Rabies is caused by a group of viruses (lyssaviruses) which can infect all warm-bloodied animals. Rabies can also infect humans, which is probably why it is one of the most well known viruses; Worldwide, 1 person dies from rabies every 10 minutes. The virus has its devastating effects by causing inflammation of the brain. The delay between contracting the disease and the first symptoms is usually 1 to 3 months, however, it can vary from less than 7 days to more than one year. The delay is dependent on the distance the virus must travel through the body to reach the central nervous system of the newly infected animal.
The transmission of rabies is almost exclusively the result of an infected animal biting a non-infected animal. Rarely, it can also be transmitted by scratches or infected saliva falling on the mucous membranes of the non-infected animal. Amongst wildlife, foxes, coyotes, skunks, raccoons and bats are most likely to transmit the virus. It has been reported that in caves containing many infected bats, transmission of the virus has resulted from aerosolization. The rabies virus does not live for long outside the host. For example, it remains viable for less than 24 hours in the carcass of an infected animal. The saliva of an infected animal contains high concentrations of the virus, however, being bitten by an infected animal does not necessarily mean that the bitten animal, or human, will become infected.
After infection by the rabies virus, the bitten animal may go through one or all of several stages. Initial symptoms include itchiness at the site of infection and fever. Usually, the virus spreads along the peripheral nerves of the animal towards the brain. The virus is relatively slow moving. The average time between exposure to brain involvement is between 3 to 8 weeks in dogs, 2 to 6 weeks in cats, and 3 to 6 weeks in humans. However, incubation periods as long as 6 months in dogs and 12 months in humans have been reported. Once the virus reaches the brain, it then moves to the salivary glands where it can be transmitted to another animal through a bite. After the virus reaches the brain, the animal will show one or more of 3 distinct phases.
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The first phase is known as the “prodromal phase”. In dogs, this usually lasts for 2 to 3 days. Behavioral changes such as apprehension, nervousness, anxiety and solitude may become noticeable, and a fever may develop. Animals that are normally friendly may become shy, irritable and may even snap or nip. On the other hand, normally aggressive animals may become very affectionate and docile. The site of the bite will receive much attention from the animal with constant licking and perhaps rubbing. In cats, the prodromal phase is a little shorter than for dogs as it lasts for only 1 to 2 days. Cats also usually experience more fever spikes and changes in behavior than dogs.
After the prodromal phase, infected animals may enter what is called the “furious stage”. Cats are particularly susceptible to developing this phase. In dogs, the furious stage usually lasts for 1 to 7 days. Animals are restless, irritable and become hyper-responsive to auditory or visual stimuli. As the restlessness increases, the animal begins to wander, progressively becoming more irritable and vicious. If caged, rabid animals may bite and attack their enclosure or its contents. Animals become progressively more disoriented, begin to have seizures and eventually, they will die.
Some animals may develop a third phase, the “paralytic phase”. This occurs either after the prodromal or furious stage. The paralysis is produced when the virus attacks motor neurones. This phase usually develops within 2 to 4 days after the first symptoms of rabies are observed. The nerves affecting functions of the head and throat are usually the first to be involved. Animals may become unable to swallow and as a result begin salivating. As the muscles of the diaphragm and face become increasingly paralyzed, the animal may show deep labored breathing and a dropped jaw. The animals may make a choking sound, as if there is something lodged in the throat. By progressively losing muscular control, the animal gets weaker, eventually going into respiratory failure and subsequently, it dies.
The current method of diagnosing rabies is a microscopic examination of the brain. There are new techniques being developed which use skin or blood samples as a method of testing potentially exposed animals (and humans), although they are not yet being used routinely.
As a precaution, if your pet is bitten or scratched by any carnivorous wildlife (including bats) that is not available for testing, your pet should be considered as having been exposed to rabies. The bitten pet should be placed into complete isolation for 6 months. One month before being released, your pet should be vaccinated. If your pet’s vaccination has expired, it will need to be to be evaluated on a case-by-case basis. Dogs and cats with current vaccinations are kept under observation for 45 days if they are bitten.
If an animal bites a human and it is suspected that the animal may have rabies, the animal will either be quarantined, or observed for at least 10 days to monitor for symptoms that indicate it has rabies. Other factors will affect the requirements of the quarantine such as whether or not the biting animal was currently vaccinated, and the legalities and local concerns of the community in which you live.
Humans that have been bitten by a potentially rabid animal are usually given post-exposure vaccinations and a globulin (antibody) injection to protect them from becoming infected. If you are bitten by any animal that might have rabies, you should immediately wash the wound thoroughly for 15 minutes with soap and water and then seek medical attention.
Currently, there is no treatment for rabies. Only a small number of people have survived rabies and this required extremely intensive medical care; if the disease develops in humans, death is almost certain. Similarly, although there are reported cases of dogs surviving rabies infection, these are extremely rare.
VACCINATION AND PREVENTION
To prevent infection by the rabies virus, animals must be vaccinated. If done correctly, this provides a very high level of protection. Although vaccination for rabies is mandatory for dogs in all states, it is estimated that 50% are not vaccinated. Some communities also require cats to be vaccinated. This is very important because currently, there are a greater number of cats being infected by rabies than dogs. It has been estimated that less than 10% of cats are vaccinated and this is causing the high incidence of cat rabies.
The standard protocol to vaccinate cats and dogs is a first injection at 3 to 4 months of age and then again at one year of age. A year later, your pet can be given a 3-year vaccination which has proven to be very effective. The veterinarian can explain their recommendations for your pet.