Rabies

General information

Rabies is a viral disease that is usually fatal. It is caused by a neurotropic Lyssa virus. Several species of Lyssaviruses have been identified, of which the rabies virus (worldwide), the Mokola virus (Africa), the Duvenhage virus (South Africa) and the European and Australian bat lyssaviruses are responsible for fatal encephalomyelitis. Rabies is transmitted by a percutaneous bite from a rabies-infected animal or by wound contamination with saliva from a rabid animal (MSD, 2021). Air born infection through aerosols can occur when visiting bat caves.

Reservoir hosts vary geographically. In the U.S. hosts include skunks, bats, raccoons, foxes, and coyotes. Civets, mongooses and hyenas are the main hosts in Africa; domestic dogs are hosts in Asia, South America, and Africa. Certain bat species in southern Africa are host for a Lyssa virus

After infection of the bite wound, the virus migrates from the wound to the brain via the nerves that run from the wound area, resulting in neurological signs. Virus replication takes place in the brain, from where the virus migrates to the salivary glands. The incubation period varies from 3 weeks to many months.

In most species affected by rabies, the animal shows an increase of aggressive behaviour and will try to bite other animals. Hydrophobia can be one of the accompanying symptoms. In a few species (e.g. domestic cat), the animal becomes more quite or even soporous.

Once the virus has reached the brain, there is no cure. Treatment is only possible in the short period between infection and start of the migration. In this short time window, the animal should be treated daily with a rabies vaccine (described below). If available, locally anti-rabies serum should be injected around the wound area.

Diagnose of rabies is based on PCR or histopathology of brain tissue by demonstrating the presence of typical Negri bodies using a special stain especially in pyramidal cells within the Ammon's horn of the hippocampus. Wound tissue, saliva and cerebrospinal fluid can be used when the animal is still alive (CDC, 2021).

Rabies in elephants

Rabies has been diagnosed in a few elephants and was fatal in all reported cases. The source of the infection was attributed to canids (Wimalaratne et al. 1999, Nanayakkara et al. 2003, Sharma et al. 2005, Aravind et al. 2006). The incubation time for rabies in elephants is unknown. Depending on the distance between the bite wound and the elephant's brain, a long incubation period can be expected. Rabies should be included in the differential diagnosis whenever there are neurological signs.

The initial signs of rabies in elephants may be vague but most often the elephant (FAO 2005):

Is listless.
Prefers to stay in dark places.
Eats very little.

As the disease progresses the elephant likely:

Writhes in pain.
Does not recognize the mahout.
Chases and attacks humans and animals.
Has eyes that roll and wander.
Does not eat.
Walks unsteadily and the legs lose strength.
Goes to the ground in paralysis.
Has locked jaws and the tail hangs still.
Has saliva flowing continuously.

Death may shortly follow the appearance of these more severe signs.

The differential diagnose in case of rabies comprises any disease that can cause central nervous system symptoms, like:

Tetanus
Trauma
Snakebite
Toxicity (e.g. heavy metal; pesticide)

FAO Manual: Elephant care manual for mahouts and camp managers

Anytime an elephant is bitten, particularly if the bite has drawn blood, the mahout and owner should take four actions:

1.Write the day on a calendar; then you will be able to predict when the elephant may show clinical signs if it was infected.

2. Talk to people who know the dog and ask about its behaviour in the days prior to the attack; if the dog has been acting strangely (staring fixedly, foaming at the mouth, etc.) there is a good chance the dog is rabid.

3. Inform everybody in the community of the health hazard, because the disease also attacks humans, and ask them to help track down the dog.

4. Very carefully capture the dog, confine it securely, and observe its condition; if after ten days it is normal then the elephant does not have rabies.

If the elephant dies, consult Disposal of carcasses, page 55 of the FAO manual.

Treatment of rabies in elephants

Immediately after a suspected dog bite, wash the wound intensively with soap and water. Then apply tincture of iodine or Povidone-iodine 1% in and around the wound (FAO 2005).

There is no effective treatment once the symptoms have appeared. Even though the disease is not contagious to other elephants, separate the elephant, taking it to a shady, clean and quiet place. Make sure the elephant is chained tightly and securely (FAO 2005). Although there is no report on post-exposure vaccination, emergency vaccination of the elephant can be considered, if a rabies vaccine is available. One study describes the successful post-exposure treatment in pigs that where heavily exposed to rabies. The affected pigs were repeatedly vaccinated with an inactivated rabies vaccine 0, 3, 7, 14 and 30 days after the bite incident, while equine rabies immune globulins were injected in and around the bite wound (Mitmoonpitak et al. 2002). When an elephant is exposed to rabies, consider to inject the animal intramuscularly with a 2 ml dose of an (inactivated = killed) rabies vaccine as soon as possible after it was bitten by a rabid animal. These vaccinations should to be given daily for at least 5 days. During this period the elephant should be kept under close observation.

Anytime an elephant is bitten, particularly if the bite has drawn blood, the mahout and owner should take four actions:

Write the day on a calendar; then you will be able to predict when the elephant may show clinical signs if it was infected.
Talk to people who know the dog and ask about its behaviour in the days prior to the attack; if the dog has been acting strangely (staring fixedly, foaming at the mouth, etc.) there is a good chance the dog is rabid.
Inform everybody in the community of the health hazard, because the disease also attacks humans, and ask them to help track down the dog.
Very carefully capture the dog, confine it securely, and observe its condition; if after ten days it is normal then the elephant does not have rabies.

If the elephant dies, consult Disposal of carcasses, page 55 of the FAO manual.

Prevention

Regular rabies vaccination is recommended for all elephants kept under human care in areas where rabies is endemic.

Because rabies is incurable the best prevention is to annually vaccinate all the dogs and cats in the community.

For many years, following the recommendation for rabies vaccination in horses has been considered prudent: (inactivated!) vaccine (2 ml IM) given from the age of 6 months, to be repeated after 3-4 weeks and annually boostered. When using this vaccination schedule in elephants, antibodies against rabies could be demonstrated after 24 months (Isaza et al. 2006, Miller et al. 2009).

However, this rabies vaccination strategy was evaluated in a herd of 9 African elephants, including two calves, four subadults, and three adults which lead to new conclusions about rabies vaccination strategy. Prior to 2017, elephants were vaccinated opportunistically IM. Starting in 2018, calves at least 4 months of age were administered 2 ml of a commercially available inactivated vaccine and received boosters at 1 y of age. Adults and subadults underwent annual vaccination at the same dose. After 1 year, neutralization titers in five of nine elephants were below levels considered protective in domestic animals (< 0.5 IU/ml). Therefore the dose of rabies vaccine was increased to 4 ml, which resulted in titers more consistently greater than or equal to 0.5 IU/ml for at least 6 months. Institutions with elephants under human care may consider performing rabies vaccination neutralizing titers when possible to help guide vaccination.