Hemorrhagic fever with renal syndrome pathophysiology
|
Hemorrhagic fever with renal syndrome Microchapters |
|
Differentiating Hemorrhagic fever with renal syndrome from other Diseases |
|---|
|
Diagnosis |
|
Treatment |
|
Case Studies |
|
Hemorrhagic fever with renal syndrome pathophysiology On the Web |
|
American Roentgen Ray Society Images of Hemorrhagic fever with renal syndrome pathophysiology |
|
FDA on Hemorrhagic fever with renal syndrome pathophysiology |
|
Hemorrhagic fever with renal syndrome pathophysiology in the news |
|
Blogs on Hemorrhagic fever with renal syndrome pathophysiology |
|
Directions to Hospitals Treating Hemorrhagic fever with renal syndrome |
|
Risk calculators and risk factors for Hemorrhagic fever with renal syndrome pathophysiology |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Pathophysiology
VHFs are caused by viruses of four distinct families: arenaviruses, filoviruses, bunyaviruses, and flaviviruses. Each of these families share a number of features:
- They are all RNA viruses, and all are covered, or enveloped, in a fatty (lipid) coating.
- Their survival is dependent on an animal or insect host, called the natural reservoir.
- The viruses are geographically restricted to the areas where their host species live.
- Humans are not the natural reservoir for any of these viruses. Humans are infected when they come into contact with infected hosts. However, with some viruses, after the accidental transmission from the host, humans can transmit the virus to one another.
- Human cases or outbreaks of hemorrhagic fevers caused by these viruses occur sporadically and irregularly. The occurrence of outbreaks cannot be easily predicted.
- With a few noteworthy exceptions, there is no cure or established drug treatment for VHFs.
- In rare cases, other viral and bacterial infections can cause a hemorrhagic fever; scrub typhus is a good example.
Viruses associated with most VHFs are zoonotic. This means that these viruses naturally reside in an animal reservoir host or arthropod vector. They are totally dependent on their hosts for replication and overall survival. For the most part, rodents and arthropods are the main reservoirs for viruses causing VHFs. The multimammate rat, cotton rat, deer mouse, house mouse, and other field rodents are examples of reservoir hosts. Arthropod ticks and mosquitoes serve as vectors for some of the illnesses. However, the hosts of some viruses remain unknown -- Ebola and Marburg viruses are well-known examples.
Transmission
Viruses causing hemorrhagic fever are initially transmitted to humans when the activities of infected reservoir hosts or vectors and humans overlap. The viruses carried in rodent reservoirs are transmitted when humans have contact with urine, fecal matter, saliva, or other body excretions from infected rodents. The viruses associated with arthropod vectors are spread most often when the vector mosquito or tick bites a human, or when a human crushes a tick. However, some of these vectors may spread virus to animals, livestock, for example. Humans then become infected when they care for or slaughter the animals.
Some viruses that cause hemorrhagic fever can spread from one person to another, once an initial person has become infected. Ebola, Marburg, Lassa and Crimean-Congo hemorrhagic fever viruses are examples. This type of secondary transmission of the virus can occur directly, through close contact with infected people or their body fluids. It can also occur indirectly, through contact with objects contaminated with infected body fluids. For example, contaminated syringes and needles have played an important role in spreading infection in outbreaks of Ebola hemorrhagic fever and Lassa fever.
The risk for person-to-person transmission of hemorrhagic fever viruses is greatest during the latter stages of illness when virus loads are highest; latter stages of illness are characterized by vomiting, diarrhea, shock, and, in less than half of infected patients, hemorrhage. No VHF infection has been reported in persons whose contact with an infected person occurred only during the incubation period (i.e., before onset of fever). The incubation period for VHF ranges from 2 days to 3 weeks, depending on the viral agent. There are reports of Ebola virus transmission occurring within a few days after onset of fever; however, the presence of other symptoms in the source patients and the level of exposure to body fluids among secondary cases are unknown in these instances (CDC, unpublished data, 1995). In studies involving three monkeys experimentally infected with Ebola virus (Reston strain), fever and other systemic signs of illness preceded detection of infectious virus in the animals’ pharynx by 2-4 days, in the conjunctivae and on anal swabs by 5-6 days, and in the nares by 5-10 days.