Microbiology
Summary
The rabies virus, part of the Rhabdoviridae family, is an enveloped, negative-sense, single-stranded, helical RNA virus with a bullet-shaped morphology. It is often transmitted by bats, but also other animals like foxes, skunks, and squirrels. The virus attaches to the nicotinic acetylcholine receptors at the postsynaptic membrane of the neuromuscular junction via spike-shaped envelope glycoproteins, initiating infection at the motor end plate, and then replicates within muscle tissue. It then travels retrogradely along nerve axons towards the central nervous system (CNS), while spreading centrifugally from the CNS to peripheral tissues via autonomic and somatic nerves. In the CNS, it affects structures like the hippocampus, thalamus, hypothalamus, and brainstem, and is marked by the presence of eosinophilic inclusions called Negri bodies. These bodies are found post-mortem in hippocampal pyramidal cells and cerebellar Purkinje cells.
The rabies virus has a variable incubation period, which averages about 1 to 3 months, with flu-like symptoms and abnormal sensations at the bite wound site as prodrome. Rabies concentrates in submaxillary salivary glands, causing foaming of the mouth due to laryngeal spasm and increased saliva production. It also causes severe encephalitis, hydrophobia due to throat muscle spasms, and ascending flaccid paralysis. The comatose phase brings convulsions, coma, and death. Passive immunity through rabies immune globulin and active immunity via the rabies vaccine (killed or inactivated) play vital roles in disease management, with pre-exposure prophylaxis advised for high-risk occupations and travelers to endemic regions.
Lesson Outline
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FAQs
The initial symptoms of rabies are often nonspecific and may include fever, headache, and general malaise. As the disease progresses, neurological symptoms appear and may include anxiety, confusion, agitation, hyperactivity, difficulty swallowing, fear of water (hydrophobia), paralysis, and often encephalitis (inflammation of the brain). As the disease progresses, it eventually leads to coma and death in nearly all cases.
The rabies vaccine is used in two ways: for pre-exposure prophylaxis which is given to people who are at high risk of exposure like lab workers, and for post-exposure prophylaxis. Post-exposure prophylaxis requires prompt treatment to prevent the onset of symptoms and includes rabies vaccine and rabies immune globulin. It is crucial to administer the treatment right after exposure to the virus, typically from a bite or scratch from a rabid animal.
Rabies is mainly transmitted through the bite or scratch of an infected animal. The rabies virus is present in the saliva and neural tissue of the rabid animal. Transmission can also occur when infectious material, usually saliva, comes into direct contact with human mucosa or fresh skin wounds.
Rabies encephalitis is inflammation of the brain, caused by the rabies virus. The virus travels to the brain by following the peripheral nerves. Once the virus reaches the brain, it rapidly causes encephalitis. This results in a severe and fatal neurological syndrome characterized by hallucinations, delirium, and other aggressive behavior.
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