biology

Rift Valley fever

Rift Valley 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 Rift Valley fever rather than just read about it. In short: Rift Valley fever (RVF) is a viral disease of humans and livestock that can cause mild to severe symptoms. The mild symptoms may include: fever, muscle pains, and headaches which often last for up to a week.

Key takeaways

Rift Valley 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 Rift Valley fever to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Rift Valley fever from memory before moving on to harder problems.

Reference excerpt

Rift Valley fever (RVF) is a viral disease of humans and livestock that can cause mild to severe symptoms. The mild symptoms may include: fever, muscle pains, and headaches which often last for up to a week. The severe symptoms may include: loss of sight beginning three weeks after the infection, infections of the brain causing severe headaches and confusion, and bleeding together with liver problems which may occur within the first few days. Those who have bleeding have a chance of death as high as 50%. The disease is caused by the RVF virus. It is spread by either touching infected animal blood, breathing in the air around an infected animal being butchered, drinking raw milk from an infected animal, or the bite of infected mosquitoes. Animals like cows, sheep, goats, and camels may be affected. In these animals it is spread mostly by mosquitoes. It does not appear that one person can infect another. The disease is diagnosed by finding antibodies against the virus or the virus itself in the blood. Prevention of the disease in humans is accomplished by vaccinating animals against the disease. This must be done before an outbreak occurs because if it is done during an outbreak it may worsen the situation. Additional preventive measures include avoiding contact with infected animal blood or tissues, safe handling of animal products, and protection against mosquito bites. Stopping the movement of animals during an outbreak may also be useful, as may decreasing mosquito numbers and avoiding their bites. A human vaccine has been developed, but it is not licensed or commercially available. There is no specific treatment and medical efforts are supportive. Outbreaks of the disease have only occurred in Africa and Arabia. Outbreaks usually occur during periods of increased rain which increases the number of mosquitoes. Outbreaks typically occur during years of unusually heavy rainfall and flooding, which increase mosquito hatching and transmission.The disease was first reported among livestock in Rift Valley of Kenya in the early 1900s, and the virus was first isolated in 1931.

Signs and symptoms In humans, the virus can cause several syndromes. Usually, they have either no symptoms or only a mild illness with fever, headache, muscle pains, and liver abnormalities. In a small percentage of cases (< 2%), the illness can progress to hemorrhagic fever syndrome, meningoencephalitis (inflammation of the brain and tissues lining the brain), or affect the eye. Patients who become ill usually experience fever, generalised weakness, back pain, dizziness, and weight loss at the onset of the illness. Typically, people recover within two to seven days after onset. About 1% of people with the disease die of it. In livestock, the fatality level is significantly higher. Pregnant livestock infected with RVF abort virtually 100% of foetuses. In livestock, outbreaks of RVF are often first recognized by a wave of unexplained abortions. Other signs in livestock include vomiting and diarrhea, respiratory disease, fever, lethargy, anorexia, and sudden death in young animals.

Cause

Virology

The virus belongs to the Bunyaviricetes class. This is a class of enveloped negative single-stranded RNA viruses. All bunyaviruses have an outer lipid envelope with two glycoproteins—G(N) and G(C)—required for cell entry. They deliver their genome into the host-cell cytoplasm via endocytosis of prepackaged virions . The virus' G(C) protein has a class II membrane fusion protein architecture similar to that found in flaviviruses and alphaviruses. This structural similarity suggests that there may be a common origin for these viral families. The virus' 11.5 kb tripartite genome is composed of single-stranded RNA. As a Phlebovirus, it has an ambisense genome. Its L and M segments are negative-sense, but its S segment is ambisense. These three genome segments code for six major proteins: L protein (viral polymerase), the two glycoproteins G(N) and G(C), the nucleocapsid N protein, and the nonstructural NSs and NSm proteins.

Transmission

The virus is transmitted through mosquito vectors, as well as through contact with the tissue of infected animals. Two species—Culex tritaeniorhynchus and Aedes vexans—are known to transmit the virus. Other potential vectors include Aedes caspius, Aedes mcintosh, Aedes ochraceus, Culex pipiens, Culex antennatus, Culex perexiguus, Culex zombaensis and Culex quinquefasciatus. Contact with infected tissue is considered to be the main source of human infections. The virus has been isolated from two bat species: the Peter's epauletted fruit bat (Micropteropus pusillus) and the aba roundleaf bat (Hipposideros abae), which are believed to be reservoirs for the virus.

Pathogenesis Although many components encoded by RVFV's RNA play an important role in the virus' pathology, the nonstructural protein encoded on the S segment (NSs) is the only component that has been found to directly affect the host. NSs is hostile and combative against the host interferon (IFNs) antiviral response. IFNs are essential for the immune system to fight off viral infections in a host. This inhibitory mechanism is believed to be due to several reasons, the first being, competitive inhibition of the formation of the transcription factor. On this transcription factor, NSs interacts with and binds to a subunit that is needed for RNA polymerase I and II. This interaction cause competitive inhibition with another transcription factor component and prevents the assembly process of the transcription factor complex, which results in the suppression of the host antiviral response. Transcription suppression is believed to be another mechanism of this inhibitory process. This occurs when an area of NSs interacts with and binds to the host's protein, SAP30 and forms a complex. This complex causes histone acetylation to regress, which is needed for transcriptional activation of the IFN promoter. This causes IFN expression to be obstructed. Lastly, NSs has also been known to affect regular activity of double-stranded RNA-dependent protein kinase R. This protein is involved in cellular antiviral responses in the host. When RVFV can enter the host's DNA, NSs forms a filamentous structure in the nucleus. This allows the virus to interact with specific areas of the host's DNA that relates to segregation defects and induction of chromosome continuity. This increases host infectivity and decreases the host's antiviral response.

… excerpt ends here. Continue reading the full article.

Illustrations

Rift Valley fever: Distribution of Rift Valley fever in Africa: Blue, countries with endemic disease and substantial outbreaks of RVF; green, countries known to have some cases, periodic isolation of virus, or serologic evidence of RVF — Distribution of Rift Valley fever in Africa: Blue, countries with endemic disease and substantial outbreaks of RVF; green, countries known to have some cases, periodic isolation of virus, or serologic evidence of RVF

Worked examples

Example 1 — a first encounter with Rift Valley fever

Start with the simplest possible case. Write down what Rift Valley 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 Rift Valley 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 Rift Valley 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 Rift Valley fever

In research: Rift Valley 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 Rift Valley 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: Rift Valley fever is common in secondary-school and first-year university syllabi. It links to neighbouring topics Arthropod-borne viral fevers and viral haemorrhagic fevers, Biological agents, Biological anti-agriculture weapons, so understanding it makes those chapters shorter.
In everyday life: Look for Rift Valley 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.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Rift Valley fever in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Rift Valley 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 Rift Valley fever out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Rift Valley fever in simple terms?

Why does Rift Valley 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 Rift Valley 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 Rift Valley fever.