Nothing excites Prof Atanu Basu, a noted virologist, and senior deputy director, National Institute of Virology, Pune, more than hunting down new viruses. He talks to Gunjan Sharma about Lassa fever, which is emerging as next health challenge in Africa after Ebola, its symptoms and if India is at risk.

Lassa fever is being compared with Ebola. Why?

The recent upsurge of Lassa fever in West Africa is a major global concern. While Lassa infections have been endemic in parts of Africa and south America, the 2018 outbreak in Nigeria with 1849 reported cases between Jan and April is worrisome.

We have not seen such a major outbreak of Lassa virus in recent times. Lassa fever can be very severe and is a hemorrhagic disease. It is similar to Ebola and can spread human-to-human.
The fatality ratio is also very high at about 25 %. Lassa can further spread into other countries through travellers. So, public health emergency measures are needed to control it. 

Thankfully, the cases of Lassa fever have begun to drop significantly especially in Adamawa, Kogi and Ebonyi provinces in Nigeria, thanks to the World Health Organisation and the Nigeria government. It has reduced the threat of the spread of Lassa fever.
 
What is Lassa fever? What causes it?

Lassa fever is a hemorrhagic fever that was first identified by Dr J D Frame in 1969. It is caused by an Arenavirus, an endogenous resident virus in rodents. But it doesn't cause disease in these animals. The rodent scientifically called Mastomysis natalensis is the major reservoir for Lassa virus.

Though there are many Arenaviruses that are quite widespread in rodents, not all are not pathogenic to humans. Interestingly, the three most lethal arenaviruses-- Guanarito, Sabia and Whitewater Oryo-- are from America. These viruses can cause severe hemorrhagic-- often fatal—disease in humans.

How contagious is it? 

Lassa fever is highly contagious. It is primarily contracted through exposure to infected rodent excreta, but then it can spread from human to human via infectious aerosol, body fluids, etc.

However, one has to understand that a community response to Lassa outbreak depends on many factors. These include genetics of the host and virus, biology of the rodent reservoirs, socio-economic pattern and herd immunity acquired from an endemic circulation of Lassa and other closely related viruses that are non-pathogenic.

A recent research paper has shown the presence of a new Lassa virus lineage isolated from a patient from Togo. It is now called the Togo strain lineages. Import of new virus strains can be a threat and need well co-ordinated international monitoring.

Are people in India at risk? Do we need to take any precautions?

Till date, there is no report of Lassa virus infection detected in humans or rodents in India. We do have aggressive surveillance systems conducted through multiagency programs of the Government networks such as the Integrated Disease Surveillance Program (IDSP); ICMR, National Institute of Virology, Department of Health Research.

The laboratory diagnostic capabilities are also in place and the ICMR-National Institute of Virology has a fully operational Biosafety Level 4 laboratory.

What we need to do is to increase the awareness about Lassa virus among people and primary healthcare workers and put in place state and central health response protocols.

Like Ebola, does it also have any long-term effect on health?

Lassa fever is typically characterized by an acute febrile illness with muscle pain, gastrointestinal symptoms and acute pharyngitis. In 25-30 % of the cases, the disease can progress to very severe forms with haemorrhage and capillary leakage, pulmonary edema and shock. It could be fatal if not treated immediately.

The average median period for the appearance of symptoms is around 10 days but in some cases, the virus can stay dormant for a long period of time. These cases, known as persistent infections, can pose a health challenge. Residual damage is a possibility in a small number of people. We also need to study the role of pre-existing co-morbid factors.

What is the treatment for Lassa fever? Do we have a vaccine against the virus?

As of now, doctors give medicines to relieve the symptom and to prevent haemorrhage, shock and multisystem organ failure. There are reports that early use of an antiviral drug, ribavirin can help. Currently, there are no vaccines but the research is on.