Asymptomatic Infection with Visceral Leishmaniasis in a Disease-Endemic Area in Bihar, India

Abstract

Abstract. A prospective study was carried out in a cohort of 355 persons in a leishmaniasis-endemic village of the Patna District in Bihar, India, to determine the prevalence of asymptomatic persons and rate of progression to symptomatic visceral leishmaniasis (VL) cases. At baseline screening, 50 persons were positive for leishmaniasis by any of the three tests (rK39 strip test, direct agglutination test, and polymerase chain reaction) used. Point prevalence of asymptomatic VL was 110 per 1,000 persons and the rate of progression to symptomatic cases was 17.85 per 1,000 person-months. The incidence rate ratio of progression to symptomatic case was 3.36 (95% confidence interval [CI] = 0.75-15.01, P = 0.09) among case-contacts of VL compared with neighbors. High prevalence of asymptomatic persons and clinical VL cases and high density of Phlebotomus argentipes sand flies can lead to transmission of VL in VL-endemic areas.

Visceral Leishmaniasis Prevalence and Associated Risk Factors in the Saran District of Bihar, India, from 2009 to July of 2011

“…Additionally, asymptomatic individuals can still act as a reservoir for parasite transmission. Topno and others 27 found that 13% of neighbors of VL cases were seropositive for leishmaniasis without showing symptoms. 15,28 In South Asia, it has been reported that living close to a previous case of VL strongly increases the risk of contracting the disease as well as acquiring a subclinical infection.…”

Usefulness of the rK39-Immunochromatographic Test, Direct Agglutination Test, and Leishmanin Skin Test for Detecting Asymptomatic Leishmania Infection in Children in a New Visceral Leishmaniasis Focus in Amhara State, Ethiopia

“…35 However, our study population was asymptomatic and higher positivity rates have been reported for DAT versus rK39-ICT when these methods are used to assess asymptomatic infection in other VL-endemic areas. 7 Given that performance of a serologic test can depend on the stage of the disease/infection, the lower performance of rK39-ICT can be explained by its ability to detect antibody response against only a single antigen (rK39), whereas the DAT relies on detection of antibodies against a wide range of Leishmania antigens (whole freeze-dried promastigote). 36 Another explanation is based on the nature of the tests.…”

“…5,6 In stable disease-endemic areas, clinical disease appears only in a fraction of those infected, and another fraction will not develop the disease and remain asymptomatic. 7 The prevalence of asymptomatic infection is different between and within different disease-endemic countries, and the number of asymptomatic infections usually exceeds the number of symptomatic infections, although this ratio can vary from 0.4:1 to 50:1. 2 Visualization of parasite amastigotes by microscopic examination of bone marrow, spleen, or lymph node aspirates has been the gold standard method of VL diagnosis for many years.…”

“…17,18 In areas where VL transmission is anthroponotic, asymptomatic persons might play a role as reservoirs, and even in areas where VL is zoonotic it is speculated that these persons could also contribute to transmission. 7,19 Thus, assessment of the prevalence and distribution of asymptomatic cases would contribute to a better understanding of VL transmission and help in developing control efforts.…”

Endemic Transmission of Visceral Leishmaniasis in Bhutan

“…[26][27][28][29] The paucity of overt kalaazar cases in this community is unusual for anthroponotic transmission based on epidemiological studies in India and Bangladesh. [30][31][32] The explanation is not clear, but could include the possibility of transmission from asymptomatically infected humans, or an unidentified animal reservoir. None of the dogs studied in the Trashigang canine shelter showed any marker of Leishmania infection, but the sample size was too small to yield a definitive answer regarding a potential canine reservoir role.…”