Research Article: Molecular Epidemiology of Rabies Viruses Circulating in Two Rabies Endemic Provinces of Laos, 2011–2012: Regional Diversity in Southeast Asia

Date Published: March 31, 2015

Publisher: Public Library of Science

Author(s): Kamruddin Ahmed, Phouvong Phommachanh, Phengphet Vorachith, Takashi Matsumoto, Pheophet Lamaningao, Daisuke Mori, Minako Takaki, Bounlom Douangngeun, Bounkhouang Khambounheuang, Akira Nishizono, Charles E Rupprecht.

Abstract: BackgroundAlthough rabies is endemic in Laos, genetic characterization of the viruses in this country is limited. There are growing concerns that development in the region may have increased transport of dog through Laos for regional dog meat consumption, and that this may cause spillover of the viruses from dogs brought here from other countries. This study was therefore undertaken to evaluate the current rabies situation and the genetic characteristics of rabies viruses currently circulating in Laos.MethodsWe determined the rate of rabies-positive samples by analyzing data from animal samples submitted to the Lao Ministry of Agriculture and Forestry’s National Animal Health Centre rabies laboratory from 2004 through 2011. Twenty-three rabies-positive samples were used for viral genetic characterization. Full genome sequencing was performed on two rabies viruses.ResultsRabies-positive samples increased substantially from 40.5% in 2004 to 60.2% in 2009 and continued at this level during the study period. More than 99% of the samples were from dogs, followed by cats and monkeys. Phylogenetic analyses showed that three rabies virus lineages belonging to the Southeast Asian cluster are currently circulating in Laos; these are closely related to viruses from Thailand, Cambodia and Vietnam. Lineages of the circulating Laos rabies viruses diverged from common ancestors as recently as 44.2 years and as much as 55.3 years ago, indicating periodic virus invasions.ConclusionThere is an increasing trend of rabies in Laotian animals. Similar to other rabies-endemic countries, dogs are the main viral reservoir. Three viral lineages closely related to viruses from neighboring countries are currently circulating in Laos. Data provide evidence of periodic historic exchanges of the viruses with neighboring countries, but no recent invasion.

Partial Text: Globally, an estimated 60,000 people die of rabies annually, and more than 31,000 of these deaths occur in Asia [1,2]. Among various Asian regions, the countries of the Association of South East Asian Nations (ASEAN) have been working towards substantial economic development. A call for elimination of rabies by 2020 highlights the political importance of rabies control [3]. Seven out of the 10 ASEAN member states are rabies-endemic: Cambodia, Indonesia, Laos, Myanmar, the Philippines, Thailand and Vietnam [3]. Among these countries, Laos has the lowest reported number of human deaths from rabies. However, the precise morbidity, mortality and molecular epidemiology of rabies in Laos is largely unknown. This is due to difficulty in collecting data and samples from remote areas of the country, and to the country’s modest data collection system at the centralized diagnostic facility. Survey of prevalence of canine rabies is still in its initial stages and limited to a small central part of Laos. The first reported phylogenetic study showed that Laotian rabies viruses are grouped with viruses from Thailand, Myanmar, Cambodia and Vietnam [4]. Combined analyses from geographic information system data showed that China is the likely source of the Asian rabies viruses, whereas individual migration event suggested that Cambodia may be a source of Asian rabies viruses transmission to China, Laos and Thailand [5].

In Laos, a National Committee for Rabies Control was formed in 1999 and ASEAN has also called for action to eliminate rabies by 2020 from South East Asia [12]. Therefore there have been continued activities such as attempt to increase rabies awareness among people, campaign for animal and human vaccines, and campaign for sterilizing roaming dogs. Whether the gradual increase of rabies samples as noted in this study indicating an increase of rabies in dogs or rabies awareness among the people is not known. If this indicates an increase of rabies then it needs urgent measures to contain the situation before it become big. In Laos annual number of humans with animal bite has increased from 8,277 in 2008 to 14,156 in 2011, (Expanded Program on Immunization unit, Mother and Child Health Centre, Hygiene and Health Promotion Department, Ministry of Health, Lao PDR). Vientiane Capital accounts for 73% of the national data for bites and rabies vaccination in humans, 99% of the bite victims are given postexposure treatment but in the form of vaccination only since rabies immunoglobulin is not available and only 30% receive a full course of vaccine [12]. Dog vaccination coverage was also found to be low, only 11% of the owned dogs were vaccinated for rabies [13]. Other study showed that 71–83% of dog vaccination occurs in the capital, covering 6% of the estimated dog population [12]. All samples used in the present study for genetic characterizations of rabies viruses were from owned dogs but none of them were vaccinated, over that no owner restricted the dog movements at all times through fencing, leashing or confined to indoors. The low rate of vaccination might be multifactorial and one of them may be cost. Government sponsored campaign is done once a year and mainly in the big cities therefore it does not have an impact on the rural population where the burden of rabies is possibly more. Although on the campaign day the vaccine is free but other than that the dog owner has to pay for the vaccination which may cost between 20,000 and 50,000 Kip (approximately between 2.5 and 6.2 US$). Despite the inadequate level of human and animal vaccination why the reported number of human death from rabies remains at the level of 0–1 per year deserve further investigation. Rabies epidemiology depends on human- and dog-population densities as well as to the cultural and socioeconomic environments [14]. For rabies control public education on dog vaccination and responsible dog ownership is essential.



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