Rabies pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
The rabies virus is categorized as a Lyssavirus. The molecular biology of rabies consists of bullet shaped virus with helical symmetry that has a length of approximately 180 nm. Rabies typically has its greatest effect on the brain. It is typically defined by encephalitis and myelitis. It is very important to avoid being bitten by a rabid animal because the virus is typically transmitted through the saliva of an infected organism.
Pathophysiology
The organism causing rabies is called Rabies virus (RV), a negative-stranded RNA virus of the rhabdovirus family. Rabies is an acute encephelomyelitis that causes disease in the human host via two features associated with the Rabies virus (RV):[1][2]
- Neurotropism
- Neuroinvasiveness
Transmission
- In Africa and Asia, domestic dogs are the main reservoirs of infection from Rabies virus[5]
- In the United States, racoons, foxes, skunks, coyotes and bats rather than dogs spread the infection through bites[6]
- Transmission of the Rabies virus starts when a human is bit by an animal harboring the virus in its salivary glands[7]
- The RV remains cell-free after initial inoculation because rigorous wound cleaning may reduce the chances of infection[8]
- RV infects peripheral nerves and then reaches the central nervous system (CNS) via retrograde axonal transport
Virology
The rabies virus is a Lyssavirus. This genus of RNA viruses also includes the Aravan virus, Australian bat lyssavirus, Duvenhage virus, European bat lyssavirus 1, European bat lyssavirus 2, Irkut virus, Khujand virus, Lagos bat virus, Mokola virus and West Caucasian bat virus. Lyssaviruses have helical symmetry, so their infectious particles are approximately cylindrical in shape. This is typical of plant-infecting viruses; human-infecting viruses more commonly have cubic symmetry and take shapes approximating regular polyhedra. Negri bodies in the infected neurons are pathognomonic.
- The virus has a bullet-like shape with a length of about 180 nm and a cross-sectional diameter of about 75 nm.
- One end is rounded or conical and the other end is planar or concave.
- The lipoprotein envelope carries knob-like spikes composed of Glycoprotein G. Spikes do not cover the planar end of the virion (virus particle).
- Beneath the envelope is the membrane or matrix (M) protein layer which may be invaginated at the planar end. The core of the virion consists of helically arranged ribonucleoprotein.
- The genome is unsegmented linear antisense RNA. Also present in the nucleocapsid are RNA dependent RNA transcriptase and some structural proteins.
Longitudinal and cross-sectional schematic view of rabies virus
Pathogenesis
Incubation period and eclipse phase
- The incubation period may vary from a few days to several years, but is typically 1 to 3 months[9][10]
- After gaining entry into human host, the RV enters into an eclipse phase, during which, the host immune defenses may confer cell-mediated immunity against viral infection because RV is a good antigen[11][12]
Neuromuscular junction invasion
- The neuromuscular junction is the major site of entry into neurons[13]
- The RV uses the acetylcholine receptors and other receptors such as the neutral cell adhesion molecule (NCAM) to gain entry into the neuron[14]
Inter-neuronal spread
- The main mechanism involved in the neuroinvasion of RV is transsynaptic neuronal spread
- The following proteins lead to the spread of virus between the neurons, once the virus gains entry into the body:[15]
- Rabies virus G protein: RV to spread from the post-synaptic site to the pre-synaptic site
- Rabies virus P protein: important determinant of retrograde transport of the virus within axons
Rabies and Possums
Experimental studies of rabies infection in the Virginia opossum have shown the importance of the mode of transmission. Possums became infected when exposed to air-borne virus but were found to be fairly resistant to intramuscular inoculations [16][17][18].The aerosol transmission of rabies in opossum was investigated following the death from rabies of two men who had visited the Frio Caves, Texas, and did not remember any direct contact with bats.
Microscopic Pathology
Histologic examination of biopsy or autopsy tissues is occasionally useful in diagnosing unsuspected cases of rabies that have not been tested by routine methods. When brain tissue from rabies virus-infected animals are stained with a histologic stain, such as hematoxylin and eosin, evidence of encephalomyelitis may be recognized by a trained microscopist. This method is nonspecific and not considered diagnostic for rabies.
Before current diagnostic methods were available, rabies diagnosis was made using this method and the clinical case history. In fact, most of the significant histopathologic features (changes in tissue caused by disease) of rabies infection were described in the last quarter of the 19th century. After Louis Pasteur's successful experiments with rabies vaccination, scientists were motivated to identify the pathologic lesions of rabies virus.
