Lassa fever is an acute viral hemorrhagic fever first described in 1969 in the town of Lassa, in Borno State, Nigeria located in the Yedseram river valley at the south end of Lake Chad.[1] Clinical cases of the disease had been known for over a decade earlier but not connected with this viral pathogen. The infection is endemic in West African countries, and causes 300-500,000 cases annually with ~5,000 deaths.[2] Outbreaks of the disease have been observed in Nigeria, Liberia, Sierra Leone, Guinea, and the Central African Republic, but it is believed that human infections also exist in Democratic Republic of the Congo, Mali, and Senegal.[citation needed] Its primary animal host is the Natal Multimammate Mouse (Mastomys natalensis), an animal indigenous to most of Sub-Saharan Africa.[3] Although the rodents are also a source of protein for peoples of these areas, the virus is probably transmitted by the contact with the feces and urine of animals accessing grain stores in residences.[3]

Genome

Lassa fever is caused by the Lassa virus, a member of the Arenaviridae family; it is an enveloped, single-stranded, bisegmented RNA virus.[2]

Replication for Lassa virus is very rapid, while also demonstrating temporal control in replication. There are two genome segments. The first step involved is making mRNA copies of the - sense genome. This ensures that there is adequate proteins, which are required for replication. The N and L proteins are made from the mRNA produced. The - sense genome then makes viral complementary RNA (vcRNA) copies of itself which are + sense. The vcRNA is a template for producing - sense progeny but mRNA is also synthesized from it. The mRNA synthesized from vcRNA translate the G (spike) proteins and Z proteins. Thus, with this temporal control, the spike proteins are produced last, making the infection further undetected by the host immune system.

Lassa virus will infect almost every tissue in the human body. It starts with the mucosa, intestine, lungs and urinary system, and then progresses to the vascular system.




Prevalence

The dissemination of the infection can be assessed by prevalence of antibodies to the virus in populations of:
Sierra Leone 8–52%
Guinea 4–55%
Nigeria approx. 21%

Like other hemorrhagic fevers, Lassa fever can be transmitted directly from one human to another. It can be contracted by an airborne route or with direct contact with infected human blood, urine, or semen. Transmission through breast milk has also been observed.


Symptoms

In 80% of cases the disease is inapparent, but in the remaining 20% it takes a complicated course. It is estimated that the virus is responsible for about 5,000 deaths annually. The fever accounts for up to ⅓ of deaths in hospitals within the affected regions and 10 to 16% of total cases.

After an incubation period of six to twenty-one days, an acute illness with multiorgan involvement develops. Non-specific symptoms include fever, facial swelling, and muscle fatigue, as well as conjunctivitis and mucosal bleeding.

Treatment

All persons suspected of Lassa fever infection should be admitted to isolation facilities and their body fluids and excreta properly disposed of.

Early and aggressive treatment using Ribavirin was pioneered by Joe McCormick in 1979. After extensive testing, it was determined that early administration is critical to success. Additionally, Ribavirin is almost twice as effective when given intravenously as when taken by mouth.[6] Ribavirin is a prodrug which appears to interfere with viral replication by inhibiting RNA-dependent nucleic acid synthesis, although the precise mechanism of action is disputed.[7] The drug is relatively inexpensive, but the cost of the drug is still very high for many of those in poverty-stricken West African states. Fluid replacement, blood transfusion and fighting hypotension are usually required. Intravenous interferon therapy has also been used.

When Lassa fever infects pregnant women late in their third trimester, it is necessary to abort the pregnancy for the mother to have a good chance of survival.[8] This is because the virus has an affinity for the placenta and other highly vascular tissues. The fetus has only a one in ten chance of survival no matter what course of action is taken; hence focus is always on saving the life of the mother. Following abortion, women should receive the same treatment as other Lassa fever patients.

Siga Technologies is developing an antiviral drug that has been shown effective in treating experimentally infected guinea pigs. In a study conducted at the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID), treatment with ST-193 once a day for 14 days resulted in significant reduction in mortality (71% of the animals survived at the low dose), whereas all untreated animals and those treated with ribavirin died within 20 days of the infection

Vectors

Lassa virus is zoonotic (transmitted from animals), in that it spreads to man from rodents, specifically multi-mammate rats (Mastomys natalensis). This is probably the most common rodent in equatorial Africa, ubiquitous in human households and eaten as a delicacy in some areas.[citation needed] In these rats infection is in a persistent asymptomatic state. The virus is shed in their excreta (urine and feces), which can be aerosolized. In fatal cases, Lassa fever is characterized by impaired or delayed cellular immunity leading to fulminant viremia.

