Risk factors and reservoir species for leptospirosis in Sri Lanka

A 2009 review of leptospirosis in the Asia Pacific region reported that the incidence of human leptospirosis in Sri Lanka was high at >10 cases per 100,000 people per year. In fact, the incidence of this disease has been rapidly increasing in recent years, and the largest outbreak ever reported occurred in 2008, involving more than 7000 reported cases.

Data gaps

The reasons for this increase are not currently understood. Most research reports in the country are based on probable cases and this lack of diagnostic confirmation hampers the understanding of the epidemiology of this disease. 

Furthermore, key prevention and control interventions recommended in the Asia-Pacific Review include rodent control and domestic animal vaccination. However, there is a dearth of information about Leptospira in animals in Sri Lanka. Although the small number of reported studies indicate that cattle and rodents are exposed to a variety of pathogenic leptospires.

Knowledge enhancement

This project combines a case-control study of hospital patients with a serosurvey of the livestock and dogs belonging to the households of the study participants. Thus risk factors for human cases of disease will be investigated, and blood samples will be collected from people and their in-contact animals and tested for a suite of serovars known to be endemic in Sri Lanka.

View preliminary results.

Intended outcomes

Improved understanding of the epidemiological links between animal and human infection with common Leptospira serovars/serogroups, and recommendations on policy enhancements which can be derived from this information. 

Project objectives

  1. To determine the proportion of people with suspected leptospirosis who are laboratory-confirmed cases, and to determine the infecting serovars/groups.
  2. To evaluate risk factors associated leptospirosis.
  3. To determine the prevalence of antibodies to selected serovars/groups in cattle, buffalo, pigs, and dogs associated with human cases and controls, and to obtain household information for evaluation.
  4. To determine the prevalence of antibodies to selected serovars/groups in rats and bandicoots in up to six ecological environments.
  5. To use satellite-derived remote sensed data to relate the rat seroprevalence data to study household environments.
  6. To develop hypotheses concerning the epidemiological patterns of leptospirosis, and the mechanisms of exposure of affected people.
  7. To evaluate associations between serovars and serogroups in human cases and various mammalian species.
  8. To formulate recommendations on enhancements to the leptospirosis control policy in Sri Lanka.

Study design

  1. Recruiting participants for the case-control study:
  • Study population = hospital patients presenting with clinical signs indicative of leptospirosis at sentinel site hospitals in seven districts in Sri Lanka. The chosen districts have all reported high numbers of cases of in recent years.
  • Eligible population = all patients who conform to the WHO case definition for suspected leptospirosis. Those who consent to participate will be interviewed, and blood will be collected for serological testing.
  • A questionnaire will be administered to gather clinical, demographic, environmental and animal contact information from patients.
  • The microscopic agglutination test (MAT) will be used to assay acute and convalescent sera to classify patients into cases and controls.
    • Cases = recruited participants with laboratory-confirmed leptospirosis.
    • Controls = recruited participants with MAT antibody titres that were below the threshold for a confirmed case.
  1. Patients will be recalled for review of clinical findings two weeks after their initial presentation, and re-bled to provide convalescent samples.
  2. Household visits:
  • All patients will be visited at home and household information collected.
  • Blood samples will collected from cattle, buffalo, pigs and dogs associated with the household.
  • Rats associated with selected ecological environments in the study area will be captured and sampled.
  • MAT testing will be undertaken to determine which serovars/serogroups are circulating in the various environments.
  1. Univariate and multivariate statistical analysis will be used to estimate odds ratios for factors of interest in the case-control study of human patients, and spatial analysis will be conducted on the animal and human data, in conjunction with satellite-derived remote sensed environmental variables.