Lassa fever: what it is, symptoms, transmission and treatment


What is Lassa fever?

Fever Lassa or viral hemorrhagic fever (ICD-10 A96.2) is an infectious, contagious disease that can reach several human organs and injure blood vessels. The virus is zoonotic, that is, it is transmitted to humans through animals.

The agent was first recognized in 1969 due to the death of two nurses who treated an infected patient in the city of Lassa, Nigeria, where he was named.

Nigeria, Guinea, Liberia, and Sierra Leone are the hardest hit countries, totaling about 300,000 to 500,000 infected people, culminating in an estimated 5,000 annual deaths. However, neighboring countries are also at risk, as the main host (rodent of the species Mastomys natalensis ) can be found throughout the region.

According to the World Health Organization (WHO), the number of cases since the beginning of the year is already greater than that of the entire period of 2017. There are 317 people affected against 143 cases registered in the past year.

Although the death rate is low (around 1%), 90 deaths have been recorded across Nigeria since January 2018, according to WHO data. In this new outbreak, the data reveals more than 20% of deaths among confirmed and suspected patients.

In addition to bleeding into internal organs, the patient may suffer from abdominal pain and hearing loss. In more severe cases, deafness is permanent.


It is caused by an RNA virus ( ribonucleic acid , in translation “ribonucleic acid”), a member of the Arenaviridae family . The virus is acellular, that is, it has no cells, but a protein capsule , called a capsid.

To proliferate, the virus needs to insert its genetic material into cells. To do this, it is incorporated into the cell wall or membrane, joining with receptor molecules that are on the cell surface.

Once this process is finished, the invading agent starts to affect the functioning of the infected cell, in addition to extracting substances present in order to multiply its genetic material and to generate capsids for the new viruses.

The RNA virus affects dendritic cells (white blood cells), antigen-presenting cells (APC) and endothelial cells (which cover the inside of blood vessels), where the hemorrhage comes from.

The virus incubation period is 2 to 21 days.


The spread of Lassa fever can occur from animal to human or from human to human. Transmission takes place in the individual’s own social environment or in hospitals.

Transmission by animals

The contamination is made through contact with urine, feces and saliva of rodents – especially the species Mastomys natalensis , found in savannas and forests of West Africa and that can carry the virus throughout their lives – and infected spiders, which can be oral or respiratory.

Due to the precarious health conditions in certain regions of Africa, the food is exposed to the animal, which will feed on the food that will later be consumed by human beings.

Cleaning activities, such as sweeping the floor, can cause inhalation of tiny particles derived from contaminated rat droppings. In addition, it is common for residents to consume Mastomys class rodents .

Human-to-human transmission

Transmission can also be done by direct contact with contaminated content through body fluids, such as urine, blood, saliva and vomit. This type of contagion is also common in the hospital environment, and can spread to contaminated medical equipment, including reused needles.

It is worth mentioning, however, that skin-to-skin contact is not sufficient to cause the spread of viral disease. There is also evidence that the contagion is spread sexually.

According to the Nigeria Center for Disease Control (NCDC) – the disease control center in Nigeria – the types of contact can be classified into 3 categories, considering the risk of contagion:

Category 1 – No risk
  • No direct contact with the patient or body fluids
  • Casual contact, no contact with potentially infectious substances
  • Handling of laboratory samples under contained conditions
Category 2 – Low risk
  • Direct contact with patient
  • Handling of body fluids with proper protection
  • Break of laboratory containment without direct contact with specimen
Category 3 – High risk
  • Unprotected exposure of the skin or mucous membranes to blood or potentially infectious body fluids, including needle injury, sexual contact, unprotected laboratory sample handling

Can Lassa fever reach Brazil?

Despite the ease in spreading the disease precisely because of the various options for locomotion between one country and another, the probability of the disease getting here is low.

In addition to the virus being associated with the tropical climate, according to experts, the outbreak is endemic, that is, it occurs in a specific geographic region and sporadically. In addition, poorer countries are more likely to have less structure in public health and in fighting contagious diseases.

Risk factors

Lassa fever affects people of all ages and both sexes, in situations that include:

  • Reside or travel to regions with incidence of cases of the disease;
  • Get in contact with urine, feces, saliva or blood from rodents;
  • Sharing needles with infected people;
  • Having sex without a condom with a patient with a suspected or confirmed diagnosis of the disease;
  • Being exposed to salivary droplets from people with the virus, such as sneezing or coughing;
  • Have direct contact with infected blood, in cases of injury, for example;
  • Living in a place with a lack of basic sanitation;
  • Pregnant women, especially in the 3rd trimester.

