February 1, 2023

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What is Lassa fever and its causes?

Lassa fever is a viral hemorrhagic disease endemic to West Africa. Although its death rate is lower than that of Ebola, its effect on pregnant women and fetuses is devastating.

The Lassa fever is a fever viral hemorrhagic much more common than Ebola and yet, a great unknown in our country. It is produced by a virus that is spread to people through the waste of certain rodents. However, it can also be spread from person to person very easily, so anyone who suffers from this infection should be subjected to isolation measures until its resolution. 

This virus is endemic to West Africa, where it causes about 300,000 cases a year and thousands of deaths. Its symptoms include a high fever, headache, and sore throat, nausea, and vomiting, as well as intense discomfort. Although it is a hemorrhagic fever, not all patients present significant bleeding. This infection is severe in pregnant women, with a fatal effect on the woman who suffers it and more on the fetus, almost invariably.

Diagnosing this infection is not easy because it requires specific laboratory techniques that are not readily available in the countries where most cases occur. 

Despite everything, a sporadic traveler or tourist in areas with Lassa fever does not have to be affected by this virus if they do not visit rural areas or other areas where rodents are present. Health care or refugee aid workers or the military who go to endemic countries.

This is one more of the neglected diseases suffered by the people of the West African countries. Although the number of cases and, therefore, deaths is higher than in Ebola, this disease has not had much media coverage in the most privileged part of the world. There are currently very few cases imported.

Causes of Lassa fever

The Lassa virus causes Lassa fever. This virus belongs to the Arenaviridae. Other arenaviruses are the lymphocytic choriomeningitis virus (also in Africa), which, together with the Lassa virus, makes up the Old World Arenaviruses group; The New World Arenaviruses are various American hemorrhagic fever viruses (such as Machupo or Junín). It is an RNA-type virus, which has an envelope.

Although Lassa fever has been known since the 1950s, it was first isolated in 1969 from a missionary nurse working in Lassa’s small town in northeastern Nigeria. This nurse caught the virus while caring for an obstetric patient and died within a week. Two other nurses who cared for her also ended up infected, one of them dying.

Several West African countries were initially identified as endemic for the Lassa virus or LASV: Sierra Leone, Guinea, Liberia, and Nigeria. Afterward, analytical and epidemiological studies were carried out, which revealed that the Lassa virus is also found in the Ivory Coast, Mali, and the Central African Republic and has also been described in Burkina Faso, Ghana, Gambia, and Senegal. It is therefore considered to be an endemic West African virus. The few cases diagnosed in the rest of the world are imported, that is, acquired by travelers to that area of ​​Africa. The most affected countries are those of the Mano River Union (Guinea, Liberia, and Sierra Leone) and Nigeria.

This virus is transmitted to people from rodents by direct or indirect contact (aerosols) with infected animals’ excretions. The species most likely to be related to the virus is Mastomys natalensis, a harmless-looking African mouse that lives in the vicinity of human dwellings. Also, the infection can occur in the laboratory or spread from person to person through direct contact with blood or other body fluids of patients. Health personnel who care for patients are at special risk of acquiring the infection.

There are an estimated 300,000 cases of Lassa fever each year, with 5,000-20,000 deaths annually. However, it has been detected that between 5 and 55% of the population in endemic areas have antibodies against Lassa, so it is likely that the number of affected is much higher than estimated and that there are asymptomatic cases or with mild pictures that are not diagnosed. 

Lassa fever symptoms

The incubation period, that is, the time that elapses from when you come into contact with the virus until Lassa fever symptoms begin, is between 7 and 21 days. That is why a traveler who has been in an endemic area for this viral hemorrhagic fever can return to his country without symptoms and later begin to manifest them.

Initially, the patient affected by Lassa fever presents a picture similar to the flu, with high fever, weakness, and general malaise. Also, the affected person may have pain or irritation and throat inflammation, cough, and more or less intense headache. Other relatively frequent symptoms are nausea, vomiting, and diarrhea. More than half of the patients have joint, back, or chest pain. One-third of patients may have conjunctivitis. They are very nonspecific symptoms that also appear in many other diseases, which complicates their diagnosis.

Lassa fever is considered a hemorrhagic fever (other hemorrhagic fevers are yellow fever and Ebola ). In Lassa fever, hemorrhagic manifestations occur in 15-20% of patients, affecting mainly the mucous membranes, the conjunctiva, the gastrointestinal tract, or the vagina. There may be bleeding from the mouth, intestines, stomach, or vagina, in addition to the eyes.

Lassa fever complications

In severe cases, the so-called capillary or vascular permeability occurs, which involves the appearance of edema or swelling of the neck and arms, and legs. It is an ominous sign and indicates a worse prognosis. Severe pulmonary edema, severe encephalopathy, and, finally, terminal shock can also appear in severe cases. Despite this, overall mortality can be only 1-2%, but among patients who need to be admitted to hospital, it rises to 15-30%.

Lassa fever is severe in pregnant women, with a 25-40% mortality in pregnant women affected by Lassa fever. If the woman survives, a miscarriage, or the newborn’s death, occurs in 75-80% of cases.

An additional complication of Lassa fever is deafness. Up to 30% of patients with Lassa fever may have impaired hearing acuity in one or both ears. Of these, only one in three subsequently regain their hearing ability. Typically this deafness appears in the convalescent phase or even after some time after the infection. It is thought to occur through a mechanism mediated by the patient’s own immune system defenses.