A possible misdiagnosis of rabies

By Liou Pei-pai 劉培柏  / 

Wed, Aug 14, 2013 - Page 8

On July 17 the Council of Agriculture made its initial report to the World Organization for Animal Health concerning the rabies situation in Taiwan. In the pathogen field it had identified the cause of the disease as “Lyssavirus,” entering “not typed” in the blood type field.

By Aug. 1, when the council issued its fifth report, it identified the blood type as “RABV,” which is the rabies virus. The designation RABV generally refers to the strain of rabies that is fatal to carnivores: dogs, cats and humans. It is unknown on what basis the council decided to revise the report in this way.

Since May, when the first case of rabies infection in a ferret-badger was discovered, until today, with cases of rabies infection limited to central, southern and eastern Taiwan, there have been no cases of rabies infection in dogs, cats or humans. Isn’t that rather strange?

According to the Analysis of the Taiwan Isolation Rabies Genetic Sequencing issued by the council, the similarities between the rabies virus in ferret-badgers and the strain found in China is under 90 percent, so it should be regarded as a different virus. Yet this lab says that the virus is closest to the one found in China.

Differences in the nucleoprotein genetic sequences of all Lyssavirus strains can be used to determine where the virus exists. Changes in the glycoprotein sequence can be used to evaluate the strain’s antigenicity — the ability of an antigen to bind with an antibody — toxicity and pathogenicity, which is the potential of a virus to cause a disease.

However, the glycoprotein sequence provided by the council lab was too short. It did not show the antigenic determinants for the virus’ antigenicity or pathogenicity.

At the moment, we can only make a comparison of these two limited protein sequences, and speculate that the strain of the virus found infecting ferret-

badgers in Taiwan is a different type to that found in China, which means the ferret-badger virus here is not the dog rabies virus that everyone imagines it to be. The council should look into this.

The conditions of the so-called rabies outbreak in Taiwan are increasingly clear: Up until Aug. 5 the virus had only been found in 44 ferret-badgers and one shrew. As I understand it, there have been many incidences of dogs being bitten by ferret-badgers in the areas in which the latter have tested positive for the virus, and of dogs coming home with ferret-badgers clamped in their jaws, and yet we are still to have one case in which a dog has been found to be infected.

Also, according to provisions by the Centers for Disease Control for ferret-badger bites or scratches, anyone who has been bitten or scratched by a ferret-badger over the past year can be given free rabies vaccinations.

As of Aug. 5, a total of 815 people qualified for the vaccination, of which 27 were actually bitten by one of the animals. That figure could be lower than the actual amount of people who have been bitten, and many were bitten several months ago, but no cases of rabies infection in people have emerged yet. It is quite clear that the ferret-badger virus in Taiwan is not the same as the rabies virus that is fatal to dogs and humans.

The glycoprotein genetic sequence provided by the council is too short to be useful in determining whether the rabies vaccination currently used in Taiwan offers protection against the virus found in the ferret-badgers.

In 2010, researchers in China discovered with rabies viruses taken from ferret-badgers that several isolation strains were of low pathogenicity or had no toxicity at all. Lab rats were injected in their brains with large amounts of the virus, but they did not develop the disease.

The council has yet to provide any data to establish whether the nature or pathogenicity of the virus found in Taiwan’s ferret-badger population means that it will harm dogs, cats or people, let alone to clarify the efficacy of vaccinating dogs and cats against it.

According to the Central Epidemic Command Center, there will be plenty of vaccines available by late this month, with 1.13 million for dogs and cats and 47,000 for humans. Fortunately, the pathogenicity of the ferret-badger virus in Taiwan for dogs, cats and people is very low or non-existent.

Are the vaccines being provided at the state’s expense to prevent “genuine” rabies useful against the ferret-badger virus? My feeling is that these are just vaccinations being administered to give peace of mind.

Liou Pei-pai is a former director of the Taiwan Animal Health Research Institute.

Translated by Paul Cooper