How to tackle Lassa fever epidemic, by WHO

Lassa fever is currently spreading in Nigeria like wild fire during Harmattan, killing over nine persons in six states with over 20 confirmed cases. The states include: Taraba; Nasarawa; Edo; Ondo; Rivers; and Plateau.

The Nigeria Centre for Disease Control (NCDC), last week, alerted Nigerians on the increasing number of Lassa fever cases even as it advised increased focus on prevention and preparedness.

However, the World Health Organisation (WHO), between August 2015 and May 17, 2016, was notified of 273 cases of Lassa fever, including 149 deaths in Nigeria. Of these, 165 cases and 89 deaths have been confirmed through laboratory testing (Case Fatality Ratio/CFR: 53.9 per cent). The cases were reported from 23 states in Nigeria.

Since August 2015, ten health care workers (HCW) have been infected with Lassa fever virus, of which two have died. Of these ten cases, four were nosocomial infections.

As of May 17, 2016, eight states were reporting Lassa fever cases (suspected, probable, and confirmed), deaths and/or following of contacts for the maximum 21-day incubation period. 248 contacts were followed up in the country. The other 15 previously affected states had completed the 42-day period following last known possible transmission.

Currently, two national laboratories are supporting the laboratory confirmation of Lassa fever cases by polymerase chain reaction (PCR) tests. All the samples were also tested for Ebola, Dengue, Yellow fever and so far have tested negative.

The two laboratories that are currently operational are: Virology laboratory, Lagos University Teaching Hospital (LUTH); and Lassa fever research and control centre, Irrua specialist hospital, Edo State.

Along with other key partners, WHO is supporting ministry of health in surveillance and response of Lassa fever outbreaks including contacts tracing, follow up and community mobilization. One of a concern since the onset of Lassa fever outbreaks is the high proportion of deaths among the cases that is still under investigation.

Meanwhile, the WHO in this Fact Sheet noted how to tackle the virus.

Though first described in the 1950s, the virus causing Lassa disease was not identified until 1969. The virus is a single-stranded Ribo Nucleic Acid (RNA) virus belonging to the virus family Arenaviridae.

About 80 per cent of people who become infected with Lassa virus have no symptoms. One in five infections result in severe disease, where the virus affects several organs such as the liver, spleen and kidneys.

Lassa fever is a zoonotic disease, meaning that humans become infected from contact with infected animals. The animal reservoir, or host, of Lassa virus is a rodent of the genus Mastomys, commonly known as the “multimammate rat.” Mastomys rats infected with Lassa virus do not become ill, but they can shed the virus in their urine and faeces.

Because the clinical course of the disease is so variable, detection of the disease in affected patients has been difficult. When presence of the disease is confirmed in a community, however, prompt isolation of affected patients, good infection prevention and control practices, and rigorous contact tracing can stop outbreaks.

Lassa fever is known to be endemic in Benin (where it was diagnosed for the first time in November 2014), Ghana (diagnosed for the first time in October 2011), Guinea, Liberia, Mali (diagnosed for the first time in February 2009), Sierra Leone, and Nigeria, but probably exists in other West African countries as well.

Symptoms
The incubation period of Lassa fever ranges from six to 21 days. The onset of the disease, when it is symptomatic, is usually gradual, starting with fever, general weakness, and malaise. After a few days, headache, sore throat, muscle pain, chest pain, nausea, vomiting, diarrhoea, cough, and abdominal pain may follow. In severe cases facial swelling, fluid in the lung cavity, bleeding from the mouth, nose, vagina or gastrointestinal tract and low blood pressure may develop.

Protein may be noted in the urine. Shock, seizures, tremor, disorientation, and coma may be seen in the later stages. Deafness occurs in 25 per cent of patients who survive the disease. In half of these cases, hearing returns partially after one to three months. Transient hair loss and gait disturbance may occur during recovery.

Death usually occurs within 14 days of onset in fatal cases. The disease is especially severe late in pregnancy, with maternal death and/or fetal loss occurring in more than 80 per cent of cases during the third trimester.

