Arboviruses Flashcards
From the name, what are arboviruses?
arthropod-borne viruses
In virology, what is a dead-end host?
In virology, a dead-end host (also known as an incidental or accidental host) is an organism that becomes infected with a virus but does not contribute to the transmission of the virus to other susceptible hosts. This means that the virus cannot complete its life cycle or spread further from the dead-end host.
The virus does not reach sufficient levels in the blood to be transmitted to other hosts.
List four families of arboviruses.
Togaviridae, Flaviviridae, Bunyaviridae, Reoviridae
Eastern Equine Encephalitis Virus
(a) Family
(b) Genus
(c) Reservoir host
(d) Vector
(e) Dead end host
(a) Family: Togaviridae
(b) Genus: Alphavirus
(c) Reservoir host: birds
(d) Vector: mosquitoes
(e) Dead end host: horses, humans
[Diagram]
Briefly discuss the structure and genome of EEEV.
➤ EEEV is an enveloped virus with an icosahedral capsid. The envelope contains glycoproteins E1 and E2, which form spikes on the virus surface. These spikes are crucial for the virus’s ability to infect host cells.
➤ EEEV has a positive-sense single stranded RNA genome.
[Diagram 1] [Diagram 2] [Diagram 3]
symptoms of EEEV infection
In humans, symptoms can include high fever, headache, vomiting, diarrhea, seizures, and behavioral changes. Severe cases can lead to encephalitis (inflammation of the brain), which can cause long-term neurological problems or even be fatal.
Further notes:
➤ The illness lasts 1 to 2 weeks, and most people recover completely when there is no central nervous system involvement.
➤ Approximately 1/3 of all people with encephalitis due to EEE die. Death usually occurs 2 to 10 days after onset of symptoms but can occur much later.
➤ Many people who recover are left with long-term physical or mental impairments, which can range from mild brain dysfunction to severe intellectual impairment, personality disorders, seizures, paralysis, and cranial nerve dysfunction.
➤ People with severe impairments often require long-term care and die within a few years.
Briefly discuss treatment of EEEV infection.
➤ No vaccine or specific antiviral treatmens for EEE are available.
➤ Over-the-counter pain relievers can be used to reduce fever and relieve some symptoms.
➤ In severe cases, patients often need to be hospitalized to receive supportive treatment, such as IV fluids, pain medication and nursing care.
Family Flaviviridae
(a) structure
(b) genome
(c) vectors
(d) genera
(a) structure: These viruses have an icosahedral geometry and are enveloped.
(b) genome: single-stranded positive-sense RNA
(c) vectors: arthropods - primarily ticks and mosquitoes
(d) genera:
➤ Flavivirus: Includes viruses like Dengue, Zika, and West Nile virus, Yellow Fever virus
➤ Hepacivirus: includes the hepatitis C virus
➤ Pestivirus: Includes viruses that infect livestock, such as bovine viral diarrhea virus.
Dengue Fever Virus
(a) Family
(b) Serotypes
(c) Main hosts
(d) Clinical manifestations
(a) Family, Genus: Flaviviridae, Flavivirus
(b) Serotypes: DEN1, DEN2, DEN3, DEN4
(c) Main hosts: non-human primates
(d) Clinical manifestations
febrille illness associated with headache, bone, muscle and joint pain, rash and leucopenia. In severe cases, symptoms manifest as dengue hemorrhagic fever (DHF): severe abdominal pain, persistent vomiting, bleeding from gums or nose, petechiae (bleeding under the skin), blood in urine, stools or vomit… [Diagram 1] [Image 1]
Further notes:
A febrile illness refers to any medical condition that causes a rise in body temperature above the normal range.
Leukopenia (also spelled leucopenia) is a condition characterized by a lower-than-normal number of white blood cells (WBCs) in the blood.
Discuss the transmission of dengue fever virus.
Dengue virus is primarily spread through the bites of infected Aedes mosquitoes, particularly Aedes aegypti and Aedes albopictus.
[Image]
In relation to dengue fever virus, explain the following statement: “Infected mosquitoes can also transmit the virus via the trans-ovarian mode.”
Trans-ovarian transmission refers to the process where an infected female mosquito passes the dengue virus to her offspring through her eggs. This means that the virus can be transmitted from one generation of mosquitoes to the next without the need for the offspring to bite an infected person.
causes of bleeding in dengue haemorrhagic syndrome
(a) thrombocytopenia: This is a condition where the platelet count drops significantly.
(b) increased vascular permeability: The dengue virus can cause the blood vessels to become more permeable.
(c) coagulopathy: This refers to a condition where the blood’s ability to clot is impaired, leading to prolonged excessive bleeding.
