deck_4983975 Flashcards
Describe the structure of Flaviviridae?
small, enveloped, nonsegmented,(+) strand RNA virus
What are the three genera of Flaviviridae?
-Flaviviruses-Pestiviruses-Hep C virus
What are some important subtypes of Flaviviruses?
-Dengue virus-Yellow fever virus
How do Flaviviridaes enter cells?
pH-dependent endocytosis
Describe the replication process of Flaviviridae (and all + strand RNA viruses).
The genomic RNA has a 5’-cap (like host mRNAs) and is translated by host ribosomes to generate a single polyprotein, which is then cleaved by a combination of viral (cis-cleavage) and host (trans-cleavage)proteases.Cleavage of polyprotein generates the viral RNA-dependent RNA polymerase which replicates the genomic RNA.Structural proteins (capsid and envelope glycoproteins), which are also derived from the polyprotein, assemble genomic RNA into virions which “bud” into the endoplasmic reticulum or Golgi and enveloped viruses released from cells following transport to the cell surface.
T or F. All Flaviviridae are transported via insect vectors.
T. They are the most important group of arboviruses (arthropod-borne viruses) in terms of disease causation.
What is the disease course of Flaviviridaes?
-initial replication at site of infection (endothelium or epithelial cells)-next, replicates in macrophages, spleen or lymph nodes- aka primary viremia (3-7 days post exposure)
How does most Flaviviridae disease progress after primary viremia?
most don’t progress, so the result is a mild systemic disease
However, some Flaviviridae infections can progress. What happens?
If infection is not controlled by immune response, then secondary viremia ensues.Secondary viremia results in severe systemic disease (e.g. hemorrhagic fever/shock syndrome).
Where is Dengue fever common?
Primarily in South America, Southeast Asia, and Africa.Most cases of dengue in the U.S. have been acquired abroad.
How does classical dengue fever present?
self-limited-high fever (sustained up to 6-7 days)-headache-retrolobullar pain-lumbosacral aching-conjunctival congestion-facial flushingabout 2-7 day after initiationThe initial symptoms are followed by generalized myalgia with increasing severity of muscle and joint pain. (Dengue fever is sometimes called “bonebreak fever” due to the severity of the bone pain)
Are there any symptoms present with CDF in the first two days?
A mottled rash may appear on the first or second day and often patients complain of a metallic taste in their mouths.
Lab findings of CDF?
-thrombocytopenia (less than 100K/ul)
What is DHF characterized by?
diffuse capillary leakage of plasma and a hemorrhagic diathesis.
What symptoms signal the development of DHF?
-Abdominal pain in conjunction with restlessness-change in mental status-hypothermia-drop in the platelet count
If left untreated, dengue hemorrhagic fever most likely progresses to what?
dengue shock syndrome.Increased vascular permeability results in:hemoconcentration, decreased effective blood volume, tissue hypoxia, lactic acidosis, and shock.
What are some common signs that dengue shock syndrome is developing?
-abdominal pain,-vomiting, and -restlessness. Patients also may have symptoms related to circulatory failure
In >90% of the cases of fatal DHF, there is evidence for that the person had been infected previously with at least one heterologous dengue serotype. What does this indicate?
Indicates that an immune-mediated pathology initiates the events that cause the hemorrhagic syndrome
Diagnosis of DHF?
-fever-hemorrhagic manifestations (hemoconcentration, thrombocytopenia, positive tourniquet test)-circulatory failure (hypoproteinemia, effusions)-hepatomegalyFor, crab, harry, and hermione
Because the signs and symptoms of dengue fever are nonspecific, and symptoms can be easily confused with those of other diseases such as malaria, leptospirosis and typhoid fever, laboratory confirmation of dengue infection is important. Like what?
1) Serodiagnosis is made on the basis of a >4-fold rise in antibody titer in paired IgG or IgM specimens.o Other diagnostic methods include: Culture of virus from serum (or autopsy tissue) Detection of viral genome sequences by RT-PCR
Where is yellow fever common?
South and Central America, and in Africa.
What are the three transmission cycles of yellow fever virus?
jungle (sylvatic), intermediate (savannah), and urban
Describe the jungle cycle.
The jungle (sylvatic) cycle involves transmission of the virus between primates andmosquito species found in the forest canopy. The virus is transmitted by mosquitoes from monkeys to humans
Describe the intermediate cycle.
Involves transmission of virus from mosquitoes to humans living or working in jungle border areas. In this cycle, the virus can be transmitted from monkey to human or from human to human via mosquitoes.