Infection in humans typically occurs via exposure to animal excrement through the respiratory or gastrointestinal tracts. Inhalation of tiny particles of infective material (aerosol) is believed to be the most significant means of exposure. It is possible to acquire the infection through broken skin or mucous membranes that are directly exposed to infective material. Transmission from person to person has also been established, presenting a disease risk for healthcare workers. Frequency of transmission v

Prevention

Control of the Mastomys rodent population is impractical, so measures are limited to keeping rodents out of homes and food supplies, as well as maintaining effective personal hygiene. Gloves, masks, laboratory coats, and goggles are advised while in contact with an infected person.

No vaccine against Lassa fever is currently available, though development is underway. The Mozambique virus closely resembles Lassa fever, while lacking its deadly effects. This virus is being considered for possible use as a vaccine.

Researchers at the USAMRIID facility, where military biologists study infectious diseases, have a promising vaccine candidate.[4] They have developed a replication-competent vaccine against Lassa virus based on recombinant vesicular stomatitis virus vectors expressing the Lassa virus glycoprotein. After a single intramuscular injection, test primates have survived lethal challenge, while showing no clinical symptoms.[5]

Multimammate Mouse, Common African Rat, Soft-furred or African Soft-furred Rat.

Introduction

One of the commonest African rodents, this is an ideal species for the tyro breeder, being undemanding, easy to keep and (a definite plus for those keeping it in a bedroom) odour-free. Multimammate Rats are so-called because the females possess a superfluity of teats, more than any other rodent. (Multimammate = Latin, meaning literally "many-breasted".) It possesses long, soft, silky fur, hence its alternative name of Soft-furred Rat. There are about seven species (authorities disagree on the exact number), but Praomys coucha and Praomys natalensis are almost identical and, where the two ranges overlap in southern Africa, are impossible to tell apart, and usually the only way to be certain is to count the chromosomes.

The Multimammate Rat appears to be a connecting link between the true mice and rats, though it shows slightly more affinity to the rats than it does to the mice. Since no one can be quite sure about its relationship to other members of the Muridae, it has been alternatively classified at various times within the genus Mus (the true mice), Rattus (the true rats) – although it shares features of both genera, latest research shows that it is not directly related to either – and Mastomys. Indeed some sources, including the venerable Walker's Mammals of the World, still discuss the species under Mastomys, which is why this is included in parenthesis within the scientific name given at the top of this page, since the two names are currently interchangeable. It is a popular laboratory animal but only in recent years has it started to emerge on the pet market. It lacks a gall bladder and females – yes, females – possess a well-developed prostate gland. American readers should be aware that in some western states the import, transport and possession of all species of Praomys is strictly prohibited. The semi-dry terrain of certain states such as Nevada is very similar to Southern Africa and the authorities are paranoid that, in the event of their escape, there is a danger of their becoming naturalised. This would be disastrous, as not only is the Multimammate Rat a serious crop pest, but there is a possibility of feral animals forming a link between wild reservoirs of plague and man.

How can cases of viral hemorrhagic fever be prevented and controlled?


With the exception of yellow fever and Argentine hemorrhagic fever, for which vaccines have been developed, no vaccines exist that can protect against these diseases. Therefore, prevention efforts must concentrate on avoiding contact with host species. If prevention methods fail and a case of VHF does occur, efforts should focus on preventing further transmission from person to person, if the virus can be transmitted in this way.Because many of the hosts that carry hemorrhagic fever viruses are rodents, disease prevention efforts include
controlling rodent populations;
discouraging rodents from entering or living in homes or workplaces;
encouraging safe cleanup of rodent nests and droppings.

What are the symptoms of viral hemorrhagic fever illnesses?


Specific signs and symptoms vary by the type of VHF, but initial signs and symptoms often include marked fever, fatigue, dizziness, muscle aches, loss of strength, and exhaustion. Patients with severe cases of VHF often show signs of bleeding under the skin, in internal organs, or from body orifices like the mouth, eyes, or ears. However, although they may bleed from many sites around the body, patients rarely die because of blood loss. Severely ill patient cases may also show shock, nervous system malfunction, coma, delirium, and seizures. Some types of VHF are associated with renal (kidney) failure.

oyb:

perhaps this should be in health. . .