Assessment of the risk for rabies introduction and establishment in Lombok, Indonesia

Abstract

Rabies, a zoonotic disease, is maintained in the domestic dog population in Indonesia and has caused human fatalities since its introduction to this country in the 1880s. Although rabies control strategies have been implemented on rabies-infected islands, this disease is still spreading to other parts of Indonesia, with newly infected islands as recent as 2012. Live dog movement on fishing or cargo boats is believed to have facilitated the introduction of rabies virus into previously rabies-free islands in Indonesia, such as to Bali and Flores. Until today, of the total 33 provinces, only nine provinces remain rabies-free including Lombok Island in West Nusa Tenggara (NTB) Province. This research was conducted from 2011 to 2013 to investigate pathways for rabies entry to Lombok Island via dog movement and to assess the probability of rabies entry and exposure to the susceptible dog population on Lombok. Further, this research aimed to provide knowledge of the pathways and probability of rabies entry to Lombok in order to inform development of quarantine and surveillance strategies to prevent rabies entry and establishment on Lombok. Pathways for rabies entry to Lombok were first defined based on the literature and then refined and prioritised based on expert opinion. After this process, two pathways of release of a rabiesinfected dog were identified: boat and ferry pathways. Scenario trees were developed for each pathway to describe the release of a rabies-infected dog to Lombok, as well as scenario trees to describe the exposure of a rabies-infected dog to the susceptible dog population on Lombok. Four surveys were conducted on Bali and Lombok islands to obtain data used to refine the pathways and to inform the release and exposure models. The first survey obtained data on dog numbers and dog management practices of dog owning households belonging to different ethnic groups at an urban site and a rural site on Lombok. A total of 400 households were interviewed, 300 at the urban site and 100 at the rural site. The majority of the interviewed households belonged to Balinese ethnic group. Sasakese households owning dogs were more frequent at the rural site compared to the urban site. Owning dogs born on Lombok was common (96% households), however, 4% of households reported owning dogs obtained from outside Lombok (Bali and Java). The latter was more common at the urban site and among Balinese ethnic group. All households that reported imported dogs mentionedtransporting the dog/s in a vehicle by ferry from Padang Bai harbour Bali to Lembar harbour Lombok. All these households also reported that the imported dogs did not have the documentation required by the quarantine agency and 11 reported that the imported dogs had been vaccinated but were not able to identify the type of vaccination. The dog owning households kept their dogs either fully restricted, semifree roaming or free-roaming but full restriction was reported only at the urban site. Dog bite cases were reported to be higher at the urban site. For the second survey, to investigate dog transportation on boats docking on Lombok, interviews were conducted with captains of boats that originated from other parts of Indonesia and of local Lombok boats at seven informal ports (no quarantine post). Over three consecutive days at each port, a total of 117 captains of outside boats and 52 captains of local boats were interviewed. This survey found that dogs are not common on boats. All of the captains interviewed, except one captain from Bali, reported never having a dog on board their boat. More than half (61.5%) of the captains of outside boats knew that rabies is transmitted to people through dog bites compared to only 7.7% of captains of local boats. Dog observation was also conducted during the survey visits to these ports to document the presence of dogs on boats, and the presence of dogs and interactions between people and dogs at the port area. No dogs were seen on boats, which confirmed the finding of the boat captain survey. To further investigate the role of illegal dog movement through ferry route, the thirdsurvey interviewed people travelling with a vehicle to Lombok by ferry from Padang Bai Bali. Interviews were conducted at Padang Bai harbour over ten days and 158 people were interviewed. The people interviewed consisted of Lombok residents (51.3%) and non-residents (48.7%); 10.8 % of which reported experience bringing dogs to Lombok. All of the 21 imported dogs were pedigree dogs; majority were male; and all had originated from Bali, Jakarta or West Java. Although these dogs were transported in several types of vehicles, the majority had been transported in a truck. Transportation for most of these dogs (14) was done at the request of dog owners living in Lombok and payment provided by the dog owners. Only two dogs werereported to have been vaccinated against rabies. None of the people who had transported these imported dogs reported the dogs undergoing quarantine inspection at either Padang Bai harbour or Lembar harbour Lombok. A fourth survey was undertaken to estimate the number of unowned dogs at the urban and rural sites on Lombok where the household survey was conducted. A photographic-recapture method was employed and the number of unowned dog was estimated using a Chapman estimate from Beck (1973). A higher number of unowned dogs was observed at the urban site than at the rural site. Information obtained from the surveys was incorporated into the risk assessment models to quantify the probability of that one rabies-infected dog is released at Lombok via boat and ferry pathway and the probability of a susceptible dog at the informal port, urban site and rural site becoming infected with rabies virus after the release of a rabies-infected dog via the boat and ferry pathway. Data from published literature and expert opinion were also utilised. Monte Carlo stochastic simulation modelling was performed with @Risk 6.0 (Palisade Corporation, USA). Each simulation consisted of 5,000 iterations sampled using the Latin hypercube method with a fixed random seed of one. Sensitivity analysis was also conducted to identify which input parameters were the most influential to the overall outputs of the release and exposure assessment models. This was performed using the @Risk 6.0 Advanced Sensitivity Analysis (Palisade Corporation, USA). Based on the results of this study, the probability of rabies being introduced into Lombok via both boat and ferry pathways was very low. However, these estimates were not negligible and to estimate the overall risk of virus introduction into Lombok for a specific period of time, the total number of boats, ferries and passengers in eachferry coming into Lombok should be considered. The sensitivity analyses for the release assessments indicate that the prevalence of rabies in Bali has a significant influence on the probability of rabies virus being introduced into Lombok. The presence of dogs on boats travelling to Lombok and the probability of ferry passengers bringing dogs to Lombok were also influential parameters. The exposure assessments suggest that the overall median probability of a rabid dog released in Lombok exposing and infecting a susceptible dog in Lombok was low. This probability was similar for a rabid dog being released at an informal Lombok port and for a rabid dog released by a person travelling in a ferry that resided in rural/urban Lombok. These results suggest that the probability of exposure is not negligible. The probability of the rabid dog confinement was an influential parameter on the probability of susceptible dogs in Lombok being exposed. These findings have provided information on pathways and probability forto Lombok and for rabies exposure to the susceptible dog population on Lombok. The practice of illegal dog movement via the ferry route can now be addressed to prevent rabies entry to Lombok, through rabies control at source (that is, on rabies-infected islands); improvement of performance of the quarantine agency ; and through education about rabies for the general public and dog owners as well as for animal health and public health officials. Preventing establishment in the event of rabies incursion through early disease detection and preparedness planning is also important. Early disease detection includes animal disease surveillance and monitoring the level of human dog bite cases. Preparedness can include responsible dog ownership that incorporates dog registration and identification, dog vaccination, neutering and confinement; dog population control through a better waste collection and disposal system by government agencies to reduce food sources for roaming dogs; and dog rabies vaccination for Lombok. In particular vaccination in advance of an incursion deserves serious consideration because it can create a barrier to prevent rabies transmission to people