Reassessment of the prevalence of soil-transmitted helminth infections in Sri Lanka to enable a more focused control programme: a cross-sectional national school survey with spatial modelling

BACKGROUND

In Sri Lanka, deworming programmes for soil-transmitted helminth infections became an integral part of school health in the 1960s, whereas routine antenatal deworming with mebendazole started in the 1980s. A 2003 national soil-transmitted helminth survey done among schoolchildren found an overall prevalence of 6·9%. In our study, we aimed to reassess the national prevalence of soil-transmitted helminth infections to enable implementation of a more focused control programme that targets smaller administrative areas at risk of continued transmission.

METHODS

We did a cross-sectional, school-based, national survey using multistage stratified cluster sampling, covering all nine provinces as well as populations at high risk of soil-transmitted helminth infections living in urban slums and in plantation-sector communities. Our study population was children aged 5-7 years attending state schools. Faecal samples were collected and analysed with duplicate modified Kato-Katz smears. We modelled the risk of soil-transmitted helminth infection using generalised linear mixed-effects models, and we developed prevalence maps to enable informed decision making at the smallest health administrative level in the country.

FINDINGS

Between Jan 23 and May 9, 2017, we recruited 5946 children from 130 schools; 4276 (71·9%) children provided a faecal sample for examination. National prevalence of soil-transmitted helminth infection was 0·97% (95% CI 0·63-1·48) among primary schoolchildren. Prevalence in the high-risk communities surveyed was higher than national prevalence: 2·73% (0·75-6·87) in urban slum communities and 9·02% (4·29-18·0) in plantation sector communities. Our prevalence maps showed that the lowest-level health administrative regions could be categorised into low risk (prevalence <1%), high risk (prevalence >10%), or intermediate risk (1-10%) areas.

INTERPRETATION

Our survey findings indicate that the national prevalence of soil-transmitted helminth infection has continued to decline in Sri Lanka. On the basis of WHO guidelines, we recommend discontinuation of routine deworming in low-risk areas, continuation of annual deworming in high-risk areas, and deworming once every 2 years in intermediate-risk areas, for at least 4 years.

FUNDING

Task Force for Global Health and WHO.

A surveillance system for lymphatic filariasis after its elimination in Sri Lanka

Lymphatic filariasis (LF) has been declared eliminated in Sri Lanka in September 2016. To maintain elimination status, a surveillance system to detect hidden endemic foci or LF resurgence is of highest priority. In this paper, we have reported an investigation of LF transmission in Trincomalee district where a surveillance program was not carried out due to 30 years of civil unrest. Proposed surveillance system included, measurement of anti-filarial IgG4 in urine of schoolchildren in areas where LF transmission could exist and assessment of circulating filarial antigen (CFA) and microfilaria (mf) in all urine antibody positive schoolchildren, their family members and 10-15 neighbours of each urine antibody positive household. Spatial distribution of the anti-filarial antibody titers in urine in a high antibody suspected area was analyzed using GPS logger data. Among 2301 school children from 11 schools studied, 41 (1.8%) urine antibody positives were found. The antibody positive rates of the schools ranged between 0 and 4.0%. Nine of the 630 (1.4%) examined became positive for CFA but were negative for mf. Although there were no mf positives, positive CFA and antibody results indicated the existence of Wuchereria bancrofti in Trincomalee. Highest antibody titres in an area correlated with the prevalences of urine antibodies and CFA. Spatial analysis showed LF transmission foci. Therefore, a combination of the non-invasive methods, urine ELISA and GPS mapping, will be a new effective surveillance system to identify hidden LF transmission foci.

Epidemiology and factors associated with amoebic liver abscess in northern Sri Lanka

Background

Clinically diagnosed amoebic liver abscess (ALA) caused by Entamoeba histolytica has been an important public health problem in Jaffna district, northern Sri Lanka for last three decades. In order to draw up a control strategy for elimination of this condition, knowledge of its epidemiology and factors associated with this condition in the local context is vital.

Methods

All clinically diagnosed ALA patients admitted to the Teaching Hospital, Jaffna during the study period were included in the study and the data were collected using an interviewer administered questionnaire. One hundred blood samples from randomly selected toddy (a local alcoholic drink consisting of the fermented sap of the Palmyrah palm) consumers and 200 toddy samples were collected. Toddy samples were cultured in Robinson’s medium to establish the presence of Entamoeba histolytica in the sample. Climatic data and the total toddy sales in the district were obtained from the Meteorological and Excise Departments respectively. A sub group of randomly selected 100 patients were compared with 100 toddy consumers who were negative for E. histolytica antibody to explore the potential risk factors.

