Effects of climatic, socio–economic and behavioural factors on the transmission of hookworm (Necator americanus) on two low-country plantations in Sri Lanka

Abstract

The climatic, socio-economic and behavioural factors influencing hookworm (Necator americanus) infection in Sri Lanka were explored between February 2000 and June 2001. In February 2000, a single stool sample was collected from each of the 477 subjects investigated, who were aged 2-74 years (median = 13 years) and lived on the 'lowcountry' Maliboda and Ayr plantations. The 'baseline' prevalence (28.5%) and intensity of hookworm infection (0- 4828.5 eggs/g faeces, with a mean of 128.4 eggs/g) were then determined by examining these initial samples, as Kato-Katz smears. Subsequently, each participant was treated with a single, 500-mg dose of mebendazole and then followed-up, at monthly intervals, for the next 15 months. Whenever a subject was found smear-positive for hookworm eggs at one of the monthly follow-ups, he or she was treated again with mebendazole. This approach allowed the monthly incidence of hookworm infection to be determined for each subject, assuming that subjects became smear-positive approximately 6 weeks post-infection. During the study period, rainfall and mean temperature were recorded daily and then converted to monthly values so that the relationship between the incidence of infection over each month and the rainfall and mean temperature over the same period could be explored. In addition, potentially relevant data on the socio-economic status and behaviour of each subject were collected, in questionnaire-based interviews with the adult subjects and the caregivers of the children investigated. Odds ratios (OR) and their 95% confidence intervals (CI) were then calculated for each factor that might increase the risk of hookworm infection. The monthly incidence of hookworm infection showed three peaks -- in September 2000 (21.3%), January 2001 (20.8%) and May 2001 (17.5%) -- at Maliboda, and two peaks -- in September 2000 (25.0%) and February 2001 (29.2%) -- at Ayr. With the data for all subjects combined, incidence showed a statistically significant correlation with mean temperature (r = -0.468; P = 0.018). The results of a multivariate analysis also revealed that mean temperature was significant (beta = -5.296; P = 0.01) in hookworm incidence. Bathing and washing with water from rock-pools formed by waterfalls (OR = 1.33; CI = 1.35-4.01), the use of wells (OR = 2.35; CI = 1.29-4.30), and a lack of toilets (OR = 1.60; CI = 1.01-2.53) each appeared to increase the risk of hookworm infection significantly. Those living on the two study plantations, and perhaps many other similar plantations in Sri Lanka, would clearly benefit from improved access to the public water supply (especially to pipe-borne water) and toilets.

The Impact of a School-Based Hygiene, Water Quality and Sanitation Intervention on Soil-Transmitted Helminth Reinfection: A Cluster-Randomized Trial

“…17,24,[35][36][37] The current study found WASH impacts on the prevalence of A. lumbricoides to other intervention trials of household-and school-based hygiene promotion programs that have shown a reduction in A. lumbricoides reinfection on primary school-age children. 38,39 In Brazil, Moraes and colleagues 40 found great reductions in the prevalence of infection because of community sanitation improvement.…”

Prevalence and Correlates of Intestinal Parasites among Patients Admitted to Mirembe National Mental Health Hospital, Dodoma, Tanzania

“…Again, since albendazole which was offered at admission is efficacious to hookworms, the observed high prevalence hookworm infection in our study may signify infections acquired after admission. This correlates with documented risk factors which are common among patients admitted to psychiatric hospitals such as poor personal hygiene [ 33 – 36 ], poor sanitation [ 34 , 37 ], and exposure to soil with filariform larvae that penetrate the skin [ 35 , 38 , 39 ]. Psychiatric patients in the study site tend to walk around bare-footed, the majority of them with poor personal care including poor defecation practices which are the common risks for hookworm infection [ 25 – 29 ].…”

Incidence and Risk Factors of Hookworm Infection in a Rural Community of Central Thailand

“…Acquiring hookworm infection is directly related to exposure to soil where filariform larvae, the infective stage, live in and penetrate human skin. 4,15,16 Poor personal hygiene, particularly defecation practices [16][17][18][19] and sanitation, 17,20 have been reported as risk factors of hookworm infection. Hookworm infection has been associated with low socioeconomic status 16 and low educational attainment.…”