According to a World Health Organization (WHO) summary and assessment on 26 April 2013, from 12 March to 26 April 2013, there were a total of six new laboratory confirmed human cases with avian influenza A(H5N1) virus infection. The cases were from the following countries: Bangladesh (1), Cambodia (1), Egypt (2), and Viet Nam (2). The UN agency says that after investigation, the six cases are considered sporadic.
So far in 2013, Cambodia has reported 10 cases of the lethal virus in humans, resulting in eight fatalities. Health authorities say cases do not seem to be linked directly, and most had contact with sick poultry in their villages. Since 2003, there have been 628 laboratory confirmed human cases of avian influenza A(H5N1) virus infection officially reported to WHO from 15 countries, of which 374 died (about 60%).
According to WHO, the H5N1 virus subtype (different from the H7N9 strain circulating in the current China outbreak) is a highly pathogenic AI virus, which first infected humans in 1997 during a poultry outbreak in Hong Kong SAR, China. Since its widespread re-emergence in 2003 and 2004, this avian virus has spread from Asia to Europe and Africa and has become entrenched in poultry in some countries, resulting in millions of poultry infections, several hundred human cases, and many human deaths.
The case fatality rate for H5N1 virus infections in people is much higher than that of seasonal influenza infections. Clinically, in many patients, the disease caused by the H5N1 virus follows an unusually aggressive clinical course, with rapid deterioration and high fatality. Like most emerging disease, H5N1 influenza in humans is poorly understood.
The incubation period for H5N1 avian influenza may be longer than that for normal seasonal influenza, which is around two to three days. Current data for H5N1 infection indicate an incubation period ranging from two to eight days and possibly as long as 17 days. WHO currently recommends that an incubation period of seven days be used for field investigations and the monitoring of patient contacts.
(The Global Dispatch 4/28/2013)