Rabies

Rabies is a viral encephalomyelitis caused by lyssaviruses, transmitted through the bite or scratch of an infected mammal (dogs remain the dominant source of human cases globally, though any mammal can theoretically transmit infection, with bats a particularly important reservoir in some regions), or, less commonly, through mucous membrane or broken skin contact with infected saliva.

Once established, rabies is essentially universally fatal, which is what makes prompt post exposure management so critical: rabies is one of the few infectious diseases where effective prevention after exposure but before symptom onset is highly successful, even though there is essentially no effective treatment once clinical disease develops.

The virus travels retrogradely along peripheral nerves from the site of inoculation to the central nervous system, a process that can take anywhere from days to, occasionally, many months or even years, depending largely on the distance from the bite site to the central nervous system and the viral inoculum, which is why the incubation period is so variable and why post exposure prophylaxis remains valuable even with some delay after exposure.

• A prodromal phase lasting several days may include fever, headache, malaise, and, distinctively, paresthesia or pain at the original bite site even after the wound itself has apparently healed, reflecting viral replication and inflammation along the nerve pathway.

Clinical disease then typically manifests in one of two forms.

• Furious (encephalitic) rabies, the more common and classically described presentation, involves agitation, confusion, hyperactivity, and the hallmark features of hydrophobia (severe, painful pharyngeal spasm triggered by attempts to drink water) and aerophobia (similar spasm triggered by a draft of air), alongside autonomic instability and hypersalivation.

• Paralytic (dumb) rabies, a less common but likely under-recognized presentation, involves an ascending, symmetric or asymmetric flaccid paralysis resembling Guillain-Barré syndrome, without the dramatic hydrophobia and agitation of furious rabies, and is more prone to misdiagnosis as a result.

Both forms progress relentlessly to coma and death, typically from respiratory failure or cardiac arrhythmia, generally within days to a couple of weeks of symptom onset once established clinical disease has begun.

Diagnosis in a patient with a compatible exposure history and the classic clinical syndrome, particularly hydrophobia, is often made clinically, given the near uniform fatality and limited practical impact of laboratory confirmation on management of established disease.

• Antemortem diagnostic testing, where pursued, may include PCR or immunofluorescence testing of saliva, skin biopsy (from the nape of the neck, sampling nerve twigs around hair follicles), or cerebrospinal fluid, though sensitivity of any single antemortem test is imperfect and results can be falsely negative even in confirmed rabies.
• The primary diagnostic and management priority in practice is not confirming established disease, which carries no realistic treatment options once symptomatic, but rather assessing and managing the exposure before symptoms develop.

Differentials for the clinical syndrome include other causes of encephalitis, tetanus (though the clinical pattern, particularly the specific triggered spasms of hydrophobia, is generally distinguishable), and, for the paralytic form, Guillain-Barré syndrome.

Post exposure prophylaxis, the central and genuinely effective intervention, applies regardless of the specific biting animal species.

• Immediate, thorough wound washing with soap and water for a minimum of 15 minutes is the first and one of the most effective interventions, substantially reducing viral inoculum at the wound site.
• Rabies vaccine, given as a multi dose intramuscular series per WHO recommended schedule, should be started as soon as possible after any exposure meeting WHO Category II or III criteria.
• Rabies immunoglobulin, infiltrated into and around the wound with any remainder given intramuscularly at a distant site, is added for Category III exposures (or Category II in immunocompromised patients), providing immediate passive immunity to bridge the gap before the patient's own vaccine induced immune response develops.
• Post exposure prophylaxis remains valuable and should be given even with a delayed presentation after exposure, given the often prolonged and variable incubation period, unless the patient has already developed clinical symptoms, at which point prophylaxis is no longer effective.

Established clinical disease has no proven effective treatment. Management at this stage is exclusively palliative and supportive, focused on comfort and symptom control, given the essentially uniform fatality of the condition once symptoms have developed; occasional survivor case reports using aggressive intensive care protocols exist but do not represent a reliable or generalizable treatment approach.

Pre-exposure prophylaxis with rabies vaccine is recommended for individuals at particularly high ongoing risk, including certain veterinary and laboratory workers, and travelers to highly endemic areas with anticipated significant animal exposure risk or limited access to prompt post exposure care, and simplifies (though does not eliminate the need for) subsequent post exposure management should an exposure occur.

Referral: emergency assessment for any potential rabies exposure to determine post exposure prophylaxis needs, ideally without delay given the time sensitive nature of wound care and vaccine initiation; infectious disease or tropical medicine input for complex exposure scenarios.