Infectious Diseases and Microbiology - Rabies ( Rabies Virus)

​Infectious Diseases and Microbiology - Rabies ( Rabies Virus) 
The rabies virus, a member of the rhabdovirus family, is the cause of rabies, a viral zoonotic infection. Aerosol contact with mucosal membranes, infectious saliva from a rabid animal bite, or (very rarely) human-to-human transmission to recipients of solid organ transplants from a rabies-infected donor are the three ways that the rabies virus can spread. In the US, foxes, coyotes, skunks, bats, and raccoons are among the natural carriers of infection.

The time it takes for rabies to incubate varies, often taking 30 to 60 days following a bite. Fever, lethargy, nausea, vomiting, and pain or itching at the bite wound site are the hallmarks of a prodromal phase. The symptoms of the neurologic phase include encephalitis, coma, hydrophobia, agitation, and hyperactivity. Rabies usually results in death.

The rabies virus grows at the bite site and attaches itself to the acetylcholine receptor to infect sensory neurons. In the central nervous system, the virus replicates in gray matter by ascending axons. The virus then travels to the skin and salivary glands by peripheral nerves. To prevent disease, cell-mediated immunity is insufficient.

The diagnosis of rabies is made either by immunochemically detecting viral antigen in autopsied brain tissue or by cytologic identification of Negri bodies (cytoplasmic eosinophilic inclusion-bodies) in neurons. Immunocytochemistry can identify rabies virus antigens in biopsy samples taken from the skin at the nape of the neck or from corneal scrapings in live patients. By using PCR, rabies virus RNA in saliva can be found.

 Once clinical signs have appeared, there is no particular treatment for rabies. Prophylactic measures taken both before and after exposure help prevent rabies. Post-exposure prophylaxis, or treatment following exposure to a rabid animal bite, entails three steps: (1) a complete cleaning of the site; (2) a human rabies immune globulin injection into the wound; and (3) an active rabies vaccine injection. For people who are at a high risk of contracting rabies, such as veterinarians and animal handlers, it is advised to vaccinate against the disease in advance of exposure.

---