The effect of pest control on the incidence of trichinosis in Virovitica-Podravina County, Croatia

The aim of the study was to assess the role of pest control as a preventive measure in the control of trichinosis. The investigation was designed as a retrospective cohort study in the Virovitica-Podravina County. The incidence of trichinosis was determined according to the presence or absence of exposure to protective pest control measures. Differences in the rate of trichinosis infection were determined by calculating relative risk (RR), i.e., the ratio of absolute risk in the two groups. In this epidemiological study, data collected in the County area regularly covered by pest control (exposure area) were compared with other areas not covered by regular pest control measures (non-exposure area). The study included 132 subjects living in the County and locally infected with trichinosis. Patient data were obtained from their medical history, epidemiological survey and epidemiological questionnaire on the source (autochthony) of the disease. The study also included 133,028 domestic pigs, 875 wild animals (mostly wild boar) and 111 trapped rats. All samples were examined by the method of trichinoscopy at authorized veterinary institutions of the County. Trichinosis infection was recorded in 1012 of 79,534 domestic pigs in the area exposed to pest control measures and in 51 of 53,494 domestic pigs from the rest of the County. RR for the exposure area vs. non-exposure area was 13.35 (95% CI 10.08-17.68; p<0.05); according to particular areas, RR was 3.66 (95% CI 2.62-5.13) for Pitomaca, 22.47 (95% CI 13.27-38.08) for Slatina and 118.89 (95% CI 29.7-476.01) for Orahovica (p<0.05 all). Domestic pigs from the County areas exposed to regular pest control measures had a 13-fold likelihood of infection recorded in pigs from County areas where pest control measures were not or were only occasionally performed. Quite unexpectedly, these results revealed a failure of pest control to reduce the incidence of trichinosis. The spread of trichinosis obviously occurs by some routes obviating the impact of pest control.