biology

Viral hemorrhagic fever

Viral hemorrhagic fever is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Viral hemorrhagic fever rather than just read about it. In short: Viral hemorrhagic fevers (VHFs) are a diverse group of infectious diseases characterized by fever and systemic damage to the circulatory system caused by RNA viruses. Viral hemorrhagic fevers cause symptoms ranging from mild to life-threatening, depending on the virus involved, but generally cause internal bleeding that leads to sudden onset of muscle pain, fever, and hypotension.

Key takeaways

Viral hemorrhagic fever belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Viral hemorrhagic fever to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Viral hemorrhagic fever from memory before moving on to harder problems.

Reference excerpt

Viral hemorrhagic fevers (VHFs) are a diverse group of infectious diseases characterized by fever and systemic damage to the circulatory system caused by RNA viruses. Viral hemorrhagic fevers cause symptoms ranging from mild to life-threatening, depending on the virus involved, but generally cause internal bleeding that leads to sudden onset of muscle pain, fever, and hypotension. In severe cases, it can cause life-threatening shock and bleeding from internal organs. While some VHFs are generally mild, such as nephropathia epidemica (caused by two species of hantavirus), many are debilitating or lethal without treatment. Outbreaks of VHFs tend to have high case fatality rates and disproportionately affect communities with poor health infrastructure. Therefore, the emergence of VHFs is a growing public health concern. VHFs are often zoonoses, meaning they can be transmitted from wild animals to human populations; for instance, the Lassa arenavirus is spread by mice. Viral hemorrhagic fevers are caused by members of seven families of single-stranded RNA viruses: Arenaviridae, Filoviridae, Flaviviridae, Nairoviridae, Phenuiviridae, Hantaviridae and Peribunyaviridae.

Symptoms Signs and symptoms of most or all viral hemorrhagic fevers can be divided into "wet" and "dry" symptoms. The disease typically progresses from dry symptoms to wet symptoms.

Dry symptoms Headache Malaise (a general feeling of sickness) Fever (high body temperature) Hypotension (low blood pressure) Flushing (redness) of the face and chest Myalgia (muscle pain)

Wet symptoms Circulatory shock Diarrhea (feces which resemble more liquid than solid) Hemorrhage (bleeding) and sometimes bleeding diathesis (a person loses more blood than usual from an injury – for example, getting only a little cut, and losing a lot of blood) Petechiae (small red or purple spots) Swelling caused by edema The severity of symptoms varies with both individual immune competence and the type of virus. The "VHF syndrome" causes bleeding diathesis, capillary leak, and circulatory shock. It happens to most people who have Filoviridae infections (such as Ebola virus or Marburg virus), Crimean–Congo hemorrhagic fever (CCHF), or the South American hemorrhagic fevers (which are caused by Arenaviridae). VHF syndrome only happens to a small minority of people who have dengue fever or Rift Valley fever.

Causes All known viruses causing hemorrhagic fever are part of the Orthornavirae kingdom.

The order Hareavirales includes the families Arenaviridae, Nairoviridae and Phenuiviridae The family Arenaviridae includes the viruses responsible for Lassa fever (Lassa virus), Lujo virus, Argentine (Junin virus), Bolivian (Machupo virus), Brazilian (Sabiá virus), Chapare hemorrhagic fever (Chapare virus), Venezuelan (Guanarito virus) and Whitewater Arroyo virus hemorrhagic fevers. The family Nairoviridae includes the Crimean-Congo hemorrhagic fever (CCHF) virus from the genus Orthonairovirus. The family Phenuiviridae includes the Rift Valley fever (RVF) virus from the genus Phlebovirus The order Elliovirales includes the families Peribunyaviridae and Hantaviridae. The family Hantaviridae includes the causative agents of Hantavirus hemorrhagic fever with renal syndrome (HV-HFRS). The family Peribunyaviridae includes the Ngari virus. The order Mononegavirales contains the family Filoviridae. The family Filoviridae includes Ebola virus and Marburg virus. The order Amarillovirales includes the family Flaviviridae. The family Flaviviridae includes dengue, yellow fever, and two viruses in the tick-borne encephalitis group that cause VHF: Omsk hemorrhagic fever virus and Kyasanur Forest disease virus. In September 2012 scientists reported the discovery of a member of the Rhabdoviridae family potentially causing hemorrhagic fever. In a 2009 outbreak of acute hemorrhagic fever they discovered a new viral genome in one of the three people affected. The virus was named Bas-Congo virus. The virus could not be isolated and has since then not been detected in any other patient, raising doubts on whether the virus is actually the causative agent of a disease.

Pathophysiology Different hemorrhagic fever viruses act on the body differently, resulting in variable symptoms. In most VHFs, several mechanisms likely contribute to symptoms, including liver damage, disseminated intravascular coagulation (DIC), and bone marrow dysfunction. In DIC, small blood clots form in blood vessels throughout the body, removing platelets necessary for clotting from the bloodstream and reducing clotting ability. DIC is thought to cause bleeding in Rift Valley, Marburg, and Ebola fevers. For filoviral hemorrhagic fevers, there are four general mechanisms of pathogenesis. The first mechanism is the dissemination of the virus due to suppressed responses by macrophages and dendritic cell (antigen-presenting cells). The second mechanism is prevention of antigen specific immune response. The third mechanism is apoptosis of lymphocytes. The fourth mechanism is when infected macrophages interact with toxic cytokines, leading to diapedesis and coagulation deficiency. From the vascular perspective, the virus will infect vascular endothelial cells, leading to the reorganization of the VE-cadherin catenin complex (a protein important in cell adhesion). This reorganization creates intercellular gaps in endothelial cells. The gaps lead to increased endothelial permeability and allow blood to escape from the vascular circulatory system. The reasons for variation among patients infected with the same virus are unknown but stem from a complex system of virus-host interactions. Dengue fever becomes more virulent during a second infection by means of antibody-dependent enhancement. After the first infection, macrophages display antibodies on their cell membranes specific to the dengue virus. By attaching to these antibodies, dengue viruses from a second infection are better able to infect the macrophages, thus reducing the immune system's ability to fight off infection.

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Illustrations

Worked examples

Example 1 — a first encounter with Viral hemorrhagic fever

Start with the simplest possible case. Write down what Viral hemorrhagic fever claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Viral hemorrhagic fever before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Viral hemorrhagic fever ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Viral hemorrhagic fever

In research: Viral hemorrhagic fever appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Viral hemorrhagic fever in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Viral hemorrhagic fever is common in secondary-school and first-year university syllabi. It links to neighbouring topics Animal viral diseases, Hemorrhagic fevers, Tropical diseases, so understanding it makes those chapters shorter.
In everyday life: Look for Viral hemorrhagic fever outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Viral hemorrhagic fever in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Viral hemorrhagic fever means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Viral hemorrhagic fever out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Viral hemorrhagic fever in simple terms?

Why does Viral hemorrhagic fever matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Viral hemorrhagic fever?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Viral hemorrhagic fever.