Rabies

Rabies is a viral disease that affects the central nervous system of mammals, including humans. It's primarily transmitted through the saliva of infected animals, commonly through bites or scratches. Its major clinical manifestations include Hydrophobia, aerophobia, pharyngospasm , and progressive paralysis.

The virus incubation period : 10-90 days

  • Most cases are males < 15 yrs

  • the disease has 4 phases :

    • first phase: asymptomatic

    • second phase: Prodromal

    • third phase: neurological signs

    • fourth phase: Coma

Rabies Virus

  • Belongs to the rhabdoviridae Lyssavirus.

  • 5 structural proteins

  • envelope contains G-protein spikes, which bind to cells.

Suspected rabies animal

  • dog, cat, bat, wolf, fox, raccoon

What is the transmission route of rabies?

  1. Infected animal saliva inoculation by bite or scratch

  2. Infected saliva : contact with mucous membrane, transdermal exposure.

  3. Virus shed in the saliva during, before or after clinical symptoms.

  4. human - human : few reported cases

  5. Aerosol transmission : caves containing bats.

Clinical manifestation:

Prodromal phase

  • lasts for 2 to 10 days

  • Viral invasion of CNS

  • Symptoms: Anorexia, fatigue, headache, fever, discomfort at the site of the bite or scratch.

  • Local pain itching, numbness (50%-80% of patients)

Neurological signs

Once the virus reaches the central nervous system, more severe symptoms develop.

  • 1-3 days

  • Symptoms: hyperactivity, confusion, agitation, hallucinations, hydrophobia (fear of water), aerophobia (fear of drafts or fresh air), difficulty swallowing, and paralysis, Hyper-reflexia, cholinergic manifestations, lacrimation, salivation, mydriasis, pyrexia.

  • This phase progresses rapidly and is usually fatal within a few days of the onset of symptoms.

fourth phase

  • inspiratory spasm

  • sinus tachycardia

  • supra-ventricular and ventricular arrhythmias

  • main cause of death; circulatory collapse.

What are the symptoms of rabies?

both forms:

  • fever

  • nuchal rigidity

  • paresthesia

  • fasculation

  • convulsions

  • hypersalivation

  • hyperventilation

  • Extensive cortical virus spread

  • death usually in 7 days

  • respiratory arrest

  • myocarditis

  • supportive care : sedation and anagesia

Related inspections

Frequently missed

  • Lab test are non diagnostic

  • hyponatremia

  • CSF analysis normal in 1/3 of patients in the 1st wk of illness

  • CSF : Viral meningeoencephalitis

  • EEG and head Ct : normal in early illness

  • MRI: abnormal, ill defined, increase signal intensity on T-2 images

  • Areas involved: brainstem, hippocampi, hypothalami, deep & grey matter

  • Godalinium enhancement only in late stages

    Viral culture

    • Skin biopsy of the hair follicles

    • Virus culture: saliva, CSF, Urine, respiratory secretions

    • Culture in mice or in mouse neuroblastoma cell line.

    • sensitivity 50-94%, specificity 100%

Tissue studies

  • Brain tissue : culture, histology for negri bodies Yield low

  • Immunohistochemestry on tissue

Diagnosis

History of bites or scratches by sick or wild animal.

  • fear of water

  • fear of wind

  • Throat spasm

  • fear of light

  • fear of sound

  • exessive sweating

  • salivation and numbness

  • paresthesia at the bite

    Viral antigen:

    • viral nucleic acid

    • endosomes in brain tissue

Differential diagnosis

  • meningitis/ encephalitis

  • epilepsy

  • drug toxicity

  • acute hepatic porphyria

  • neuropsychiatric disturbances

  • substance abuse, acute serotonin syndrome

  • tetanus

  • paralytic rabies

prevention

  • Pre-exposure prophylaxis: Vaccination of people in high risk group (veriterinarians, certain lab workers…)

    • Vaccine types : human diploid cell vaccine (HDCV), rabies vaccine absorbed (RVA) , purified chicken embryo cell (PCEC)

  • Post-exposure wound care :

    • prevent virus in wound from reaching neural tissue

    • prompt and thorough cleaning: flush wound with soap and water.

    • Update tetanus immunization

    • treat secondary bacterial infection

    • do not suture wound if possible

  • Post-exposure immuno-prophylaxis

    • Passive and active

    • Start ASAP

    • Rabies immunoglobulin (RIG) and rabies vaccine.

    • 5 doses : 1.0ml at 0, 3, 7, 14, 28 day

    • or 2 Doses on day 0, 1

  • immuno-prophylaxis/ RIG

    • Human RIG is given at the same time with the vaccine

    • Dose: 20 IU/kg

    • RIG and vaccine are given at different sites & in different syringes

  • Rabies prevention in our life

    • Educating children to avoid contact with stray or wild animals

    • Avoid touching animal carcasses

    • avoid trying to capture or provoke stray animals

Rabies Mind Map

Central Idea: Rabies

  • Transmission

    • Bite from infected animal

    • Scratch from infected animal

    • Contact with infected animal's saliva

  • Symptoms

    • Fever

    • Headache

    • Hydrophobia

    • Agitation

    • Confusion

  • Prevention

    • Vaccination for pets

    • Avoid contact with wild animals

    • Seek medical attention after animal bites

  • Treatment

    • Post-exposure prophylaxis

    • Rabies vaccine

    • Supportive care for symptoms

  • Impact

    • Fatal if untreated

    • Rare in developed countries

    • High mortality rate