Mass vaccination can keep this neglected disease under control

3 October 2014 by DUR

Mass dog vaccination campaigns can have a substantial impact on keeping rabies under control.

Mass vaccination campaigns that reach 70% of dogs will control and, hopefully, eventually eliminate rabies. This is the message that Prof. Darryn Knobel of the Faculty of Veterinary Science at the University of Pretoria (UP) would like us to hear.
 
Anyone who has a dog knows they must be vaccinated regularly against rabies – both to keep the dog and the human family healthy. Not only is it essential for public health but it is also a legal requirement. Of course, this is more challenging in disadvantaged communities where there may not be money for expensive veterinary services, and this is where the State steps in with mass vaccination campaigns. Prof. Knobel’s work in the Hluvukani settlement in Bushbuckridge in Mpumalanga has shown that if the government can achieve a 70% coverage rate in annual mass vaccination campaigns in such areas, we will achieve herd immunity and keep the incidence of rabies down.

“There is clear evidence that 70% is sufficient and do-able and that this target would have a substantial impact on rabies control,” explains Prof. Knobel. “This was found even in a very dynamic dog population where there is both a high annual birth and death rate.”

Although rabies vaccines have been around for many years, no vaccine for any disease is completely protective. What you want to achieve is to have enough coverage in the population (animal or human) to reduce the amount of virus in circulation – this is called herd immunity and is the goal in vaccination campaigns. The magic threshold of coverage needed to achieve such immunity varies by virus but is actually fairly moderate for rabies – estimated at about 40%. However, in a community with a high turnover in the dog population (due to deaths and births) it’s hard to keep the level of vaccinated dogs consistent therefore you have to go for a higher coverage to maintain herd immunity until the next campaign.

“Between campaigns, the proportion of immune individuals in the population declines as vaccinated dogs die and susceptible dogs enter the population through birth or migration,” says Prof. Knobel.

“The World Health Organisation recommends 70% coverage but there was little theoretical and empirical evidence to support this percentage, especially in less-advantaged areas,” explains Prof. Knobel.

“Our work in Bushbuckridge has confirmed that this is the appropriate and required level of coverage,” he continues.

Dogs in disadvantaged, rural communities are often free roaming increasing their risk for rabies, however, there is a misconception that they are not owned. Prof. Knobel’s research has shown that this is not necessarily the case.

“There was no evidence of a large-scale, un-owned dog population,” says Prof. Knobel. “More than 90% of the dogs are owned which means they are accessible for vaccination.”

Rabies is one of the oldest infectious diseases known to man but is classified as a neglected tropical disease. Rabies is caused by infection with strains of Lyssavirus in the family Rhabdoviridae. Rabies can be found in any mammals but two main strains occur in Africa - one in the dog population and one in mongooses. Globally the dog strain is the most prevalent and the most likely to be transmitted to humans. Over 90% of human cases in Africa are attributed to dog bites. Around 10 - 30 human cases of rabies are confirmed each year in South Africa, and result almost exclusively from dog bites, however, it is likely that this number is underreported particularly in remote rural areas.

In another study, Prof. Knobel has reviewed work done on rabies in wildlife in Africa. Surveillance in the Serengeti and Kruger Parks and elsewhere has shown that, despite its presence in adjacent dog populations, rabies is not a significant conservation concern for wildlife in Africa. However, where it does occur, it seems to be most likely in small, already-vulnerable populations, such as African wild dogs and Ethiopian wolves. Controlling the disease in domestic dog populations through wide-scale mass vaccination would therefore be an important component of protecting and conserving these species as well. Prof. Knobel’s work also points to the importance of ongoing surveillance for rabies in wildlife populations. “There is a need to maintain and intensify rabies surveillance in wildlife alongside efforts to control the disease in dogs,” he says.

Prof. Knobel will be presenting this work at the 39th World Small Animal Veterinary Association Congress in Cape Town this week (16 – 19 September 2014). He will also launch a small project at the congress where attendees will be encouraged to donate their conference name-badge holders to be turned into dog collars which will be used to identify (and therefore track) dogs in the study community. The collars would also provide a visible sign of dog ownership in the community. More details on this project can be found at http://www2.kenes.com/wsava/congress/Pages/AccompanyingProgram.aspx

28 September 2014 is World Rabies Day, a global health observance that seeks to raise awareness about rabies and enhance prevention and control efforts.

Prof Darryn Knobel

October 3, 2014

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