Investigation to determine staff exposure and describe animal bite surveillance after detection of a rabid zebra in a safari lodge in Kenya, 2011

Introduction Rabies is a fatal viral infection, resulting in >55,000 deaths globally each year. In August 2011, a young orphaned zebra at a Kenyan safari lodge acquired rabies and potentially exposed >150 tourists and local staff. An investigation was initiated to determine exposures among the local staff, and to describe animal bite surveillance in the affected district. Methods We interviewed lodge staff on circumstances surrounding the zebra's illness and assessed their exposure status. We reviewed animal bite report forms from the outpatient department at the district hospital. Results The zebra was reported bitten by a dog on 31st July 2011, became ill on 23rdAugust, and died three days later. There were 22 employees working at the lodge during that time. Six (27%) had high exposure due to contact with saliva (bottle feeding, veterinary care) and received four doses of rabies vaccine and one of immune-globulin, and 16 (73%) had low exposure due to casual contact and received only four doses of rabies vaccine. From January 2010 to September 2011, 118 cases of animal bites were reported in the district; 67 (57%) occurred among males, 65 (57%) in children <15 years old, and 61 (52%) were inflicted in a lower extremity. Domestic and stray dogs accounted for 98% of reported bites. Conclusion Dog bites remains the main source of rabies exposure in the district, but exposure can result from wildlife. This highlights the importance of a one health approach with strong communication between wildlife, veterinary, and human health sectors to improve rabies prevention and control.


Introduction
Rabies virus (family Rhabdoviridae, genus Lyssavirus) causes an acute and fatal encephalomyelitis characterized by apprehension, headache, fever, malaise, and sensory changes, such as paresthesia at the site of an animal bite or even the entire extremity [1].
Worldwide >10 million persons are potentially exposed to the rabies virus each year, resulting in an estimated 55,000 deaths. Over 95% of mortality due to rabies infection occurred in Africa and Asia [2,3].
Rabies transmission is usually through saliva via the bite of an infected animal, though infection can also occur through scratches.
The incubation period in humans is highly variable, ranging between three to eight weeks, but in some cases could be as short as a few days or as long as several years depending on site of the bite, severity of wound, and amount and type of rabies virus involved [1].
The viral shedding period is known in dogs, cats, and ferrets, and is usually three to seven days before onset of clinical manifestations of rabies and throughout the course of the disease. Longer shedding periods of 10-14 days prior to the onset of symptoms have been observed with certain canine rabies virus variants in experimental infections, but these are the exception [8]. Viral excretion in other animals is highly variable, for example, in one study in bats viral shedding for 12 days before evidence of illness was documented [9].Thus, infectious periods for wildlife are typically conservatively estimated as at least 10-14 days before onset of illness.
Management after potential exposure to the rabies virus consists of post exposure prophylaxis (PEP) [10]. The level of exposure risk guides PEP recommendations, as per the World Health Organization (WHO) guidelines [3,11]. In general, rabies PEP consists of thorough wound cleansing and infiltration of the site bite with human or equine rabies immune globulin (RIG) immediately after the exposure. This is followed by five intramuscular doses of rabies vaccination on days 0, 3,7,14 and 28 after [12]. RIG is administered to immediately neutralize the virus at the bite site and bridge the immunological gap after administration of the rabies vaccine.
In Kenya, rabies is a significant public health concern that in some districts results in approximately three deaths per 100,000 persons annually [13][14][15]. The majority of human rabies cases are acquired from dog bites. The annual incidence of animal bites in humans in Kenya is estimated as 234 per 100 000 persons [16]. In Kenya, animal bite surveillance is conducted passively [13]. The main incentive for reporting animal bites is the provision of free rabies vaccine by the government healthcare system. Exposures to rabies from wildlife bites sometimes occur, but such events are rarely reported and the role of wildlife in the epidemiology of the disease is not well documented [15].
On July 31, 2011, a zebra foal housed at a Kenyan safari lodge in Loitoktok District was bitten by a feral dog. Approximately one month later, the zebra died after experiencing a neurological illness consistent with rabies. Brain tissue was submitted to the Central Veterinary Laboratories (CVL) in Kabete on August 30, 2011. The rabies diagnosis was laboratory confirmed by a fluorescent-antibody test. There was an immediate health concern given that both staff tourists who visited the affected lodge was initiated to ensure that travelers potentially exposed to the rabies virus received appropriate rabies PEP. On September 12, 2011, we conducted an investigation to better characterize the events surrounding the zebra's illness and death, to determine the levels of potential exposure to rabies virus among local staff and other animals housed in the lodge stables, conduct a site inspection, and to evaluate animal bite surveillance in the district.