Results

Between July 2012 and July 2015, 346 of 367 ALA patients were enrolled in this study. Almost all patients (98.6%) were males with a history of heavy consumption of alcohol (100%). Almost all (94.2%) were within the age group 31–50 years. None of the cultured toddy samples grew E. histolytica. The monthly incidence of disease peaked in the dry season, matching the total toddy sales in the district. Age, type of alcohol and frequency of drinking were identified as potential risk factors whereas frequency of alcohol consumption and type of alcohol (consuming toddy and arrack) were identified as the independent risk factors. Moreover, the knowledge, attitude and practices towards ALA were poor among participants and the control group.

Conclusions

Though the number of cases has declined in recent years, ALA still remains as an important public health problem in Jaffna district. The transmission route of E. histolytica leading to ALA has to be further explored. Moreover, greater awareness among the public who are at risk would be beneficial in order to eliminate the disease.

Electronic supplementary material

The online version of this article (10.1186/s12889-018-5036-2) contains supplementary material, which is available to authorized users.

Amoebic liver abscess in northern Sri Lanka: first report of immunological and molecular confirmation of aetiology

Background

Since 1985, amoebic liver abscess (ALA) has been a public health problem in northern Sri Lanka. Clinicians arrive at a diagnosis based on clinical and ultrasonographic findings, which cannot differentiate pyogenic liver abscess (PLA) from ALA. As the treatment and outcome of the ALA and PLA differs, determining the etiological agent is crucial.

Methods

All clinically diagnosed ALA patients admitted to the Teaching Hospital (TH) in Jaffna during the study period were included and the clinical features, haematological parameters, and ultrasound scanning findings were obtained. Aspirated pus, blood, and faecal samples from patients were also collected. Pus and faeces were examined microscopically for amoebae. Pus was cultured in Robinson’s medium for amoebae, and MacConkey and blood agar for bacterial growth. ELISA kits were used for immunodiagnosis of Entamoeba histolytica infection. DNA was extracted from selected pus samples and amplified using nested PCR and the purified product was sequenced.

Results

From July 2012 to July 2015, 346 of 367 clinically diagnosed ALA patients admitted to Jaffna Teaching Hospital were enrolled in this study. Almost all patients (98.6%) were males with a history of heavy alcohol consumption (100%). The main clinical features were fever (100%), right hypochodric pain (100%), tender hepatomegaly (90%) and intercostal tenderness (60%). Most patients had leukocytosis (86.7%), elevated ESR (85.8%) and elevated alkaline phosphatase (72.3%). Most of the abscesses were in the right lobe (85.3%) and solitary (76.3%) in nature. Among the 221 (63.87%) drained abscesses, 93.2% were chocolate brown in colour with the mean volume of 41.22 ± 1.16 ml. Only four pus samples (2%) were positive for amoeba by culture and the rest of the pus and faecal samples were negative microscopically and by culture. Furthermore, all pus samples were negative for bacterial growth. Antibody against E. histolytica (99.7%) and the E. histolytica antigen were detected in the pus samples (100%). Moreover, PCR and sequencing confirmed these results.

Conclusion

To our knowledge, this is the first report from Sri Lanka that provides immunological and molecular confirmation that Entamoeba histolytica is a common cause of liver abscesses in the region.

Space-time clustering characteristics of dengue based on ecological, socio-economic and demographic factors in northern Sri Lanka

The aim of the present study was to identify geographical areas and time periods of potential clusters of dengue cases based on ecological, socio-economic and demographic factors in northern Sri Lanka from January 2010 to December 2013. Remote sensing (RS) was used to develop an index comprising rainfall, humidity and temperature data. Remote sensing data gathered by the AVNIR-2 instrument onboard the ALOS satellite were used to detect urbanisation, and a digital land cover map was used to extract land cover information. Other data on relevant factors and dengue outbreaks were collected through institutions and extant databases. The analysed RS data and databases were integrated into a geographical information system (GIS) enabling space-time clustering analysis. Our results indicate that increases in the number of combinations of ecological, socio-economic and demographic factors that are present or above the average contribute to significantly high rates of space-time dengue clusters. The spatio-temporal association that consolidates the two kinds of associations into one can ensure a more stable model for forecasting. An integrated spatiotemporal prediction model at a smaller level using ecological, socioeconomic and demographic factors could lead to substantial improvements in dengue control and prevention by allocating the right resources to the appropriate places at the right time.

