DRIT and rabies surveillance in Québec

This fall marked a milestone in the annual rabies surveillance program in Québec: the 10,000^th animal was tested for rabies in the province!  This surveillance is a multi-agency program and rabies testing is an essential part of the ongoing vaccination and surveillance efforts to prevent rabies introduction within the province from neighboring American states.  Although the bulk of the animals tested annually are raccoon’s, other species such as skunks, red foxes, coyotes and bats may also be submitted.

Although the initial testing process involved the collection of tissue samples from wild animals by the CCWHC – Québec Regional Center which were then submitted to CFIA for rabies testing, the protocol was modified in 2010 to allow for direct testing by CCWHC personnel using the DRIT diagnostic procedure. The acronym stands for Direct Rapid Immunohistochemical Test.  Immunohistochemistry is a method which allows the detection of proteins within a cell, such as infectious agents, using a specific antibody that reacts with a given antigen.  More specifically, the DRIT technique is an immunoperoxydase method in which rabies viral particles are visualized within infected cells using a special staining system. Developed to diagnose rabies by a Centre for Disease Control (CDC) scientist, this method was evaluated using more than 25,000 specimens and was determined to be extremely sensitive and specific.  A research associate for the CCWHC – Québec Regional Center was sent in 2010 to Ottawa for a training session given by a CDC scientist with the collaboration of CFIA rabies experts.  Participants came from most Maritime provinces, Québec and Ontario.

This testing procedure has distinct advantages over the traditional gold standard used for rabies testing (IFAT), including the fact that it can be performed by labs other than the CFIA as a very adequate surveillance and screening tool which means that less samples have to be shipped around to other labs and can be tested locally.  Also, using this method, a high number of samples can be tested simultaneously (20 to 60 samples on a weekly basis) and the rapid turnover (approximately 1h30 to 2 hours to obtain a result) with this procedure could allow field personnel to react quickly when confronted with a positive/infected animal.

The DRIT procedure was initiated in 2010, when the 6,500^th raccoon had been processed by the CCWHC – Québec Regional Center for rabies surveillance. Three years later and with 3,500 raccoon’s more, the 10,000^th animal was recently tested this fall using this procedure. The vaccination protocol used by the Ministère des Ressources naturelles et de la Faune (MRNF) of the provincial government has so far proved very effective at preventing rabies introduction in the southern part of the province.  Positive animals detected this year with the DRIT procedure included only two bats. Five other bats and more recently a skunk from Longueuil, south of Montréal, tested positive for rabies virus this year and had been submitted to CFIA for confirmation. The skunk was infected with the bat variant of the rabies virus.