Rabies

RABIES

Field diagnosis

  • It is based on characteristic symptoms of rabies coupled with presence of Negri bodies in the brain.

Direct detection of virus antigen in tissue materials

The ideal clinical materials for rabies virus identification are brain, salivary gland and saliva. In the brain, rabies virus is particularly abundant in the thalamus, pons and medulla.

  • Histological identification of characteristic lesions – Demonstration of Negri bodies by Sellers method (for unfixed sections) or Mann’s method (for fixed sections).
  • Fluorescent antibody test – Thisis the most widely used test for rabies diagnosis and is recommended by both WHO and OIE.
  • Immunoperoxidase test
  • ELISA – Referred as rapid rabies enzyme immunodiagnosis test (RREID)
  • PCR and DNA sequencing
  • DNA probe
  • Electron microscopy
  • Monoclonal antibody based typing

Isolation and identification

It is attempted FAT gives an uncertain result or when the FAT is negative in the case of known human exposure.

  • Mouse inoculation test: The infected suckling mice develop paralysis and death occurs within 28 days. Upon death, the brain should be examined for the presence of the virus by immunofluorescence.
  • Cell culture system: Neuroblastoma cell lines, e.g. CCL-131 is commonly used for isolation of rabies virus. Presence of rabies virus in the cells is revealed by the FAT.

Serological tests

Serological tests are rarely used due to late seroconversion and the low percentage of animals surviving the disease having post-infection antibodies. The tests that are normally performed are

  • Virus neutralisation test in cell culture: fluorescent antibody virus neutralisation test – FAVN (accepted for international trade). The principle of the fluorescent antibody virus neutralisation (FAVN) test is the neutralisation in vitro of a constant amount of rabies virus before inoculating cells susceptible to rabies virus in BHK-21 C13 cells
  • Rapid fluorescent focus inhibition test (RFFIT) for determining rabies virus-neutralising antibody (accepted test for international trade)
  • Virus neutralization in mice
  • ELISA - Indirect ELISA is used to determine the level of rabies antibodies in individual dog and cat serum samples following vaccination
Last modified: Saturday, 3 December 2011, 10:24 AM