Thursday, September 6, 2012

The Hemorrhagic Fevers


This week begins a new series on the hemorrhagic fevers. These are typically viral infections that can frequently present with symptoms of bleeding and high fever. However, bleeding is not particularly sensitive or specific for many of the hemorrhagic fevers. Indeed, many of these infections initially present with much more generic, flu-like symptoms. Nevertheless, many of these infections do share two very important features. First, many (but, not all) of the viruses causing hemorrhagic fever are zoonotic in origin, which can create difficulty in identifying the sources of outbreaks, as well as implementing effective control measures. Second, many of these infections are highly virulent and potentially associated with high mortality in outbreak settings. Two of the hemorrhagic fevers have already been covered at Infection Landscapes, namely dengue fever and yellow fever.

Viral hemorrhagic fevers are caused by RNA viruses in the following four families:

Flaviviridae: These are enveloped viruses with single-stranded RNA genomes. Those that cause hemorrhagic fever are generally arthropod-borne, and include dengue virus and yellow fever virus.

Dengue virus (cluster of black spots)

Bunyaviridae: These are enveloped viruses with single-stranded RNA genomes in three segments. Most of those that cause hemorrhagic fever are arthropod-borne, except the Hantaviruses, which are rodent-borne. These viruses include the Hantaviruses, Nairoviruses, and Phleboviruses.

Hantavirus

Filoviridae: These are enveloped viruses with single-stranded RNA genomes, further characterized by a distinctive, pleomorphic thread-like structure that can take on circular, branched, or coiled shapes. These viruses cause severe infections in humans, while the natural reservoir is probably fruit bats. These viruses are transmitted zoonotically and nosocomially.

Ebolavirus

Arenaviridae: These are enveloped viruses with single-stranded RNA genomes in two segments. Those that cause hemorrhagic fevers are generally rodent-borne, and include Lassa virus, Machupo virus, Junin virus, Sabia virus, and Guanarito virus.

Lassa virus

We have already covered the major hemorrhagic fevers in the Flaviridae family, so these will not be revisited in this series. However, we will cover all the major viruses that cause hemorrhagic fevers in the remaining three families. Next time, we will begin with the Bunyaviridae family, and with the hantaviruses in particular.

5 comments:

  1. I was confused by the graph depicted in the posting that one finds after following the dengue fever link. The number of infections of dengue fever per year is believed to be between 50 and 100 million cases per year. However, in the graph it simply shows 968,564 for the last time interval, with number of countries labeled, vertically, to the right. Is this simply the average number of cases per country per year?

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  2. Since I have just finished reading a chapter in Ebola, I wanted to add to the Filoviridae family that causes hemorrhagic fevers.
    Marburg virus and Ebola virus are the only two species identified so far in this classification. The Ebola virus has five subdivisions. The host is thought to be fruit bats. It was discovered that not only does Ebola affects humans, but it can also affects primates (monkeys, apes, Gorillas). Transmission can spread from the primates to humans. The common timeframe for the onset of symptoms are 8-10 days; however, it can take as long as 21 days and symptoms can appear as early as 2 days.
    Diagnosis is very difficult based on symptoms alone, as many diseases have similar symptoms. Laboratory tests are normally used to confirm diagnosis, either by ELISA, PCR or virus isolation.
    There are no special medications or vaccines for Ebola virus. Supportive therapy is treatment of choice.
    Prevention is done by isolation of infected persons and wearing personal protective equipment, such as gowns, gloves, masks, eyewear, etc.
    It is important to know that currently there is an outbreak of Ebola going on in Africa (Guinea, Liberia, and Sierra Leone). In Guinea, as of 7/6/14, there are 408 suspected and confirmed cases, per of which 307 have died. OF the 408, 294 cases were confirmed by laboratory analysis. This goes to show the severity (high virulence) of the disease.
    Reference: http://www.cdc.gov/vhf/ebola/ and http://www.cdc.gov/vhf/ebola/outbreaks/guinea/index.html

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    1. Both Marburg and Ebola virus are similar and have caused dramatic outbreaks in the early 2000s but what preventative measures have been taken in decreasing the rapid onset of this virus that cannot be applied to the Ebola today?

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  3. What fascinates me about this blog is how hemorrhagic fever, is an illnesses caused a group of four families of viruses that may be transmitted zoonotically or nosocomially. These four families are also responsible for causing Ebola, Junin virus, Lassa fever, and Sabia viruses, to name a few. Symptoms such as high fever, damage blood vessels (bleeding), and preventing the body from regulating itself are commonly shared amongst these viruses which may cause difficulty in identifying what virus a person has without confirming it with laboratory testing.

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  4. The CDC had some really interesting info about the transmission dynamics of hemorrhagic fevers. Apparently the first outbreaks of Marburg (in Germany and Yugoslavia) occurred occurred when laboratory workers handled imported monkeys infected with Marburg virus. It reminded me a lot about HIV/AIDS originated, although there are some differences (Marburg originated in East Africa, HIV/AIDS in Central and West). It was also interesting to learn that Marburg is classified as biosafety level 4 and that the fatality rate can be as high as 88%.

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