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Anthropod borne(Arbo) Viruses . Arthropod- borne Viruses • Def:Arthropod-borne viruses (arboviruses) are viruses that can be transmitted to man by arthropod vectors • Is a group of infectious viruses (agents) that are transmitted by blood sucking arthropods from one infected vertebrate host to another • They can multiply in the arthropods without causing any damage or disease. Arthropod borne Viruses • An arthropod acquires virus through ingestion of blood from viremic vertebrate • All arboviruses have an RNA genome and lipid contained envelope • They are inactivated by ether or sodium deoxycholate • Most of individual viruses are named after disease or after geographic area where were first isolated • ( dengue,yellow fever or West Nile fever,Zika fever etc). Arthropod borne Viruses • Despite being common in tropical rain forests they are also found in temperate areas • There are more than 350 arboviruses based on antigenic groups • Chemical and physical properties are also used to group them. • Many of them are grouped under toga,bunya,reo,arena,picorna and rhabdovirus groups. • Arboviral diseases are seasonal and regional based on life cycle of the vectors Arthropod borne Viruses • Inclusion in group is based on ecological and epidemiological hence has viruses of diverse physical and chemical properties • Classification: Arboviruses belong to three families 1. Togaviruses e.g. EEE, WEE, and VEE 2. Bunyaviruses e.g. Sandfly Fever, Rift Valley Fever, Crimean-Congo Haemorrhagic Fever 3. Flaviviruses e.g. Yellow Fever, dengue, Japanese Encephalitis Hemorrhagic Fever Viruses: Taxonomy Arenaviridae Argentine HF ( Junin Virus) Bolivian HF (Machupo Virus) Venezuelan HF (Guanarito Virus) Brazilian HF (Sabia Virus) Lassa Fever Rodents Bunyaviridae Rift Valley Fever Crimean-Congo HF Hantavirus Genus HFRS Filoviridae -Ebola HF -Marburg HF ¨TickBorne: ¨Kyasanur Mosquitoes Flaviviridae Forest Disease (KFD Virus) ¨Omsk HF ( OHF Virus) ¨Mosquito-Borne: Yellow Fever West Nile Fever Dengue HF Arthropod-borne viruses Transmission Cycles: • Man - arthropod -man • e.g. dengue, urban yellow fever(Reservoir may be in either man or arthropod vector) • Latter transovarial transmission may take place • Animal - arthropod vector – man • e.g. Japanese encephalitis, EEE, WEE, jungle yellow fever. • The reservoir is in an animal • Virus is maintained in transmission cycle involving arthropod vector and animal. Man becomes infected incidentally. Man-Arthropod-Man Cycle Animal-Arthropod-Man Cycle Arthropod-borne viruses • General properties: The arboviruses share some common biological properties All members produce fatal encephalitis in suckling mice after intracerebral inoculation They possess haemagglutinin and agglutinate erythrocytes of goose or day-old chicks They can be grown in tissue cultures of primary cells like chick embryo fibroblasts and in cultures of appropriate insect tissues Arthropod-borne viruses They may also be isolated in the yolk sac or CAM of chick embryo 5. In general, arboviruses are readily inactivated at room temperature and by bile salts, ether and other lipid solvents Examples of Arthropods are: Aedes aegyti , Culex Mosquito, Ixodid Ticks, Phlebotomine Sandfly Some of arthropod Vectors Mosquitoes: Diseases transmitted Japanese encephalitis, dengue, yellow fever, St. Louis encephalitis, Zika fever, Ebola, VEE etc. Ticks: Crimean-Congo haemorrhagic fever, various tickborne encephalitides etc. Sandflies: Sicilian sand fly fever, Rift valley fever. Some of Arthropod Vectors Aedes Aegyti Assorted Ticks Culex Mosquito Phlebotmine Sandfly Some animal reservoirs In many occasions the actual reservoirs are unknown. but the following animals are implicated : •Birds: Japanese encephalitis, St Louis encephalitis •Pigs: Japanese encephalitis •Monkeys: Yellow Fever •Rodents: VEE,Russian Spring-Summer encephalitis Arboviral diseases 1. Bunyaviridae 