Reverse zoonotic transmission of influenza virus in Lagos State Nigeria

Abstract

Background: Influenza virus is a major cause of infections in animals and human resulting in an annual 3–5 million cases of severe illness, and 290,000–650,000 deaths worldwide. It can spread from pigs to man and from man to pigs. Pigs have receptors that can allow human and avian influenza viruses to mix and produce new subtypes capable of causing pandemic disease. But there are limited information on the transmission of human influenza virus into pig population in Nigeria and sub-Saharan Africa. We therefore aimed to investigate the pattern of transmission of influenza virus in pigs and pig-handlers in Lagos State, Nigeria. Methods and materials: Between April, 2013 and May, 2017, 25 pig farms were visited in different divisions of Lagos State. Nasal and oropharyngeal swabs collected from pigs (n = 1972) and human (n = 432) were extracted and investigated for the presence of influenza virus matrix gene by one-step RT-PCR. Further molecular characterisation was performed. Phylogenetic analysis was done in MEGA 6.0 using BioNJ method with 1000 times bootstrapping replicates of the alignment. Chi-square and Fisher's exact tests were used to calculate p values at 95% confidence interval using GraphPad Prism, USA. Results: Our findings revealed influenza A virus of 1.3% in pigs and 0.005% in pig-handlers. Interestingly, human influenza A (H1N1) was isolated in pig. Phylogenetic analyses showed close relatedness to influenza viruses from several African countries such as Ethiopia and Egypt with 99% homology. Conclusion: In conclusion, this study provided for the first time, molecular evidence of reverse zoonotic transmission of human influenza A (H1N1) to pigs in Nigeria. A condition referred to as anthroponosis. The introduction of human influenza virus into pigs can lead to the emergence of new strains previously unknown to human and animal population thereby posing a great threat that can result in unpredictable fatal consequences. A nationwide surveillance to evaluate and determine the actual burden of influenza reverse zoonosis in Nigeria is hereby advocated. This will assist in the development of policies to prevent the continuous transmission of human influenza virus to pigs in order to avoid a similar occurrence of the last influenza pandemic.