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Health & Management / Effects of Raccoon Biology and Behaviour on Raccoon Rabies / List of hyperlinked Techniques & Protocols:

< > Rabies in the Raccoon Host:

Introduction and General Information
Rabies is a neurological disease, almost invariably fatal once clinical signs develop, affecting all warm-blooded animals (including humans). The main species which act as reservoirs and vectors of rabies are small to medium sized carnivores, and bats.
  • Raccoons are a major reservoir and vector of rabies in the eastern USA and parts of eastern Canada, associated with a specific, raccoon-adapted variant of rabies (the raccoon rabies virus variant). (B358.4.w4, B395.2.w2)

This page is designed to provide an overview of rabies, both raccoon rabies and other variants, in Procyon lotor - Common Raccoon. 

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Susceptibility of Raccoons to Rabies
Raccoons may be infected by both raccoon rabies virus variant and other rabies virus variants, and this infection can be fatal. However, it is also apparent, both from experimental studies and from the prevalence of seropositive raccoons in wild populations, that rabies infection in raccoons is not always fatal and that raccoons may encounter rabies virus and seroconvert, but not develop fatal illness. Experimental evidence suggests that raccoons have intermediate susceptibility to rabies virus, with higher resistance than foxes or skunks but lower resistance than Didelphis virginiana - Virginian opossum.
  • It is not known whether male or female, adult or juvenile raccoons are more susceptible to rabies. Percentage of different classes of raccoons positive for rabies in different epidemiological studies have varied.
  • It is possible that raccoon susceptibility to rabies may be increased by stress and by concurrent disease.
For further information see:
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Incubation Period of Rabies in Raccoon
The incubation period for rabies in raccoons has been recorded in laboratory studies to be as short as 10 days and as long as 107 days. From a study of naturally occurring raccoon rabies in raccoons in Ontario, Canada it was suggested that the most usual incubation period might be about five weeks, but with the possibility of both shorter and longer periods. 

Information on the incubation period for rabies in other species is provided in Rabies (Viral Disease) - Incubation Period, Time Course and Persistence of Disease

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Duration of Illness in Rabid Raccoons
While raccoons inoculated with a street rabies virus originating from a dog have sometimes been found dead without prior clinical signs, more usually raccoons with natural or experimental rabies infection have shown clinical signs for periods of less than one day up to 17 days.
  • Note: there is little data from recent experiments, since, as part of humane experimental protocols, animals are usually euthanised as soon as definite clinical signs are noticed.

Information on the duration of clinical signs for rabies in other species is provided in Rabies (Viral Disease) - Incubation Period, Time Course and Persistence of Disease

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Distribution of Rabies Virus in the Raccoon Host
In general, rabies virus may be found in the brain and salivary glands of rabid raccoons. However, in two experiments with a rabies virus variant originating in Mexican free-tailed bats Tadrida brasiliensis mexicana, the salivary glands were virus negative. Rabies virus may also be found in other tissues, such as the pancreas, adrenal, kidney and spleen, but it is found much less consistently in such organs, and in levels not considered to pose a public health risk if humans are exposed to these tissues.
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Clinical Effects of Rabies on the Raccoon Host
Raccoons with rabies often show altered behaviour, such as appearing around human dwellings during daylight or wandering aimlessly, and may appear obviously sick, incoordinated or paralysed. Raccoons with rabies often lack aggression, but lose their fear of humans and dogs. Aggressive behaviour is also reported. "Sick" animals may bite when handled.
  • In one experiment with a raccoon rabies virus variant, sudden onset of neurological signs was seen, including combinations of circling; head-pressing; head-tilt; excess licking, mainly of the genital area and tail tip; and occasionally self-mutilation of the limbs or genital area.
  • In experimental infections with rabies virus variants other than raccoon rabies virus variant, vague signs of depression; anorexia and lethargy;  increased alertness or apprehension; aggression; increased vocalisation; excessive friendliness; incoordination and paralysis have all been noted.
  • It is possible that more severe clinical neurological signs may be seen in raccoons infected with raccoon rabies virus variant than in raccoons infected with other rabies virus variants.
  • Note: Individual raccoons without any recognized behavioural signs of rabies have also tested positive for rabies.

Further information and an overview of clinical findings for rabies in other species is provided in:

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Pathological Effects of Rabies on the Raccoon Host
Gross lesions
  • Normally, there are no gross lesions in raccoons with rabies. Areas of alopecia and skin reddening were seen in association with excess licking/self mutilation in raccoons in one experiment.
Typical histopathological findings
  • The main affected area is the CNS. The usual finding is of multifocal nonsuppurative encephalitis, bilateral but not necessarily symmetrical, affecting the brain stem, cerebrum and spinal cord, with perivascular mononuclar cell cuffing of blood vessels, multifocal gliosis and, in severely affected areas, neuronal degeneration.
  • Outside the CNS, lesions may be found in the Gasserian ganglia, with inflammatory infiltration, mainly mononuclear. 
  • Negri bodies are usually visible in the CNS; these may be larger and more numerous in raccoons infected with raccoon rabies virus variant than in raccoons infected with other rabies virus variants. Negri bodies may also be found in the Gasserian ganglia and in cells of other ganglia.
  • Atypical findings have included:
    • Absence of lesions of rabies encephalitis, in a naturally infected raccoon with concurrent canine distemper virus (CDV) infection (lesions typical of canine distemper virus infection were present);
    • Eosinophilic encephalitis in a raccoon experimentally infected with the canine MD5951 rabies virus variant; the raccoon had at least three different concurrent parasitic infections, which may be relevant in these findings.

Further information and an overview of pathological findings for rabies in other species is provided in: Rabies (with special reference to Raccoons) - Detailed Pathological Findings - (Necropsy-Post Mortem) (Disease Reports)

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Development of Antibodies and Immunity to Rabies in Raccoons
  • Antibodies may be detected in the blood of raccoons. Antibodies have been detected in raccoons following survival of experimental rabies infection; prior to death from experimental infection; and in wild raccoons, particularly those captured during or shortly after a rabies epizootic. Repeated sampling has shown the presence of antibodies to be maintained, sometimes for many months.
Relationship between serological titre and survival of challenge
  • In general, raccoons with high levels of serum neutralising antibodies appear more able to survive challenge with lethal street rabies (either raccoon rabies virus variant or other rabies virus variants) than raccoons with only low levels of antibodies, or without antibodies. However, the relationship between serum neutralising antibody titre and resistance to rabies virus is not exact: in some vaccination experiments, some raccoons with relatively low antibody titres have survived challenge while other individuals with relatively high titres have succumbed to challenge.
Transfer of antibodies to offspring?
  • It is not known whether raccoons with antibodies to rabies transmit these antibodies to their offspring and whether this is protective. In one experiment with a vaccinia-rabies glycoprotein recombinant vaccine, cubs of females which were vaccinated during pregnancy were born with virus neutralising antibodies. However, it was not known whether this reflected passive transfer of antibodies or transmission of the vaccine virus in utero. 
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Effects of Rabies on Raccoon Populations
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Authors & Referees
Authors Debra Bourne MA VetMB PhD MRCVS (V.w5)
Referee Dr Robert G. McLean (V.w42), Rick Rossatte (V.w95)

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