A simple intervention to prevent cutaneous larva migrans among devotees of the Nallur Temple in Jaffna, Sri Lanka

Background

A cross sectional study conducted during the annual festival at Nallur temple in Jaffna, Sri Lanka, in 2010, showed that the prevalence of cutaneous larva migrants (CLM) among the devotees who performed the side roll ritual was 58.2% (95%CI: 51.2%–65.0%).

Objective

To test the hypothesis that the deworming stray dogs around the temple premises effectively reduces the prevalence of CLM among devotees.

Methodology/Principal Findings

All stray dogs (8) in the vicinity of the temple were treated, with mebendazole (100 mg) crushed and filled into sausages, 10 days before the commencement of festival in 2011. The same procedure was repeated a week later to ensure complete coverage. A cross-sectional study was conducted among 200 systematically selected devotees in August 2011 using an interviewer-administered questionnaire and the clinical examination of the skin. Baermann's technique was used for the recovery of nematode larvae from 40 soil samples collected from the temple premises. Ten samples of dog faeces collected from the same premises were also examined for nematode eggs. Prevalence of CLM among devotees in 2010 (Pre intervention) and 2011(Post intervention) were compared to test the hypothesis. Prevalence of CLM declined from 58% to 8% (Chi-square = 112.90, p<0.001) following the intervention. None of the subjects practiced new precautionary measures compared to the previous year. Soil and fecal samples were negative for parasites.

Conclusions/Significance

Regular dog deworming is an important and effective method for the prevention of CLM among the devotees doing side roll ritual and represents a pragmatic intervention that municipal authorities could perform on annual basis.

Salinity-tolerant larvae of mosquito vectors in the tropical coast of Jaffna, Sri Lanka and the effect of salinity on the toxicity of Bacillus thuringiensis to Aedes aegypti larvae

Background

Dengue, chikungunya, malaria, filariasis and Japanese encephalitis are common mosquito-borne diseases endemic to Sri Lanka. Aedes aegypti and Aedes albopictus, the major vectors of dengue, were recently shown to undergo pre-imaginal development in brackish water bodies in the island. A limited survey of selected coastal localities of the Jaffna district in northern Sri Lanka was carried out to identify mosquito species undergoing pre-imaginal development in brackish and saline waters. The effect of salinity on the toxicity of Bacillus thuringiensis israelensis larvicide to Ae. aegypti larvae at salinity levels naturally tolerated by Ae. aegypti was examined.

Methods

Larvae collected at the selected sites along the Jaffna coast were identified and salinity of habitat water determined in the laboratory. The LC₅₀ and LC₉₀ of B. thuringiensis toxin, the active ingredient of a commercial formulation of the larvicide BACTIVEC®, were determined with Ae. aegypti larvae. Bioassays were also carried out at salinities varying from 0 to18 ppt to determine the toxicity of Bacillus thuringiensis to fresh and brackish water-derived larvae of Ae. aegypti.

Results

Larvae of four Anopheles, two Aedes, one Culex and one Lutzia species were collected from brackish and saline sites with salinity in the range 2 to 68 ppt. The LC₅₀ and LC₉₀ of B. thuringiensis toxin for the second instar larvae of Ae. aegypti in fresh water were 0.006 ppm and 0.013 ppm respectively, with corresponding values for brackish water populations of 0.008 and 0.012 ppm respectively. One hundred percent survival of second instar fresh water and brackish water-derived Ae. aegypti larvae was recorded at salinity up to 10 and 12 ppt and 100% mortality at 16 and 18 ppt, yielding an LC ₅₀ for salinity of 13.9 ppt and 15.4 ppt at 24 h post-treatment respectively for the two populations. Statistical analysis showed significantly reduced toxicity of B. thuringiensis to fresh and brackish water-derived Ae. aegypti larvae at high salinities.

Conclusion

A variety of mosquito vectors of human diseases undergo pre-imaginal development in brackish or saline waters in coastal areas of the Jaffna district in northern Sri Lanka. Salinity has a small but significant negative impact on the toxicity of B. thuringiensis toxin to Ae. aegypti larvae at salinity levels where Ae. aegypti larvae are found in the environment. This has implications for the use of B. thuringiensis toxin as a larvicide in brackish waters.

