Rabies and RITA in Puerto Rico

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The 22nd Rabies in the Americas (RITA) meeting was recently held in San Juan, the capital of Puerto Rico, with a blend of informative presentations, interesting workshops and enjoyable social activities. Several special presentations and two workshops gave participants an understanding of the special features of rabies in the Caribbean.

Mongooses were introduced to several Caribbean islands in a misguided attempt to control rat populations. Now there are an estimated 2 million mongooses on Puerto Rico, with up to 2% infected with rabies (about 80% of rabies cases). Around 25 people are exposed to suspected rabid mongooses every day, with about 2/day requiring PEP treatment. The mongoose is now present on many Caribbean islands, with Cuba, Dominican Republic, Grenada, and Haiti also having to deal with mongoose rabies. Many of the islands, including Puerto Rico, also struggle with large free-roaming dog populations that can transmit rabies. Translocation of dogs and mongooses that are unknowingly infected with rabies to new areas in the Caribbean remains a real risk.

Mongoose rabies control options were reviewed by Dr Dennis Slate (USDA wildlife services, USA) who concluded that oral vaccination of mongooses against rabies was the most feasible means to eliminate the virus. As mongooses are generalist feeders, baiting is relatively easy and at least one vaccine is known to be effective (though not registered for use) in mongooses. However, mongoose densities can be very high, and bait distribution needs to be planned to avoid non-target species (eg rats and cats) eating them instead. Combining vaccination with injectable contraceptives would be even more effective, as but more research is needed before this is an option. Many of the necessary surveillance, mapping and modelling tools are already in place, and in Puerto Rico, local support is mounting for rabies elimination. Results of a study on mongoose population densities at two sites in Puerto Rico was presented by Kurt VerCauteren (USDA wildlife services, USA), with baiting strategy design in mind. The data from capture-mark-release and camera trap techniques suggest around 50 mongooses/km2 .

Dr. Andres Velasco (CDC, USA) presented genetic data on dog-mongoose rabies virus variants from the Caribbean region, collected to better understand the transmission of mongoose rabies. Analyses suggest that in Puerto Rico, both dogs and mongooses play an important role in virus maintenance, with dogs implicated in the longer distance spread. Elimination attempts need to consider both hosts, and possibly also feral cat populations, in their design. Canine rabies cases in Latin America and the Caribbean have been reduced from around 15,000 in the early 1980s to just 268 in 2010, due to a huge international collaboration directed at canine vaccination, the provision of PEP and surveillance. Dr Hugo Tamayo (PAHO) presented the current status, with foci of infection remaining in a few countries, including Cuba and Haiti in the Caribbean. The goal of elimination of canine rabies is very close, but all countries need to remain engaged in the elimination programme.

Rabies transmitted from bats has not been documented in Puerto Rico, although little testing has been carried out. Dr Amy Turmelle (CDC) presented a study on the potential for northern spread of vampire bats from Latin America, based on predicted global warming trends, bat dispersal behavior and geographic barriers. Currently there are vampire bats in the Caribbean only on Trinidad, despite suitable habitat and temperatures elsewhere, suggesting that the ocean forms a barrier to migration. However, islands such as Cuba and Grenada, both close to the mainland, are at risk of chance introductions. This is substantiated by genetic evidence presented by Dr Janine Seetahal, a veterinary officer in Trinidad and Tobago. Her data suggested that rabies virus infected bats flew across the 7 mile stretch of ocean from Venezuela into Trinidad, and caused outbreaks of paralytic rabies in cattle there.

Two workshops also gave participants an opportunity to experience the beautiful Puerto Rican countryside. Participants in one workshop visited the El Yunque rainforest in the east, to see the ongoing mongoose density assessment study and also to perform dRIT testing, a tool commonly used out in the field in surveillance programs. Participants in the second workshop trekked out westwards, to visit one of many limestone cave systems where they were treated to the sight of some of the 300,000 resident bats emerging at dusk, trying to avoid the jaws of the small Puerto Rican boa as they gathered above the cave mouth to capture them (pictured).

Summarised by Louise Taylor. The next RITA meeting will be held in October 2012 in Sao Paulo, Brazil.