Dengue Fever Virus
Explain Antibody Dependent Enhancement.
This is a phenomenon whereby non-neutralizing antibodies from a previous infection can bind to a different serotype of dengue virus during a subsequent infection. Instead of neutralizing the virus, these antibodies facilitate its entry into host cells, potentially leading to more severe disease.
[Diagram 1] [Diagram 2]
Further notes:
Non-neutralizing antibodies are antibodies that can bind to viruses but do not prevent the virus from infecting cells. They mark the virus for destruction by the immune system.
Discuss the transmission of the yellow fever virus.
The virus is primarily transmitted to humans through the bite of infected Aedes and Haemagogus mosquitoes. These mosquitoes become infected by feeding on infected primates, including humans and monkeys. [Diagram]
Discuss the pathogenesis of the yellow fever virus.
➤ After entering the blood stream, YFV initially replicates in local lymph nodes and then spreads to the liver, spleen, heart, kidneys and other organs.
➤ YFV primarily targets the liver, infecting hepatocytes, leading to widespread cell death and liver dysfunction. This leads to jaundice and impaired production of clotting factors, contributing to bleeding tendencies.
➤ YFV can also cause disseminated intravascular coagulation (DIC), a condition where small blood clots form throughout the bloodstream, leading to organ damage and severe bleeding.
➤ [Diagram]
Further notes:
The relationship between liver dysfunction and DIC
◾ The liver is responsible for producing most of the body’s clotting factors. When the liver is dysfunctional, it cannot produce these factors adequately, leading to an imbalance in the coagulation system.
◾ The liver also plays a role in clearing activated clotting factors from the bloodstream. Liver dysfunction can result in the accumulation of these factors, promoting excessive clot formation.
Discuss the symptoms and treatment of the yellow fever disease.
Discuss treatment and prevention measures against Yellow Fever.
Treatment
💉 There is no cure for yellow ever.
💉 Treatment is aimed at alleviating symptoms.
Prevention measures
(a) Vaccination
💉 Prevention is achieved mainly by administration of the highly effective yellow fever vaccine which is a live, attenuated virus vaccine. It is given as a single injection, typically into the upper arm. A single dose of the vaccine provides long-lasting protection, often considered life-long.
💉 The vaccine should not be administered to children aged less than 9 months, pregnant women, people with severe allergies to egg protein and people with severe immunodeficiency.
(b) Mosquito control
This involves elimination of potential mosquito breeding sites and use of mosquito nets.
Bunyaviridae were previously classified as a family of viruses. However with reclassification, it is now part of the order ____(a)____. Some notable members include the [state the family of each (b)]:
i. Hantaviruses
ii. Crimean-Congo hemorrhagic fever virus
iii. Rift Valley fever virus
(a) Bunyavirales
(b)
i. Hantaviruses: family Hantaviridae
ii. Crimean-Congo hemorrhagic fever virus: family Narioviridae
iii. Rift Valley fever virus: family Phenuiviridae
Rift Valley Fever Virus
(a) Order
(b) Family
(c) Genus
(d) basic structure and genome
(a) Order: Bunyavirales
(b) Family: Phenuiviridae
(c) Genus: Phlebovirus
(d) Basic structure and genome: (1) spherical, enveloped, (2) segmented, single-stranded, negative-sense or ambisense RNA genome [Baltimore Group V]
Further notes:
ambisense: The genome has regions that can be read in both the positive-sense (5’ to 3’) and negative sense (3’ to 5’) directions.
Rift Valley Fever Virus
(a) Transmission modes (2)
(b) Clinical features of infection (Mild Form)
(c) Clinical features of infection (Severe Form)
(a) Transmission modes
🧪 Mosquito bites: primary mode of transmission to both animals and humans
🧪 Direct contact with blood, body fluids, or tissues of infected animals, particularly during slaughtering, butchering, or veterinary procedures.
(b) Clinical features (Mild Form)
🧪 Incubation period varies from 2 to 6 days.
🧪 Those infected either experience no detectable symptoms or develop a mild form of the disease characterized by a feverish syndrome with sudden onset of flu-like fever, muscle pain, joint pain and headache.
(c) Clinical features (Severe Form)
In a small percentage of cases, RVFV can cause severe complications such as:
🧪 Hemorrhagic fever: Bleeding disorders and liver damage
🧪 Meningoencephalitis: Inflammation of the meninges and brain, leading to headaches, stiff neck, confusion and seizures.
🧪 Ocular disease: retinal lesions that can lead to vision loss
Zika virus is transmitted by which species of mosquito?
