New World screwworm (Cochliomyia hominivorax) myiasis in feral swine of Uruguay: One Health and transboundary disease implications

Abstract

BackgroundFeral swine (Sus scrofa) are highly invasive and threaten animal and public health in the Americas. New World screwworm (Cochliomyia hominivorax) is listed by the World Organization for Animal Health as a notifiable infestation because myasis cases affect livestock, wildlife, and humans in endemic areas, and outbreaks can be of high socioeconomic consequence in regions where screwworm was eradicated. However, a knowledge gap exists on screwworm infestation of feral swine in South America where C. hominivorax is endemic. Here, we report infestation with C. hominivorax in feral swine harvested in the Department of Artigas where the Republic of Uruguay shares borders with Brazil and Argentina. MethodsMyiasis caused by the larvae of C. hominivorax were identified in feral swine with the support and collaboration of a local feral swine hunting club over a three-year period in the Artigas Department of Uruguay. Harvested feral swine were examined for the presence of lesions where maggots causing the myiasis could be sampled and processed for taxonomic identification. The sites of myiasis on the body of infested feral swine and geospatial data for each case were recorded. Feral swine sex and relative size were registered along with ambient temperature and precipitation.ResultsMyiases caused by screwworms were recorded in 27 of 618 feral swine harvested. Cases detected in males over 40 kg were associated with wounds that, because of their location, were likely caused by aggressive dominance behavior between adult males. The overall prevalence of screwworm infestation in feral swine was associated with ambient temperature, but not precipitation. Case numbers peaked in the warmer spring and summer months. ConclusionThis is the first report for South America of myasis caused by C. hominivorax in feral swine. In contrast to myasis in cattle that can reach deep into host tissues, screwworms in feral swine tended to cause superficial infestation. Feral swine present challenges to control screwworms in endemic areas. Screwworm populations maintained by feral swine may contribute to human cases in rural areas of Uruguay, which highlights the One Health importance of this invasive species-ectoparasite interaction.

Historical perspective and new avenues to control the myiasis-causing fly Cochliomyia hominivorax in Uruguay

“…More recently, the importance of wildlife as NWS fly host was highlighted during Florida Keys (USA) outbreak in 2016, which resulted in the death of 135 endangered Key deer (Odocoileus virginianus clavium) (113) . In 2021, a total of 27 NWS myiasis in feral swine were reported in the north of Uruguay (114) . Therefore, myiasis surveillance in wildlife could enhance the efficiency of area-wide NWS fly management programs (115) .…”

“…The potential effect of the NWS fly as a regulator of wildlife can be evaluated as positive in the case that native warmblooded animals are beneficiated, but negative when alien species considered pests are the beneficiaries. Special attention called the effect on feral swine (114) , and a preliminary analysis estimates a low risk since its population density depends on other more determining factors than the NWS fly.…”