25. RABIES Flashcards
What is Rabies?
Rapidly progressive, acute infectious diseases of the central nervous system (CNS) in humans and animals
Rabies virus, transmitter through animal vectors
ENCEPHALITIC + PARALYTIC forms —> DEATH
Etiologic Agent of Rabies
Rabies virus is a member of the family Rhabdoviridae
It is specifically a lyssavirus. Most human rabies is transmitted from dogs in countries with endemic canine rabies and dog-to-dog transmission
Incubation period
20 to 90 days
Pathogenesis
Through the wound, the virus infects the nicotonic acetylcholine receptors first at the post synaptic membranes of the NMJ and spreads centripetally along peripheral nerves —> CNS through retrograde axonal transport —> spinal cord/brainstem
Once in the CNS —> rapidly disseminates to other regions via fast axonal transport along neuroanatomic connections
NEURONS ang affected
Once CNS infection is established, CENTRIFUGAL spread along SENSORY and Autonomic Nerves to other tissues including Salivary Glands, Heart, Adrenal Glands and Skin
Acinar glands in salivary glands is where it reciprocates.
Rabies usually present as _____ encephalitis with relative preservation of _______
Rabies may be difficult to recognize late in the clinical course when progression to coma has occurred
CLINICAL STAGES of RABIES (goes hand in hand with CLINICAL MANIFESTATIONS)
Incubation Period
Prodrome
Acute Neurologic Disease (Encephalitic, Paralytic)
Coma Death
What are the prodromal features of rabies?
Earliest specific neurologic manifestation? 3 Ps
(+) fever, malaise, headache, n/v, anxiety, agitation
Paresthesis, Pain, Pruritus near the site of exposure (wound has healed at this point) but syptoms probably reflect infection with associated inflammatory changesin Local Dorsal Root Ganglion or Cranial Sensory Ganglia
Cardinal Features of ENCEPHALITIC RABIES
What causes these?
Hyperexcitability, Hydrophobia, Aerophobia
classic features d/t dysfunction of infected
brainstem neurons= exaggerated defense reflexes
- Hydrophobia - involuntary, painful contraction of the DIAPHRAGM and accessory respiratory, laryngeal and pharyngeal muscles in response to swallowing liquids
- Aerophobia - same features caused by stimulation from a draft of air.
What causes foaming at the mouth?
Hypersalivation (ANS dysfunction) + Pharyngeal Dysfunction (foaming at the mouth)
What about Paralytic Rabies?
In paralytic rabies, muscle weakness predominates and cardinal features of encephalitic rabies (hyperexcitability, hydrophobia, and aerophobia) are lacking
Patients with paralytic rabies generally survive a few days longer (2-10 days) than those with encephalitic rabies (2-7 days), but multiple organ failure nevertheless ensues.
Diagnostics for Rabies
Currently, there is no diagnostic tool available which is economically suitable in our country to confirm rabies and only supportive care is given once acute neurologic disease has ensued.
In an ideal setting, RT PCR Amplification is highly sensitive and specific test to detect rabies virus RNA in fresh saliva samples, CSF and brain tissue
Direct Fluorescent Antibody Test - GOLD STANDARD **
Also a highly sensitive and specific test employing the use of rabies virus antibodies conjugated to fluorescent dyes
It is used to detect rabies antigen in skin biopsies and brain tissue. The utility of these diagnostic tests in patients with obvious signs and symptoms of rabies is generally low considering the outcome of the disease
How to manage rabies?
A palliative approach is typically pursued in patients who are unlikely to survive or who would not accept survival with severe neurologic sequelae.
- QUIET ROOM
- BENZOS > Physical Restraints
- IV MORPHINE - analgesia
- SCOPOMAINE - salivation
- ANTIPYRRECTICS - fever
What do other countries do for a more aggressive approach?
MILWAUKEE PROTOCOL or WISCONSIN PROTOCOL which starts by putting the patient into chemically-induced coma using high-dose anesthetic agents as well as use of multiple intrathecal anti-viral drugs.
Cases of survival, however with moderate to severe neurologic sequelae.
PREVENTION of RABIES
- Wound must be vigorously washed and flushed with soap and water for at least 10 minutes (betadine can also be used but soap and water pinakaeffective)
- frankly infected open wounds, ANTIBIOTICS may be started. CO-AMOXICLAV or CEFUROXIME
- Tetanus Toxoid also
Things to consider in Post Exposure Prophylaxis
Effective ONLY during the Incubation period (20-90 days)
→ Given when the virus is still localized in the muscle. If given during the prodromal period and beyond, you can no longer save the patient.
→ If immunization status is unrecalled, consider unimmunized.
