Zoonosis Flashcards
Togaviridae (family)
Classified into Alphavirus and Rubivirus (rubella). Rubella virus is NOT an arbovirus, whereas alphaviruses are arboviruses
Togaviridae (family): Struture and replication scheme
The structure of Alphaviruses include an icosahedral capsid surrounded by an envelope, which covered with fine glycoprotein spikes. To differentiate it from Flaviviruses (see next section) Togaviruses are protease sensitive particles.
Togaviruses have a SSRNA (+) polarity genome which code for 4-5 viral proteins. Viral multiplication occurs within cytoplasm and acquire their envelop by budding at cell membranes.
Replication scheme that was presented for poliovirus will suffice for all of the + stranded RNA viruses
Togaviridae (family): Clinical Manifestations: First stage
First stage of Togavirus (alphavirus) infection: Togavirus infections are all similar in initial stages.
Virus is introduced into blood via the insect bite, removed from circulating blood and multiples in RE system (esp. spleen and lymph nodes). Viremia then follows (systemic phase of disease) and is associated with minor illness, chills, fever, vomiting, pain. (1st stage symptoms)
Togaviridae (family): Clinical Manifestations: Second stage
of Togavirus (alphavirus) infection which leads to an encephalitis.
Virus crosses Blood Brain Barrier which causes lesions in all parts of brain. This is accompanied by neuronophagia (phagocytic destruction of nerve cells) and encephalomalacia (destruction of neurons + support structures). Symptoms include neck muscle rigidity, confusion, and convulsions (CNS symptoms).
Togaviridae (family): Clinical Manifestations: Eastern Equine Encephalitis (EEE)
Eastern Equine Encephalitis (EEE) causes severe human illness often with a high mortality (50-70%). It is the least prevalent of the various equine encephalitis viruses in the US. It has a higher incidence in certain geographical areas due to heavy spring rains and higher numbers of mosquitoes in a geographical region.
Experimental vaccine is available to lab workers, but horse vaccine available commercially. Reduction of EEE in horses, which is its natural host, leads to less of a chance of humans being bitten by infected mosquitoes and transfer of the virus to humans who serve as an accidental host.
Togaviridae (family): Clinical Manifestations: Western EE, Venezuelan EE
Western EE - less severe - 2-3% mortality
Venezuelan EE - primarily in horses - mild in man - 0.5% mortality
WEE infects children at a rate of 50:1( infections/clinical case). In adults the WEE rate of infection is 1000:1 infections./clinical case) and most are asymptomatic. In the case of EEE infections most fatal infections are seen in the elderly, ie >30 % fatality rate.
Chikungunya Virus
Chikungunya Virus has symptoms very similar to Dengue Fever Virus (Flavivirus, see below).
Symptoms include acute fever, joint pain, maculopapular rash on trunk and possibly limbs, headache, nausea, vomiting, conjunctivitis and retinal lesions
Arbovirus transmitted by mosquitoes
Must be distinguished from Dengue in order to determine treatment with NSAIDs and fluids. Aspirin is not recommended. If Dengue the aspirin can enhance hemorrhaging
Family: Flaviviridae: Structure
an icosahedral capsid surrounded by an envelope, which covered with fine glycoprotein spikes
have a SSRNA (+) polarity genome which code for 4-5 viral proteins. Viral multiplication occurs within cytoplasm and acquire their envelop by budding at cell membranes.
Replication scheme that was presented for poliovirus will suffice for all of the + stranded RNA viruses
Family: Flaviviridae: Clinical Manifestations: First Stage
First Stage of infection by Flaviviruses:
Infected insect bites animal or human and inject virus into blood stream. Replication in RE system and a viremia is established. Fever, chills, malaise, vomiting are possible.
Family: Flaviviridae: Clinical Manifestations: Second Stage:
Virus invades various tissues during the second stage of infection which follows first stage viremia.
For Flaviviruses that cause encephalitis (St. Louis encephalitis, Japanese encephalitis, West Nile encephalitis and many others) virus crosses the BBB and infects the CNS
Other Flaviviruses cause infections that involve multiple systems. These viruses infect the skin and endothelial cells of the blood vessels as well as various visceral organs. The two primary viruses of this type are Yellow Fever Virus and Dengue virus, the latter having 4 serotypes.
