Multi-Species Leptospirosis in an Urban Zoo: Exhibit Modification Impact on a Wildlife Point Source
Current trends in zoological parks seek to provide more natural environments for zoo inhabitants. In response to this and to visitor needs, exhibit construction and grounds renovation is frequently ongoing. Within the urban zoo, an essentially confined native habitat also exists that supports its own wildlife populations. Concurrent or substantial exhibit alterations produce territory changes for these native animals and can alter their interactions with collection animals.
Oftentimes, these encounters go unnoticed except for observation of increased traffic as wildlife relocates. However, some of these interactions can result in enhanced disease transmission. These situations should be considered during a disease outbreak in previously healthy groups of exhibit animals. Recently, the impact of wildlife relocation in an urban zoo was demonstrated during a multi-species leptospirosis outbreak.
Epidemiology of the disease was determined as follows. In late 1998, transfer of most small nonhuman primates (NHPs) in the collection occurred. The NHPs were moved from sloped concrete and chain link exhibits to planted and meshed exhibits with wooden feeding platforms. In early 1999, a major exhibit construction for Sumatran tigers (Panthera tigris sumatrae) was completed from a park area and groundbreaking was held for a 3.5-acre Children's Zoo complex that essentially removed wooded habitat from the central zoo grounds. The incident fatality of a young adult male titi monkey (Callicebus moloch) occurred in May 1999. Concurrent vague illness in a young adult female black-handed spider monkey (Ateles geoffroyi) and a pair of juvenile white-cheeked gibbons (Hylobates concolor concolor) was also diagnosed. These animals were essentially located between the tiger exhibit and the construction zone. Shortly after the primate cases occurred, a young female bighorn sheep (Ovis candensis mexicana), housed on the border of the construction, presented with hematuria.
Probable leptospirosis at gross necropsy of the titi monkey was verified by histopathology within 1 wk of death and allowed for rapid serosurvey of the affected areas. Repeated identification of Leptospirosis grippotyphosa was made throughout the NHP exhibit chain, in the bighorn sheep exhibit, and in euthanatized feral squirrels from and around these areas. An additional serovar of L. autumnalis was detected in both squirrels and a juvenile black rhinoceros (Diceros bicornis minor). Feral rats trapped and tested during this time were not positive for leptospirosis serovars. Interestingly, the original Children's Zoo, located centrally in the problem areas and essentially embedded in the construction zone, never presented a symptomatic or serologically positive collection animal or squirrel.
Control for the leptospirosis outbreak was focused in the affected areas and included treatment of infected individuals, trapping for humane euthanasia of squirrels, and repeated surveys of the affected areas in the year following the incident case. Random serologic surveys of unaffected areas of the zoo were also performed but were uniformly negative. The primary contributing factor in this leptospirosis outbreak was increased encounters of collection species with an urban wildlife point source (i.e., squirrels). The exposure potential was enhanced by substantial exhibit renovation resulting in habitat destruction and wildlife displacement. Furthermore, recent exhibit modifications relocated susceptible collection animals into a situation of increased leptospirosis density by squirrel traffic and decreased ability of effective exhibit disinfection. Lastly, feral animal control also did not increase with the squirrel traffic until a clinical problem presented.