viral hemorrhagic fever
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What are viral hemorrhagic fevers?
Viral hemorrhagic fevers are a group of highly dangerous illnesses caused by viruses that damage the vascular system, leading to severe bleeding. Initial symptoms include fever, fatigue, muscle aches, and exhaustion.
These viruses belong to four families: Flaviviridae, Arenaviridae, Bunyaviridae, and Filoviridae. Specific animals or insects often transmit them, restricting these diseases to certain geographic areas. Examples include dengue, yellow fever, Lassa fever, and Ebola.
Transmission to humans usually occurs via contact with infected animals like rodents and insects. Avoiding contact with these hosts and controlling their populations can prevent infection. Isolation of infected individuals can also prevent the virus from spreading from person to person.
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Which viruses can cause viral hemorrhagic fevers?
Viral hemorrhagic fevers (VHFs) are a group of severe illnesses characterized by bleeding, fever, and shock. These diseases are caused by viruses from four families: Flaviviridae, Arenaviridae, Bunyaviridae, and Filoviridae.
- Flaviviruses Dengue and yellow fever viruses, often transmitted by Aedes mosquitoes, are the most common causes. While yellow fever affects the liver and causes severe bleeding, dengue induces only minor bleeding but can result in dengue shock syndrome.
- Arenaviruses are spread to humans through contact with food or soil contaminated by rodent excreta. This family of viruses causes Lassa fever, Argentine hemorrhagic fever, Bolivian hemorrhagic fever, Brazilian hemorrhagic fever, and Venezuelan hemorrhagic fever.
- Bunyaviridae includes Hantaviruses, Rift Valley fever virus, and Crimean-Congo hemorrhagic fever virus. Hantaviruses are transmitted to humans through rodent contact, while Rift Valley fever is a mosquito-borne disease. Crimean-Congo hemorrhagic fever is a tick-borne disease.
- Filoviruses such as Ebola virus and Marburg virus, are highly fatal and may also cause disease in primates. The origin of filovirus epidemics remains unclear, but scientists suspect that fruit bats may be responsible for outbreaks of Marburg disease.
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How do viral hemorrhagic fevers affect the human body?
Viral hemorrhagic fevers (VHFs) are a group of highly dangerous illnesses caused by bloodborne viruses that harm the vascular system, resulting in significant bleeding. Initial symptoms include fever, fatigue, and muscle aches.
The viruses attack cells and may suppress the immune system, which allows the virus to reproduce. Disseminated intravascular coagulation, a condition marked by blood clots and hemorrhaging, can occur. Clots concentrated in organs force capillaries to bleed into surrounding tissue. This leads to bleeding from body openings, the gastrointestinal tract, skin, and internal organs.
Some VHFs, such as dengue, induce only minor bleeding that is rarely fatal, while others, such as Ebola, can cause death in up to 90% of victims.
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What role do blood vessels play in the disease process?
In viral hemorrhagic fevers, blood vessels play a central role in the disease process. These diseases are caused by bloodborne viruses that damage the vascular system, leading to extensive bleeding internally, externally, and under the skin. Symptoms often include fever, fatigue, muscle aches, and exhaustion.
These viruses are typically transmitted to humans via animals such as rodents and insects. There are no vaccines available, and treatment is mainly supportive. Preventing infection involves avoiding contact with host species and controlling rodent and insect populations. Isolation of infected individuals can also prevent human-to-human spread through physical contact.
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Why do people with these fevers sometimes bleed or bruise easily?
Viral hemorrhagic fevers (VHFs) are a group of illnesses caused by bloodborne viruses that damage the vascular system. This damage leads to bleeding under the skin, in internal organs, and from body orifices.
Several factors contribute to the ease of bleeding and bruising:
* Vascular Damage VHFs can cause vascular damage.
* Coagulation Abnormalities Viral infections can cause abnormalities in blood clotting.
* Cytokine Release Unregulated cytokine production may lead to vascular damage and hemorrhaging.Some VHFs are highly fatal; certain Ebola strains have mortality rates of up to 90%. Isolation of infected individuals helps prevent the spread of VHFs, as transmission can occur through physical contact.
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How does the body respond to fight off a viral hemorrhagic fever?
