Arthropod-borne Viruses Arboviruses

Small spherical particle(40-70nm), +ssRNA, icosahedral nucleocapsid, envelope and spike

Arthropod-borne Viruses Arthropod-borne viruses (arboviruses) are viruses that can be transmitted to man by arthropod vectors. The WHO definition is as follows “Viruses  maintained  in nature principally, or  to  an  important extent,  through  biological  transmission  between   susceptible vertebrate  hosts by haematophagus arthropods or through  transovarian and possibly venereal transmission in arthropods.” Arboviruses belong to three families 1. Togaviridae (Alphavirus) e.g. EEE, WEE, and VEE (equine encephalitis) 2. Bunyaviruses e.g. Sandfly Fever, Rift Valley Fever, Crimean-Congo Haemorrhagic Fever 3. Flaviviruses e.g. Yellow Fever, dengue, Japanese Encephalitis

Transmission Cycles Man - arthropod -man Animal - arthropod vector - man Both cycles may be seen with some arboviruses such as yellow fever.

Man-Arthropod-Man Cycle e.g. dengue, urban yellow fever. Reservoir may be in either man or arthropod vector. In the latter transovarial transmission may take place.

Animal-Arthropod-Man Cycle Animal - arthropod vector - man e.g. Japanese encephalitis, EEE, WEE, jungle yellow fever. The reservoir is in an animal. The virus is maintained in nature in a transmission cycle involving the arthropod vector and animal. Man becomes infected incidentally.

Arthropod Vectors Mosquitoes Ticks Sandflies Japanese encephalitis, dengue, yellow fever, St. Louis encephalitis, EEE, WEE, VEE etc. Ticks Crimean-Congo haemorrhagic fever, various tick-borne encephalitides etc. Sandflies Sicilian sandfly fever, Rift valley fever.

Examples of Arthropod Vectors Aedes Aegyti Assorted Ticks Phlebotmine Sandfly Culex Mosquito

Animal Reservoirs In many cases, the actual reservoir is not known. The following animals are implicated as reservoirs Birds Japanese encephalitis, St Louis encephalitis, EEE, WEE Pigs Japanese encephalitis Monkeys Yellow Fever Rodents VEE, Russian Spring-Summer encephalitis

Diseases Caused Fever and rash - this is usually a non-specific illness resembling a number of other viral illnesses such as influenza, rubella, and enterovirus infections. The patients may go on to develop encephalitis or haemorrhagic fever. Encephalitis - e.g. EEE, WEE, St Louis encephalitis, Japanese encephalitis. Haemorrhagic fever - e.g. yellow fever, dengue, Crimean-Congo haemorrhagic fever.

Diagnosis Serology - usually used to make a diagnosis of arbovirus infections. Culture - a number of cell lines may be used, including mosquito cell lines. However, it is rarely carried out since many of the pathogens are group 3 or 4 pathogens. Direct detection tests - e.g detection of antigen and nucleic acids are available but again there are safety issues.

Prevention Surveillance - of disease and vector populations Control of vector - pesticides, elimination of breeding grounds Personal protection - screening of houses, bed nets, insect repellents Vaccination - available for a number of arboviral infections e.g. Yellow fever, Japanese encephalitis, Russian tick-borne encephalitis

Japanese Encephalitis First discovered and originally restricted to Japan. Now large scale epidemics occur in China, India and other parts of Asia. It include West Nile Virus. Flavivirus, transmitted by culex mosquitoes. The virus is maintained in nature in a transmission cycle involving mosquitoes, birds and pigs. Most human infections are subclinical: the in apparent to clinical cases is  300:1 In clinical cases, a life-threatening encephalitis occurs. The disease is usually diagnosed by serology. No specific therapy is available. Since Culex has a flight range of 20km, all local control measures will fail. An effective vaccine is available.

Yellow Fever (1) Flavivirus, mainly found in West Africa and S America Yellow fever occurs in 2 major forms: urban and jungle (sylvatic) yellow fever. Jungle YF is the natural reservoir of the disease in a cycle involving nonhuman primates and forest mosquitoes. Man may become incidentally infected on venturing into jungle areas. The urban form is transmitted between humans by the Aedes aegypti mosquito Classically Yellow Fever presents with chills, fever, and headache. Generalized myalgias and GI complaints . Some patients may experience an asymptomatic infection or a mild undifferentiated febrile illness.

Yellow Fever (2) After a period of 3 to 4 days, the more severely ill patients with a classical YF course will develop bradycardia (Faget's sign), jaundice, and haemorrhagic manifestations. 50% of patients with frank YF will develop fatal disease characterized by severe haemorrhagic manifestations, oliguria and hypotension. Diagnosis is usually made by serology There is no specific antiviral treatment An effective live attenuated vaccine is available against yellow fever and is used for persons living in or traveling to endemic areas.

Dengue (1) Dengue  is the biggest arbovirus problem in the world today  with over 2 million cases per year. Dengue is found in SE Asia, Africa and the Caribbean and S America. Flavivirus, 4 serotypes, transmitted by Aedes mosquitoes which reside in water-filled containers. Human infections arise from a human-mosquitoe-human cycle Classically, dengue presents with a high fever, lymphadenopathy, myalgia, bone and joint pains, headache, and a maculopapular rash. Severe cases may present with haemorrhagic fever and shock with a mortality of 5-10%. (Dengue haemorrhagic fever or Dengue shock syndrome.)

