Rabies

Rabies• Causative agent:– Rabies virus

• Lyssavirus • Enveloped ssRNA• Spiked bullet shaped virus

– Virus multiplies in brain forming Negri bodies

• Signs & Symptoms – Pain and itching at site of infection– Fever, headache, myalgia, sore throat, fatigue– Progress rapidly to secondary symptoms • Encephalitis, agitation, confusion, hallucinations,

seizure, increased sensitivity to light and touch, coma• Increased salivation and difficulty swallowing– Results in frothing of mouth

• Hydrophobia occurs in 50% of cases• About 50% of patients die within 4 days

• Virus enters through bite

• Attaches to skeletal muscle cells triggering endocytosis

• Pathogen moves across neuromuscular junction into nerve cell and travels to CNS

• Slow moving so long incubation period– 1-2 months up to several years

• Viruses travel back to the salivary glands and are secreted in saliva

• Epidemiology– Zoonotic– Skunks, raccoons and

bats considered chief reservoir• 75% of human cases

linked to bat bites

– 0 to 4 reported cases in US annually

• Prevention– Vaccination of domestic animals and Vets – Wash wound immediately and thoroughly• apply antiseptic

• Treatment– Risk lowered if vaccine administered as soon as possible– Interferon may be applied to wound – No effective treatment for rabies• Only six known survivors of disease

• Causative agent– Arboviruses

• mosquitoes

– Zoonotic diseases• Horses, birds and rodents

– West Nile encephalitis, LaCrosse encephalitis, WEE, EEE, VEE, St. Louis encephalitis

Viral Encephalitis

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• Signs & Symptoms– 3-7 day incubation period – Characterized by mild flu-like symptoms • Fever; headache; vomiting• One or more nervous system abnormalities– Disorientation, localized paralysis, deafness, seizures

or coma

• Only minority infected develop encephalitis• Others may develop viral meningitis

• Most reported human cases in immunosuppressd individuals– Elderly and very young– Healthy immune system typically fights off virus with only mild

flu-like symptoms

– Viruses multiply at site of bite and in local lymph nodes• viremia

– Virus crosses blood-brain barrier• Damages neurons

– Causes extensive damage to brain tissue in severe cases

– Progression of disease halted by neutralizing antibody

– Mortality ranges from 2% to 50% depending of type of infecting agent and host

• Epidemiology– Disease are all zoonoses• Maintained naturally in birds and rodents

– Humans are accidental hosts

– LaCrosse encephalitis usually causes most reported cases

– West Nile an emerging disease in US• Appeared in New York in 1999

• Prevention – Eliminate vector habitat – Avoiding outdoor activities at night– Windows and porches properly screened– Use insect repellents and insecticides– Vaccine available for horses

• Treatment– No proven antiviral therapy