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Parkview Veterinary Hospital

Rabies is a Zoonotic Disease | Newsletters

The Latin word ‘rabidus’ means ‘mad’, which is the traditional understanding of the consequences of getting infected with the Rabies virus. A zoonotic disease is one that an animal can contract and then has the potential to transmit it to or infect human beings. The latter means that an animal infected with Rabies has the potential to transmit the disease and infect humans that come in contact with the animal in one way or another. Disease caused by the rabies virus is one that is considered extremely serious due to the very high numbers of mortality or deaths. There are 55,000 human cases of human rabies every year, worldwide. Survival rate is very low. Only one human survivor has been identified thus far, that wasn’t previously vaccinated for rabies. Another five human survivors have been recorded in the history books; however, they had received rabies immunization before been exposed to the infection.

Researchers differentiate between Sylvatic Rabies, which is rabies occurring in wild animals, and Urban rabies which is primarily dog rabies. The actual rabies virus itself is bullet-shaped, sensitive to sunlight and ultraviolet radiation, and can be deactivated by various chemical that are heat detergents, halogens and/or lipid solvents.

Dog rabies is further classified into two main biotypes in southern Africa. “Biotypes” refers to the genetic adaptation of the rabies virus within a specified geographical area. First we have the canid (dog or jackal) biotype, and secondly we have a mongoose biotype. The latter simply means that the dog, jackal and mongoose are the maintenance hosts for the virus in southern Africa. It is possible that there may be more biotypes that we haven’t yet identified and studied.  Wild animals that have been involved thus far in maintaining sylvatic rabies include kudus, lions, caracals, bat-eared foxes, jackals, mongooses, genets, striped polecats, African wild cats, honey badgers and even ground squirrels.  

Highly developed nations in North America and Western Europe have virtually eliminated dog and human rabies and are only recording high numbers of sylvatic rabies in wild vertebrates. Rabies is least well monitored in Africa. In South Africa specifically all sorts of animals have been involved with rabies and historic records have shown us that we had successfully eradicated the disease in 1968 through vaccination. Subsequently, efforts to maintain the status quo became progressively less efficient allowing the disease to spread along the east coast between 1976 and the early 1990s. Looking at currently available statistics the incidence of rabies amongst animals seems to be higher in late winter and early spring months of July to September. The latter was demonstrated when a state veterinarian reported a case of rabies in a dog in the suburb if Linden in Johannesburg at the beginning of August 2009.

Urban rabies occurs when there are large populations of unrestricted dogs, informal settlements, a lack of sanitation and refuse disposal, as well as rats, cats and dogs. Dogs may be abandoned e.g. during a civil war as in Angola. India is one place in the world where they have truly feral packs of dogs.

Transmission of the rabies virus from infected animals to other animals or humans can occur through superficial bites, licking of mucous membranes or shallow skin wounds and abrasions. The virus enters the nervous system and leaves the inoculation site (entry point) rapidly. It has been suspected that the virus may replicate in muscle before infecting the nervous system. In humans, the virus is incubated for 20-60 days (average of 34 days), also known as the prodromal phase, which is characterized by fever, headache, malaise, sore throat, nausea, anorexia, diarrhoea and fatigue. One third to two thirds of human patients experience paraesthesia (increased sensitivity and pain at the site of the infecting bite or affected extremity). Other symptoms include intense itching, anxiety, irritability, depression and insomnia. The next phase in humans has been called the “agitated phase” which involves hyperactivity, running/thrushing about, convulsive seizures spontaneous or precipitated by sensory stimuli, as well as anxious behaviour where the person is still lucid and co-operative. The disease then progresses where the patient loses their swallowing reflex, develop hypersalivation, hydrophobia (a fear of water), laryngeal/pharyngeal spasms, diaphragmatic and accessory inspiratory muscle contractions, making it very difficult to breathe. Eventually the disorientation, hallucinations, confusion and stupor lead to coma, paralysis and death. In approximately 5-20% of human cases the agitated behaviour does not manifest leading to the paralysis which predominates the clinical signs – this is called the “dumb form” of rabies.

In animals cases of rabies the virus usually incubated for 2-8 weeks (mostly 2-4 weeks) and the prodromal phase is very difficult to identify. Dogs and cats that are normally affectionate become highly strung, while shy and irritable individuals tend to become almost devoted and clingy pets. Dogs infected with rabies enter the furious phase within 2-3 days and display restlessness, nervousness, exaggerated responses, some snap at imaginary flies, and may even injure their very own wound site – sometimes down to the bone. Dogs become increasingly irritable, disorientated (fixed stare), tend to drool, or develop a hoarse howl (caused by spasm and paralysis of the laryngeal muscles). Symptoms may involve a drooping jaw & salivation, paralysis of the chewing and swallowing muscles, choking sounds, a hoarse cough and full body paralysis leading to death. More than 70% of rabid dogs develop the “furious form” while the remainder develop the “dumb form” of the disease.

Rabid cats generally become more aggressive than dogs (furious form) within 1-5 days of the clinical signs starting, froth at the mouth, show muscular tremours, dilated pupils and often guilty of unprovoked attacks (often the face). Cats tend to bite without releasing their grip (uncharacteristic), develop convulsions, uncoordinated gait, paralysis (purr, hide), coma and death within 1-2 days. 

Vaccination of pets against rabies is compulsory by law in South Africa. Animals are first vaccinated at 12 weeks of age, then given a booster vaccination within the next 1-9 months, and then repeated annually. It is generally claimed that 70-80% vaccination coverage is required to achieve control of the disease in dogs. Fully susceptible (unvaccinated) domestic pets that have been exposed to infection by a proven rabid animal will be destroyed. Pets that have been vaccinated (as stated by law) may be given a booster vaccination after exposure and kept under observation.

Travelling animals are also subject to quarantine policies. South Africa requires that animals travelling internationally are vaccinated 1 month prior to importation and 1 month quarantine after arrival.