LASSA FEVER: THE RODENT EPIDEMIC

What is Lassa Fever?

The zoonotic disease, Lassa fever, is an acute viral haemorrhagic disease transmitted to man by a specie of rodent known as ‘Mastomys Rats’. The Lassa Virus, which is responsible for this disease is a member of the family of arenaviruses, and derives its name from the Lassa village in Borno State, Nigeria, where it was first documented. Lassa fever has since then become an epidemic of serious public health concern in West African countries like Nigeria, Ghana, Sierra Leone, Liberia and Guinea, where exposure to the Mastomys rat is common due to its predominance in the rural environments common to these countries. Rough estimates suggest that West Africa records between 100,000 to 300,000 cases of this rodent epidemic each year, with a death toll of about 5,000 annually. Lassa fever is neither as contagious nor as deadly as the Ebola virus disease (EVD), but is usually life-threatening in extreme cases where it damages internal organs like the kidneys, liver and spleen

How does Lassa fever spread?

Being a zoonotic disease, Lassa fever is spread by a multimammate rodent specie known as Mastomys natalensis, common to rural settings with unhygienic practices in Nigeria. The virus spreads easily as the rats can inhabit human homes and breed rapidly, and also have a lifelong potential to shed the virus in their urine and faeces. Humans become infected either from direct contact with the infected animals or via contact with household and food items contaminated with the rodent’s urine or faeces. Inhalation of contaminated aerosols from the rat is also possible. Poor food hygiene in places where wild rats (popularly called “bush meat”) are prized as a delicacy contribute to the spread of the virus. Lassa fever can be transmitted among health workers and patients in hospitals lacking adequate infection prevention and control measures. This person-to-person transmission may occur following exposure to the blood, tissues, body secretions or excretions of a Lassa virus-infected individual. However, transmission does not occur through touch – except in the cases of deep cuts or open sores. Also, a few cases of sexual transmission have also been recorded.

Individuals at risk of contracting Lassa fever include:

  • People visiting or living in Lassa fever endemic regions of West Africa
  • Primary healthcare givers of Lassa fever-infected individuals
  • Immunosuppressed individuals, especially women in their third trimester of pregnancy

Laboratory workers handling samples from Lassa fever patients without adequate sterilization methods and protective measures.

What are the signs and symptoms of Lassa Fever?

The incubation period of the virus spans 2-21 days, after which symptoms may become clinically apparent. Although it is a haemorrhagic disease, 8 out of every 10 people infected with the virus present no symptoms. In the other 20% who are symptomatic, the signs and symptoms of Lassa fever usually commence with fever, general weakness and malaise. After a few days, sore throat, chest pain, muscle aches, headache, abdominal pain, vomiting, nausea, diarrhoea and cough may follow. In severe cases, however, the disease could be life-threatening, presenting with serious signs and symptoms like hypotension (low blood pressure), bleeding from the mouth, nose, vagina or gastrointestinal tract, fluid in the lung cavity, pericarditis (inflammation of the heart’s external layer), and facial swelling. Neurological problems like tremours, hearing loss and encephalitis may also occur. Hearing loss, which occurs in 25% of survivors of the disease, is the commonest complication of Lassa fever. The deafness occurs in varying degrees and does not necessarily depend on severity of the disease. Although total and permanent loss of hearing is likely, partial recovery of hearing usually occurs in half of the cases after 1-3 months. Death from Lassa fever occurs within 14 days of onset, usually due to multiple organ damage and go away without treatment, however, the disease is fatal (causes death) in about 10% of cases.

Source: Al Jazeera

How can Lassa Fever be diagnosed?

The clinical diagnosis of Lassa fever is difficult because the disease is mostly asymptomatic, and even when symptoms manifest, they are very similar to those of other viral haemorrhagic fevers such as the Marburg disease and Ebola virus disease. Thus, the only diagnosis for Lassa fever is laboratory-based and begins with a differential diagnosis to rule out other diseases. Enzyme-linked immunosorbent assays (ELISA), which detect IgM and IgG antibodies, as well as Lassa antigens, are performed. Reverse transcription-polymerase chain reaction (RT-PCR) can also be used, but only in the early stages of the disease. The virus itself may be cultured within 7-10 days, but this is done only in specialized institutions due to the highly hazardous nature of Lassa fever specimens. For postmortem diagnosis, immunohistochemistry, performed on formalin-fixed tissue specimens, can be used.

How can Lassa Fever be treated?

Currently, there are no specific treatments or licensed vaccines for Lassa fever. However, patients can receive supportive care which consists of maintenance of appropriate fluid and electrolyte balance, oxygenation and blood pressure regulation, as well as treatment of any other complicating infections. Also, the antiviral drug Ribavirin has been used with recorded success in Lassa fever patients, although it does not provide post-prophylactic protection.

How can Lassa Fever be prevented?

A smallpox vaccine can provide protection against monkeypox, but its use is currently limited to people who work in a lab with the variola (smallpox) virus. Prevention depends on decreasing human contact with infected animals and limiting person-to-person spread. You can prevent monkeypox virus by:

Avoiding contact with infected animals (especially sick or dead animals)

Avoiding contact with bedding and other materials contaminated with the virus

Washing your hands with soap and water after coming in contact with an infected animal

Thoroughly cooking all foods that contain animal meat or parts

Avoiding contact with people who may be infected with the virus

Using personal protective equipment (PPE) when caring for people infected with the virus.

References

  1. World Health Organization (2022). Monkeypox. https://www.who.int/news-room/fact-sheets/detail/monkeypox

2. Nunez K (2022). All About Monkeypox. Healthline. https://www.healthline.com/health/monkeypox

3. Cleveland Clinic (2022). Monkeypox. https://my.clevelandclinic.org/health/diseases/22371-monkeypox

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