Influenza virus subtypes in wild birds within selected sites along the major migratory fly-ways in Kenya
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Human influenza pandemics are rare but recurring events that have periodically affected humanity since ancient times. They are associated with a rapid surge, experienced globally, in the number of cases of respiratory illness and death. Three pandemics occurred during the previous century; the Spanish flu in 1918, the Asian flu in 1957 and the Hong Kong flu in 1968. The world is at risk of another pandemic. For almost two years, health experts have been monitoring a new and severe influenza virus, the highly pathogenic H5Nl strain. Since mid- 2003, this virus has caused the largest and most severe outbreaks of highly pathogenic disease ever recorded in poultry. The current H5Nl strain is a fastmutating and is found in multiple bird species. It is both epizootic and panzootic. Since 1~97, studies of H5Nl indicate that these viruses continue to evolve, with changes in antigenicity and internal gene structure with an expanded host range in avian species and the ability to infect other animal species with enhanced pathogenicity and increased environmental stability. Kenya is a part of the migratory bird fly-way from Europe and Western Asia. Surveillance along the flyway is essential to identify possible HPAI infection and the nature of infection in order to be able to predict possible spillover into human populations. Due to limited data on circulating Influenza strains in wild birds in Kenya, the study was initiated to determine what subtypes of avian influenza viruses are harbored by wild birds in four migration seasons between October 2005 to June 2009. Specimens were collected in 13 sites from 3,618 birds representing 150 species with majority of the specimens being collected from sandpipers, plovers and ducks. The specimens were screened for influenza A by real-time Reverse Transcriptase Polymerase Chain Reaction. All positive Influenza A specimens were further screened for the H5 subtype.Influenza A virus was detected in 1.68% (61/3618) of the all birds representing 23 different species. Of the 61 Influenza A virus positives 21 (34%) were from resident birds, 21 (34%) from paleartic migrants and 19 (32%) from intra African migrants. All the positives were detected during the migration period between October to April. Chi-square was used to determine if there was a significant difference in the number of positive samples in each of the 4 years and among the various categories of birds based on their migration patterns. This variation in prevalence was significant among the four year migration seasons. No highly pathogenic avian influenza viruses were detected during the study period. However, 1 low pathogenic avian influenza virus (LPAI) H12N2 and 4 LPAI H5 subtypes whose neuraminidase subtype was not established were detected in 4 bird species representing both resident and migratory species sampled in 3 sites. The findings demonstrate the potential for wild birds as reservoirs and disseminators of HPAI viruses to areas that may be free from the viruses. The study has given animal and public health experts a baseline of influenza virus activity in wild birds. The study should be strengthened and maintained to continuously monitor influenza virus subtypes circulating in wild birds. In addition to screening for H5 subtypes, other subtypes like the H7 should also be screened for as they are known to cause outbreaks in poultry and have been associated with disease in humans.