Control of tungiasis through intermittent application of a plant-based repellent: an intervention study in a resource-poor community in Brazil

Abstract

Background: Tungiasis, an ectoparasitosis caused by the female sand flea Tunga penetrans, is an important health problem in many impoverished communities in the tropics. Sand flea disease is associated with a broad spectrum of clinical pathology and severe sequels are frequent. Treatment options are limited.

Methodology/principal findings: We assessed the effectiveness of the intermittent application of the plant-based repellent Zanzarin to reduce infestation intensity and tungiasis-associated morbidity in a resource-poor community in Brazil, characterized by a very high attack rate. The study population was randomized into three cohorts. Initially, during a period of four weeks, the repellent was applied twice daily to the feet of all cohort members. This reduced the number of embedded sandfleas to 0 in 98% of the participants. Thereafter members of cohort A applied the repellent every second week twice daily for one week, members of cohort B every fourth week for one week, and members of cohort C served as controls. Infestation intensity and tungiasis-associated morbidity were monitored during five months. The intermittent application of Zanzarin for one week every second week significantly reduced infestation intensity from a median 4 lesions (IQR 1-9) during the whole transmission season. In contrast, in cohort B (application of the repellent every fourth week) the infestation intensity remained twice as high (median 8 lesions, IQR 9-16; p = 0.0035), and in the control cohort C 3.5 times as high (median 14 lesions; IQR 7-26; p = 0.004 during the transmission season). Tungiasis-related acute pathology remained very low in cohort A (median severity score 2; IQR 1-4) as compared to cohort B (median severity score 5; IQR 3-7; p<0.001), and control cohort C (median severity score 6.5; IQR 4-8; p<0.001).

Conclusions/significance: Our study shows that in a setting with intense transmission, tungiasis-associated morbidity can be minimized through the intermittent application of a plant-based repellent.

Figure 1. Flow diagram of the study.

Figure 2. Intensity of infestation (Stage I-IV+ manipulated lesions) during the whole study period.

The data indicate the number of median lesions per individual. No follow-ups were carried out between calendar weeks 45–47 (see Materials and Methods).

Figure 3. Number of viable lesions (stage I-III of the Fortaleza Classification) during the study period.

No follow-ups were carried out between calendar weeks 45–47 (see Materials and Methods).

Figure 4. Proportion of manipulated lesions during study period.

No observations were carried out between calendar weeks 45–47 (see Materials and Methods).

Figure 5. SSAT-scores (median and interquartile range) during the study period.

During the first round of application of Zanzarin (twice daily for 4 weeks) the SSAT decreased in an identical manner in the three cohorts. For sake of clarity the data points of cohort B and C were shifted +/−0.1 calendar weeks on the x-axis, although the assessment of the SSAT was done simultaneously in the three cohorts.

Figure 6. SSCT-Score during the study period.

During the first round of application of Zanzarin (twice daily for 4 weeks) the SSCT decreased in an identical manner in the three cohorts. For sake of clarity the data points of cohort B and C were shifted +/−0.1 calendar weeks on the x-axis, although the assessment of the SSCT was done simultaneously in the three cohorts.