In the category of hemorrhagic fever causing viruses, yellow fever virus or dengue fever viruses cause clinical disease that can be severe. Other hemorrhagic fever viruses are part of other virus families (see Bunya, Arena and Filoviruses)
In certain situations Dengue virus can produce a less severe disease without hemorrhagic fever. In the latter case after the Dengue induced viremia, the virus infects cells of the skin, muscle and viscera.
Family: Flaviviridae: Clinical Manifestations: YELLOW FEVER VIRUS:
Yellow fever is mosquito transmitted. Clinical disease (second stage) includes a very severe, saddle back (diphasic) fever. Infection of the liver causes necrosis of liver (jaundice) and kidney. Hemorrhages occur in stomach which causes the hemoglobin of the RBCs to react with the acid of the stomach to cause a black colored product. Black vomit is characteristic of yellow fever.
Family: Flaviviridae: Clinical Manifestations: Dengue (breakbone) fever
Dengue (breakbone) fever is caused by primary infection by one of four serotypes of Dengue virus. The immunity against one serotype does not protect against the other three serotypes. Dengue is endemic in the tropics but can be imported into the US.
Dengue fever in its less severe form appears as a maculopapular rash, pain in joints and muscles. Other symptoms include ocular pain in association with a saddle back fever. Under certain scenarios the initial disease can progress to hemorrhagic fever (DHF) and even further into a shock syndrome.
Progression into a shock syndrome occurs most often, if a primary infection by serotype X (1,3,4) is followed later by a second infection by Dengue virus type 2. An antibody-antigen reaction activates monocytes with the production of cytokines which in turn causes an immunopathology . Concomitant hemoconcentration ( more frequent in females) and thrombocytopenia occur as determined by hematocrit and platelet counts. Acetaminophen is preferred over aspirin, the latter having anticoagulant properties.
Hemoconcentration should be treated aggressively by hydration therapy
Increased frequencies and increased severity of dengue has been reported in the Americas and Caribbean. Significant outbreak in Hawaii have also been reported.
Family: Flaviviridae: Clinical Manifestations: Flavivirus induced encephalitis: West Nile virus ( WNV)
West Nile virus ( WNV) first identified in the US in New York about 14 years ago, but now it has spread to almost every state. WNV can be transmitted to humans via 1) insect vector, 2) blood transfusions, and 3) organ transplants. A viremia is established and the virus crosses BBB to infect the CNS.
Birds and horses seem to be primary animal reservoirs, but dog and cats and a variety other animals have been shown to be infected.
Laboratory Diagnosis of WNV Viral isolation is not practical
Serology test acute and convalescent sera using CF antibodies
Family: Flaviviridae: Clinical Manifestations: Zika virus: Spread, associations, history
Zika virus is a Flavivirus that is transmitted by Aedes albopictus and aegypti sexual intercourse and blood transfusions
The virus infection has be linked to encephalitis and Guillain Barre syndrome (rarely).
Zika virus has been in the news over the last several years for its ability to cause congenital infections of the fetus, which can manifest a variety of symptoms in the affected individual (developing child) throughout life. Although the virus was first recognized in the late 1940s, it has not been a major concern of health officials until recently. Zika virus infections of humans appears to particularly prevalent in South America and particularly in Brazil. The 2016 summer Olympic Games was held in Rio de Janeiro and athletes, spectators and support agencies traveled to this destination from throughout the world. Without the implementation of appropriate health measures, these groups were susceptible to infection.
Family: Flaviviridae: Clinical Manifestations: Zika virus 2: prevention, SX
Zika virus is an arbovirus that is spread by mosquito vectors, primarily the Aedes aegypti and Aedes albopictus. The virus is a member of the Flaviviridae along with dengue fever and yellow fever viruses, several encephalitis viruses and West Nile virus. A key component in controlling any arbovirus infection is to reduce numbers or eliminate the insect vectors that transmit the virus. Brazil and many other countries do not routinely have processes in place to control insects. Lack of screens on windows, failure to use of insect repellants, failure to eliminate standing water as breeding grounds and lack of air conditioning (windows opened) all contribute to the high prevalence of mosquito vectors. Mosquitoes can lay their eggs in dry season which remain dormant for about 4 months. Eggs exposed to rain can than develop into larvae.
Zika virus can also be spread by sexual intercourse and blood transfusions in addition to the mosquito bites.
Symptoms include fever, rash, joint pain and inflamed eyes. Muscle pain and headache also reported. Symptoms may last for one week. Most people will have mild symptoms or be asymptomatic.
