Rabies in Cambodia

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Introducing the basics

--> Rabies is an acute neurological syndrome caused by a lyssavirus in the Rhabdoviridae family. One hundred percent of declared cases are fatal. Rabies has the highest death rate of all known diseases in humans. It may, however, be prevented in 100% of cases by means of post-exposure prophylaxis (PEP), following a bite, for example. This consists of vaccination, where applicable associated with the administration of immunoglobulins.

--> It is estimated that the Cambodian population suffers 600,000 severe dog bites each year, with the total number of bites probably being somewhere in the region of one million.

--> Nearly 60% of severe bites occur in children under 17.

--> Fewer than 5% of people who are bitten (about 40,000) seek subsequent vaccination. In other words, 95% of bite victims do not receive PEP.

--> It is estimated that rabies kills 800 people annually in Cambodia (2007 survey).

--> The Institut Pasteur in Cambodia (IPC) vaccinates 21,000 people a year against rabies. The protocol followed consists of four intradermal injections (on days 0, 3, 7 and 21) at a total cost of just US$ 10. At each session the vaccine is administered in the form of two injections of 0.1 ml. Half of patients with dog bites referred to IPC are from Phnom Penh and nearby Kandal Province.

--> Rabies in Cambodia is mainly transmitted by dogs. Cambodia has five million dogs, most of which are not vaccinated. The majority of these dogs have owners, with very few being strays.

--> Since 2000, the Institut Pasteur in Cambodia has tested on average 200 biting dogs each year. Nearly 50% of them have been found to be infected with rabies (about 2 cases per week). A dog vaccination program would help to reduce the risk of transmission to humans.

The general situation in Cambodia

According to a number of studies carried out by the Epidemiology and Public Health Unit at the Institut Pasteur in Cambodia (IPC), rural communities have on average one dog for every three people – the highest reported figure in the world. This means that, with about 80% of its population living in the countryside, rural Cambodia is home to over four million dogs. These animals are not vaccinated, despite having owners.

Data from a prospective study by the Institut Pasteur in Cambodia, carried out in rural villages in the Cambodian province of Siem Reap, suggest that the frequency of dog attacks is 40% higher than previous global reports have estimated. It is estimated that there are 5 attacks per 100 person-years (95% CI: 3.6-6.8). Using a different methodology, these figures are approximately the same as those documented by IPC in studies of communities in Kampong Cham Province in 2012-2013. In these studies frequency was estimated at 4 bites per 100 person-years, with 90% of people being bitten by dogs belonging to other households (A. Tarantola, unpublished study). If this frequency is applied to Cambodia’s rural population, we have a rough but credible estimate of 600,000 bites from dogs annually.

Rabies is endemic in Cambodia due to the lack of vaccine coverage in dogs and the high number of dog bites. Most of the population does not have access to affordable, effective PEP within the stipulated deadline. There are no reliable monitoring data on rabies cases in the Cambodian population. Epidemiological models developed by IPC nevertheless give an approximate overview of the situation, with 810 deaths from rabies in children or adults in 2007 for an incidence rate of 5.8/100,000 (95% CI: 2.8-11.5). These statistics are amongst the highest recorded worldwide. The incidence rate is 3.5 times higher than in India, where the disease takes the heaviest overall toll. If these 2007 models are reliable, it means that Cambodia suffers 1.3% of global deaths from rabies – a disproportionate share given that its population numbers barely 15 million, representing less than 0.2% of the population of affected countries.

Since 2007, Cambodia's population has grown, no canine vaccination campaign has been put in place and centers offering post-exposure prophylaxis (PEP) in the form of vaccination, either with or without immunoglobulins, remain few and far between. In all probability Cambodia has seen an increase in the death toll from rabies.

Rabies control in Cambodia

Like other countries in the ASEAN Plus Three group, Cambodia has pledged to eradicate canine rabies by 2030, but it faces a number of obstacles. To our knowledge there is currently no canine vaccination program, no approved strategy, no funding and insufficient expertise dedicated to wiping out canine rabies in the country. The single weapon against human rabies cases in Cambodia is PEP, to which only a minority of patients have access.

The IPC rabies prevention center is specifically mentioned in Article 7 of the Memorandum of Agreement (MoA) of August 27, 1992, between the Cambodian Ministry of Health and the Institut Pasteur, which laid the foundation for a new Institut Pasteur in Cambodia. The center administers anti-rabies PEP to over 21,000 people each year. It is now the country's top provider of post-exposure prophylaxis. IPC subsidizes these procedures, with a cost to the patient of only US$ 10 for a full vaccine protocol. IPC’s Virology Unit is a reference center for animal and human rabies. It performs timely and state-of-the-art RABV diagnosis free of charge.

The center applies the only intradermal protocol currently approved by the WHO. This protocol was developed in Bangkok, Thailand, by the Thai Red Cross and subsequently simplified and shortened following WHO recommendations in 2005. The new TRC post-exposure regimen in unvaccinated subjects now associates intradermal injections of 0.1 ml in two sites on days 0, 3, 7 and 28.

Added to the cost of vaccine (US$ 10 for a full intradermal, 4-session IPC-subsidized protocol) and ERIG where applicable, the total out-of-pocket expenditure for four return trips for one person was estimated on average at US$ 64 in 2012. Children must be accompanied by an adult, which doubles the transport costs. These out-of-pocket expense estimates exclude the cost of a tetanus booster and that of a test to confirm rabies in the dog, both borne by IPC. In 2012 the mean monthly income per capita was US$ 44.5 in rural areas of Cambodia.

Approximately 56% of patients who received PEP in 2014 came from outside Phnom Penh, compared to 23% in 1996 (Arnaud Tarantola, unpublished study). Most Cambodians who are bitten by dogs in rural areas do not have the financial means to travel to the capital for PEP. In addition to ongoing IPC research aiming to reduce doses even further as well as the associated vaccine and transport costs without incurring risk to patients, the implementation of frontline Ministry of Health/IPC rabies prevention centers would provide geographically accessible, affordable, timely and adequate PEP to a greater number of bite victims in Cambodia.

By Didier Fontenille, IRD Director of Research and Director of the Institut Pasteur in Cambodia. February 2017. This text illustrates the report “The Geopolitics of the Mosquito” - Go further with our experts!, published to coincide with the release of Erik Orsenna's book, Géopolitique du moustique, Ed. Fayard. https://www.pasteur.fr/en/research-journal/news/rabies-cambodia

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