An introduction to Rabies (Hydrophobia)
- Part 4 -

Dr Asem Suresh Kumar Meitei *

The third stage of rabies is known as paralytic stage or Stadium paralyticum. In the course of a few days, symptom of paralysis appear in different parts of the body, the muscle of pharynx and larynx being generally affected first, and later , the muscles of locomotion. As a result, the dog makes a peculiarity hoarse sound or howl, and swallowing becomes difficulty or impossible.

There is loss of irritability and tendency to bite will disappear. Nevertheless, violent and less frequent and the patient becomes dull and extremely depressed. The paralysis becomes progressively worse. As a result of paralysis of the muscles of mastication and of the tongue, and eyes, the mouth is kept wide open, the tongue hangs out, the eyes have a squinting appearance, and there is profuse secretion of saliva.

Finally, the paralysis extends to the limbs and the tail and complete incoordination of the movement sets in. The dog becomes dumb and unable to bark and bite. It can no longer rise, lies down with a great deal, and becomes thin, emaciated and weak before it dies. As there is generally no thermal response, it is unnecessarily and also too dangerous to take temperature.

The symptoms manifested by the different species of animals do not vary very much, but the symptoms sometimes vary considerably in different individuals. Most animals show symptoms of the three types to a variable degree, and the duration of one stage may be lengthened or shortened at the expense of another. Occasionally, an animal, including dog, may not show the stage of mania (furious form).

Or, the manic phage may be inconspicuous. Such animals show the paralytic form of rabies, without showing the symptoms of the furious form. Animals showing such type of rabies are considered more dangerous for man. Animals suffering from rabies are without fear, and rabid wild animals have often been found fearlessly invading a farm-yard or human inhabitations where they furiously attack domestic animals and man.

Species Variations

Cats: Cats appear to be even more vicious than the dogs and readily assault both man and animals. They frequently attack from behind and generally inflict their bites and scratches on the face of the victims. Herbivorous animals: Herbivorous animals may also be aggressive, particularly towards dogs, but they are less inclined to bite or attack other animals. The ox may tear up the ground and furiously throw its head back. The main symptoms in cattle are acute abdominal pain, straining, salivation and bellowing. Death may occur in five days.

Cattle: Among farm animals, cattle are most commonly affected. Cattle with furious rabies can be dangerous, attacking and pursuing humans and other animals. Tenesmus, with paralysis of the anus, resulting in the suckling in and blowing out of air usually occurs late in the incoordination stages just before the animal goes down. Drooling of saliva is one of the most constant signs.

The so-called yawning movements are more accurately described as voiceless attempts to bellow. Paralysis follows; the animal goes down and is unable to rise. Bulls in the mild or paralytic stage often have paralysis of the penis.

Death usually occurs 48 hours after recumbency develops and after a total course 6 to 7 days. Common Lactation ceases abruptly in dairy cattle. The usual placid expression is replaced by one of alertness. The eyes and ears follow sounds and movement intently. A common clinical sign is a characteristic abnormal bellowing, which may continue intermittently until shortly before death.

Horses and other equine species frequently show evidence of distress and extreme agitation. They show mania. Their uncontrolled actions are often violent and dangerous and include blind charges, sudden falling and rolling and, in many cases, chewing of the skin also observed. Lastly, Paralysis and death ensued. These clinical signs, especially when accompanied by rolling, may be misinterpreted as evidence of colic.

As in other species, horses may bite or strike viciously and, because of their size and strength, become unmanageable in a few hours. People have been killed outright by such animals. These animals frequently have self-inflicted wounds.

Sheep: Affected sheep becomes excited and restless, behave abnormality, bite at the wool of their associates, fall down exhausted to the ground when handled, exhibit an abnormal sexual desire continually mounting each other, dyspnea, twitching of the lips and a wild stare.

Bleating is not a symptom, and there is no evidence of itching at the site of wound. Attacking humans or each other, vigorous wool pulling, sudden falling after violent exertion, muscle tremor and salivation are characteristic.

