Clinical Signs

The clinical signs associated to rabies demonstrate significant variation and are rarely definitive at the onset of the disease. The most accurate but well known of these characteristics (not always present) are the behavioral changes, idiopathic and progressive ataxia and/or paralysis. These signs are associated to viral replication in neurons in the brain. The behavioral changes include anxiety, hyper excitability, hydrophobia and most importantly aggression. Significantly, wild animals may lose their fear of people and be more likely to come into contact with them thus exposing the human population to a greater risk of contracting the disease and simply becoming injured by an attack.

Considering the variety of clinical presentations of animals infected with rabies, there are two described forms of the manifestations of clinical signs.

Furious rabies: This form is characterized by aggression. In the early forms of the disease there is no ataxia or paralysis. Animals with furious rabies have a loss of fear and are more likely to attack uninfected animals or people. Curiously these animals have been seen to consume inedible materials such as feces, rocks or wires. As the disease progresses we see the onset of seizures and paralysis prior to death.

Paralytic form: This form of rabies lacks the extreme aggression seen in the furious form. Instead ataxia is more prevalent and there is paralysis of the throat and masseter muscles. This is clinically seen as an inability to swallow. There is also evidence of excessive salivation. From time to time this is confused with bloat or foreign bodies in the esophagus. Veterinarians who start to explore an animal’s mouth can inadvertently expose themselves to rabies in these cases! The disease will often progress rapidly and will always lead to coma and eventual death, usually due to respiratory depression, if the animal is not euthanized prior to that point being reached.

All of our domestic species can be infected with rabies. The clinical signs in these various animal groups vary but generally follow one of these two forms. Unfortunately animals may often self-inflict injuries while under the influence of the virus.

Cattle:

Cattle may exhibit furious rabies which is extremely dangerous. The affected animals may try to attack and chase other animals including people. This highlights the fact that the danger associated to the rabies virus is not just with infection risk. Even when disease transmission does not take place the behavioral changes demonstrated by infected animals can result in death or serious injury of people. With contamination affected cattle may appear more alert than usual or begin to vocalize in abnormal ways. Death follows after the above signs decrease in frequency.

Horses and other Equids:

Often these animals show signs of anxiety, pain and nervousness. These behaviors are often paired with rolling which makes the diagnosis of rabies confounded with that of colic. Furious forms of the disease are also possible resulting in extremely dangerous conditions when horses try to bite or hoof strike.

Dogs and Cats:

Both dogs and cats can present with the paralytic form of rabies but the furious form appears more commonly in these species. The demonstration of aggressive behavior is of key importance given their proximity to humans and caution by veterinary professionals and the public must always be considered early when infection risk is high. These canine and feline species will often present with ataxic ambulation and exhibit hypersalivation as the virus takes hold.

Wild animals:

In addition to being major reservoirs of infection, wild animals with rabies often lack their classic fear of humans and are more likely to show aggression and hostility towards them. They may also attack domestic species, including our companion animals. Rabid animals in the wild may show other behavioral discrepancies such as being active at a time of day or night when they generally are not seen. As a rule of thumb, any wild animal (Bat, skunk fox, racoon etc) acting atypically should not be approached since rabies must always be considered on the list of potential differential diagnosis.