• Vets emphasise the need to expedite dog sterilisation programme

In the context of the spread of rabies, carrying out a survey to estimate dog population density within Colombo district is needed while the sterilisation of dogs, which is usually carried out in collaboration with the Public Health Veterinary Service (PHVS), should be expedited.

These recommendations were made in a brief report on “Laboratory confirmed three rabid spotted deer in the Colombo suburbs: Does it ring alarms concerning disease transmission to humans?”, which was authored by K. Kalubowila, C. Hapudeniya, and D. Liyanage (all three attached to the Office of the Regional Director of Health Services, Colombo) and published in the first issue of the 29th volume of the Journal of the College of Community Physicians of Sri Lanka in May 2023.

Stats so far

Rabies, as mentioned in the PHVS’  “About rabies“, is an encephalomyelitis (the inflammation of the brain and spinal cord) caused by infection with the rabies virus or other lyssaviruses, and is estimated to approximately cause 56,000 human deaths each year in Africa and Asia. The expenditure on post-exposure prophylaxis, according to the World Health Organisation’s (WHO) “Epidemiology and burden of disease 2022”, is the highest in Asia, with cost estimates of up to $ 1.5 billion annually. 

In Sri Lanka, as noted in the Health Ministry’s Epidemiology Unit’s “Selected notifiable diseases reported by Medical Officers of Health (MOHs) 2022. Colombo: Weekly epidemiological report”, 23 human rabies deaths occurred in 2021, indicating that rabies is also a threat to humans in the country.

Per P.L. Harischandra, A. Gunesekera, N. Janakan, G. Gongal, and B. Abela-Ridder’s “Sri Lanka takes action towards a target of zero rabies deaths by 2020”, Sri Lanka is the first country in South-East Asia, where a national strategy for the elimination of dog-mediated rabies was developed with the aim of achieving a global target of zero human rabies deaths from dog-mediated rabies by 2030. However, although human rabies is notifiable, as pointed out in D. Karunanayake, T. Matsumoto, O. Wimalaratne, S. Nanayakkara, D. Perera, A. Nishizono, and K. Ahmed’s “Twelve years of rabies surveillance in Sri Lanka, 1999–2010”, rabies surveillance in dogs and wild animals is extremely difficult to undertake in the country, and therefore, the data is unknown. Similar to other Asian countries, rabies is frequently found in dogs, yet, as observed by the University of Peradeniya’s Veterinary Medicine and Animal Science Faculty’s Rabies Diagnostic Unit in their “Rabies facts”, cats and wild animals such as jackals, mongoose, polecats, civets, and bats may also carry the disease in Sri Lanka.

New evidence

A herd of deer has spread since the mid-1980s in the Panagoda Army Camp, following their transportation from Eravur in the Batticaloa District, and one family in the same area provided a home to a couple of deer. According to the people, these deer somehow escaped to the nearby villages and up to date, a herd of around 400-500 deer are living in Homagama, Panagoda, Athurugiriya, and Moratuhena, usually in groups of between 10 and 60 animals.

Around 20 unusual deer deaths were reported from June to September 2022, in the Homagama and Athurugiriya suburbs. On 8 August, the Department of Wildlife Conservation (DWC) was informed following the death of a deer, with the drooling of saliva seen by a resident in Homagama. The brain sample of the deer was laboratory confirmed for rabies by the Medical Research Institute, Colombo. Similarly, on 16 August, from Athurugiriya and on 19 August from Homagama, two more deer heads were positive for rabies.

Several meetings were conducted with multi-stakeholder involvement including the DWC, the PHVS, the Divisional Secretariat – Homagama, the Education Ministry, and the Health Ministry to take a collective decision to prevent rabid deer-human contact. Educating the public not to feed the deer and play with them, especially children, was carried out through the MOH of Homagama, Kaduwela and the Zonal Directors of Education of Sri Jayewardenepura, Kotte, and Homagama. The ring vaccination programmes, especially targeting stray dogs, were extended in these two areas since 17 August 2022.

