Outbreaks in poultry: significance for human health

The arrival of highly pathogenic H5N1 avian influenza on the African continent would be of great concern for human as well as animal health. Though the densities of human and poultry populations are generally lower in Africa than in South-east Asia, the poultry production systems have many similarities which would create multiple opportunities for human exposure, should outbreaks occur in African poultry. In Africa as in affected Asian nations, large numbers of households keep backyard flocks, which often mingle freely with wild birds. Most such flocks scavenge for food, often entering households or sharing outdoor areas where children play.

With few exceptions, notably in large commercial farms, surveillance for avian disease is non-existent. Nutrition of the birds is poor and high mortality is common, increasing the likelihood that outbreaks of H5N1 will be missed. Few governments are in a position to offer support for disease control – let alone compensation to farmers for destroyed birds, thus further discouraging early and open reporting. As experience in Asia has shown, late detection of outbreaks increases the likelihood that the virus will become endemic. Deaths of large numbers of poultry, whether due to disease or culling for control purposes, would deprive already impoverished populations of an important source of dietary protein.

Human cases

In Africa, the risk of human infection from an avian H5N1 virus can be expected to be similar to that seen in Asia. To date, the majority of human cases in Asia have been linked to close contact with infected domestic birds, with especially high risks thought to occur during home slaughter, defeathering, butchering, and preparation for cooking. Consumption of inadequately cooked poultry and poultry products (including eggs and blood) is an additional risk. As in Asia, African households, especially in rural areas, traditionally slaughter and consume birds when signs of illness appear in backyard flocks. As in Asia, such practices could prove difficult to change.

The occurrence of human cases – even when sporadic – would create enormous new challenges for health systems and services that are already fragile and overburdened. Should human cases occur, their early detection – when treatment with antiviral drugs is most likely to improve prospects of survival – is unlikely. Surveillance systems are weak and unlikely to pick up cases of a disease with symptoms similar to illness from many other common causes. Health capacity and human and financial resources have been overwhelmed by the demands of diseases such as AIDS, tuberculosis and malaria. Laboratory confirmation of human H5N1 infections is technically challenging, expensive, and demanding on human resources. Management of H5N1 patients is very demanding. Infection control in most hospitals is difficult to introduce and sustain. Sporadic cases of H5N1 infection and the frequent reluctance of residents to comply with recommended reporting and isolation measures during outbreaks of severe disease could push fragile health systems close to the brink of collapse. Surveillance systems, with rare exceptions, are not sufficiently sensitive to pick up clusters of human cases – a critical early warning signal that the virus is improving its transmissibility. Africa has some well-equipped laboratories, but these might rapidly prove inadequate should large numbers of samples need to be tested rapidly.