Health professionals who have contact with the infected person and who do not respect due precautions also have a high risk of contracting the disease. The list includes: doctors, nurses and people who handle blood samples in suspected cases of Lassa fever.


The symptoms are similar to those of malaria and dengue and the infected person may present them only 3 weeks after the virus has contracted. That is why it is so difficult to identify Lassa fever.

The disease starts mildly, not being diagnosed in 80% of cases. In this step, the patient presents the following signs:

  • Fever;
  • Sore throat;
  • Pain in the abdomen;
  • Retrosternal pain (in the chest region);
  • Weakness;
  • Nausea;
  • Vomiting;
  • Diarrhea;
  • Conjunctivitis;
  • Hearing loss;
  • Encephalitis (inflammation in the brain);
  • Proteinuria (excess protein in the urine).

16 to 45% of the most serious cases are fatal. Infected deaths usually occur due to multiple organ failures. In pregnant women, this estimate reaches 92%. To mitigate the losses, induced births are performed in the third trimester of pregnancy. The symptoms in these cases include:

  • Hemorrhage in internal organs, through the nose, mouth and vagina (seen in only 20% of cases);
  • Facial swelling;
  • Tremors.

The clinical stages of severe Lassa fever can be divided into 4 stages, according to the NCDC:

Stage 11st to 3rd day
  • Widespread weakness and malaise
Stage 24th to 7th day
  • Sore throat
  • Headaches, back, chest or abdomen
  • Conjunctivitis
  • Nausea and vomiting
  • Diarrhea
  • Hypotension (low blood pressure)
  • Anemia
Stage 3After the 7th day
  • Edema (swelling) on ​​the face and neck
  • Convulsions
  • Bleeding from the mucosa (mouth, nose, eyes)
  • Internal bleeding
  • Confusion and disorientation
Stage 4After the 14th day
  • Coma
  • Death


It is worth mentioning that the severity of the disease will depend on some factors, such as the body’s natural immune response, mode of transmission, duration of exposure, infective dose and stage of the disease.

How is the diagnosis made?

Tests are recommended when there is a risk of contamination, for people who live or travel to areas susceptible to contagion, in addition to women at the end of their pregnancy.

These tests should exclude other causes of fever and need a detailed analysis, since the patient can present any stage of the disease. At the same time, early diagnosis is essential for treatment with the antiviral medication to guarantee good results. The analysis covers:

ELISA heads

This is a laboratory test that allows the identification of specific antibodies, such as the Lassa fever antigen.

It is also able to target the immunoglobulin G (IgG) and immunoglobulin M (IgM) antibodies that are created when symptoms are evident in response to the invading microorganism. IgC is designed to prevent future contamination throughout life.


This is a procedure that aims to search for antigens from body tissues through a microscope. With the result, it is possible to determine inflammatory, infectious pathologies and neoplasms (diseases that destroy human tissue).


The PCR is a blood test that measures the amount of C – reactive protein (CRP). CRP is produced in the liver and is linked to the onset of inflammation or infection in the body. The increase in production indicates that there is a harmful agent in the body and that it is being fought.

Does Lassa fever cure you?

Lassa fever is only curable when treated in its early stage , which occurs within the first 6 days after infection. The patient’s recovery or worsening time varies from 7 to 30 days after the onset of symptoms.

There is still no vaccine for the disease, as it is an expensive, time-consuming resource that requires a lot of research.

What is the treatment?

Before starting treatment, the infected person is isolated to prevent infection. Contact with the patient must be made with the use of gloves, glasses, aprons and masks.

Treatment consists of procedures used collectively, such as the combination of medication and methods that act to repair fluids and electrolyte instability (minerals that have an electrical charge when dissolved in liquid and that act on the functioning of nerve functions).


Antivirals are indicated to stop the action of the virus in the body, reducing its proliferation and eliminating it from the body. In addition to patients already diagnosed, the drug is also usually indicated in some suspected cases – people who have had contact with an infected person and fall into the high-risk category.

As the invading agent needs to be linked to the nucleus of the RNA cell to develop, the antiviral acts in blocking and canceling viral activities and inhibits its duplication.

Fluid intake

Maintaining a fluid intake routine helps to regulate the production of electrolytes (producers of immediate energy and responsible for body hydration) and minerals that act on the performance of nerves and muscles, preventing dehydration.