2. Flaviviridae Arbovirus encephalitis: • •Other: Arbovirus encephalitis: La Crosse encephalitis (LCV) · California encephalitis (CEV) Viral hemorrhagic fever: Rift Valley fever (RVFV) Japanese encephalitis (JEV) · Australian encephalitis (MVEV, KUNV) · St. Louis encephalitis (SLEV) · West Nile fever (WNV) •Viral hemorrhagic fever: Dengue fever (DV) Yellow fever (YFV) · Zika fever 3.Togaviridae – Arbovirus encephalitis: Eastern equine encephalomyelitis (EEEV) · Western equine encephalomyelitis (WEEV) · Venezuelan equine encephalomyelitis (VEEV) O'Nyong-nyong Virus ( OV ) - UGANDA Chikungunya (CV) - TANGANYIKA Ross River fever (RRV) 1. Bunyaviridae Viral hemorrhagic fever: Crimean-Congo hemorrhagic fever (CCHFV) 2. Flaviviridae Arbovirus encephalitis: Tick-borne encephalitis (TBEV) · Powassan encephalitis (PV) · Deer tick virus encephalitis (DTV) Viral hemorrhagic fever: Omsk hemorrhagic fever (OHFV) · Kyasanur forest disease (KFDV/Alkhurma virus) 3. Reoviridae Colorado tick fever (CTFV) 1. O'Nyong-nyong Virus (OV) – Vector: - Mosquitoes -Togaviridae, Genus: Alphavirus closely related to Chikungunya viruses – The O'nyong-nyong virus - First isolated by Uganda Virus Research Institute, Entebbe - Uganda in 1959. – The name is from Nilotic language of Uganda and Sudan (means “weakening of the joints.”) – Transmitted by an infected mosquito. – Clinical signs are polyarthritis, rash and fever, eye pain, chest pain, lymphadenitis and lethargy. – No deaths due to infection are known so far. O'Nyong-nyong cont…. Epidemics: • Two epidemics of O’nyong’nyong fever: 1st occurred in 1959 to 1962, extending from Uganda, Kenya, Tanzania, DRC, Malawi and Mozambique, >2 Mil people were infected. Is among the largest epidemics recorded. 1st virus isolates were obtained from mosquitoes & human blood samples from Gulu - Northern Uganda in 1959. • 2nd epidemic in 1996-1997 in 400 people were confirmed in Uganda. The 35-year hiatus between the two outbreaks and evidence of an outbreak in 1904-1906 in Uganda indicates a 30-50 year cycle for epidemics. Chikungunya Virus • Vector : Mosquitoes (Aedes aegypti) 1955 • Discovery in Tanganyika (along border btn Mozambique and Tz), 1952, Name from Makonde word- kungunyala, meaning to dry up or become contorted, meaning( " which bends up“) Occasional outbreaks in Africa, South Asia, SE Asia, Recently over a wider range. Example: - On 28 May 2009 Thailand - Provincial hospital first chikungunya infected women – Premature infected baby - Many confirmed cases in South India in 2009 • Common Symptoms: Fever 40 °C, petechial/maculopapular rash of the trunk and limbs, arthralgia/polyarthritis headache, conjunctitis,& Slight photophobia. Chikungunya cont…… • CHIKV illness symptoms are similar to dengue fever NB: Chikungunya was one of more than a dozen agents that the United States researched as potential biological weapons before the nation suspended its biological weapons program Rift Valley Fever Virus • Vector: Mosquitoes • The viral agent is an arbovirus, belongs to the Phlebovirus genus in the Bunyaviridae family. RVF- Virus cont…. • It causes Rift Valley Fever (RVF), an arthropod-borne, acute fever-viral disease primarily of sheep, goats, cattle can also affect humans. Mainly a disease of sheep ABORTION • RVF in Africa causes abortions in sheep, cattle and goats high mortalities in lambs and generalized disease in man. RVF- Virus cont… • Clinical sign: Normally victims are +/- symptoms or mild illness with fever, headache, myalgia and liver abnormalities. • Few cases (< 2%) illness progress to Hemorrhagic fever syndrome, Meningoencephalitis, or affecting the eye. • Ill patients experience fever, generalized weakness, back pain, dizziness, and weight loss at onset of the illness. Patients recover within 2–7 days after onset. • Appr.1% of sufferers die of the disease • Rift Valley fever was one of more than a dozen agents that the United States researched as