Rabies

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  Rabies is one of the viral diseases that infect Central nervous system. For this topic, I would explain more about medical aspect of rabies. Rabies virus belongs to rhabdoviridae family. This virus has become one of diseases that need serious attention because of its clinical manifestation that at worst can lead to death. Early prevention is necessary to prevent complications. Rabies was previously thought to have dogs as its primary hosts and vector. Surveillance and vaccination programs carried out in North America and Europe have revealed wild animals such as bats, racoon and foxes as major hosts for rabies. Basically, different animals have different specific variant or variants. Different variants in different hosts are distributed in different areas geographically. Bats have unrestricted distribution and seemed to be the major contributor for rabies infections in human. This mammalian has one specific variant known as Ln/Ps that has the ability to bind to certain cell receptors or have the greater efficiency in initial replication in non neuronal tissues. Other than rabid animal bites, other means of transmission of rabies are infected corneal transplantation, infected solid organ transplantation, exposure of mucosa or un-intact skin to saliva of rabid animal and etc.

     The pathogenesis of this virus is related to its ability to bind to nicotinic receptors. Before I explain further about the pathogenesis, I would like to give some information about the incubation period. The incubation period for rabies infection is between one month and three months. In rare cases, as short as 2 weeks or as long as more than a year incubation period can occur. Before the virus bind to nerve cells, the replication occurs in other cells, predominantly in muscle cells near the inoculation sites. The presents of specific receptors allow the invasion of both sensory and motor neurons. The transportation methods used are fast axonal transport of virus heading towards spinal cord and brainstem. Virus spread to gray matter in CNS via neuroanatomic connections and leads to inflammatory changes mostly and neuronal death in few neurons. This condition leads to neuronal dysfunction that produce rabies symptoms such as encephalitis, flaccid paralysis and other serious manifestations such coma and death.

       There are three phases of rabies disease: prodrome phase, acute neurologic phase and coma/death phase. The duration of each phase varies.  The duration of prodrome phase is between 1 -7 days. The symptoms include fever, malaise, nausea, vomiting, anxiety, agitation, pruiritus, pain and paraesthesia at the site of inoculation and headache. In acute neurologic phases, there are two kinds of manifestations: encephalitic (in 80%) and Paralytic (in 20%). The duration for the former is 1- 7 days and the latter is 2-10 days. The symptoms of the former one are fever, confusions, hallucinations, hyperactivity and pharyngeal spasm that can lead to hydrophobia as well as seizures. In paralytic rabies the symptom is ascending flaccid paralysis. The third phase duration is 1-14 days.

   In conclusion, rabies can be prevented from complication development if early intervention by rabies PEP is carried out. The awareness of the population in which the prevalence of rabies are high should be raised through education and campaign measures for examples. The information above is simplified and further information can be obtained from Harrison book. 

Reference:

1.Fauci. et al. Rabies. Harrison's Principles of Internal Medicine. 2008.