Expansion of lymphatic filariasis transmission assessment surveys (TAS) in Oceania as a pragmatic platform for key insights into the epidemiology of communicable diseases including intestinal parasite infections

Abstract

Introduction: Lymphatic filariasis (LF) and intestinal parasite infections are most prevalent neglected tropical diseases (NTDs) in Oceania. Since 1999, Pacific Programme to Eliminate Lymphatic Filariasis (PacELF) has successfully addressed critical issues and countries are able to stop mass drug administration (MDA) after a decade of the implementation. Transmission assessment surveys (TAS) is a standard methodology to assess whether MDA has reduced the LF prevalence to levels equal to or below the critical cut-off threshold. The aim of this thesis is to present the successful examples of expanding TAS as a pragmatic platform in providing insights into the epidemiology of the key communicable diseases in Oceania. Method: In Wallis Futuna (WAF), grade 2-5 students for the TAS and grade 4-5 for the hepatitis B virus (HBV) infection prevalence assessment were enrolled. The timeliness of vaccination was defined as being vaccinated no later than 4 weeks in comparison to the recommended immunization schedules. In Fiji, all class 1 and 2 students were targeted in 77, 82, and 50 selected schools for the Western TAS 2, Central TAS 1 and Northern Division TAS 2, where same students of 30, 20, and 20 schools were subsampled for stool sample collection. For the diagnosis of intestinal parasite infections, stool samples were examined by coproscopy. In the Eastern, stool samples of class 1-8 students in 24 schools were additionally collected. For the selected stool samples of the Western Division, the Baermann-concentration technique (BC) was added to diagnose strongyloidiasis. All positive samples for intestinal parasites and a systematic sub-sample (every 10th) from the Western Division were transferred to the reference laboratory for real-time PCR. Results: In Wallis Futuna (WAF), TAS 1 had a passing result. The overall HBsAg prevalence was close to 2%. The HBV vaccine coverage for 3 doses was 96%, and the proportion of timeliness was 65%. In the Western Division of Fiji, 7 children in an island out of 3,242 were circulating filariasis antigen (CFA) positive. In the Central and Northern Divisions, the results were all passing, with 2 and no CFA positives, respectively. As for the assessment of intestinal parasite infections in Fiji, 12.4% of children in 3 Divisions were found positive either with Ascaris or hookworm eggs. The overall any intestinal protozoan infection prevalence was 4.8%, and the Giardia infection prevalence was 1.6%. The spatial analysis confirmed that there are still areas with high endemicity at school levels, where Ascaris infection was more clustered in the Central, and Eastern Division and hookworm in the Northern, and hotspots of Giardia infections were clustered around in the urban centres of the Western Division. As for associated factors with STH infections, shoes wearing and main water supply at home from Fiji Water Authority had protective effects. For strongyloidiasis, BC found 1 positive and the overall S. stercoralis infection prevalence via real-time PCR was 3.5 %, from which also higher levels of polyparasitism were reported as well as per species specificity. Discussion and conclusion: The study shows that LF programmes in WAF and in Fiji are on track towards achieving the global goal of LF elimination as a public health problem. For WAF, the HBV infection prevalence is close to meet the regional goal of elimination, but timely vaccination should be more actively encouraged. As for STH infections in Fiji, a low-level of endemicity was observed, but the infections at schools were clustered. Overall any intestinal protozoan infection prevalence was not high, but there were hotspots of Giardia infection clustered, possibly due to contaminated water or foods following the floods caused by a cyclone. An analysis of factors associated STH infections in Fiji suggesting that there is a need to urgently resume preventive chemotherapy for the population at risk as well as to deliver integrated WASH interventions. Given that the estimated prevalence of S. stercoralis infections is endemic (>1 %) in Fiji, some 1.5K children are likely to have strongyloidiasis, implying the needs for curative measures, which was further assessed by molecular technique. In conclusion, LF TAS is a practical platform for assessing epidemiological features of the key communicable diseases in Oceania and should be actively utilized in accessing school-aged children in monitoring and evaluating public health interventions