Dynamics of Tunga penetrans infections and severity of associated morbidity among pigs during the dry season in rural Uganda

Background Tungiasis is a neglected tropical disease which is common in impoverished communities. In sub-Saharan Africa, it is caused by female sand fleas, Tunga penetrans, and pigs are amongst the major domestic animal reservoirs. Depending on the environment, tungiasis occurs throughout the year or preferentially in the dry seasons. This study investigated changes in sand flea abundance and associated morbidity in pigs during a dry season. Methods Tunga penetrans lesions were counted and staged in 35 pigs amongst 22 households with at least one affected pig. Five weekly examinations were performed per animal during a dry season. Enrolment of pigs into the study lasted 17 days and examination was performed for 43 days. The severity score for acute pig tungiasis (SSAPT) was determined for each visit. Generalised linear mixed models (GLMM) were fitted on an absolute time scale to understand factors influencing the changes in abundance of sand flea lesions and SSAPT. Results The prevalence/abundance of tungiasis-associated lesions increased from 57.1%/median 1 lesion at baseline to 71.4%/median 11 lesions after 4 weeks. In parallel, the median SSAPT increased from zero to six. The GLMM analyses fitting negative binomial models to the lesion numbers revealed that time had a linear and a quadratic effect for the viable stages 2 and 3a, and all viable sand flea stages in general with maximal abundance of sand fleas on days 17–18, 33 and 35 from the beginning of the study, respectively. The model for the total number of sand flea lesions, which included dead and excoriated sand fleas, showed the same trend but the peak was not reached within the study period. The number of stage 3b lesions was unexpectedly low. The SSAPT increased linearly over time and was highly dependent on the initial number of sand fleas at enrolment. Conclusions There were increasing intensities of sand fleas and SSAPT in domestic pigs during the dry season. The ensuing environmental contamination by off-host stages of T. penetrans increases the risk of transmission to other susceptible hosts, including humans.