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. 2019 Aug 17;24(1):53.
doi: 10.1186/s12199-019-0808-6.

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

Eric Mogaka Osoro  1 , Shirley Lidechi  2 , Doris Marwanga  2 , Jeremiah Nyaundi  2 , Athman Mwatondo  3 , Mathew Muturi  4 , Zipporah Ng'ang'a  5 , Kariuki Njenga  6
Affiliations

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

Eric Mogaka Osoro et al. Environ Health Prev Med. .

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.

Keywords: Acute respiratory illness; Influenza A virus; Pig workers; Zoonoses.

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Conflict of interest statement

The authors declare that they have no competing interests

Figures

Fig. 1
Fig. 1
Map of Kiambu County showing the selected administrative locations where households were sampled. The households were sampled from within two sub-counties of Kiambu County—Kikuyu and Ruiru. The inset is a map of Kenya with Kiambu County highlighted in dark color
Fig. 2
Fig. 2
Schema of households’ and participants’ enrolment, follow-up, and lost to follow-up. Participants from pig-keeping and non-pig-keeping households were enrolled and had a follow-up visit after 12 or 14 weeks. *Only households where no participant was available during the follow-up were included
Fig. 3
Fig. 3
Proportion of pigs sampled (n = 2066) in pig-keeping households by maturity status, Kiambu, 2013–2014
See this image and copyright information in PMC

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