Rabies testing and surveillance - what's it all about?

Post by

Andy Gibson

October 13th 2016

When fighting to eliminate a disease such as rabies, surveillance could be compared to intelligence on the battle field. By detecting where possible rabies cases are occurring in dogs and confirming presence of the virus through testing, we can map out the hotspots. We are also able to compare where we have vaccinated with where rabies cases occur to monitor the success or failure of our efforts and identify where a change in approach might be needed. Ultimately, we aim to see a decline in human deaths from rabies - however we focus our surveillance efforts on dog rabies because the vast majority of people contract rabies from a dog bite.

How does surveillance work?
There are three main components to successful surveillance, each one dependent on the last.

Step 1 – Rabies Reporting - Who to call?
The first challenge is reporting. In many parts of the world, there is not a clear reporting channel, so possible rabies cases aren’t centrally recorded anywhere. When a ‘mad dog’ starts biting people and dogs in the street, people don’t know who to call; the police…? The local animal shelter…? The government animal department…? One of the first things Mission Rabies established in Goa, India, was the Rabies Hotline; a 24 hour phone number distributed as widely and loudly as possible – “CALL THE RABIES HOTLINE IF YOU SEE A DOG WITH SIGNS OF AGGRESSION, BITING, SALIVATION, DISORIENTATION”. Of course the symptoms can vary more widely than this, but these are the most recognisable signs of rabies. Calls to the number are further screened by a veterinary doctor and in cases where it sounds like rabies, the rabies response team of expert dog catchers is deployed to the region.

Step 2 – Rabid Dog Management - It looks like rabies, what next?
The rabies response team are pre-vaccinated against rabies and are trained and equipped to handle animals with rabies. They serve to protect public safety by telling people to stay away from the dog and protect the dog’s welfare by catching it humanely. Without this service, people are forced to either attempt to incapacitate the dog themselves or scare it away and risk spreading the virus further, both of which have serious implications for the welfare of the dog and the safety of the wider community. Dogs showing signs of rabies are often portrayed in the media as monsters as they are often aggressive - however they are mere victims, not in control of their behaviour, with their mind being driven by this terrible virus. Sadly, for these animals, there is no treatment and in cases where rabies is highly suspected from the symptoms – which are often quite distinctive and rapidly worsening - the only kindness is to humanely end their suffering as quickly as possible. Mission Rabies have established protocols for the isolation, observation and management of these dogs once they have been removed from the community.

Step 3 – Getting a Diagnosis – is it definitely rabies?
Although new tests for rabies are in development, the current tests at our disposal only allow us to confirm rabies using a brain sample after the animal has died.  This is where the virus can be found in highest concentrations. The gold standard test is called the direct Fluorescent Antibody Test (or dFAT for short). This is performed by viewing the stained brain sample through a fluorescent microscope, which causes the virus to glow if present. This test requires specialist equipment which is not widely available in India, however has recently been installed in the Government Veterinary Laboratory through collaboration with the Department of Animal Husbandry and Veterinary Services and will enable rabies surveillance to be maintained in Goa long into the future.
A new test called the Lateral Flow Test is used at the time of post mortem and gives a result within ten minutes, however the result must be interpreted with great caution. Recent research has shown that a positive test result means the animal definitely had rabies, but unfortunately some dogs with rabies will show as negative on the test. Therefore, where we have a positive result, we can inform the community immediately that the animal had rabies, but negative results must be seen as inconclusive until the laboratory test is done and people should still seek the correct post-exposure treatment.

The Future
We have seen a dramatic decline in rabies cases in the areas in which we have conducted mass dog vaccination for several years and we won’t stop until there is not a single case of rabies. Beyond that, surveillance becomes even more crucial in detecting re-introduction of the virus and responding to this quickly. Our eventual goal in all our project sites is to eliminate rabies from the dog population through sustained vaccination, and then to prevent its reintroduction through solid disease surveillance – just as is the situation in many European and North American countries.