Distribution of Dengue

Dengue (2) Dengue haemorrhagic fever and shock syndrome appear most often in patients previously infected by a different serotype of dengue, thus suggesting an immunopathological mechanism. Diagnosis is made by serology. No specific antiviral therapy is available. Prevention of dengue in endemic areas depends on mosquito eradication. The population should remove all containers from their premises which may serve as vessels for egg deposition. A live attenuated vaccine is being tried in Thailand with encouraging results.

Equine Viral Encephalitis Arboviral Infections 1. West Nile Virus 2. Eastern Equine Encephalitis 3. Western Equine Encephalitis 4. Venezuelan Equine Encephalitis

West Nile Virus Emerging disease, migratory birds are the reservoir (crows, black birds), mosquitoes are the vector, very serious infection in horses, usually a mild infection in people, Vaccination in horses may be helping decrease the incidence of the disease.

Eastern Equine Encephalitis EEE Present in North, Central and South America. Also found in the Caribbean. First recognized in Massachusetts in 1831 when 75 horses died of encephalitis.* Found primarily in the eastern USA Isolated from a horse’s brain in 1933. In 1938 first human cases documented, 30 children died of the viral encephalitis. JAVMA,

Eastern Equine Encephalitis EEE Zoonotic Disease Endemic in the Northeastern USA Reservoir is in birds in North America. In the tropics small mammals are the reservoir. Spread by primarily by mosquitoes, primarily Culex spp. Ticks, lice and mites also can transmit the infection. Virus can infect mammals, birds, reptiles and amphibians.

Eastern Equine Encephalitis EEE Symptoms: Equine 1-3 weeks after exposure horses typically get a very high fever (106) Fever can last 1-2 days. Neurological signs include sensitivity to sound, periods of excitement and restlessness. As the disease progresses drowsiness, drooping ears, circling paralysis of the throat and face, coma and death. Mortality can approach 70-90%

Eastern Equine Encephalitis EEE in Man Human cases: 220 cases from 1964-2004 High mortality 30-50% Common Name was sleeping sickness Signs of encephalitis, sore neck, headache, visual problems, seizures, coma. Common to have permanent neurological signs in survivors.

EEE Diagnosis 1. Clinical symptoms 2. Serology 3. PCR Tests 4. Virus isolation

Eastern Equine Encephalitis Treatment: Symptomatic and with life support measures for both humans and horses. Prevention: Equine: Vaccine Humans: No vaccine currently on the market MOSQUITO CONTROL

Western Equine Encephalitis First identified in 1930 in horses. First human fatality occurred in 1938 1938 180,000 horses died in Calif. 1941 epidemic occurred in the US and Canadian Plains: 300,000 horses and 3336 human cases. Last human fatality occurred in WYO in 1994.

Western Equine Encephalitis Found in North, Central and South America but most cases have been reported from the plains regions of the western and central USA and the Canadian plains. Infects Man, Horses, Birds and other small mammals. Zoonotic.

Western Equine Encephalitis Reservoir host: birds Vector: Mosquitoes Horses and Humans are incidental hosts (dead end hosts).

Western Equine Encephalitis WEE Symptoms: CNS disease in horses and humans. Headaches, stiff neck, stumbling gait, coma and possibly death. In man it is more severe in children and infants. Has a mortality rate of 3-4% in people. Tends to be more common in rural locations.

Diagnosis 1. Symptoms of encephalitis 2. PCR and Serology 3. Virus Isolation

Venezuelan Equine Encephalitis First recognized in 1936 in Venezuelan in an outbreak in horses. From 1936-1968 several severe outbreaks occurred in horses in South America. In 1969 the disease migrated north thru central America went northward into Mexico and reached Texas by 1971. In 1993 a southern Mexico outbreak initiated a large quarantine area with a wide surveillance of horses and mosquitoes. In 1971 local, federal, state and military took part is a massive vaccination and quarantine program to stop the spread of the disease.

Venezuelan Equine Encephalitis Vector; Mosquitoes Reservoir: bats, birds, rodents, equine and small tropical mammals. Aerosol Transmission, People to People transmission is possible Virus has been isolated from the throats of patients and accidental infection has occurred in laboratory setting. Potential for biowarfare agent???

Venezuelan Equine Encephalitis Diagnosis: Symptoms, Serology,PCR Treatment: Supportative and Symptomatic Prognosis: Less than 1% death rate in humans High death rate reported in horses

active treatment : that directed immediately to the cure of the disease or injury. causal treatment : treatment directed against the cause of a disease. conservative treatment : that designed to avoid radical medical therapeutic measures or operative procedures. empiric treatment : treatment by means which experience has proved to be beneficial. expectant treatment,  symptomatic treatment : treatment directed toward relief of untoward symptoms, leaving cure of the disease to natural forces. palliative treatment : treatment designed to relieve pain and distress with no attempt to cure. preventive treatment , prophylactic treatment : that in which the aim is to prevent the occurrence of the disease; prophylaxis. rational treatment  : that based upon knowledge of disease and the action of the remedies given. shock treatment  obsolete term for electroconvulsive therapy. specific treatment  treatment particularly adapted to the disease being treated. supporting treatment , supportive treatment that which is mainly directed to sustaining the strength of the patient.