Detection of hemagglutination inhibition antibodies against equine influenza viruses (subtypes: H7N7 and H3N8) in horses from São Paulo State

The Equine influenza Virus (EIV) (H3N8 and H7N7) belong to Orthomyxoviridae family and Influenza A genus. Although there are few reports of human infection with EIV zoonotic and interspecies infection risk is known. OIE and WHO services on epidemiological surveillance report that H3N8 subtypes are isolated and characterized from worldwide outbreaks while H7N7 subtype less pathogenic has not being isolated since 1980 considered an extinct virus. Although the EIV is endemic in our country there are few national studies that had versed on the current evaluation of horses antibodies (Ab) from São Paulo State which motivated the present study. The study objectives were: 1) to evaluate the effects of different serum treatments described by OIE and WHO for the removal of nonspecific inhibitors of hemagglutination in 10 vaccinated (H3N8 - A/Equi/Kentucky/1/1997) horses sera being: a) TPH: trypsin, potassium metaperiodate followed by adsorption of erythrocytes b) KH: kaolin 20% followed by adsorption of erythrocytes and c) RDEH: RDE followed by adsorption of erythrocytes; 2) investigate the presence of antibodies against H3N8 and H7N7 viruses in 84 unvaccinated equines in São Paulo State; 3) compare the frequency of antibodies against H3N8 sampled between São Paulo State and a panel of equines sera from Mossoró - RN where there are no studies on EIV circulation. There was no statistical difference between the treatments for serum nonspecific inhibitors of hemagglutination removal (p>0.05; 95% confidence) however RDEH treatment showed results more consistent confirming OIE and WHO recommendation to use this treatment with priority. The serological profile of SP samples suggests H3N8 subtype circulates in those animals and H7N7 subtype might circulate in a subclinical form in equines, which is supported by other studies conducted in Brazil. There is evidence of antibodies detection against equine H7N7 subtype in Brazil, even without since 1980 isolation in the world. In animals from RN State which had Equus asinus representing a major fraction there was statistical equal frequencies of Equus caballus and Equus asinus positivity in HI test against H3N8 subtype (p>0.05; 95% of confidence), as unprecedented in the world. The frequency of positive equine against H3N8 subtype on HI test in SP was statistically higher (p<0.05; 95% of confidence) than in RN. (AU)