In this step, we are going to see that from the epidemiologic point of view, rabies can be urban, wild or sylvatic, and be transmitted by bats. Rabies is one of the most deadly zoonoses in the world. According to the OIE, rabies causes the death of around 50,000 people every year, mostly in the young. Ninety- five percent of these deaths take place in developing countries, especially in Asia and Africa with the majority being due to bites by infected dogs. This is what is called urban rabies since it is acquired in human population nuclei, generally in small villages where control measures have not been implemented yet.
In addition to the dog, the cat can play an important role role in maintaining the infection active. In developed countries, urban rabies is almost eradicated, thanks to effective vaccination measures (which we will see in a future step). In many industrialized countries where there is almost no urban rabies, there is what is called wild or sylvatic rabies. It is transmitted by species that are not integrated in urban communities. For example, in Western Europe the main reservoir host is the red fox, whereas in Eastern Europe it is the wolf and the raccoon dog.
The terrestrial reservoir in Northern Asia is the Arctic fox, and in those of southern Asia and in the Arabic peninsula it is the dog as it is mostly urban rabies. In Africa, the reservoirs are the hyena and mongoose. In North America, in addition to the red and Arctic foxes, the main reservoir species are the raccoon and the skunk, although the coyote also plays an important role in the South-western zone. In the Caribbean, sylvatic rabies is transmitted by mongooses and in Central and South America by the grey fox. The big problem of wild rabies is that it can reach domestic animals. In the 30s, rabies began to spread in Europe from the Eastern countries, mainly through foxes.
At the end of the 80s, cases were detected in the Southern Atlantic slope of France, near the Pyrenees. Decreasing the population of foxes was attempted to control the problem. But rabies did not begin to regress until an oral recombinant vaccine, administered in bait tossed from helicopters was used, which vaccinated wild animal reservoirs of rabies. Presently, although there are still foci, these are much more reduced and concentrated in Eastern Europe. As we have said, the great danger of wild rabies is that it reaches domestic animals, specifically the dog, and from there to humans. We can see that a great number of cases in human beings have coincided with the regions of greater concentration of cases of wild rabies.
But on this map we can observe that there have been human cases where no wild rabies (or urban rabies) have been diagnosed for the last 100 years; in Great Britain, for example. The third type of rabies is transmitted by bats, responsible for those cases that we have mentioned as being non-attributable to the other two epidemiological types of rabies. All bats are not infected by the rabies virus. There are studies that have detected the rabies virus in only 6% of sick bats. But those bats found in unusual places for them, such as within a house, and that have difficulty to fly, could be ill. Both insectivorous bats, fruit-eating bats, and carnivorous bats, can transmit rabies.
Bats can transmit rabies through bites or scratches, but rabies can also be contracted by breathing air in caves where the population of bats is very dense, with even 800 or 900 individuals. In this case, aerosol particles from the saliva, urine or faeces reach the brain-crossing mucosa, such as the respiratory or conjunctiva. There have been cases distributed throughout Europe, although the greater concentration has occurred in central Europe. In countries such as USA, bats are the most usual source of human rabies, representing 90% of the cases. And with this we conclude this step. In a following one, we will see various ways of controlling the progress of rabies, which is different for each of these three types.