Viral hemorrhagic fevers are a group of severe illnesses caused by various virus families that damage the vascular system, leading to bleeding. The body's response involves several complex mechanisms.
The infection typically begins with the virus entering the body through contact with an infected animal or insect. Once inside, the virus targets cells in the vascular system, such as endothelial cells, which line blood vessels. The damage to these cells leads to increased vascular permeability and impaired blood clotting. This results in both internal and external hemorrhaging, as blood leaks from the vessels.
The immune system responds by releasing cytokines, which are signaling molecules that help coordinate the immune response. However, in severe cases, this can lead to a "cytokine storm," where an excessive amount of cytokines are released, causing inflammation, shock, and organ failure.
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viral hemorrhagic fever, any of a variety of highly fatal viral diseases that are characterized by massive external or internal bleeding or bleeding into the skin. Other symptoms vary by the type of viral hemorrhagic fever but often include fever, malaise, muscle aches, vomiting, and shock. Most viral hemorrhagic fevers are geographically restricted because they are transmitted by specific animal or insect hosts (reservoirs) that occupy narrow and sometimes localized ecological niches. Viral hemorrhagic fevers are caused by viruses of four families: Flaviviridae, Arenaviridae, Bunyaviridae, and Filoviridae.
The most common viral hemorrhagic fevers are dengue and yellow fever, caused by related mosquito-borne flaviviruses, often being transmitted by Aedes mosquitoes. In the late 18th century, yellow fever epidemics in American coastal cities caused widespread panic, but the disease currently occurs only in developing countries of Africa and South America. It is the only major viral hemorrhagic fever for which an effective preventive vaccine exists and is widely used. Most cases of dengue, seen in tropical areas, are mild and influenza-like, but all four dengue viruses may produce dengue hemorrhagic fever or its severe form, dengue shock syndrome. Unlike yellow fever, which affects the liver and causes severe bleeding, dengue involves the liver only minimally and tends to induce only minor bleeding that is rarely fatal. However, if dengue shock syndrome occurs, patients may die when fluids and electrolytes in their vascular compartments shift into tissues, collapsing the blood volume and precipitating low blood pressure and shock. Dengue is unique among the fatal hemorrhagic fevers in that even severe cases can be effectively treated with simple fluid administration.
The arenaviruses are highly adapted to specific rodent hosts, which may become silently infected and excrete the virus in feces, urine, and saliva. However, when humans come into contact with food or soil contaminated by these rodent excreta, disease may result. The arenaviruses cause the diseases Lassa fever (occurring in Africa), Argentine hemorrhagic fever, Bolivian hemorrhagic fever, Brazilian hemorrhagic fever, and Venezuelan hemorrhagic fever.
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Hantaviruses, Rift Valley fever virus (genus phlebovirus), and Crimean-Congo hemorrhagic fever virus (genus nairovirus) belong to the family Bunyaviridae. The hantaviruses, like the arenaviruses, are spread to humans by rodent contact. Hantaviruses cause Korean hemorrhagic fever and hantavirus pulmonary syndrome, which is highly fatal because of accumulation of fluid in the lungs but features only minor hemorrhagic manifestations. Rift Valley fever, a mosquito-borne disease that is fatal in sheep and cattle, occurs in East and Southern Africa and the Middle East. Most people who contract Rift Valley fever survive, but a minority develop fatal hemorrhagic fevers, encephalitis, or severe eye disease. Crimean-Congo hemorrhagic fever, found in East and Southern Africa, the Middle East, and Russia, is a tickborne disease of cattle and other farm animals that is occasionally transmitted to humans.
The filoviruses, seen in Central and East Africa, include Ebola virus and Marburg virus. These are among the most highly fatal of the hemorrhagic fevers; some strains of Ebola cause death in up to 90 percent of victims. The filoviruses may also cause disease in primates. Marburg virus was discovered when it was transported with imported monkeys to Marburg, Germany, and caused a fatal outbreak. The origin of filovirus epidemics remains unclear; however, the virus has been found in the Old World fruit bat Rousettus aegypticus, which lives in areas throughout sub-Saharan Africa. Scientists suspect that these bats may be responsible for outbreaks of Marburg disease.