Site Investigation
We interviewed lodge staff concerning the zebra's clinical history, their exposures to the zebra, and rabies vaccination status of the staff. Since the zebra was housed within the stables compound, we conducted a site inspection of the stables to better assess and Page number not for citation purposes 3 determine the potential level of exposure to rabies virus among local staff working at the lodge and in the stables, as well as other animals housed in the stables compound.

Animal bite surveillance
We conducted a retrospective review of animal bite cases reported

Ethics
This investigation was considered a public health response to an acute event by the Kenyan Ministry of Public Health and Sanitation, and as such, did not require review by an institutional review board.
The investigational protocol was approved by the Kenyan Ministry of Public Health and Sanitation. During the site inspection informed consent was not obtained from the staff, as these interviews were conducted strictly as a public health response activity. Measures were taken to assure confidentiality of the information provided during these interviews. For the review of animal bite surveillance, data analyzed for this purpose were collected as part of routine surveillance conducted by the Ministry of Public Health and Sanitation, and did not include any personal identifying information.
Measures were taken to assure collected data were properly stored and secured.

Lodge investigation
A one month old zebra was adopted by the mobile safari company associated with the safari lodge in January 2011. The zebra was kept within the horse stables and it was free to mingle with the horses and other stable animals, staff, and lodge guests. The zebra had not been vaccinated against rabies. The zebra had become an attraction to tourists visiting the mobile safari and the lodge, and for zebras is unknown, the infection period was estimated to be 14 days before illness until death or from August 10 th to August 26 th [17]. High risk exposures to the zebra during the infectious period among humans included petting, feeding, grooming, and conducting necropsy on the dead zebra. Six (18%) employees were considered having a high risk exposure status such as hand feeding the zebra, whereas 28 (82%) employees had low risk exposure status, which included visiting or working in the stables or lodge.
Employees with low exposure risk were initiated on the five vaccine dose regimen, with the first vaccine given at the time of presentation followed by additional doses on days three, seven, 14 and 28 after presentation. Those with high risk received the same regimen plus one dose of RIG on the first day of presentation.
There were no observed human cases as a result of these exposures.

Site inspection
The stables housed 36 horses, one dog and one cat. The stable compound was clean and well kept. Each horse was kept in a separate stall where it was fed separately from other animals. Each Page number not for citation purposes 4 stall had a wooden door which was locked when a horse was inside.
The stable yard was fenced with a barbed wire, but there was the possibility that small animals like wild or feral dogs, could gain access. However, apart from the feral dog that bit the zebra, there were no additional reports of feral animals entering the stable compound. All the animals housed in the stable had up-to-date vaccination against rabies, and none of the animals developed any symptoms suggestive of rabies.

Conclusion
Though rabies virus exposures from owned dog bites continue to be a challenging problem in Kenya, the large-scale exposure of staff and guests at a safari lodge highlighted that non-canine wildlife species can also become infected with rabies virus and pose an exposure risk. To ensure effective control of rabies in Kenya, a one health approach with strong linkages and communications between the public health and veterinary officials, as well as officials from the wildlife services, is critical for prompt and adequate rabies diagnosis, surveillance, prevention and control. There is a need for increased reporting of animal bites and sharing of data regarding suspected rabies cases between public health, wildlife and veterinary authorities. There should also be deliberate efforts to ensure inclusion of RIG within national guidelines for the management of potential rabies virus exposures, as well as an adequate and uninterrupted supply of rabies PEP in all government health facilities. Rabies is a preventable disease, but effective prevention requires a multisectoral approach for adequately addressing the various components within the human and animal sectors in an effort to control and prevent rabies in Kenya. management staff who readily facilitated access to the lodge and its staff during this investigation. We thank CDC's Global Disease Detection and Emergency Response and the Ministry's of Public Health and Sanitation Division of Disease Surveillance and Response for their technical support and coordination during this investigation.