Research Article: Predominant Leptospiral Serogroups Circulating among Humans, Livestock and Wildlife in Katavi-Rukwa Ecosystem, Tanzania

Date Published: March 25, 2015

Publisher: Public Library of Science

Author(s): Justine A. Assenga, Lucas E. Matemba, Shabani K. Muller, Ginethon G. Mhamphi, Rudovick R. Kazwala, Pamela L.C. Small.

Abstract: BackgroundLeptospirosis is a worldwide zoonotic disease and a serious, under-reported public health problem, particularly in rural areas of Tanzania. In the Katavi-Rukwa ecosystem, humans, livestock and wildlife live in close proximity, which exposes them to the risk of a number of zoonotic infectious diseases, including leptospirosis.Methodology/Principal FindingsA cross-sectional epidemiological study was carried out in the Katavi region, South-west Tanzania, to determine the seroprevalence of Leptospira spp in humans, domestic ruminants and wildlife. Blood samples were collected from humans (n = 267), cattle (n = 1,103), goats (n = 248), buffaloes (n = 38), zebra (n = 2), lions (n = 2), rodents (n = 207) and shrews (n = 11). Decanted sera were tested using the Microscopic Agglutination Test (MAT) for antibodies against six live serogroups belonging to the Leptospira spp, with a cutoff point of ≥ 1:160. The prevalence of leptospiral antibodies was 29.96% in humans, 30.37% in cattle, 8.47% in goats, 28.95% in buffaloes, 20.29% in rodents and 9.09% in shrews. Additionally, one of the two samples in lions was seropositive. A significant difference in the prevalence P<0.05 was observed between cattle and goats. No significant difference in prevalence was observed with respect to age and sex in humans or any of the sampled animal species. The most prevalent serogroups with antibodies of Leptospira spp were Sejroe, Hebdomadis, Grippotyphosa, Icterohaemorrhagie and Australis, which were detected in humans, cattle, goats and buffaloes; Sejroe and Grippotyphosa, which were detected in a lion; Australis, Icterohaemorrhagie and Grippotyphosa, which were detected in rodents; and Australis, which was detected in shrews. Antibodies to serogroup Ballum were detected only in humans.ConclusionsThe results of this study demonstrate that leptospiral antibodies are widely prevalent in humans, livestock and wildlife from the Katavi-Rukwa ecosystem. The disease poses a serious economic and public health threat in the study area. This epidemiological study provides information on circulating serogroups, which will be essential in designing intervention measures to reduce the risk of disease transmission.

Partial Text: Leptospirosis is an emerging/re-emerging, worldwide, contagious, bacterial zoonotic disease that affects all mammals, including humans, livestock and wildlife [1, 2]. The disease is caused by different serovars of pathogenic species of the genus Leptospira [1, 2], which is common in tropical and subtropical regions, wherever environmental conditions favour the survival and transmission of the bacterium [3, 4]. Leptospirosis was first identified by Weil (1886) and Inada (1916) [5]. In the East and Central African regions, the disease was reported three decades ago [6]. The sources of infection for humans and other incidental hosts, such as cattle, pigs, horses, and companion animals, are subclinically infected wild and domestic animals, which are the reservoirs for over 250 known serovars of Leptospira [7]. Rodents are the most important source of infection for humans and animals [8, 9]. The role of rodents as carriers and the main source of leptospiral infection in human has been investigated in some countries. Moreover, different species of rodents, such as Rattus, R. norvegicus, Mus musculus, Bandicota bengalensis, Bandicota indica and Cricetomys gambianus, are known to carry different pathogenic leptospiral serovars [8, 9]. Leptospira spp lives for a long time in the kidney tubules of an infected animal host, from where they are excreted through the urine [10]. Humans become infected through either direct contact with the urine or other biological materials from the infected animals or indirect contact with water, soil and vegetation polluted with urine from animals harbouring pathogenic leptospires [11]. Leptospirosis is also an occupational disease affecting veterinarians, abattoir workers, sewer workers and other groups of people whose job exposes them constantly to contaminated materials [12]. A serological assay, the Microscopic Agglutination Test (MAT), is considered as the gold standard for the diagnosis of leptospiral infection [12]. The test is used to detect antibodies against different Leptospiral serovars.

The findings from this study indicate that leptospiral antibodies are prevalent in the Katavi-Rukwa ecosystem, as the antibodies were detected in humans, cattle, goats, buffaloes, lions, rodents and shrews. This is the first report of leptospira seroprevalence linking humans and animal infections in Tanzania. The demonstration of the exposure of these animals and humans at the same time provides a significant and important epidemiological picture and increases our understanding of infection patterns of leptospiral serogroups at the interface areas. Previous studies demonstrated that the seroprevalence of leptospira in healthy animals suggests levels of local exposure [28]. Animals with low prevalence of leptospira antibodies might be a significant cause of infection in humans, and high seroprevalence may signify exposure pressure from different animals and thus a high infection risk in humans as well [28].



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