May 5 (Bloomberg) -- Bird flu is spreading more slowly as warmer spring weather in the Northern Hemisphere reduces the virus's ability to survive in the environment.
Five outbreaks of the lethal H5N1 avian flu strain in poultry were reported to the World Organization for Animal Health in the week ended April 27, compared with an average of more than 40 a week in March. Diseased fowl raise the risk for humans and create opportunities for the virus to change into a form that may kill millions of people.
Scientists are counting on the slowdown in animal infections to reduce the number of human cases and fatalities. At least 29 people died of avian flu in the first three months of this year, marking the deadliest quarter yet, as the virus spread through Europe and Africa.
``The peak transmission either in poultry or to humans is in the winter months,'' said Robert Webster, the Rosemary Thomas professor at St. Jude Children's Research Hospital in Memphis, Tennessee. Webster has studied influenza viruses for more than 40 years.
Tests have shown that H5N1 can survive in bird feces for at least 35 days at about 4 degrees Celsius (39 degrees Fahrenheit), the World Health Organization said in January.
``Maybe one of the more positive possibilities is that the summer is coming and the heat of Africa may be in our advantage,'' Webster told reporters yesterday in Singapore, where he addressed an avian flu forum sponsored by the Lancet medical journal. ``Maybe we will have a summer before it starts spreading more.''
114 Deaths
The H5N1 virus has killed at least 114 of 206 people infected since late 2003, including a 27-year-old woman from Egypt who died yesterday, the Geneva-based WHO said today.
The woman had been treated at the Abbasiya Hospital for double pneumonia since May 1, Egypt's government said on its Web site. She is the country's fifth H5N1 fatality and the first new case in a month.
``Her infection has been linked to exposure to diseased poultry during a recent visit to the Minufiyah governorate,'' the WHO said in a statement. ``While there, she stayed in a household where numerous chickens were slaughtered.''
In almost all human H5N1 cases, infection was caused by close contact with sick or dead birds, such as children playing with them, or adults butchering them or taking off the feathers, according to the Geneva-based WHO.
The WHO is tracking human cases in the event the virus becomes easily transmitted from person to person, sparking a pandemic such as the 1918 outbreak that killed as many as 50 million people worldwide.
Surviving Longer
Studies have shown the virus is capable of surviving longer in warmer conditions, Webster said. A strain of H5N1 collected from ducks in Hong Kong in 1997 was able to survive for as long as two days at 37 degrees Celsius, while the current viruses from Indonesia and Thailand take up to seven days to be destroyed at that temperature, he said.
Researchers in Thailand found live H5N1 in the blood of an infected patient. If carried in the blood, the virus might be more dangerous as a result of its ability to thrive in additional tissues, researchers led by Salin Chutinimitkul of the Chulalongkorn University in Bangkok said in a letter to a U.S. government journal.
The virus was isolated from the blood of a 5-year-old Thai boy who died in December, they said. Flu infection is normally limited to the lungs and lining of respiratory tissue.
U.K., Sudan
Initial avian outbreaks were reported in only four countries last month -- the U.K., Sudan, Burkina Faso and Ivory Coast -- compared with 13 in March and 18 in February, according to the World Organization for Animal Health.
Outbreaks in Nigeria, Iraq and Turkey were caused by variants of an H5N1 strain found in China in April last year, when more than 6,000 wild birds died at the Qinghai Lake nature reserve, the WHO said in February.
The pattern of infections may be repeated this year. China's Agriculture Ministry said avian flu was found in migratory birds in a wetland in the western province of Qinghai, and has taken measures to prevent the spread to domestic poultry.
Health authorities in Qinghai's Yushu county, about 800 kilometers (500 miles) west of provincial capital Xining, reported the H5N1 strain killed 125 wild birds as of May 4, the ministry said in a statement on its Web site.
``In the past, this high pathogenic virus has not been perpetuated in wild birds,'' virologist Webster said in a May 2 interview. ``Now this high pathogenic virus is in wild birds. Is it going to be transmitted through the breeding cycle of the birds in Siberia, Australia, or wherever? That's what we are all watching out for.''
