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Understanding lassa fever

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PATHOGEN PROBLEM… Lassa virus (shown in this transmission electron micrograph) caused a bigger-than-usual outbreak in Nigeria in 2018. Analyzing viral DNA in the field helped public health officials figure out why. PHOTO CREDIT: Ami Images/Science Source

Lassa fever is an illness caused by Lassa virus, a single-stranded RNA hemorrhagic fever virus from the family Arenaviridae.

It is an acute febrile viral illness lasting one to four weeks, and it occurs in West Africa and some areas beyond. The incubation period for Lassa fever is variable, from six days to three weeks.

What are causes and risk factors for Lassa fever? Lassa fever virus is mainly a zoonosis (a disease that is animal-borne or spread to humans from animals). It is spread to people through contact with household items, food, water, or air contaminated with the droppings or urine of infected multimammate rats (Mastomyces natalensis). These rodents live throughout West Africa in homes, and they can shed this virus without being ill.

People most often become infected by inhaling air contaminated with aerosols of rodent excretions, swallowing the virus in food or contaminated utensils, preparing and eating multimammate rats (meat of wild or non-domesticated animals, called bush meat or wild meat, is often prized as a delicacy), and contact with open wounds. Lassa fever virus is believed to be endemic (always present) West and Eastern Africa countries

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Travelers to West Africa staying in homes or areas of poor sanitation or crowding, as well as health care and laboratory professionals serving in health care facilities in West Africa, are most at risk.

Infection prevention methods are critical to reducing infection of health care workers and spread within health facilities. Those at highest risk for serious complications and death are pregnant women in their third trimester. Stillbirth or fetal loss occurs in 95 per cent of pregnancies.

Is Lassa fever contagious? If so, what is the contagious period for Lassa fever? Person-to-person spread is possible but is not as frequent as with Ebola virus. It can rarely occur upon direct contact with saliva, blood, and bodily fluids and mucous membrane or sexual contact.

Casual contact of intact skin with intact skin does not transmit the virus. Laboratory workers and health care professionals can become infected through improper infection-control precautions, and patients in rural hospitals have acquired it through reuse of disposable needles.

It is not clear when infected humans are contagious or for how long they are contagious. The presence of virus in the blood is known to peak four to nine days after symptoms begin. The virus can be transmitted in semen for up to three months.

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Lassa fever is one of the hemorrhagic fevers and may appear with signs and symptoms like Ebola or Marburg hemorrhagic fever viruses, and until these viruses are ruled out, suspected cases must be managed with infection control precautions to prevent contact with blood, body fluids, and contaminated surfaces. These include basic hand washing or alcohol-based sanitizing between patients.

When working within 3 feet of an affected patient, use of additional barrier personal protective equipment should include an impermeable long-sleeved gown, gloves, and face mask with eye protection. Safe injection practices, safe laboratory handling, and safe mortuary procedures are also important.

What are Lassa fever symptoms and signs? In those who have symptoms, Lassa fever begins with a flu-like illness: fever, malaise, generalized weakness, sore throat(very similar to strep throat and without runny nose), severe headache, chest pain (especially behind the breastbone), back pain, and ringing ears. Nausea, vomiting, abdominal pain, and diarrhea also occur.

Hemorrhage is not common in less serious disease, but loss of fluid from blood vessels into tissue may occur; this causes facial swelling, reddened whites of the eyes, and fluid around lungs and heart.

Dry cough and respiratory distress may occur if illness involves fluid in the lungs. Severe disease may cause encephalitis with confusion, tremors, seizures, and coma.

Organ failure and shock are often end-stage events. Fair-skinned individuals may have a faint rash of the upper body that is not seen in dark-skinned individuals.

Some bleeding from mucous membranes occurs in severe illness. Lassa virus infects all tissues, but infection of the liver is especially typical. Hepatitis may be mild or severe, and laboratory tests may not reflect the level of injury.

Lassa fever virus often causes deafness, and this complication may be noted in late-stage disease and during recovery periods.

What is the treatment for Lassa fever? Ribavirin given intravenously and early in the course of illness is an effective treatment, in addition to support of fluid and electrolytes, oxygenation, and blood pressure.

In the only study to evaluate it in 1986, this treatment reduced mortality from 50 per cent to five per cent if given early in serious illness. Adverse effects include hemolytic anemia (rupture of red blood cells) if infused too quickly.


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