What is Lassa fever?

And what are its symptoms?

How is the virus transmitted to humans?

And what is the resulting fatality rate?

How many cases have been registered in the UK recently?

And 3 confirmed cases of Lassa fever were recorded in this country during the past week, according to a report by Bruce Wayne Lee in Forbes, citing the United Kingdom Health Security Agency (UKHSA).

One of these died at Luton and Dunstable Hospital, which is run by the NHS Foundation for Bedfordshire Hospitals.

Only 8 cases have been reported in the UK since 1980, and no cases have been reported since two cases were reported in 2009.

The cases were recorded in the same family, "and are linked to travel to West Africa," says Dr. Susan Hopkins, Senior Medical Adviser to UKHSA's Health Security Agency.

It is endemic to parts of West Africa such as Benin, Ghana, Guinea, Liberia, Mali, Sierra Leone, Togo and Nigeria.

According to the US Centers for Disease Control and Prevention (CDC), there are an estimated 100,000 to 300,000 cases of this fever globally, and it leads to the death of about 5,000 people.

What is Lassa fever?

Lassa fever is an acute viral hemorrhagic disease lasting from two to 21 days, according to the World Health Organization.

Although the virus that causes this fever was first described in the 1950s, it was not recognized until 1969. It is a single-stranded RNA virus of the virus family Arenaviridae.

How is it transmitted to humans?

Lassa virus is transmitted to humans through contact with food or household items contaminated with rodent urine or feces.

Infection can also be transmitted from person to person and in laboratories, particularly in hospitals that lack adequate infection prevention and control measures.

Where there?

Lassa fever is known to be endemic in Benin, Ghana, Guinea, Liberia, Mali, Sierra Leone and Nigeria, but it may also be present in other West African countries, according to the WHO.

What is the fatality rate?

The overall fatality rate is 1%.

The case fatality rate observed in hospitalized patients with severe Lassa fever is 15%.

Early supportive care, by replacing fluids and treating symptoms, improves chances of survival.

About 80% of people infected with Lassa virus do not show symptoms.

One case in every 5 infection causes severe disease, as the virus affects several organs such as the liver, spleen and kidneys.

What is the animal reservoir of the virus?

Lassa is a zoonotic disease, which means that humans become infected as a result of contact with infected animals.

The animal reservoir or host of the Lassa virus is a rodent belonging to the genus Mastoma, commonly called the "multimammal rat".

Such rats do not become infected with the Lassa virus, but they can pass the virus in their urine and faeces, according to the WHO.

What are the symptoms?

The incubation period for Lassa fever ranges from 6 to 21 days.

If the disease is accompanied by symptoms, it usually begins gradually, starting with:

  • fever

  • Weakness

  • malaise

    may follow after a few days suffering from:

  • headache

  • sore throat

  • muscle pain

  • chest pain

  • nausea

  • vomiting

  • diarrhea

  • cough

  • abdominal pain

In severe cases may appear:

  • swelling in the face

  • fluid in the pulmonary cavity

  • bleeding

  • Reduction of Blood pressure

And in later stages:

  • shock

  • spells

  • tremor

  • coma

25% of those recovering from the disease develop deafness.

In half of these cases, patients recover partially their hearing after a month or three.

Transient hair loss and gait disturbance may lead to the recovery period, according to the WHO.

Death usually occurs within 14 days of onset of symptoms in fatal cases.

The disease is particularly severe during the last pregnancy and causes the death of the mother and/or fetus in more than 80% of cases during the last 3 months of pregnancy.

How many cases in the UK?

The virus was first officially identified in Nigeria in 1969, and no cases were reported in the UK until the 1980s, according to the Guardian.

Since then, 11 cases have been confirmed in total, including the three cases that were identified the past few days.

These cases are the first to be confirmed in the UK since 2009.

And how many deaths?

The UK's Health Security Agency said 4 people have died from the virus since 2000. One died in 2000 and two in 2009, and the fourth death was confirmed on Friday.