Pigs: Pigs run around in all direction root up the litter of the ground and gnaw or bite at the site of injury. They also become very aggressive. Affected sows show twitching of the nose, excessive salivation and clonic convulsions. They may walk backwards. Terminally, there is paralysis and death occurs 12 to 48 hours after onset of signs.

Fowls: Fowls become very nervous; look frightened run about with the feathers ruffled. They generally emit hoarse cries and attack other fowls, and even man.

Others: Some animals affected with rabies suddenly die without showing any definite symptoms. Others are seized with a convulsive fit during which they may die. As a rule, the disease usually lasts from four to seven days and the mortality is just about 100 %.

Rabid foxes and coyotes often invade yards or even enter houses, attacking dogs and humans. In this state, sometimes an animal will attack a porcupine; finding a fox or another animal with porcupine quills is otherwise considered abnormal and can, in many cases, raise the index of suspicion for rabies.

Rabid raccoons, foxes, and skunks typically show no fear of humans and are ataxic, frequently aggressive, and active during the day, despite their often crepuscular nature. In urban and suburban areas especially, they may attack domestic pets.

In general, rabies should be suspected in wildlife acting abnormally. The same is true of bats that can be observed flying in the daytime; resting on the ground, paralyzed and unable to fly; attacking humans or other animals; or fighting.

Rodents and lagomorphs rarely constitute a risk of exposure to rabies virus. However, each incident should be evaluated individually. Reports of laboratory-confirmed rabies in woodchucks and beavers are not uncommon in association with the raccoon rabies virus variant epizootic in the eastern United States.

When, an animal, especially a carnivores, shows acute nervous symptoms associated with irritability, aggressiveness, and later with paralysis, it should be treated as a case of suspected rabies. The suspected animal should be captured, confined in custody and kept under observation for about 10 days so that the disease can be allowed to run its course. Premature killing will reduce the accuracy of a laboratory diagnosis, as the development of NEGRI BODIES related directly to the length of the clinical illness.

Negri bodies, first reported by Negri in 1903, are the CYTOPLASMIC INCLUSION BODIES in the nerve cells produced by the STREET VIRUS. They are considered to be AGGLOMERATIONS of virus particles and are acidophilic, stain magenta of bright red colour and the basophilic inner corpuscles stain dark blue to black. Negri bodies are specific for rabies and their presence is of high diagnostic value.

They occur only rarely or not at all in infections due to FIXED VIRUS. Fixed virus produces another type, known as LENTZ BODIES (first reported by Lentz in 1909). They occur extracellularly between the ganglion cells in the central nervous system.

Another type of inclusion bodies, LYSSA BODIES, which may be mistaken for Negri bodies. They are devoid of basophilic granules and may be found normally in cats and mice and also other animals that are not infected with rabies.

As soon as clinical symptoms are well established the animal should be killed without damaging the brain. If animal dies of suspected rabies, the brain should be removed, one half should be submitted in 10% formalin, and the other half in 50% glycerine saline. The better the state in which the specimen arrives at the laboratory the easier will be the diagnosis. Speed and accuracy are essential in carrying out the test.

The diagnosis of rabies is based entirely on the demonstration of Negri bodies in the central nervous system and on the results of small animal inoculations. The histological examination of the central nervous system is obviously the method of choice as it can be carried out in a matter of few hours. When Negri bodies can be demonstrated, ther is no doubt about the presence of rabies, but a negative or doubtful histological examination is much less reliable.

Unless small animal inoculations are performed many negative diagnosis are liable to be made in animals that are definitely infected. Intra-cerebral inoculation of Swiss mice with suspected brain material is a much more reliable method of diagnosis rabies than the demonstration of Negri bodies. Paralytic symptoms of infected mice are usually manifested in about seven days.

When Negri bodies are present in sufficient numbers they can be readily demonstrated in smears or impressions of Ammon's horn and can be stained with Seller's carbolFuchsin or methylene blue. Fluorescent antibody test is the one which gives very quick and reliable diagnosis of rabies. For this one needs the specific test reagent and an access to a fluorescent microscope.

To be continued...