Ceylon spotted deer (Axis axis ceylonensis) is endemic to Sri Lanka, where they are usually found in most parts of the country except in the highest hills. Usually, according to K. Gowrithasan, A.M. Ahamed, and M. Dharmaretnam’s “A behavioural study of free-ranging Ceylon spotted deer in Trincomalee”, they are active in the morning and evening, mostly feeding and playing, with the afternoon spent in resting. Although it is not currently practised in Sri Lanka, the vaccination of deer for rabies, as done in Pennsylvania, USA, is expected to have similar safety and efficacy as it does in other ruminants. However, it is less feasible as they are extremely nervous and always on alert for any sign of imminent danger. Thus, the prevention of human-deer contact, especially among children, is essential, which was carried out in this region. 

Further, the catching of deer and relocating to remote areas is less feasible, due to several reasons such as the risk of the spread of rabies to a new area, the lack of familiarity with the new environment leading to preying by other wild animals and the lack of familiar food for those herds of deer. Therefore, relocating needs to be implemented gradually. In suburban settings, where deer densities are often the highest, administering anti-gonadotropin-releasing hormone injections to bucks is less feasible due to the need for repeated doses as a contraceptive method, the difficulty in the identification of the injected bucks once the injection is administered, and adverse events following the injection, it was noted in an Argentinean study. Therefore, frequent health-related monitoring of spotted deer is carried out through field visits.

Complications

The risk of rabies transmission from deer to humans is, per Gowrithasan et al., very low. Further, rabies in deer occurred infrequently in other countries such as the US, Argentina, China, and South Korea, per B.W. Petersen, D.M. Tack, A. Longenberger, A. Simeone, M.E. Moll, M.P. Deasy, J.D. Blanton, and C.E. Rupprecht’s “Rabies in captive deer, Pennsylvania, USA, 2007–2010”. The rabies virus, Kalubowila et al. opined, was most likely transmitted to the deer through contact with wildlife, however, deer-to-deer transmission cannot be excluded in Homagama where multiple rabid deer have been reported. 

The other explanation by Kalubowila et al. is that these deer were bitten by a rabid stray dog, causing rabies in these deer herds. Further, domestic dog-to-deer transmission can occur once a dog escapes the house, although, with less of a possibility due to the mass vaccination of dogs, which was carried out in March 2022, in the affected area with a coverage of 7,768 dogs including 736 stray dogs. Further, around 1,500 dogs were vaccinated following the deaths of deer around the areas, specifically those that were inhabited by stray dogs.

Effective preventative methods

The vaccination of domestic and community dogs has been shown to be a successful and cost-effective way of preventing human rabies, which is routinely undertaken in Sri Lanka. It is reported that by vaccinating 70% of the dogs in areas where rabies is present, the number of human cases can rapidly drop to almost zero. However, as elaborated by the WHO Rabies Modelling Consortium’s “Zero human deaths from dog mediated rabies by 2030: Perspectives from quantitative and mathematical modelling”, due to the unknown figure of dog estimation, this data could not be extrapolated into this community.

Despite the numerous deer deaths mentioned in this case study, only three cases were confirmed for rabies. Although several deer deaths were not tested for rabies, these cases can be taken as evidence to further explore the current situation. Further, no human rabies death has been reported recently in these areas. Following the first stakeholder meeting, a knowledge-sharing platform was established among participants to report further cases, to increase awareness on preventing human-deer contact, and to share the intervention that was carried out, which will be helpful in further stepping up the reduction of disease transmission.

Systematic data collection and compilation to provide accurate information on confirmed cases of animal and human rabies at the MOH area level would be helpful in developing control roadmaps. As the spread of the virus to deer is strange, it is of critical importance to perform the genetic typing of brain samples to identify the species.

The multi-faceted nature of the disease complicates control and the prevention of rabies via deer, and therefore a multi-sectoral health-based singular approach could be a better strategy with the inclusion of all stakeholders (human, animal, and environmental health sectors) in disease management programmes.