Impact of the 2014-2016 El Niño on Geohelminth Control in Stray Dogs and Cats Without Anthelmintic Treatment

Soil-transmitted helminthiases (STHs) in stray dogs and cats, including hookworm infection, strongyloidiasis, and toxocariasis, are prevalent globally. The lack of STH control in these stray animals leads to an increased prevalence of STHs in southern Thailand. Suddenly, the El Niño 2014-2016 induced a 14-month-long drought. We thus aimed to compare the prevalence of STHs in stray cats in artificial wet sandy soil (unaffected area) and dry sandy soil (affected area) before and after drought. Furthermore, we also observed the prevalence of STHs in stray dogs in another study area before and after drought.

A comparative study was conducted on 77 stray cats, 17 in the unaffected area and 60 in the affected area. Stools were collected before (2014) and after the drought (2016 and 2020). In study area 2, the respective 122 and 131 stools were collected from stray dogs before (2014) and after the drought (2020). STHs were detected using a modified formalin-ether concentration technique, agar plate culture, and 1:20 water-diluted stool suspension. Rainfall and rainy-day data, serving as drought indicators, were retrieved from the two nearest local meteorological stations.

In stray cats, the prevalence of STHs in the unaffected area remained unchanged pre- and postdrought. In the affected area, the prevalence of hookworm infection, but not strongyloidiasis and toxocariasis, decreased after drought. However, over time, the unchanged prevalence of strongyloidiasis in 2016 decreased in 2020 compared to that in 2014. Furthermore, the prevalence of hookworm infection in stray dogs in study area 2 decreased after the drought, while eliminating strongyloidiasis and toxocariasis. Notably, the prevalence of Spirometra spp. infection in stray dogs and in cats in the unaffected area remained unchanged.

El Niño 2014-2016-induced drought, one of the climatic factors, demonstrates the significant impact of climatic factors on STH transmission in stray animal populations where anthelmintic treatment is not applied, highlighting the need to integrate climate forecasting into future control strategies.