Histopathologic evidence of rabies encephalomyelitis (inflammation) in brain tissue and meninges includes the following:
- Mononuclear infiltration
- Perivascular cuffing of lymphocytes or polymorphonuclear cells
- Lymphocytic foci
- Babes nodules consisting of glial cells
- Negri bodies
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Rabies and Dogs
Three stages of rabies are recognized in dogs. The first stage is a one to three day period characterized by behavioral changes and is known as the prodromal stage. The second stage is the excitative stage, which lasts three to four days. It is this stage that is often known as furious rabies due to the tendency of the affected dog to be hyperreactive to external stimuli and bite at anything near. The third stage is the paralytic stage and is caused by damage to motor neurons. Incoordination is seen due to rear limb paralysis and drooling and difficulty swallowing is caused by paralysis of facial and throat muscles. Death is usually caused by respiratory arrest.[19]
References
- ↑ Mrak RE, Young L (1994). "Rabies encephalitis in humans: pathology, pathogenesis and pathophysiology". J. Neuropathol. Exp. Neurol. 53 (1): 1–10. PMID 8301314.
- ↑ Lafon M (2004). "Subversive neuroinvasive strategy of rabies virus". Arch. Virol. Suppl. (18): 149–59. PMID 15119770.
- ↑ Swanepoel R, Barnard BJ, Meredith CD, Bishop GC, Brückner GK, Foggin CM, Hübschle OJ (1993). "Rabies in southern Africa". Onderstepoort J. Vet. Res. 60 (4): 325–46. PMID 7777317.
- ↑ Bingham J, Foggin CM, Wandeler AI, Hill FW (1999). "The epidemiology of rabies in Zimbabwe. 2. Rabies in jackals (Canis adustus and Canis mesomelas)". Onderstepoort J. Vet. Res. 66 (1): 11–23. PMID 10396757.
- ↑ "www.who.int" (PDF).
- ↑ "CDC - Rabies Surveillance in the U.S.: Wild Animals - Rabies".
- ↑ The Merck manual of Medical Information. Second Home Edition, (2003), p. 484.
- ↑ "Rabies | Clinical Infectious Diseases | Oxford Academic".
- ↑ Charlton KM, Nadin-Davis S, Casey GA, Wandeler AI (1997). "The long incubation period in rabies: delayed progression of infection in muscle at the site of exposure". Acta Neuropathol. 94 (1): 73–7. PMID 9224533.
- ↑ "Rabies | Clinical Infectious Diseases | Oxford Academic".
- ↑ "CDC - Doctors: Transmission - Rabies".
- ↑ Israsena N, Mahavihakanont A, Hemachudha T (2011). "Rabies virus infection and microRNAs". Adv. Virus Res. 79: 329–44. doi:10.1016/B978-0-12-387040-7.00015-9. PMID 21601053.
- ↑ Burrage TG, Tignor GH, Smith AL (1985). "Rabies virus binding at neuromuscular junctions". Virus Res. 2 (3): 273–89. PMID 3890406.
- ↑ Thoulouze MI, Lafage M, Schachner M, Hartmann U, Cremer H, Lafon M (1998). "The neural cell adhesion molecule is a receptor for rabies virus". J. Virol. 72 (9): 7181–90. PMC 109940. PMID 9696812.
- ↑ Dietzschold B, Schnell M, Koprowski H (2005). "Pathogenesis of rabies". Curr. Top. Microbiol. Immunol. 292: 45–56. PMID 15981467.
- ↑ Constantine DG, Woodall DF. Related Articles, Links Transmission experiments with bat rabies isolates: reactions of certain Carnivora, possum, rodents, and bats to rabies virus of red bat origin when exposed by bat bite or by intrasmuscular inoculation. Am J Vet Res. 1966 Jan;27(116):24-32. No abstract available. PMID: 5913032 [PubMed - indexed for MEDLINE]
- ↑ Constantine DG 1967 Rabies transmission by air in bat caves. US Pub Health Serv, Publ. 1617
- ↑ 1: Am J Vet Res. 1960 May;21:507-10.Links Resistance of the opossum to rabies virus.BEAMER PD, MOHR CO, BARR TR. PMID: 13797881 [PubMed - indexed for MEDLINE]
- ↑ Ettinger, Stephen J.;Feldman, Edward C. (1995). Textbook of Veterinary Internal Medicine (4th ed. ed.). W.B. Saunders Company. ISBN 0-7216-6795-3.