Aedes aegypti, Aedes albopictus
[Image]
Besides mosquito bites, how else can Zika virus be transmitted? [Hint: 3 routes of transmission]
Zika virus can also be transmitted through sexual contact, from mother to fetus, and through blood transfusions.
What are the common symptoms of Zika virus infection?
Common symptoms include fever, rash, joint pain, conjunctivitis (red eyes), muscle pain, headache, pain behind the eyes, and vomiting.
What severe complications can Zika virus cause in pregnant women?
What neurological disorder has been associated with Zika virus in adults?
Zika virus has been associated with Guillain-Barré Syndrome (GBS), a disorder where the immune system attacks the nerves.
Diagnosis is based on clinical symptoms, travel history, and laboratory tests such as RT-PCR and serological tests to detect Zika-specific antibodies.
West Nile Virus
(a) Family and genus
(b) Basic structure
(c) Genome structure
(d) Transmission
(e) Hosts
(a) Family and genus: Flaviviridae, Flavivirus
(b) Basic structure: icosahedral symmetry, enveloped
(c) Genome structure: single-stranded, positive-sense RNA genome
(d) Transmission: mosquitoes, particularly those of genus Culex
(e) Hosts: Birds are the main reservoir hosts. Mosquitoes become infected when they feed on infected birds and then transmit the virus to humans and other animals. Humans are dead-end hosts.
Discuss the pathogenesis of West Nile virus.
🧪 After a mosquito bite, the virus replicates in the skin and then spreads to the lymph nodes and bloodstream.
🧪 The virus can cause viremia, leading to its spread to various organs, including the central nervous system.
🧪 In severe cases, WNV can cross the blood-brain barrier, causing menengitis or encephalitis.
[Diagram 1]
Discuss signs and symptoms of West Nile Virus infection.
🧪 Most people (about 80%) infected with WNV do not develop symptoms.
🧪 About 20% of infected individuals develop mild symptoms such as fever, headache, body aches, joint pains, vomiting, diarrhea, or rash.
🧪 A few people develop severe neurological disease, including encephalitis or menengitis. Symptoms of severe illness include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, seizures, muscle weakness and paralysis.
For each of the following viruses, state its Family and Genus:
(a) EEEV
(b) Dengue Fever virus
(c) Yellow Fever virus
(d) Rift Valley Fever virus
(e) West Nile virus
(f) Zika virus
(a) EEEV: Togaviridae, Alphavirus
(b) Dengue Fever virus: Flaviviridae, Flavivirus
(c) Yellow Fever virus: Flaviviridae, Flavivirus
(d) Rift Valley Fever virus: Phenuiviridae, Phlebovirus
(e) West Nile virus: Flaviviridae, Flavivirus
(f) Zika virus: Flaviviridae, Flavivirus
Which one of the following statements about yellow fever vaccine is true?
(a) it is recommended for all pregnant women in endemic areas
(b) it was licensed less than ten years ago
(c) it offers cross-protection against dengue
(d) it causes life-long immunity
(e) it is an inactivated sub-unit vaccine
(d) it causes life-long immunity
Which of the following is true about Crimean-Congo haemorrhagic fever virus?
(a) It does not affect domestic animals
(b) Human-to-human transmission does not occur
(c) Itis vaccine-preventable
(d) Favipravir is effective for treatment
(e) It is transmitted by ticks
(e) It is transmitted by ticks
Which of the following is true about Rift valley fever virus?
(a) Ribavirin is effective for treatment
(b) Human-to-human transmission is common
(c) Most cases are contracted through tick bites
(d) It is vaccine-preventable in humans
(e) The main route of transmission is contact with a contaminated animal tissue
(e) The main route of transmission is contact with a contaminated animal tissue
Which one of the following is used to culture dengue virus?
(a) CLED media
(b) Chocolate blood agar
(c) Monkey kidney Cells
(d) Virus transport media
(e) Thayer-Martin media
(c) Monkey kidney Cells
Which of the following is true about Crimean-Congo haemorrhagic fever virus?
(a) Favipravir is effective for treatment
(b) It is vaccine-preventable
(c) Most cases are contracted through Aedes mosquitoes
(d) It does not affect domestic animals
(e) Human-to-human transmission is common
(a) Favipravir is effective for treatment
Which one of the following is used to culture Chikungunya virus?
(a) CLED media
(b) Thayer-Martin media
(c) Chocolate blood agar
(d) Monkey kidney cells
(e) Virus transport media
(d) Monkey kidney cells
Which of the following is the main vector of yellow fever in tropical rain forest environment in Africa?
(a) Aedes aegypti
(b) Aedes albopictus
(c) Sabethes chloropterus
(d) Aedes simpsoni
(e) Aedes africanus
(e) Aedes africanus
