Of Mice, Cattle, and Men: A Review of the Eco-Epidemiology of Leptospira borgpetersenii Serovar Ballum

Abstract

In New Zealand (NZ), leptospirosis is a mostly occupational zoonosis, with >66% of the recently notified cases being farm or abattoir workers. Livestock species independently maintain Leptospira borgpetersenii serovar Hardjo and L. interrogans serovar Pomona, and both are included in livestock vaccines. The increasing importance in human cases of Ballum, a serovar associated with wildlife, suggests that wildlife may be an overlooked source of infection. Livestock could also act as bridge hosts for humans. Drawing from disease ecology frameworks, we chose five barriers to include in this review based on the hypothesis that cattle act as bridge hosts for Ballum. Using a narrative methodology, we collated published studies pertaining to (a) the distribution and abundance of potential wild maintenance hosts of Ballum, (b) the infection dynamics (prevalence and pathogenesis) in those same hosts, (c) Ballum shedding and survival in the environment, (d) the exposure and competency of cattle as a potential bridge host, and (e) exposure for humans as a target host of Ballum. Mice (Mus musculus), rats (Rattus rattus, R. norvegicus) and hedgehogs (Erinaceus europaeus) were suspected as maintenance hosts of Ballum in NZ in studies conducted in the 1970s–1980s. These introduced species are distributed throughout NZ, and are present on pastures. The role of other wildlife in Ballum (and more broadly Leptospira) transmission remains poorly defined, and has not been thoroughly investigated in NZ. The experimental and natural Ballum infection of cattle suggest a low pathogenicity and the possibility of shedding. The seroprevalence in cattle appears higher in recent serosurveys (3 to 14%) compared with studies from the 1970s (0 to 3%). This review identifies gaps in the knowledge of Ballum, and highlights cattle as a potential spillover host. Further studies are required to ascertain the role that wild and domestic species may play in the eco-epidemiology of Ballum in order to understand its survival in the environment, and to inform control strategies.

Animals Exposed to Leptospira Serogroups Not Included in Bacterins in the United States and Puerto Rico

“…Ballum is not in any of the available bacterins, and it is not commonly included in many MAT panels. The data here as well as in previous studies show it is a serogroup of concern [ 38 ].…”

“…A seroprevalence study showed that cattle have been exposed to serogroup Ballum in the U.S. [ 12 ]. Ballum is emerging as an important problem in humans and animals in New Zealand [ 38 ]. The L. borgpetersenii serogroup Ballum has been isolated from rodents, and it is virulent in the hamster model, which emulates the pathology associated with acute lethal forms of human leptospirosis [ 28 , 39 ].…”

A cross-sectional investigation of Leptospira at the wildlife-livestock interface in New Zealand

“…Several studies in the 1950s -1970s investigated NZ wildlife as a potential reservoir of Leptospira [18]. Black rats (Rattus rattus), brown rats (R. norvegicus), house mice (Mus musculus) and hedgehogs (Erinaceus europaeus) were described as maintenance hosts for Ballum and possums (Trichosurus vulpecula) for Balcanica [19].…”

“…In contrast to numerous countries worldwide, rodents and wildlife at the time were identified as a minor public health concern for leptospirosis in NZ [20][21][22]. At the time, Ballum was rarely reported (< 1%) in the notified human cases and thus did not warrant investment into research on Leptospira infection in wildlife [18].…”

“…Several studies in the 1950s – 1970s investigated NZ wildlife as a potential reservoir of Leptospira [ 18 ]. Black rats ( Rattus rattus ), brown rats ( R .…”