Today’s post comes from Rachel Gagnon, Rabies Science Transfer Specialist with the Ontario Ministry of Natural Resources and Forestry (MNRF), highlighting some of the amazing work being done in Ontario in the ongoing battle against wildlife rabies.
Ontario’s rabies control program is a world leader when it comes to controlling and eliminating rabies. The MNRF program was successful in eliminating the raccoon variant of rabies from Ontario in 2005 and has been highly effective in keeping the current rabies outbreak – which started in 2015 – contained to within about 50 km of the original case. The Ontario rabies program also reduced an epidemic of fox strain rabies from 46,000 cases (from 1957 – 1986) down to 0 by 2012 through the implementation of the large scale rabies program which began in the 1990s.
To control and eliminate rabies from Ontario, wildlife are vaccinated by two methods; trap- vaccinate-release, and by distributing oral rabies vaccine baits. Where these management techniques are used is informed through surveillance testing of dead or sick animals, enabling cost effectiveness response. The blend of these key elements is what has made the rabies program a success in the past and presently.
During the most recent Ontario outbreak, which began in December 2015, the MNRF implemented a new cost-effective test developed by the Centers for Disease Control (CDC) to assess large volumes of rabies samples in wildlife quickly and accurately. The method, called the direct Rapid Immunohistochemical Test or dRIT, has allowed for a new approach to assessing the most recent outbreak in Ontario. The MNRF has been using dRIT in conjunction with the Canadian Food Inspection Agency’s (CFIA) direct fluorescent antibody test (FAT), which has long been considered the ‘gold standard’ of rabies testing, but requires expensive fluorescence microscopy and specialized lab equipment. In contrast, dRIT uses a significantly more economical light microscope and can be done in relatively simple lab spaces. dRIT has allowed MNRF to test more animals and get results quickly and accurately to better assess the size and spread of the rabies outbreak and to make effective management and control decisions. [Image: MNRF staff test wildlife samples in the lab.]
This test has been a game changer in the global work of rabies control, and has played an important role in assessing where rabies is present and how it is moving across the landscape here in Ontario. As of May 2018, MNRF tested its 10,000th sample using dRIT, enabling Ontario to achieve unprecedented detail in the monitoring of the current rabies outbreak. During this most recent outbreak, 393 of the 405 (97%) rabies cases in Ontario have been discovered by the MNRF lab through the dRIT method.
When MNRF began implementing the dRIT test, knowing the accuracy of the test results was crucial. Beginning in 2016, research was conducted to validate Ontario dRIT test results against gold standard FAT results. In the study, agreement between rabies positive dRIT and FAT results was 98.8% and agreement between the tests for rabies negative samples was 100%. MNRF staff have since implemented two changes related to staff training and diagnostic determination, and have since been able to achieve 100% agreement of positive results between both tests.
Each week, the MNRF lab receives an average of 85 samples for testing from within the rabies surveillance area. Numbers will fluctuate depending on the time of year. The rabies surveillance zone is a buffer zone of 50 km around any rabies cases. Targeted mammal species found dead in the zone can be submitted to MNRF for rabies testing.
MNRF tests animals each week by creating a tissue impression of available brain tissue onto a microscopic slide. These slides are put through a series of chemical baths, and incubated with a rabies specific stainable antibody. Slides are viewed by light microscopy to determine the results. A negative test slide would show as all blue, if rose-red round masses are detected the sample is diagnosed as positive. Once MNRF has completed their testing, positive samples are shipped to the Canadian Food Inspection Agency for secondary FAT confirmation. [Image: left – positive dRIT result showing red specific staining; right – negative dRIT result.] When new cases of rabies are detected, MNRF notifies partners in the Ontario Ministry of Health and Long-Term Care, Ontario Ministry of Agriculture, Food and Rural Affairs and local public health units who will conduct follow-up investigations to ensure no members of the public had been exposed to the rabid animal. Rabies maps are also updated on the MNRF website weekly to reflect the number and locations of the new cases. [The maps are also reposted on the OMAFRA rabies website and on the OAHN website.]
Though human deaths from rabies in Ontario are rare, it is still a major global problem. The World Health Organization states that tens of thousands of people die each year from rabies, most often through canine exposure. dRIT was developed by the Centre for Disease Control and Prevention to provide a means to test animals for rabies in developing countries, where funding and infrastructure would prohibit the traditional standard and more expensive test. dRIT has proven to be such an important tool for the diagnosis of rabies cases all over the world that the test has very recently been approved as an official diagnostic test by the World Organization for Animal Health General Assembly.
For more information about rabies in Ontario, the rabies program, and to see updated maps visit the Ontario.ca rabies website.