Cutaneous larva migrans among devotees of the Nallur temple in Jaffna, Sri Lanka

BACKGROUND

Many cases of Cutaneous Larva Migrans (CLM) have been observed among devotees, during and immediately after the annual festival at the Nallur Hindu temple in Jaffna.

OBJECTIVE

To ascertain the risk factors associated with infestation and devotees' knowledge and practices regarding the condition.

METHODOLOGY/PRINCIPAL FINDINGS

A cross-sectional study using an interviewer-administered questionnaire and observation was conducted in August 2010. Out of 200 selected devotees 194(97%) responded. Soil and dog faecal samples were collected from the temple premises and examined for the presence of nematode larva and egg respectively. Among 194 male respondents, 58.2%(95% CI: 51.2%-65.0%) had lesions of CLM. One hundred and thirty (67%) respondents performed the ritual everyday; whereas 33% did so on special days. One hundred and twelve (57.7%) participants performed the ritual before 5.00am and remaining 42.3% performed after 5.00am. Among the participants, 77(36.7%) had the similar condition in previous years. One hundred and fifty seven (80.9%) were aware about this disease and 52(27%) devotees adopted some kind of precautionary measures. Bivariate analysis showed significant association between occurrence of CLM lesions and frequency of performing the ritual (p<0.001, OR-15.1; 95% CI:7.2-32.0), the timing of ritual performance (p = 0.022, OR-1.96; 95% CI:1.10-3.52), similar condition in previous year (p<0.001, OR-6.83; 95% CI: 3.39-13.76) and previous awareness of the condition (p = 0.005; OR-0.59;95% CI:0.43-0.82). Multivariate analysis showed that the frequency of ritual performance (OR-11.75; 95% CI 5.37-25.74) and similar conditions in previous years (OR-4.71; 95% CI: 2.14-10.39) were the independent risk factors. Two of the 20 soil samples were positive for the nematode larvae and three out of five dog faeces were positive for hookworm eggs.

CONCLUSIONS/SIGNIFICANCE

Deworming the stray dogs around the temple premises combined with the awareness programs among the public may be the effective and feasible precautionary measures to control similar epidemics in future.

Studies on prevalence of anopheline species and community perception of malaria in Jaffna district, Sri Lanka

BACKGROUND & OBJECTIVES

Over two decades of civil unrest and the conflict situation have had detrimental effects on vector control activities and management of malaria in Jaffna district which is an endemic region for malaria in Sri Lanka. With the background that only a few small-scale studies on malaria and its vectors have been reported from this district, a study was designed to explore the current status of malaria in the Jaffna district in relation to vector and community aspects.

METHODS

Adults and larvae of anopheline mosquitoes were collected monthly from selected endemic localities. Species prevalence of the collected mosquitoes was studied while the collected adults of Anopheles subpictus, a potential vector in the district, was screened for sibling species composition based on morphological characteristics and exposed to common insecticides using WHO bioassay kits. Knowledge, attitude and practices (KAP) of the community were tested using a pre-tested structured questionnaire in high-risk and low-risk localities in the district.

RESULTS

The anopheline mosquito species distribution in the district was--An. culicifacies (0.5%), An. subpictus (46%), An. varuna (4%), An. nigerrimus (44%) and An. pallidus (5.5%). Among the collected larvae the percent prevalence of An. culicifacies was 13% and other species follows as: An. subpictus (71%), An. varuna (4%), An. nigerrimus (10%) and An. pallidus (2%). Sibling species B, C and D of An. subpictus were present in the district with the predominance of B in both coastal and inland areas, while all members showed both indoor and outdoor resting characteristics, they were highly resistant to DDT (4%) and highly susceptible to malathion (5%). KAP study in the district showed a reasonable level of knowledge, positive attitude and practices towards malaria.

CONCLUSION

An. subpictus, the reported major vector of Jaffna and a well-established secondary vector of malaria in the country, continues to be the predominant anopheline species. The distribution of sibling species of An. subpictus complex in the Jaffna district, revealed for the first time, has implications for future studies on its bionomics and malaria transmission pattern in this area and the planning of control strategies for this region. The community perception of disease, which revealed a satisfactory knowledge indicates the potential for better community participation in future malaria control activities in this region. As potential vectors are still present, health authorities need to be vigilant to prevent any future epidemics of malaria.