Anyone who has been bitten by a wild animal or a pet behaving strangely is terrified of the idea of getting rabies. If you don’t receive treatment soon after infection, rabies is overwhelmingly fatal. Each year worldwide, 60,000 people die from rabies.
Rabies is a virus that can infect all mammals. Skunks, raccoons, coyotes, bats and pet cats and dogs are all common carriers in North America. The virus is typically transmitted to other animals or people through a bite that transfers infected salvia. When viewed under an electron microscope, the virus is bullet-shaped, characteristic of a family of viruses called Rhabdoviruses.
After entering the body, the virus travels from the bite site and infects nerve cells in the spinal cord and the brain. It can take anywhere from three to 12 weeks for the virus to get to the brain. During these first few weeks, there are no symptoms to indicate that the person or animal is infected. Once in the brain, the virus multiplies rapidly and signs of disease appear. Symptoms include vomiting, fatigue and double vision and then nearly all patients die. Current treatments are not effective after symptoms start.
The slow spread through the body from the bite wound to the brain provides an opportunity for medical intervention and treatment. Treatment involves receiving a series of five injections over several weeks that contain killed rabies virus. This activates the immune system, producing antibodies that can inactivate and destroy the rabies virus. This treatment must start soon after infection, so a fast diagnosis is essential.
Current diagnosis relies on testing the brain of the “biting” animal. A lab technician takes brain tissue and stains it with a fluorescent stain. Under a microscope, the rabies virus proteins glow brightly. However, the test isn’t perfect — there are false positives and false negatives, the microscope is expensive and not available in many places, and the test doesn’t work if the brain tissue is decaying.
Recently, scientists at the Centers for Disease Control and Prevention developed a new test called LN34. The test is simple, and many labs already have the technology for it. A study of 3,000 brain samples from 60 different mammals showed no false negatives and few false positives. The lack of false negatives means that if the virus is present, it will not be missed. This is important in making sure everyone infected is treated. There were few inconclusive results compared to the current test, and it works on decomposing tissue in dead animals.
This will improve testing in the U.S. and in developing countries, which only have testing available in select urban areas. Because the rabies vaccine is so expensive, it’s important to only use it when needed.
Between 40 and 50 thousand U.S. residents get the rabies test every year, costing up to $500 million annually. Eliminating unnecessary vaccine treatment will help reduce these costs. With its higher efficiency, lower cost, and widespread availability, we look forward to the approval of LN34 for clinical diagnostic use.