LASSA FEVER - Key facts, symptoms and prevention

   Key facts

• Lassa fever is an acute viral haemorrhagic illness of 2-21 days duration that occurs in West Africa.
• The Lassa virus is transmitted to humans via contact with food or household items contaminated with rodent urine or faeces.
• Person-to-person infections and laboratory transmission can also occur, particularly in hospitals lacking adequate infection prevention and control measures.
• Lassa fever is known to be endemic in Benin, Ghana, Guinea, Liberia, Mali, Sierra Leone, and Nigeria, but probably exists in other West African countries as well.
• The overall case-fatality rate is 1%. Observed case-fatality rate among patients hospitalized with severe cases of Lassa fever is 15%.
• Early supportive care with rehydration and symptomatic treatment improves survival.                                          

Lassa fever or Lassa hemorrhagic fever (LHF) is an acute viral hemorrhagic fever caused by the Lassa virus and first described in 1969 in the town of Lassa, in Borno State, Nigeria. Lassa fever is a member of the arenaviridae virus family. Similar to Ebola, clinical cases of the disease had been known for over a decade but had not been connected with a viral pathogen. The infection is endemic in West African countries, and causes 300,000–500,000 cases annually, with approximately 5,000 deaths. 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. The primary animal host of the Lassa virus is the Natal Multimammate Mouse (Mastomys natalensis), an animal indigenous to most of Sub-Saharan Africa. The virus is probably transmitted by contact with the feces or urine of animals accessing grain stores in residences. 

Lassa fever is a viral hemorrhagic fever in West Africa. Studies show up to half a million cases of Lassa fever per year in West Africa, with about 5,000 resulting in death. Results Lassa virus was detected in 25 of 60 (42%) patients in northern and central Edo. The Lassa Virus affects adults and children alike; no matter your age you can be at risk for Lassa.

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 one third 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. The other symptoms arising from the affected organs are:

·         Gastrointestinal tract

·         Nausea

·         Vomiting (bloody)

·         Diarrhea (bloody)

·         Stomach ache

·         Constipation

·        (difficulty swallowing)

·         Hepatitis

·         Cardiovascular system

·         Pericarditis

·         Hypertension

·         Hypotension

·         Respiratory tract

·         Cough

·         Chest pain

·         Dyspnoea

·         Pharyngitis

·         Nervous system

·         Encephalitis

·         Meningitis

·         Unilateral or bilateral hearing deficit

·         Seizures

Clinically, Lassa fever infections are difficult to distinguish from other viral hemorrhagic fevers such as Ebola and Marburg, and from more common febrile illnesses such as malaria.

Diagnosis 

There is a range of laboratory investigations that are performed to diagnose the disease and assess its course and complications. ELISA test for antigen and IgM antibodies gives 88% sensitivity and 90% specificity for the presence of the infection. Other laboratory findings in Lassa fever include lymphopenia (low white blood cell count), thrombocytopenia(low platelets), and elevated aspartate amino transferase (AST) levels in the blood. Lassa fever can also be found in cerebrospinal fluid. In West Africa, where Lassa is most prevalent, it is difficult for doctors to diagnose due to the absence of proper equipment to perform tests. In cases with abdominal pain, diagnoses in endemic countries are often made for other illnesses, such as appendicitis and intussusceptions, delaying treatment with Ribavirin.

Research has been done in the last few years by a team of specialists in order to diagnose the Lassa fever on a molecular level.

Prognosis

About 15%-20% of hospitalized Lassa fever patients will die from the illness. It is estimated that the overall mortality rate is 1%, however during epidemics mortality can climb as high as 50%. The mortality rate is greater than 80% when it occurs in pregnant women during their third trimester; fetal death also occurs in nearly all those cases. Abortion decreases the risk of death to the mother.

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.

·    In health-care settings, staff should always apply standard infection prevention and control precautions when caring for patients, regardless of their presumed diagnosis. These include basic hand hygiene, respiratory hygiene, use of personal protective equipment (to block splashes or other contact with infected materials), safe injection practices and safe burial practices.

·     Health-care workers caring for patients with suspected or confirmed Lassa fever should apply extra infection control measures to prevent contact with the patient’s blood and body fluids and contaminated surfaces or materials such as clothing and bedding. When in close contact (within 1 metre) of patients with Lassa fever, health-care workers should wear face protection (a face shield or a medical mask and goggles), a clean, non-sterile long-sleeved gown, and gloves (sterile gloves for some procedures).

·     Laboratory workers are also at risk. Samples taken from humans and animals for investigation of Lassa virus infection should be handled by trained staff and processed in suitably equipped laboratories under maximum biological containment conditions.

Treatment

There is currently no vaccine that protects against Lassa fever.

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. 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. The drug is relatively inexpensive, but the cost of the drug is still very high for many of those in 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 induce delivery for the mother to have a good chance of survival. 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 delivery, women should receive the same treatment as other Lassa fever patients.

            

COURTESY FROM: World Health Organization and Wikipedia 

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