Lassa fever was first discovered nearly 50 years ago in Nigeria. Since then, it has been reported in other West African countries including Sierra Leone, Liberia and Guinea. There is also evidence of Lassa fever presence in southern Mali, Burkina Faso, Côte d’Ivoire and Ghana, all of which share a similar tropical wooded savanna ecological zone. But there is still no vaccine against the disease. A new outbreak in 19 Nigerian states and in Lagos city – the most populated city on the continent – has sparked fears that the disease will get out of control and result in a public health event of international concern. Conversation Africa editor at large Declan Okpalaeke spoke to Oyewale Tomori about the outbreak.
What is Lassa fever and how prevalent is it?
It is a fatal viral haemorrhagic disease caused by the Lassa virus, a member of the Arenaviridae family of viruses, which naturally infects the widely distributed house rat.
The disease is transmitted through the urine and droppings of an infected species of the rat – the Mastomys natalensis or multimammate – found in most tropical and subtropical countries in Africa. They are able to contaminate anything they come in contact with: surfaces, food and water. And they are prolific breeders. A female Mastomys rat can produce between 98 and 156 babies in one year.
The Lassa virus spreads through human to human contact with tissue, blood, body fluids, secretions or excretions. This includes coughing, sneezing, kissing, sexual intercourse and breastfeeding. In hospitals the disease is spread through contaminated equipment.
Each year, the number of Lassa virus infections in west Africa is estimated at 100,000 to 300,000, and between 5000 and 10 000 people die each year. About 80% of those infected do not show any symptoms, the remaining 20% suffer severe multi-organ damage. However, such estimates are crude, because there isn’t uniform surveillance of cases. In some areas of Sierra Leone and Liberia about 10%-16% of people admitted to hospitals every year have Lassa fever, which indicates the serious impact of the disease on the population of this region.
People become ill six to 21 days after they are infected. A fever is usually the first symptom followed by headaches and coughing, nausea and vomiting, diarrhoea, mouth ulcers and swollen lymph glands. Some patients also complain of muscle, abdomen and chest pains. And later, patients’ necks and faces swell and they bleed from their orifices and into their internal organs.
Lassa fever is endemic in Benin, Ghana, Guinea, Liberia, Mali, Sierra Leone, and Nigeria. But in the last six years Nigeria has carried the bulk of the caseload.
What is the reason for the latest outbreak?
There are several possible reasons: an increase and spread of rodents through the country; unplanned urbanisation; and sanitation and garbage disposal problems.
It is clear that outbreaks are becoming more widespread in Nigeria. Between 1969 and 2008, Lassa fever cases were reported in only six to seven of Nigeria’s 36 states. But between 2009 and 2015 this doubled to between 10 and 14 states reporting outbreaks.
In 2016 at least 26 states reported cases and at least 18 states have reported outbreaks so far this year.
And although outbreaks previously only occurred during the dry season, the disease is now found throughout the year.
Despite these increases, the outbreaks have been accepted as “normal” and not elevated to a national emergency status. As a result Nigerian authorities have been caught unprepared with each outbreak.
There is also a technical challenge. Diagnosing Lassa fever is difficult because the early symptoms are similar to other endemic diseases in the region like malaria, typhoid, influenza, leptospirosis and trypanosomiasis.
The biggest issue is that Nigeria has failed to sustain any reliable disease surveillance system.
In 2015 Nigeria set up an emergency operation centre to monitor and control the spread of the Ebola virus which resulted in the country containing the disease in three months. But it’s since been dismantled.
Why is there an Ebola vaccine but not one for Lassa fever?
Lassa fever – like Ebola – is a fatal haemorrhagic disease. The difference is that the severity of Ebola in the region in 2015/2016 and the fear of its spread beyond the borders of West Africa led to unprecedented efforts to license a vaccine against the disease. Lassa fever, on the other hand, has not spread beyond the region since it was first described in 1969. It is therefore unlikely that it will be treated in the same way.
There are several experimental vaccines that have been developed and are being tested on animals. Only one vaccine (VSVΔG/LASVGPC) has protected monkeys against the disease. Others in development have demonstrated an immune response in laboratory animals so offer some protection. But all have failed to offer full protection.
The drug Ribavirin can be used to treat cases, but it’s more successful if treatment is started early. This means that an early and reliable laboratory diagnosis is vital for the proper management of cases.
The challenge in developing a vaccine is that so long as the category of Lassa Fever threat is lower than that of Ebola virus disease, foreign donors and agencies won’t be focused on the issue.
Governments and scientists in countries where Lassa fever is endemic should spearhead the development of a vaccine against the virus. They must re-order their priorities and putt funds into vaccine trials as a service for public good.
In the meantime, what needs to be done to contain and control Lassa fever?
There are three areas that need attention.
Firstly, Nigeria needs to develop disease control and surveillance strategies. Central to this is rodent control. This should include environmental health authorities establishing a regular surveillance strategy for rats.
Secondly, community and environmental hygiene needs to be improved. Houses need to be kept clean and garbage should be disposed far from residential areas. And special care needs to be taken in storing and preparing food.
Thirdly, hospitals must follow strict standard infection control practices. Corpses of people who have died must be treated with care to avoid transmitting the infection. Health workers and laboratory personnel must get the necessary specialised training in handling infectious cases. And the traditional washing of bodies after death should be avoided.
Lastly, infection control practices must be followed, such as restricting access to laboratories and decontaminating material before it leaves the laboratory.