Potential Biological and Climatic Factors That Influence the Incidence and Persistence of Highly Pathogenic H5N1 Avian Influenza Virus in Egypt

Abstract

Highly pathogenic H5N1 avian influenza virus (A/H5N1) of clade 2.2.1 is endemic in poultry in Egypt where the highest number of human infections worldwide was reported. During the last 12 years the Egyptian A/H5N1 evolved into several genotypes. In 2007-2014 vaccinated poultry suffered from antigenic drift variants of clade 2.2.1.1 and in 2014/2015 an unprecedented upsurge of A/H5N1 clade 2.2.1.2 occurred in poultry and humans. Factors contributing to the endemicity or re-emergence of A/H5N1 in poultry in Egypt remain unclear. Here, three potential factors were studied: climatic factors (temperature, relative humidity, and wind speed), biological fitness in vitro, and pathogenicity in domestic Pekin and Muscovy ducks. Statistical analyses using negative binomial regression models indicated that ambient temperature in winter months influenced the spread of A/H5N1 in different geographic areas analyzed in this study. In vitro, at 4 and 56°C 2.2.1.1 and recent 2.2.1.2 viruses were more stable than other viruses used in this study. Further, Pekin ducks were more resistant than Muscovy ducks and the viruses were excreted for up to 2 weeks post-infection assuming a strong role as a reservoir. Taken together, ambient temperature in winter months potentially contributes to increasing outbreaks in some regions in Egypt. Heat stability of clade 2.2.1.1 and recent 2.2.1.2 viruses probably favors their persistence at elevated temperatures. Importantly, asymptomatically infected Pekin ducks may play an important role in the spread of avian and human-like A/H5N1 in Egypt. Therefore, control measures including targeted surveillance and culling of silently infected Pekin ducks should be considered.

Possible ramifications of climate variability on HPAI-H5N1 outbreak occurrence: Case study from the Menoufia, Egypt

“…HPAI outbreaks have been clustered globally in three Asian countries -Bangladesh, Indonesia and Vietnam and in Middle east in Egypt [ 4 ] with enzootic H5N1-HPAI clinical disease in poultry [ 5 ]. Outside Asia the longest endemic status of H5N1-HPAI is reported in Egypt [ 6 ]. The highest human cases were recorded in Egypt with a case fatality rate coming to 53.2% according to the World Health Organization (WHO) [ 7 ].…”

“…Countries like Egypt facing significant changes in their climate likely experience a higher risk of outbreaks [ 15 ].Understanding climate variability factors may enable the expectation and control of future disease events in Egypt [ 6 ]. Unfortunately, the environmental persistence of A/H5N1 is troublesome to evaluate [ 21 ] and prediction based on climate variability has once in a while been assessed, to fill the information crevice, the evidence is required for the effect of them on HPAI-H5N1 outbreaks [ 22 , 23 ].…”

H5 Influenza Viruses in Egypt

“…Field observations showed that in contrast to chickens, ducks exhibit mild or no clinical signs after infection with A(H5N1) viruses. Pekin ducks experimentally infected with a clade 2.2.1.2 virus showed no clinical signs or mortality (Salaheldin et al 2018b;Samir et al 2018), suggesting a potential role for ducks in maintaining clade 2.2.1.2 viruses as the dominant virus in Egypt.…”

Avian influenza viruses at the wild–domestic bird interface in Egypt

“…Despite LPAI H9N2 being endemic in Egypt, the highest H9N2 incidence in domestic birds in the Nile Delta was observed in January 2012, 2013 and 2014 [25,28]. In Egypt, there is evidence for yearround AIV detection in backyard poultry, while AIV infections in backyard and commercial farms seem to peak in winter and spring [15,29].…”

“…Lastly, besides wild bird-related factors, other factors such as those related to climate [29] and, in particular, those related to the poultry industry (including vaccination coverage and efficacy [73] and improper disposal of poultry carcasses [52]) shape the AIV endemicity in Egypt. Hence, evaluation of vaccination coverage and vaccine efficacy under field condition using various analysis as the cumulative annual flock immunity (CAFI) and its correlation with the virus load should be considered.…”