Surveillance for Swine Respiratory and Diarrheal Pathogens at the Human-Animal Interface in Sarawak, Malaysia

Introduction: An estimated 75% of emerging infections in humans are zoonotic, posing a serious risk of future pandemics. The large livestock operations and dense human population of Southeast Asia are considered a hot-spot for the generation of novel viruses. The primary objective of this pilot study is to employ novel molecular laboratory analyses to examine evidence that swine pathogens including porcine circovirus 2, porcine rotaviruses, encephalomyocarditis virus, and porcine reproductive and respiratory syndrome virus, may be aerosolized at the animal-interface and that humans working in these environments may be carrying these viruses in their nasal airways.

Methods: This study took place in Sarawak, Malaysia among 11 pig farms, two slaughter houses, and three animal markets in June and July of 2017. Pig fecal, pig oral secretion, bioaerosol, and worker nasal wash samples were collected and analyzed via qRT-PCR for swine viruses. Workers were also surveyed for the nature of their occupational exposure with animals and their perceptions and use of personal protective equipment. Fisher’s Exact p-values and odds ratios were used to identify predictors of virus positivity.

Results: In all, 55 pig fecal, 49 pig oral or water, 21 bioaerosol, and 78 worker nasal wash samples were collected across 16 sites. Of these, 21 (38.2%) pig fecal, 43 (87.8%) pig oral or water, 3 (14.2%) bioaerosol, and 4 (5.1%) worker nasal wash samples were positive for PCV2 by qPCR. Porcine rotavirus C was detected in one (1.8%) pig fecal sample. No porcine rotavirus A or encephalomyocarditis virus was detected. The SYBR-based qRT-PCR assay used for PRRSv resulted in high levels of non-specific binding, omitting its inclusion in this write up. Statistically significant risk factors for PCV2 positivity among humans included having a household member with contact with pigs, farms with 1000 or more pigs, and a higher frequency of spotting rodents on the site. The personal protective equipment perceived as most effective at preventing cross-species infection and with the highest use were showering out of work and wearing dedicated boots. Among the equipment where use differed significantly from perception of efficacy were safety glasses, flu vaccination, showering out, and disposable boots.

Conclusions: Porcine circovirus has been posited as a zoonotic pathogen but limited studies have presented mixed results. Our data support the possibility of conducting a future prospective occupational study of pig workers for infection (not just nasal carriage) with this pathogen. Our data also shed light on contradictions between perception and use of personal protective equipment, stressing a need for education in farm biosecurity.