Seroprevalence of influenza A virus in pigs and low risk of acute respiratory illness among pig workers in Kenya

Abstract

Background Influenza A viruses pose a significant risk to human health because of their wide host range and ability to reassort into novel viruses that can cause serious disease and pandemics. Since transmission of these viruses between humans and pigs can be associated with occupational and environmental exposures, we investigated the association between occupational exposure to pigs, occurrence of acute respiratory illness (ARI), and influenza A virus infection. Methods The study was conducted in Kiambu County, the county with the highest level of intensive small-scale pig farming in Kenya. Up to 3 participants (> 2 years old) per household from pig-keeping and non-pig-keeping households were randomly recruited and followed up in 2013 (Sept-Dec) and 2014 (Apr-Aug). Oropharyngeal (OP) and nasopharyngeal (NP) swabs were collected from participants with ARI at the time of study visit. For the animal study, nasal and oropharyngeal swabs, and serum samples were collected from pigs and poultry present in enrolled households. The human and animal swab samples were tested for viral nucleic acid by RT-PCR and sera by ELISA for antibodies. A Poisson generalized linear mixed-effects model was developed to assess the association between pig exposure and occurrence of ARI. Results Of 1137 human participants enrolled, 625 (55%) completed follow-up visits including 172 (27.5%) pig workers and 453 (72.5%) non-pig workers. Of 130 human NP/OP swabs tested, four (3.1%) were positive for influenza A virus, one pig worker, and three among non-pig workers. Whereas none of the 4462 swabs collected from pig and poultry tested positive for influenza A virus by RT-PCR, 265 of 4273 (6.2%) of the sera tested positive for virus antibodies by ELISA, including 11.6% (230/1990) of the pigs and 1.5% (35/2,283) of poultry. The cumulative incidence of ARI was 16.9% among pig workers and 26.9% among the non-pig workers. The adjusted risk ratio for the association between being a pig worker and experiencing an episode of ARI was 0.56 (95% CI [0.33, 0.93]), after adjusting for potential confounders. Conclusions Our findings demonstrate moderate seropositivity for influenza A virus among pigs, suggesting the circulation of swine influenza virus and a potential for interspecies transmission.

A Systematic Review Analyzing the Prevalence and Circulation of Influenza Viruses in Swine Population Worldwide

“…The active IAV infection was reported in four household members having acute respiratory illness while the backyard swine were negative for the IAV and IBV in Kiambu county during September 2013-August 2014. On the contrary, the serology identified the IAV antibodies in 230 swine sera samples suggesting a past exposure of IAV [63]. The A(H1N1)pdm09 virus was again reported in five swine samples collected from a slaughterhouse in Kenya during September 2013-September 2014.…”

“…Other Influenza Virus Types References Africa Cameroon H1N1, A(H1N1)pdm09 None [51][52][53] Nigeria H1N1, H3N2, A(H1N1)pdm09, H5N1 None [52,[54][55][56][57][58][59] Ghana H3N2 None [57] Egypt H5N1, H5N2, H9N2, A(H1N1)pdm09 None [60,61] Kenya H1N1, H3N2, A(H1N1)pdm09 None [62][63][64] Benin, Cote d'Ivoire None None [65] Reunion island A(H1N1)pdm09 None [66] Togo A(H1N1)pdm09 None [67] Uganda IAV None [68]…”

“…Africa Cameroon H1N1, A(H1N1)pdm09 None [51][52][53] Nigeria H1N1, H3N2, A(H1N1)pdm09, H5N1 None [52,[54][55][56][57][58][59] Ghana H3N2 None [57] Egypt H5N1, H5N2, H9N2, A(H1N1)pdm09 None [60,61] Kenya H1N1, H3N2, A(H1N1)pdm09 None [62][63][64] Benin, Cote d'Ivoire None None [65] Reunion island A(H1N1)pdm09 None [66] Togo A(H1N1)pdm09 None [67] Uganda IAV None [68] Asia China H1N1, H1N2, H3N2, A(H1N1)pdm09, H5N1, H9N2, H4N1, H4N6, H5N3, H10N5, H4N8, H6N6, H7N9, H3N8 ICV, IDV Bhutan H1N1, A(H1N1)pdm09 None [107] Cambodia H1N1, H3N2, A(H1N1)pdm09 None [108,109] Japan H1N1, H1N2, H3N2, A(H1N1)pdm09 ICV [110][111][112][113][114][115][116][117][118][119][120][121][122][123][124][125][126] South Korea H1N1, H1N2, H3N2, A(H1N1)pdm09, H7N2, H5N2, H3N1 None [127][128][129][130][131]…”

A systematic review of influenza A virus prevalence and transmission dynamics in backyard swine populations globally

“…The second study in Kenya investigated IAV sero- and virological prevalence in backyard swine sera (n = 1990) and nasal swab (n = 2066) samples, respectively, during September 2013–April 2014. While the ELISA detected IAV-specific antibodies in 230 (11.56%) sera samples, suggesting past infection, none of the nasal swabs could amplify IAV specific sequences using RT-PCR, suggesting the absence of active IAV infection in these Kenyan backyard swine populations at the time of the surveillance [ 28 ].…”

“…10 a). Interestingly, 13 (38.24%) studies reported that swine and poultry regularly interacted in the backyards [ 12 , 20 , 23 , 27 , 28 , 33 , 35 , 37 , 39 , 40 , 47 – 49 ], while seven (20.58%) studies reported interactions among the wild birds, swine, and poultry [ 24 – 26 , 30 , 32 , 36 , 44 ]. Two (5.88%) studies reported interactions among the swine, poultry, and cattle [ 42 , 46 ], while the other remaining studies (n = 12; 35.29%) did not mention any interactions between backyard swine and other animal species [ 18 , 21 , 22 , 29 , 31 , 34 , 38 , 41 , 45 ] (Fig.…”