Epsilon Archive for Student Projects

Abstract

Rabies is a highly fatal viral disease, capable of infecting virtually all mammalian species. Once symptoms occur mortality is generally considered to be 100%. Each year the virus is responsible for the loss of approximately 59,000 human lives around the world. The most common route of trans-mission to humans is bites from domesticated dogs, where the virus is transferred through the infected dog’s saliva into the bite victim. Death can, however, be prevented through the use of vaccines or post-exposure treatments in the form of vaccinations and antibody injections to temporarily fight off the virus until the body’s own immune system can defeat it.
Despite the near certainty of death if the infection progresses into the symptomatic stage, there have been reports of dogs in rabies endemic areas around the globe who have antibodies against the disease in their serum, despite not having received any rabies vaccines. Since antibodies are not seen in the blood until a few days after the debut of symptoms, these individuals should, based on the mortality rate, not exist, or at the very least be incredibly rare. Some studies have however reported an antibody prevalence of up to 27% in some regions.
In this study the potential of rabies virus neutralising antibodies (RVNA) in non-vaccinated domestic dogs was examined, looking for signs of potential non-lethal infections of the virus. Since the majority of rabies cases caused by domestic dog bites occur in Asia and Africa, this study took place in Cambodia, which has one of the highest estimated cases of rabies mortalities in Asia. Sera was collected from 97 dogs across three different provinces. The samples were then tested for antibodies using an enzyme-linked immunosorbent assay (ELISA) test. The test both detected the samples that were positive for RVNA as well as measured the level of antibodies against the virus. All the positive samples were analysed again in a control run.
The results found that 9% of the dogs in the study were positive, despite there being no report of previous vaccination campaigns performed in the area. The owners also reported that none of the positive dogs had been vaccinated prior to the sampling. The study also found a statistically relevant correlation between age of the dog and testing positive for antibodies, where older dogs were more likely to have antibodies.
The positive dogs in one of the provinces, Kampong Speu, were also resampled a few days later and analysed again. The result was that 3/4 previously positive dogs tested positive once more, further strengthening the result that non-vaccinated RVNA positive dogs do indeed exist in rabies endemic regions.