What Is Lassa Fever? Zoonotic Virus That Just Caused A Death In UK. Know Symptoms, Treatment

Lassa fever is an animal-borne, or zoonotic, acute viral illness, that is endemic in parts of West Africa. The haemorrhagic illness is caused by the Lassa virus.

Illustration of Arenavirus (or Lassa virus, LASV) particles budding from a cell. This virus mainly infects rodents, but can infect humans through exposure to infected rodent faeces or urine. (Photo: Getty Images)

New Delhi: Three cases of Lassa fever were confirmed in the United Kingdom (UK) this month, one of whom died on February 11. This marks the first time cases of Lassa fever have been reported in the UK since 2009.

The UK Health Security Agency (UKHSA) said in a statement that it is contacting the individuals who have had close contact with the cases prior to contamination of their infection. The cases are within the same family in the East of England and are linked to recent travel to West Africa. 

What Is Lassa Fever? 

Lassa fever is an animal-borne, or zoonotic, acute viral illness, that is endemic in parts of West Africa, according to the Centers for Disease Control and Prevention (CDC), the national public health agency of the United States. The haemorrhagic illness is caused by the Lassa virus, which is a member of the virus family Arenaviridae, a single-stranded RNA virus. 

Lassa fever was discovered in 1969 when two missionary nurses died in Nigeria. The first cases were confirmed in Lassa, a Nigerian town, and the virus is named after the town. 

The animal vector for Lassa virus is Mastomys natalensis, the "multimammate rat". 

The parts of West Africa in which Lassa fever is endemic include Sierra Leone, Liberia, Guinea, and Nigeria, according to the CDC. Neighbouring countries are also at risk because the animal vector for Lassa virus is distributed throughout the region. 

The first case from Mali was reported in a traveller in southern Mali in 2009, while the first cases from Ghana were reported in late 2011. 

As many as 100,000 to 300,000 infections of Lassa fever are estimated to occur annually, with approximately 5,000 deaths. Since surveillance for Lassa fever is not standardised, the estimates are crude. 

It is known that 10 to 16 per cent of people admitted annually to hospitals in some areas of Sierra Leone and Liberia have Lassa fever. This indicates the serious impact of the disease on the population of this region, the CDC notes.

How Is Lassa Fever Transmitted?

The rodent known as the "multimammate rat" is the reservoir or host of Lassa virus. The rodent, once infected, is able to excrete virus in urine for an extended period of time, maybe for the rest of its life. 

Mastomys rodents live in large numbers in west, central, and east Africa, and readily colonise human homes and areas where food is stored. All these factors contribute to the relatively efficient transmission of Lassa virus from infected rodents to humans.

Transmission of Lassa virus to humans occurs most commonly through ingestion or inhalation, according to the CDC. Mastomys rodents shed the virus in urine and droppings and direct contact with these materials can lead to infection. The contact can be through touching soiled objects, eating contaminated food, or exposure to open cuts or sores. 

Direct contact transmission is common because Mastomys rodents often live in and around homes and scavenge on leftover human food items or poorly stored food. Mastomys rodents are sometimes consumed as food, and people may get infected with Lassa virus while catching or preparing the rodents. 

When a person inhales tiny particles in the air contaminated with infected rat urine or droppings, he or she may become infected. Cleaning activities such as sweeping may result in aerosol or airborne transmission. 

However, direct contact with infected rodents is not the only way in which people are infected. Person-to-person transmission may occur following exposure to virus in the blood, tissues, secretions, or excretions of a Lassa virus-infected individual.

Lassa virus is not transmitted through casual contact, which includes skin-to-skin contact without exchange of body fluids. 

In health care settings where proper personal protective equipment (PPE) is not available or used, person-to-person transmission is common. This mode of transmission is called nosocomial transmission. The virus may spread in contaminated medical equipment, such as reused needles.

Rarely, people can get infected through direct contact with a sick person's blood or body fluids, through mucous membranes like eyes, nose or mouth. 

People infected with Lassa fever are not believed to be contagious before they have symptoms, and the disease is not spread through casual contact like hugging, shaking hands, or sitting near someone. 

What Are The Signs & Symptoms Of Lassa Fever

The signs and symptoms of Lassa fever are usually mild and typically occur one to three weeks after a person is infected. Most people infected with the disease have mild symptoms and hence, go undiagnosed. The mild symptoms include slight fever, general malaise, and weakness, and headache, according to the CDC.

The disease may progress to more serious symptoms including haemorrhaging in gums, eyes, or nose, respiratory distress, repeated vomiting, facial swelling, pain in the chest, back, and abdomen, and shock, in 20 per cent of infected individuals. 

Hearing loss, tremors, and encephalitis are some of the neurological problems occurring due to Lassa fever. 

Within two weeks after symptom onset, death may occur due to multi-organ failure. 

The most common complication of Lassa fever is deafness. In approximately one-third of infections, various degrees of deafness occur. Hearing loss is permanent in many cases. 

Severity of disease does not affect this complication. This is because deafness may develop in mild as well as in severe cases. 

Around 15 per cent to 20 per cent of patients hospitalised for Lassa fever die from the illness. Only one per cent of all Lassa virus infections result in death. 

One in five infections results in severe disease, where organs such as the liver, spleen, and kidneys are affected. 

For women in the third trimester of pregnancy, the death rates for women are particularly high. A serious complication of infection is spontaneous abortion, with an estimated 95 per cent mortality in foetuses of infected pregnant mothers.

Clinical diagnosis of Lassa fever is often difficult because the symptoms are so varied and non-specific. The disease is also associated with occasional epidemics, during which the case-fatality can reach as high as 50 per cent in hospitalised patients.

What Is The Risk Of Exposure To Lassa Fever?

Individuals living in or visiting endemic regions, and having exposure to the multimammate rat are at greatest risk of Lassa virus infection. The risk may also exist in other west African countries where Mastomys rodents live. 

How Is Lassa Fever Diagnosed?

The disease is most often diagnosed by using enzyme-linked immunosorbent serologic assays (ELISA), which detect IgM and IgG antibodies as well as the Lassa antigen. In the early stage of the disease, reverse transcription-polymerase chain reaction (RT-PCR) can be used. 

Treatment For Lassa Fever

Ribavirin, an antiviral drug, has been used with success in Lassa fever patients, and has been shown to be most effective when given early in the course of the illness. 

The patients must receive supportive care consisting of maintenance of appropriate fluid and electrolyte balance, oxygenation and blood pressure, as well as treatment of any other complicating infections.

Early supportive care with rehydration and symptomatic treatment improves survival, according to the WHO. 

How To Prevent Lassa Fever?

Primary transmission of the Lassa virus from its host to humans can be prevented by avoiding contact with Mastomys rodents, especially in the endemic regions. Food must be stored in rodent-proof containers. Also, keeping the home clean can prevent rodents from entering homes. 

The CDC notes that using these rodents as a food source is not recommended. 

Transmission of the disease through person-to-person contact or nosocomial routes, when caring for patients with Lassa fever, can be prevented by taking precautions against contact with patient secretions. These precautions include wearing protective clothing such as masks, gloves, gowns, and goggles; using infection control measures such as complete sterilisation; and isolating infected patients from contact with unprotected persons.

People in high-risk areas must be educated about ways to decrease rodent populations in their homes. Developing more rapid diagnostic tests and increasing the availability of the only known drug treatment, ribavirin, are some challenges. 

Currently, research is underway to develop a vaccine for Lassa fever, according to the CDC.