Expanded Host Range and Clinical Presentation of Bird Flu
Recombinomics Commentary
February 23, 2005
>> "It's clear that the [H5N1] virus is evolving and getting a broad host range," Niman tells WebMD.
"We do know that these H5N1 viruses have been documented to transmit to a number of different animal species. That includes tigers and leopards and domestic cats," Uyeki says. "H5N1 is also confirmed to infect pigs in China; there have been a limited number of cases reported in pigs. The point is that these viruses are extremely concerning. They have transmitted to a number of animal species and have killed humans."
A recent report in the New England Journal of Medicine shows that human infection with H5N1 bird flu is more complicated than previously thought. The virus infected the brain and gut of two Vietnamese children who died with severe seizures and - ominously - severe diarrhea.
"The isolation of virus from a rectal specimen is a major source of concern, since it highlights a potential route of human-to-human transmission, especially in combination with crowded living conditions and diarrhea," Jenno D. de Jong, MD, and colleagues wrote.
The leader of this study, Jeremy Farrar, MD, PhD, is clearly worried.
"The great concern is there is an incredibly virulent avian flu that shows the ability to jump to humans," Farrar told WebMD in a December 2004 interview. "And when it gets to humans, it is clearly a very nasty disease with a high mortality rate." <<
The expanded host range is cause for concern. This expansion has been done in the absence of avian / human reassortants. H5N1 has undergone a series of recombinations to generate new genes with expanded host ranges. As the number of hosts expands, more novel recombinants can be generated.
These novel recombinants can also be seen in the swine isolates in Korea. These isolates are avian / human reassortants between H1N1 WSN/33 and H9N2 Korean avian isolates. In addition to forming avian / avian recombinants in N2, the PB2 recombinants which are half human and half avian have been generated. In Korea there have been recent isolates that are H9N2, H3N2, H6N1, H5N1, and H1N1. This genetic diversity can lead to more genetic instability.
In Vietnam, the clinical presentation of patients has also become more complex. Complex Cambodian cases have also been mentioned. The patients, who may not initially present with respiratory symptoms would frequently not be tested for H5N1. In the 1918 flu pandemic, patients were frequently misdiagnosed as cholera, dengue fever, or typhoid cases. Expanded screening in southeast Asia, as well as other countries with unexplained deaths, such as India and the Philippines, should be done to determine the worldwide distribution of H5N1 avian influenza.
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