PATHOGEN: West Nile virus

HOST: Birds are replicating hosts while humans and horses are incidental hosts

VECTOR: Culex mosquitoes

ENVIRONMENT:   Urban and rural especially in the vicinity of dams or standing water.

TRANSMISSION & INFECTIVITY: Bite from infected mosquito or when handling brain tissue or blood of infected animals.

SYMPTOMS IN ANIMALS: Neurological signs in animals include stumbling, weak hind and/or forelimbs, partial loss or impaired movement, complete paralysis, partial blindness and jaundice in certain cases, severe cases were unable to get up, had quadriplegia, limb paddling, teeth grinding, muscle twitching, chewing fits, seizures and coma before death.

SYMPTOMS IN PEOPLE: Rash and fever in some cases, meningo-encephalitis, GuillainBarre syndrome, possibly hepatitis and death in rare cases. Human symptoms are not yet fully defined for the other virus infections. 

MORBIDITY & MORTALITY IN ANIMALS: In horses 20-30% of infections develop clinical signs with as many as 90% of these developing severe neurological disease and 30-40% of these being fatal or euthanized for humane reasons. 

MORBIDITY & MORTALITY IN PEOPLE: Approximately 20% of infections develop West Nile fever, with symptoms including rash joint and muscle pain, fever, nausea and headache, while less than 1% of cases will develop WNV neurological disease, which includes meningitis, encephalitis, polio-like paralysis in rare cases, and death. Symptoms include a stiff neck, sore back, severe headache, eye sensitivity to light, weakness and changes in mental status in certain cases.

LABORATORY TEST FOR ANIMALS: In the first few days of symptoms, virus can be identified by viral genetic tests in the blood or in fatal cases in the brain and spinal cord. Antibodies can be detected in the blood through IgM ELISA after approximately 7-10 days, but since the viruses are endemic and may cross react with other members of the virus family, antibody testing should be confirmed with follow up testing of convalescent specimens or a neutralisation assay. Testing for animal cases can be done at the Centre for Viral Zoonoses, University of Pretoria.

LABORATORY TEST FOR PEOPLE: In the first few days of symptoms, virus can be identified by viral genetic tests in the blood. Antibodies can be detected in the blood through IgM ELISA after approximately 7-10 days, but since the viruses are endemic and may cross react with other members of the virus family, antibody testing should be confirmed with follow up testing of convalescent specimens or a neutralisation assay. Testing for human cases can be done at the National Institute for Communicable Diseases (NICD).

CASE DEFINITION FOR ANIMALS: Identified as an animal that were shown to be positive by the relevant laboratory

CASE DEFINITION FOR PEOPLE: Identified as a human that were shown to be positive by the relevant laboratory

VACCINATION / PROPHYLAXIS: A horse vaccine is licensed in South Africa and shown to protect against local WNV strains, but a human vaccine does not yet exist.

TREATMENT IN ANIMALS: No specific treatment exists for arbovirus infections in humans or animals and symptoms are mainly treated with anti-inflammatory drugs and prevention of self-injury in animals.

TREATMENT IN HUMANS: No specific treatment exists for arbovirus infections in humans or animals and symptoms are mainly treated with anti-inflammatory drugs and prevention of self-injury in animals.

PRIORITY IN GAUTENG: Notifiable to OIE

CONTACTS: Centre for Viral Zoonoses (CVZ):The CVZ, department medical virology is a DAFF approved diagnostic lab for WNV. The submission forms is on www.Zoonosesresearchunit.up.ac.za

012 319 2287/ 083 293 0884, Pretoria State Vet: 012 316 1600 Randfontein State Vet: 011 411 4300 Germiston State Vet: 011 821 7700 NICD: 011 386 6400

STUDENTS: Jumari Steyn & Louwtjie Snyman

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