Viral Hemorrhagic Fevers
Viral hemorrhagic fevers are caused by four families of viruses.
- Arenaviridae (Lassa, Lujo, Guanarito, Machupo, Junin, Sabia, and Chapare viruses)
- Bunyaviridae (Rift Valley, Crimean-Congo, Hantaan)
- Filoviridae (Marburg, Ebola)
- Flaviviridae (Yellow, Dengue, Kyasanur Forest, Alkhurma, Omsk HFs)
The best known of viral hemorrhagic fevers is the Ebola virus. First recognized in Zaire in 1976, the virus has been linked to at least 20 outbreaks in Africa. Earlier outbreaks in central Africa, with the Zaire species of the Ebola virus, had very high mortality rates (80%-90%). However, the most recent outbreaks with the same virus in Western Africa have had lower mortality rates (approximately 50%). The largest outbreak of the Ebola virus in history began in 2014, located primarily in the Western African countries of Sierra Leone, Guinea, and Liberia. In June 2016, the WHO reported that there were 28,616 confirmed or probable cases and 11,323 deaths in those three countries, including 500 healthcare workers. The World Health Organization declared Sierra Leone Ebola-free in November 2015, and in June 2016, the WHO declared Liberia and Guinea Ebola-free. However, there could be more cases identified, and there will be continued surveillance. During the outbreak, there were four cases diagnosed in the United States: One in a Liberian man who was visiting in Texas, two nurses who took care of that man, and one physician who had just returned from treating Ebola patients in Guinea.
These viruses are each characterized by an acute generalized illness that includes feeling quite ill (flulike illness) with profound exhaustion and is sometimes associated with internal bleeding. The West African Ebola outbreak was characterized more by severe gastrointestinal illness with vomiting and large-volume diarrhea. This leads to severe volume depletion, metabolic abnormalities, and hypovolemic shock. Other symptoms include fever, body and joint pain, profound and progressive weakness, loss of appetite, sore throat, headache, and fatigue.
Most agents are highly infectious via the aerosol route, and most are stable as respiratory aerosols. Thus, they possess characteristics that may make them attractive for use by terrorists.
However, the Ebola virus has not been demonstrated to be contagious person-to-person through an aerosol route. It is spread through direct contact with the blood or other body fluids of an infected person, including a corpse.
The agents that produce viral hemorrhagic fever are all simple RNA viruses. They are able to survive in blood for long periods, which means they can infect people who are around animals slaughtered domestically. These viruses are linked to the rodents, bats, or insects that help to spread them, which helps in searching for a diagnosis.
The specific viral hemorrhagic fever manifestations that develop depend on many factors such as the strength of the virus, its strain, and the route of exposure.
Signs and Symptoms
The incubation period (time from exposure to onset of symptoms) ranges from two to 21 days. Although initially, a classic symptom of all of the viral hemorrhagic fevers is bleeding, it actually only occurred in about 20% of Ebola patients in the most recent outbreak. Humans are not infectious until symptoms develop.
The incubation period is the time interval from infection with the virus to onset of symptoms is two to 21 days. Humans are not infectious until they develop symptoms. The first symptoms seen are fever, muscle aches, headaches, and sore throat. Patients then go on to develop vomiting and large-volume diarrhea. This leads to severe dehydration and results in impaired kidney and liver function. Some patients develop internal and external bleeding (blood in stools and oozing from the gums).
It is important for the doctor to know a person's travel history in making a diagnosis of viral hemorrhagic fever. These agents are linked tightly with their natural geographic area and the ecology of the species and vectors found in that specific locale. Victims often recall exposures to rodents (Arenavirus, Hantavirus), mosquitoes (Valley fever virus, yellow and dengue fever viruses), or even slaughtered horses (Rift Valley fever virus, Crimean-Congo virus).
Laboratory tests may be helpful. Testing of whole blood or serum includes antibody-capture enzyme-linked immunosorbent assay (ELISA), antigen-capture detection tests, and reverse transcriptase-polymerase chain reaction (RT-PCR) assay. Testing can be conducted at the CDC in Atlanta or the U.S. Army Medical Research Institute of Infectious Disease (USAMRIID) at Fort Detrick in Frederick, Md.
Treatment for viral hemorrhagic fevers is largely directed at easing the discomfort of the symptoms. Victims benefit from being placed in a hospital setting immediately. Air transport is not advised. Sedative and pain-relieving medications are helpful, but aspirin and similar drugs should not be given because of their tendency to make bleeding worse.
There has been a lot of controversy surrounding the use of IV fluids for victims. At the beginning of the outbreak, the medical community was divided on the topic. However, both the CDC and WHO recommend IV rehydration to treat patients with dehydration and bleeding problems. The improved survival in the recent outbreak was likely due to the extensive use of IV hydration. The treatment for bleeding is controversial. Generally, mild bleeding is not usually treated, but severe bleeding requires appropriate replacement therapy (blood transfusions through an IV line).
Specific treatment with ribavirin has been used and is currently under investigation as a therapy for Lassa fever, hantavirus, Crimean-Congo, and Rift Valley fever. Treatment is most effective if begun within seven days. Ribavirin has poor activity against the filoviruses and flaviviruses.
The only established and licensed virus-specific vaccine against any of these viruses is the yellow fever vaccine. It is mandatory for those traveling into areas of Africa and South America where the disease is commonly found. Current trials are underway for further vaccines and antibody therapies. There are ongoing trials of at least two Ebola vaccines.