Rhabdoviridae

Rhabdoviridae are enveloped viruses with a characteristic bullet or rod shape, containing a negative-sense, single-stranded, non-segmented RNA genome. They carry their own RNA-dependent RNA polymerase since the negative-sense genome cannot be directly translated. The most medically significant member is Rabies virus (genus Lyssavirus). Pathophysiology: After inoculation via animal bite (saliva), the virus replicates locally in muscle tissue, then travels retrograde along peripheral nerve axons to the dorsal root ganglia and CNS, causing severe encephalitis. Classic pathologic finding: Negri bodies—eosinophilic cytoplasmic inclusions in Purkinje cells of the cerebellum and hippocampal neurons. Clinical course: incubation period variable (weeks to months, depending on bite location/viral load), followed by prodrome (fever, malaise, paresthesias at bite site), then acute neurologic phase with hydrophobia, aerophobia, hypersalivation, agitation (furious rabies) or paralysis (paralytic/dumb rabies), progressing to coma and death. Rabies is almost universally fatal once symptoms appear. Transmission: bites from infected mammals—bats are the leading cause of human rabies in the U.S.; dogs remain the primary vector worldwide. Management: Post-exposure prophylaxis (PEP) is critical and includes wound cleaning, rabies immunoglobulin (passive immunity, infiltrated around the wound), and rabies vaccine series (active immunity). Pre-exposure prophylaxis is given to high-risk individuals (vets, spelunkers, lab workers). Diagnosis: direct fluorescent antibody testing on brain tissue (postmortem) or skin biopsy, nucleic acid amplification (RT-PCR) on saliva/CSF. There is no effective treatment once clinical symptoms begin (Milwaukee protocol has limited success). Other rhabdoviruses include Vesicular stomatitis virus (affects livestock) and some plant pathogens, but these are less emphasized on USMLE.