Rabies - Clinical Signs

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General

The clinical signs of rabies in domestic warm-blood animals are highly variable, but similar is most species. Rabies should always be suspected if the is a sudden change in behaviour, unexplained progressive paralysis and increased, decreased, or normal spinal reflexes. Pyrexia may also be present.

The incubation period can arrange from 10 days to 8 months, with some report up to 7 years. The shortest incubation periods are seen when the virus is introduced around the head and neck. The longest incubation periods are seen with virus introduction at the extremities such as the legs or tail.

The clinical signs observed in rabies can usually be divided into two forms. The two forms occur due to where the virus propagates in the brain. If the virus propagates in the limbic system, cortical control of behaviour is lost and the furious form of rabies occurs. If the virus propagates in the neocortex, which is the area of higher mental functioning, the dumb form of rabies will occur. An animal with furious rabies tends to be agitated, aggressive, anxious, and malicious. An animal with dumb rabies tends to be narcotic, depressed, and lethargic. Carnivores tend to acquire the furious form of rabies, where as ruminants and horses tend to acquire the dumb form of rabies. The forms of rabies may coalesce as the infection progresses, but sternal recumbency and convulsive seizures are usually the final clinical signs. Once clinical signs occur, the progression of the infection is fast and death occurs in 2 to 14 days after initial clinical signs. The prognosis of rabies is invariably death.




Clinical signs by species



Horseshorse

        Early clinical signs of infection are non specific. They can include muzzle tremors, pharyngeal paralysis, anorexia, depression, colic and ataxia. As the disease progresses clinical findings include abnormal posture, frequent whinnying, aggressiveness, kicking, biting, striking, head tossing, transient lameness, and apparent blindness. Over half of the clinical cases will be in the dumb form of rabies; however, the furious form will occur in 43% of infected horses. Horses in the finals stages of the disease will become sternally recumbent, progress to lateral recumbency with paddling tremors, and eventually systemic paralysis and death. Once clinical signs occur, death is usually with in 5 days.


Image Credit: http://www.horsecity.com/images/111003/rabies1.jpg




Cattlecow

        Cattle are highly susceptible to rabies, however, only one or two animals of the herd will be infected. Early clinical signs include excessive salivation, behaviour change, muzzle tremors, abnormal posture, tenemus, yawning, paraphimosis, photophobia, pica, sexual excitement, abnormal bellowing, aggression, increased libido, decreased lactation, increased interest with sound or light and pharyngeal paralysis. Late clinical signs can include opisthotonus, seizures, and widespread paralysis. Death occurs soon after late clinical signs.


Image Credit:   http://www.itg.be/itg/DistanceLearning/LectureNotesVandenEndenE/imagehtml/ppages/CD_1059_083c.htm




Sheepsheep

        Clinical signs of sheep are very similar to cattle infected with rabies. The main difference is that a group of sheep will be infected, since an infected carnivore can easily bite more than one animal. There may also be aggressive wool pulling and no abnormal bleating.



Image Credit: http://www.fao.org/ag/aGA/Agah/EMPRES/GEMP/avis/B058- rabies/tools/images/0_i_sheep.gif



Pigs

        Pigs infected with rabies are extremely rare due to most pigs being house indoors. Early clinical signs may include excitement, aggression, incoordination, excessive salivation, backwards walking, phantom chewing, and lethargy. Final stages of diease include depression, convulsions, and recumbency. Death occurs with 2 days of clinical signs.





Catscat

        Cats consistently develop the furious form of rabies; however the dumb form does occur. The clinical signs include strange and abnormal behaviour, abnormal meowing, photophobia, fractious aggression, muscle tremors, and incoordination. Mandibular and laryngeal paralysis is rare is cat. Cats with clinical signs usually die in 3 to 4 days.


Image Credit: http://www.spokesmanreview.com/stories/2006/oct/3/cat_mean3_10-03-2006_BG8LA4T.jpg





Dogsdog

        Initial clinical signs in dogs are biting, aggression, hyperesthetic, photophobic, aggressive pica, irritation, laryngeal paralysis, mastication muscle paralysis, roaming, abnormal barking, and excessive salivation. Usually infected dogs that are docile turn fractious and infected dogs that are fractious appear to be docile. Final clinical signs include coma, convulsions, and generalized paralysis. Death occurs in 2-3 days.

Video (from http://www.soonak.com/DocAndClip.htm)
Furious Rabies in a dog
Dumb Rabies in a dog


Image Credit: http://en.wikipedia.org/wiki/Image:Rabid_dog.jpg