Diálise peritoneal

Peritoneal dialysis is a blood filtration process in order to remove excess fluids and toxic substances from the body. It is indicated for patients suffering from renal failure, that is, when the kidneys fail to remove or balance the body’s fluids.

The procedure is done by adding a dialysis liquid inside the peritoneal cavity through a catheter – definitive and painless device implanted through surgery on the abdomen. The action of the liquid causes the peritoneal membranes to perform the functions of the kidneys.


The Ribavirin is in the Model List of Essential Medicines World Health Organization (WHO). The drug is an intravenous antiviral and effective if administered at the onset of Lassa fever.

The chances of mortality drop by up to 10 times if the medication is used in the first 6 days of the disease. Administration is done in a single dose followed by applications of 4 days every 6 hours and 6 days within an 8-hour interval.


NEVER self-medicate or stop using a medication without first consulting a doctor. Only he will be able to tell which medication, dosage and duration of treatment is the most suitable for his specific case. The information contained in this website is only intended to inform, not in any way intended to replace the guidance of a specialist or serve as a recommendation for any type of treatment. Always follow the instructions on the package insert and, if symptoms persist, seek medical or pharmaceutical advice.


In milder cases, recovery occurs after a few days of hospitalization. In severe clinical conditions, the patient may die, with a mortality rate of 16% to 45% in people with severe multisystem disease. Both conditions occur between 7 to 31 days after the onset of symptoms.

For pregnant women in late pregnancy, the mortality rate is between 50% to 92%. At the same time, the probability of losing the fetus is 80%.


Lassa fever can lead to a series of complications, such as viral hemorrhagic fever, permanent deafness and inflammation.

Viral hemorrhagic fever

Viral hemorrhagic fever is the name given to a number of diseases caused by RNA viruses. The most common are Ebola, Yellow fever, Lassa fever and Argentine hemorrhagic fever.

Symptoms include fever, fatigue and dizziness. In more severe cases, the virus causes damage to blood vessels, resulting in bruising and bleeding through various channels in the human body.

There is no specific treatment for these diseases, what is done is to assist the infected organ. The patient may be hospitalized in isolation.

Yellow fever and Argentine hemorrhagic fever are the only ones that have a vaccine, so prevention is essential. Travel to outbreak sites and contact with hosts of the disease should be avoided.


Women in late pregnancy who contract the disease are very likely to lose their baby or die.


The disease damages the hearing system. About a third of Lassa fever patients lose their hearing completely regardless of the severity of the disease.

You specify

Uveitis is inflammation within the eye. Among the factors that can originate it, is the infection by virus and ocular lesions. The person may have pain, sensitivity to light and a reddish eye. The disorder can be resolved by using eye drops and medications.


Characterized as inflammation in the testicles, orchitis can be caused by contusion in the region and viral infection.

The man perceives the disease when he starts to urinate and ejaculate with blood, besides presenting pain and swelling in the testicles. The recovery time is approximately 30 days, through rest and anti-inflammatory drugs.


In the most severe cases, the patient’s death may occur due to severe bleeding and organ failure.

Prevention and control

For people living in risk areas, it is recommended to close holes that facilitate the entry of rats into their homes, to throw garbage in covered containers and to conserve food and water in sealed objects.

As it is a contagious disease, gloves, glasses and masks should be adopted in contact with infected people.

Other measures also prevent the disease from contracting:

  • Avoid contact with rodents (dead or alive);
  • Wash your hands regularly;
  • Give preference to bottled water;
  • Cook food well;
  • Maintain correct intimate hygiene;
  • Keep the environment clean and free of cracks to avoid the appearance of animals carrying the virus;
  • Sterilize medical instruments;
  • Isolate the infected patient;
  • In the event of death due to the disease, ensure a safe burial to prevent further cases of transmission, since the corpse remains contagious for several days after death.

For control measures, health professionals should contact the authorities responsible for the surveillance and notification of illnesses of the local government, whenever they assist a patient with suspected infection.

There are even more measures that can be taken by these professionals in order to avoid further contamination:

  • Limit the number of employees and visitors to access the patient’s room;
  • Properly disinfect items used by the patient, including syringes, thermometers, bedding, glasses and cutlery;
  • Ensure the proper use and disposal of all personal protective equipment, such as masks and gloves;
  • Safely dispose of injectable objects and other sharp items;
  • Safely handle blood samples taken from patients with suspected virus infection;
  • Keep the entire team of the health unit informed about the risks associated with the disease.

Lassa fever is a hemorrhagic disease, highly contagious. Coming from West Africa, the chances of reaching Brazil are minimal.

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