How important are rats as vectors of leptospirosis in the Mekong Delta of Vietnam?

Nguyen Van Hoang,Juan J. Carrique-Mas,James Campbell,Hoang Kim Loan,Ratree Takhampunya,Vo Be Hien,Serge Morand,Bach Tuan Kiet,Lac Ngoc Them,Nguyen Van Cuong,Juliet E. Bryant,Bousaraporn Tippayachai

doi:10.1089/vbz.2014.1613

Abstract

Leptospirosis is a zoonosis known to be endemic in the Mekong Delta of Vietnam, even though clinical reports are uncommon. We investigated leptospira infection in rats purchased in food markets during the rainy season (October) (n=150), as well as those trapped during the dry season (February–March) (n=125) in the region using RT-PCR for the lipL32 gene, confirmed by 16S rRNA, as well as by the microscopic agglutination test (MAT). Results were compared with the serovar distribution of human cases referred from Ho Chi Minh City hospitals (2004–2012) confirmed by MAT (n=45). The MAT seroprevalence among rats was 18.3%. The highest MAT seroprevalence corresponded, in decreasing order, to: Rattus norvegicus (33.0%), Bandicota indica (26.5%), Rattus tanezumi (24.6%), Rattus exulans (14.3%), and Rattus argentiventer (7.1%). The most prevalent serovars were, in descending order: Javanica (4.6% rats), Lousiana (4.2%), Copenageni (4.2%), Cynopterie (3.7%), Pomona (2.9%), and Icterohaemorrhagiae (2.5%). A total of 16 rats (5.8%) tested positive by RT-PCR. Overall, larger rats tended to have a higher prevalence of detection. There was considerable agreement between MAT and PCR (kappa=0.28 [0.07–0.49]), although significantly more rats were positive by MAT (McNemar 29.9 (p<0.001). MAT prevalence was higher among rats during the rainy season compared with rats in the dry season. There are no current available data on leptospira serovars in humans in the Mekong Delta, although existing studies suggest limited overlapping between human and rat serovars. Further studies should take into account a wider range of potential reservoirs (i.e., dogs, pigs) as well as perform geographically linked co-sampling of humans and animals to establish the main sources of leptospirosis in the region.

Highlights

Leptospirosis is a zoonotic infection of global relevance, caused by pathogenic spirochetes within the genus Leptospira
Leptospirosis is thought to be endemic in Vietnam and other countries in the region (Laos, Cambodia, and Thailand), with seasonal peaks of incidence during the rainy season and outbreaks related to flooding events (Victoriano et al 2009)
Hurstbridge, and Canicola were most commonly associated with human leptospirosis during 2004–2012

Summary

Introduction

Leptospirosis is a zoonotic infection of global relevance, caused by pathogenic spirochetes within the genus Leptospira. Leptospirosis is thought to be endemic in Vietnam and other countries in the region (Laos, Cambodia, and Thailand), with seasonal peaks of incidence during the rainy season and outbreaks related to flooding events (Victoriano et al 2009). Leptospira organisms are notoriously difficult to detect and to culture, the most commonly used diagnostic methods are based on detecting a serological response. The microscopic agglutination test (MAT), based on detecting agglutinating antibodies against the infecting serovar using a dark-field miscrocope, is considered the gold standard for serological tests. Panels of live leptospires belonging to locally circulating serovars are maintained in the laboratory and used as antigens for the MAT (World Health Organization 2003)

Methods

Results

Conclusion