wherever there are bird flyways from Europe. In international efforts of this type, WHO, I suspect, is the only first responder, and its budget and expertise are limited. There isn't a huge critical mass of experts already funded and ready to go. One of the limitations in our modern global interaction capabilities is that virtually all the expertise and resources are still national, rather than international. Further, those regions of the world where human expertise and resources are in shortest supply, such as Africa, are most likely to serve as particularly fertile ground for getting a large-scale human flu epidemic off to a robust start.

For more on bird flu, see www.hsph.harvard.edu/review/rvwwinter06_flucatchers.html.

On May 16, HSPH Dean Barry Bloom presented a live web seminar "Bird Flu: Public Health and Pandemics." Log onto www.hsph.harvard.edu/corprelations to view an archival recording.