Multiple Outbreaks and Clinico-pathological Features of Highly Pathogenic Avian Influenza H5N1 and H5N8 in Poultry Farms in Jos Metropolis, Plateau State, Nigeria

Abstract

Outbreaks of highly pathogenic avian influenza (HPAI) in Nigeria have been reoccurring since 2015 after the country was declared free of HPAI H5N1 in 2010. Beginning from January 26, 2021, the first suspected case of HPAI from a 4-week-old broiler/cockerel flock was reported to the Veterinary Teaching Hospital, University of Jos, Nigeria followed by five other suspected cases from poultry flocks in different locations within one month. Mortality rates were high, ranging from 75% to 100% for the Broilers/Noiler-cockerels and Brahma chicken/cockerel flocks but low rates of 5.6–17.9% were reported for the layers’ farms. Clinical signs seen in the layer flocks included somnolence and nasal rales, as well as paralysis of wings and feet. The gross lesions observed in the broilers/cockerels and Brahma chicken/cockerels mixed flocks were marked subcutaneous hemorrhage on the skin as well as cyanoses of the comb, wattles, thigh, shank, and feet. There were also generalized congestion of visceral organs with frank blood in the thorax, severe ecchymotic and petechial hemorrhages in the proventricular mucosae, cloudy air sacs as well as congested and frothy lungs with severe hemorrhagic tracheitis. The pathology in the brown layer chickens was not extensive, but there were petechial hemorrhages in the thigh and breast muscles, inflamed bursa of Fabricius, and petechial hemorrhages in the proventriculus. From the history and pathologies, tentative diagnoses of HPAI were made and tissues were sent to the Regional Laboratory for Animal Influenza and Transboundary Animal Diseases, National Veterinary Research Institute, Vom, Nigeria. The cases were confirmed to be positive by qPCR and viral isolation, four of which were H5N1 and two were H5N8 subtypes. In conclusion, HPAI may become endemic in Nigeria despite the control policy of eradication by the government. It is recommended that the national policy on the control of HPAI should be modified to include controlled vaccination with close monitoring.