All warm-blooded animals are vulnerable to infection with rabies virus, but mammals are to be blamed for spreading the disease. The appearance of the infection is influenced by the quantity of virus inoculated, and the bite site.
The most susceptible species are: foxes, coyotes, jackals, wolves and rodents. Among the domestic animals are susceptible: rabbits, cows, dogs, sheep, goats and horses. Cats have a natural resistance; the infection among cats is much lower than in dogs. Younger animals are usually more susceptible to rabies infection than are older ones.
The disease is nearly always caused by the bite of an infected animal that has rabies virus in its saliva. Other modes of transmission are infrequently reminded as causes. Transmission through the exhaled virus is less likely, but it is suggested to be the main reason of infection between bats living in the same cave. This transmission way was hard to test in the laboratory, because it requires a large quantity of virus and poor ventilation.
Occasionally the disease can appear due to eating meat from ill animals. Another infection route is considered the transplacentar way in cows, bats and skunks.
Infection with the virus through the saliva has been observed, but the absence of dramatic abnormalities cannot be used to support the presence of the virus, nor can it prove the absence.
The rabies virus has an incredible adaptability. It searches for the dominant reservoir host, and uses it as only host. This is the reason for different virus reservoir host depending of the area.
The wildlife reservoir species in various geographic areas of the United States are raccoons, skunks, foxes, coyotes, and insectivorous bats. In Europe and parts of Asia, the primary species are foxes and raccoons.
Vaccination of dogs and animal control programs has been the main factors responsible for this decline. Although cases of dog rabies have declined, dogs account for the majority of reported animal bites. In some countries, where dog rabies has not been controlled, the presence of canine and human rabies is rather high.
After the bite, the virus might use the local peripheral nerves to multiply. The virus uses the neuronal network to travel. The better innervated the bite area is, the shorter it will take the virus to start its multiplication cycle. Before the virus reaches the brain, an average of 3 to 8 weeks can pass.
Once the virus reaches the brain, it will start spreading via nerve network to the salivary glands. Once the virus can be isolated in saliva, the virus has already affected the brain. Sometimes the death might occur before the virus reaches the salivary glands.
After the bite, the virus can remain inactive or start it’s multiplication in the same area. This viral behavior will make its detection impossible. This delay in the virus cycle, with a long time elapsed between the exposure until the clinical signs appear, was correlated with a high antibody titer in the nervous tissue and liquid surrounding this tissue. An adequate immunization in this stage could help to eventually eliminate the virus from the system. However recovery in this disease is not relevant for public health, since these animals continue to shed the virus through saliva.
In the first days after infection, the dog will be anxious, restless and fever will be present. Behavior changes occur; friendly animals become aggressive and aggressive animals become affectionate. Cats have about the same clinical signs, but the behavior alterations are rare in this phase.
As the diseases advances, they become more irritable to stimuli from the environment. In this stage, they might develop pica and avoid people. Sometimes muscular tremor and seizures might appear. During these seizures, they may become paralytic and die.
The second phase in cats is characterized by a furious state. These cats become wild, anxious, with a spooky blank look in their eyes. Muscular tremors and weakness might occur; some cats might die of exhaustion.
As the brain is further affected, drooling and tone changes can be noticed.
Unfortunately the disease doesn’t have a supportive treatment since there isn’t any treatment that proved effective for the encephalitis that develops during the disease. The asymptomatic animals should quarantine and observed.