potential biological weapons before suspended its biological weapons program Yellow Fever Virus Flaviviridae Family: • A 40 to 50 nm enveloped RNA virus • Causative agent of Yellow fever ( an acute viral hemorrhagic disease). • Transmission: Bite of female mosquitoes ( Aedes aegypti, and other species) Found in tropical and subtropical in (South America and Africa) not in Asia. • The hosts of the virus are primates and several species of mosquito. • The origin of the disease likely to be Africa, from where it was introduced to South America during slave trade in the 16th century. • Since 17th century, major epidemics recorded in Americas, Africa & Europe. In 19th century yellow fever was one of the most dangerous infectious diseases Yellow Fever Virus cont…. Signs: • I. Period : 3 - 6 days • Most cases present with mild fever, headache, chills, back pain, anorexia, nausea and vomiting. • The infection lasts only three to four days. 15% of cases enter a second, toxic phase of the disease with recurring fever, accompanied by jaundice due to liver damage, and abdominal pain. • Bleeding in mouth, eyes & GIT can cause vomitus containing blood (giving the name black vomit). Yellow Fever Virus…. • Toxic phase is fatal in approximately 20% of cases, making the overall fatality rate for the disease 3% • Surviving the infection causes life-long immunity normally no permanent organ damage • No therapy is known so far, vaccination programs are, along with reduction of mosquito vectors population, in affected areas. • Since the 1980s, the number of cases of yellow fever has been increasing, making it a reemerging disease. Dengue Virus • Dengue virus (DENV) one of four serotypes is the causative agent of dengue fever. • A mosquito-borne single positive-stranded RNA virus of the family Flaviviridae; genus Flavivirus. • All four serotypes can cause the full spectrum of disease Dengue Virus cont…. • Dengue fever ( breakbone fever) • Is an acute febrile infectious disease caused by the dengue virus. • Symptoms include headache, a characteristic skin rash, muscle & joint pains; in small proportion the disease progresses to life-threatening complications ie: • Dengue hemorrhagic fever (which may lead to severe hemorrhage) and dengue shock syndrome • So a very low blood pressure can cause organ dysfunction). •Transmission: Mosquitoes Aedes aegypti, and rarely Aedes albopictus. •The virus has four different serotypes, an infection with oneserotype gives lifelong immunity to that type, but short-term immunity to others. •Currently no available vaccine, •Measures to reduce the habitat , mosquitoes population & limiting exposure to bites, are useful to decrease the incidence of dengue. Treatment: Currently no approved vaccines for the dengue virus For Mild or moderate dengue disease: •Treatment is supportive, using either oral or intravenous rehydration , For severe cases: •Intravenous fluids and blood transfusions •The rate of infection has increased dramatically over the last 50 years, with around 50–100 million people being infected yearly. •Is a global disease currently is endemic in more than 110 countries. • Early descriptions of the condition is from 1779, and its viral cause and the transmission were elucidated in the early 20th century. Arthropod-borne viruses • Diagnosis • Serology: Useful in diagnosis of arboviral infections. • Culture: – Some cell lines are used, including mosquito cell lines. But , rarely carried out as pathogens are group 3 or 4. • Direct detection tests: - Detection of antigen and nucleic acids are done but there are safety issues. Prevention(General) • Surveillance :- Of disease and vector populations • Control of vector: - Pesticides, elimination of breeding grounds. • Personal protection: - Screening of houses, bed nets, insect repellants. • Vaccination - Available for a number of arboviral infections e.g. Yellow fever, Japanese encephalitis, Russian tick borne encephalitis