Assessment of animal hosts of pathogenic Leptospira in northern Tanzania

Abstract

Leptospirosis is a zoonotic bacterial disease that affects more than one million people worldwide each year. Human infection is acquired through direct or indirect contact with the urine of an infected animal. A wide range of animals including rodents and livestock may shed Leptospira bacteria and act as a source of infection for people. In the Kilimanjaro Region of northern Tanzania, leptospirosis is an important cause of acute febrile illness, yet relatively little is known about animal hosts of Leptospira infection in this area. The roles of rodents and ruminant livestock in the epidemiology of leptospirosis were evaluated through two linked studies. A cross-sectional study of peri-domestic rodents performed in two districts with a high reported incidence of human leptospirosis found no evidence of Leptospira infection among rodent species trapped in and around randomly selected households. In contrast, pathogenic Leptospira infection was detected in 7.08% cattle (n = 452 [5.1-9.8%]), 1.20% goats (n = 167 [0.3-4.3%]) and 1.12% sheep (n = 89 [0.1-60.0%]) sampled in local slaughterhouses. Four Leptospira genotypes were detected in livestock. Two distinct clades of L. borgpetersenii were identified in cattle as well as a clade of novel secY sequences that showed only 95% identity to known Leptospira sequences. Identical L. kirschneri sequences were obtained from qPCR-positive kidney samples from cattle, sheep and goats. These results indicate that ruminant livestock are important hosts of Leptospira in northern Tanzania. Infected livestock may act as a source of Leptospira infection for people. Additional work is needed to understand the role of livestock in the maintenance and transmission of Leptospira infection in this region and to examine linkages between human and livestock infections.

Fig 1. Map of Tanzania showing the administrative regions of Tanzania (main map) and the location of the Moshi Municipal and Moshi Rural Districts within the Kilimanjaro Region (inset).

Maps were made using Quantum Geographic Information System (QGIS) open access software [19]. Shapefiles were obtained from Tanzania National Bureau of Statistics [20].

Fig 2. Map of Moshi Municipal and Moshi Rural Districts showing representative locations of rodent study villages and study slaughterhouses in relation to the two study hospitals (Kilimanjaro Christian Medical Centre (KCMC) and Mawenzi Regional Referral Hospital (MRRH).

Maps were made using Quantum Geographic Information System (QGIS) open access software [19]. Districts shapefiles were obtained from Tanzania National Bureau of Statistics [20].

Fig 3. Phylogenetic tree showing the relatedness of the Leptospira secY gene (434-bp fragment) derived from qPCR-positive livestock samples.

The phylogenetic tree was constructed using the maximum likelihood method based on the Tamura-Nei nucleotide substitution model [73]. The tree with the highest log likelihood is shown and drawn to scale with branch lengths measured in the number of substitutions per site. Sequences from this study are labelled with unique identifiers (C0025-C0658); host species; and GenBank accession numbers (MF955862 to MF955882). Sequence from reference Leptospira serovars are also shown [34]. Expanded clades show reference serovars closely related to study genotypes. More distantly related species clades are collapsed and shown with species labels only. Host and country locations shown for Africa isolates are show in parentheses. Sequences from this study that show 100% identity with L. borgpetersenii serovar Hardjo are highlighted in blue; non-Hardjo L. borgpetersenii sequences are highlighted in pink; L. kirschneri sequences are highlighted in green and sequences without an attributed species are highlighted in orange. Abbreviations: (sv) serovar; DRC (Democratic Republic of Congo).