Rabies Causative agent Rabies virus Lyssavirus Enveloped ss

Rabies • Causative agent: – Rabies virus • Lyssavirus • Enveloped ss. RNA • 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

Viral Encephalitis • Causative agent – Arboviruses • mosquitoes – Zoonotic diseases • Horses, birds and rodents – West Nile encephalitis, La. Crosse encephalitis, WEE, EEE, VEE, St. Louis 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 – La. Crosse 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