49 Rabies

William Howlett 25/09/18

49.1 Intro

Is a zoonosis.

Virtually always a dog bite (>99%), but sometimes a cat bite, sometimes bats.

About 50% of people will develop rabies after a bite from a rabid animal.

What about bat transmission? Theoretically you can inhale this in bat caves, in caving.

Human to human? Super super rare, but has been seen in organ transplant. 2 cases of vertical transmission. 2 cases of inhalation in the lab!

49.2 Epidemiology

You see 55,000 deaths worldwide 20-25,000 deaths in SSA annually

Predominantely in rural areas

49.3 Vector

49.4 Dogs

Saliva of bite from rabid dog is the most common cause. Either through inflicting a wound, or contaminating a mucous membrane/unhealed wound.

A rabid dog doesn’t normally live for more than ten days.

49.4.1 Bats

Vampire bat is a big source of cattle disease in Americas

Fruit bats are the main source in SSA, but less common.

You may not notice a bat bite!

49.5 Virus

Some lyssa types in bats are not as lethal as the ones in foxes/dogs. These Genotypes (2,3,4) have either very rarely, or never had cases in humans.

Replicates at the bite site, but you don’t see a reaction. Rabies is like 4 weeks incubation. The patient does feel pain at bite site.

They get spread up the axons. To form negri inclusion bodies, with no immune response. Then spreads to the primitive brain and autonomic system. That’s when you get onset of clinical rabies.

49.6 Clinical Forms

Furious Rabies - limbic system Paralytic/Algid rabies - affects mainly spinal cord, later becomes furious rabies

Paralytic cases are more common in south africa. Present with a flaccid paralysis initially before turning into furious rabies.

60% of cases occur within 3-12 weeks.

Incubation is shorter with bites nearer to head, several bites, bites in children.

Neurological/laryngopharangeal/psychiatric symptoms in a patient with a history of possible exposure:

  • Bite
  • Wound
  • Travel

49.6.1 Starting Symptoms

Prodrome: Myalgia/fever/chillls/headache/irritability/photophobia/insomnia

First symptoms: Itching/pain/paraesthesia/pruritis

Prodrome lasts 2-3 days until main features appear

Patient will usually die within week of first symptoms appear. Can last up to 3 weeks.

Furious symptoms:

  • Encephalitic
  • Temperature
  • Hydrophobia - intermittent refelex contraction of inspiratory muscles

  • You can get opistothonus like tetanus

  • Terror
  • Pain
  • Confusion
  • Convulsions
  • Insomnia
  • Anxiety
  • Hypersalivation + Tongue Protrusion
  • Cheyne Stokes
  • Labile BP

  • Can have paralysis

Final stages are coma/death. Usually die in a spasm.

49.7 DDx

  • Tetanus
  • Cerebral Infection
  • Guillain Barre (algid rabies)

of children who died of unexplained encephalitis, up to 1/3 of rabies in S. Africa were diagnosed on post-mortem

49.8 Diagnosis

  • Culture Virus takes 1-3 weeks (patient dead by then!)
  • Antibodies - positive in 2nd week of illness
  • Antigen - Immunofluorescent stain on skin of neck (98% sensitivity)
  • Traditional way - kill the dog, look for negri bodies on brain biopsy

MRI: Significant Oedema of Brain. A HUGE encephalitis.

When to suspect Rabies?

  • Was there an exposure?
  • Where on the body?
  • What was the animal?
  • Has that animal died/developed rabies
  • Is there rabies in the area?

You can be certain it’s not rabies if the animal is healthy after 15 days (usually observed for 10 days)

49.9 Manage

These patients need palliative care

  • Sedate, Analgesia
  • Barrier Nursing
  • ITU

There may be one case of horizontal transmission. But its very very rare.

10 known survivals in high income setting. 7 vaccinated. 3 non vaccinated. Survived in ICU.

49.9.1 PEP

TAKE MANAGEMENT FROM SLIDES