Transmission
Humans usually become infected with Lassa virus from exposure to urine or faeces of infected Mastomys rats. Lassa virus may also be spread between humans through direct contact with the blood, urine, faeces, or other bodily secretions of a person infected with Lassa fever. There is no epidemiological evidence supporting airborne spread between humans. Person-to-person transmission occurs in both community and health-care settings, where the virus may be spread by contaminated medical equipment, such as re-used needles. Sexual transmission of Lassa virus has been reported.

Lassa fever occurs in all age groups and both sexes. Persons at greatest risk are those living in rural areas where Mastomys are usually found, especially in communities with poor sanitation or crowded living conditions. Health workers are at risk if caring for Lassa fever patients in the absence of proper barrier nursing and infection prevention and control practices.

Diagnosis
Because the symptoms of Lassa fever are so varied and non-specific, clinical diagnosis is often difficult, especially early in the course of the disease. Lassa fever is difficult to distinguish from other viral haemorrhagic fevers such as Ebola virus disease as well as other diseases that cause fever, including malaria, shigellosis, typhoid fever and yellow fever.

Definitive diagnosis requires testing that is available only in reference laboratories. Laboratory specimens may be hazardous and must be handled with extreme care. Lassa virus infections can only be diagnosed definitively in the laboratory using the following tests:
*reverse transcriptase polymerase chain reaction (RT-PCR) assay
*antibody enzyme-linked immunosorbent assay (ELISA)
*antigen detection tests
*virus isolation by cell culture.

Treatment and prophylaxis
The antiviral drug ribavirin seems to be an effective treatment for Lassa fever if given early on in the course of clinical illness. There is no evidence to support the role of ribavirin as post-exposure prophylactic treatment for Lassa fever.

There is currently no vaccine that protects against Lassa fever.

Prevention and control
Prevention of Lassa fever relies on promoting good “community hygiene” to discourage rodents from entering homes. Effective measures include storing grain and other foodstuffs in rodent-proof containers, disposing of garbage far from the home, maintaining clean households and keeping cats. Because Mastomys are so abundant in endemic areas, it is not possible to completely eliminate them from the environment. Family members should always be careful to avoid contact with blood and body fluids while caring for sick persons.

In health-care settings, staff should always apply standard infection prevention and control precautions when caring for patients, regardless of their presumed diagnosis. These include basic hand hygiene, respiratory hygiene, use of personal protective equipment (to block splashes or other contact with infected materials), safe injection practices and safe burial practices.

Health-care workers caring for patients with suspected or confirmed Lassa fever should apply extra infection control measures to prevent contact with the patient’s blood and body fluids and contaminated surfaces or materials such as clothing and bedding. When in close contact (within 1 metre) of patients with Lassa fever, health-care workers should wear face protection (a face shield or a medical mask and goggles), a clean, non-sterile long-sleeved gown, and gloves (sterile gloves for some procedures).

Laboratory workers are also at risk. Samples taken from humans and animals for investigation of Lassa virus infection should be handled by trained staff and processed in suitably equipped laboratories under maximum biological containment conditions.

On rare occasions, travellers from areas where Lassa fever is endemic export the disease to other countries. Although malaria, typhoid fever, and many other tropical infections are much more common, the diagnosis of Lassa fever should be considered in febrile patients returning from West Africa, especially if they have had exposures in rural areas or hospitals in countries where Lassa fever is known to be endemic. Health-care workers seeing a patient suspected to have Lassa fever should immediately contact local and national experts for advice and to arrange for laboratory testing.

WHO response
The Ministries of Health of Guinea, Liberia and Sierra Leone, WHO, the Office of United States Foreign Disaster Assistance, the United Nations, and other partners have worked together to establish the Mano River Union Lassa Fever Network. The programme supports these three countries in developing national prevention strategies and enhancing laboratory diagnostics for Lassa fever and other dangerous diseases. Training in laboratory diagnosis, clinical management, and environmental control is also included.