Lassa fever: Understanding the risk, response and global threat

The Lassa virus causes Lassa fever, a zoonotic disease; humans usually contract the virus through contact with food or items contaminated by the the Mastomys rat’s urine or faeces.

The story so far

Lassa fever, a viral haemorrhagic illness, has come into prominence after a recent case in Iowa, United States, involving the death of a traveller from West Africa. Lassa fever has been reported in Benin, Côte d’Ivoire, Ghana, Guinea, Liberia, Mali, Nigeria, Sierra Leone and Togo. The disease was first identified in the town of Lassa in Nigeria in 1969, where it continues to pose a significant health threat, affecting an estimated 1,00,000 to 3,00,000 individuals annually, with around 5,000 deaths each year. India’s Ministry of Health and Family Welfare, has classified Lassa fever as a disease of international significance. India has not recorded any documented cases until now (officially, no case reported till 2022). The recent U.S. episode however, highlights the need for proactive measures to prevent potential outbreaks through international travel.

What is Lassa fever?

The Lassa virus causes Lassa fever, a zoonotic disease that is part of the Arenaviridae family, with the Mastomys rat as its primary reservoir. Humans usually contract the virus through contact with food or items contaminated by the rodent’s urine or faeces. Secondary human-to-human transmission occurs through exposure to bodily fluids, raising significant risks, particularly in healthcare settings. The most common symptoms of Lassa fever begin with a gradual onset of fever, general weakness, and malaise, followed after a few days by more severe manifestations such as headache, sore throat, muscle and chest pain, nausea, vomiting, diarrhoea, cough, and abdominal pain. While approximately 80% of infections are asymptomatic or mild, severe cases can present with high fever, severe headaches, and haemorrhage, potentially leading to organ failure. 

Lassa fever has a case fatality rate (CFR) of approximately 1% overall. However, the CFR can escalate to as high as 15-20% among hospitalised patients. Notable sequelae include varying degrees of deafness in nearly 25-50% of patients one to three months after recovery. A definitive diagnosis requires RT-PCR and ELISA tests. Trained personnel need to handle samples under stringent biosafety level-4 (BSL-4) protocols for virus isolation. This barrier limits the widespread ability to diagnose Lassa fever, particularly in regions with under-resourced healthcare systems​​.

Lassa fever poses particularly severe risks for pregnant women and infants. Infected pregnant women, especially those in their third trimester, face an increased maternal mortality rate of over 30%. The disease’s impact on the foetus is devastating, with a foetal death rate exceeding 85%. For children up to two years old, Lassa fever can manifest as “swollen baby syndrome,“ characterised by extensive swelling and associated with a higher fatality rate than that of adults. Vertical transmission has been reported from the mother to the foetus in the transmission of Lassa fever. 

What are the treatment modalities and vaccines developments?

Intensive supportive care for Lassa fever involves closely monitoring fluid and electrolyte balance and assessing renal function, with careful rehydration playing a crucial role. Supportive drug therapy includes the use of painkillers to manage discomfort, antiemetic medication to control vomiting, and anxiolytics to address agitation. Additionally, antibiotics and antimalarial drugs may be administered as needed to manage potential co-infections. The antiviral drug ribavirin should be given in the early phase of the disease to improve survival rates.

Vaccine development for Lassa fever has faced multiple obstacles. The virus’s genetic diversity, marked by at least five known lineages, complicates the creation of a universal vaccine. Moreover, trials for vaccine efficacy often require sufficient incidence rates, which are only achievable during large outbreaks. This restricts the timing and practicality of clinical trials. Additional logistical challenges, such as high costs, vaccine supply sustainability and cold-chain requirements, further complicate widespread vaccine implementation​​. Despite these hurdles, promising research is underway. Preclinical evaluations and early-stage trials have shown progress, with several candidate vaccines advancing toward more robust testing phases. 

What should the public health strategy be?

Effective public health responses require national leadership to prioritise preparedness, enhance diagnostic capacity, and ensure the availability of medical supplies. Public health systems must be fortified to improve patient outcomes by training healthcare professionals in infection control and using personal protective equipment (PPE). 

Minimising rat-to-human transmission is vital to controlling Lassa fever. Limited infrastructure, particularly in endemic regions, constrains efforts to monitor, diagnose, and treat the disease effectively. Effective control strategies emphasise preventing human contact with infected rodents through community education on rodent-proofing homes, storing food securely, and maintaining hygiene. Human-to-human transmission must be mitigated by encouraging early treatment and isolating suspected cases. Healthcare facilities must apply rigorous infection control measures, including using PPE and safely handling patient samples. Governments must coordinate effective public health responses, mobilise resources for surveillance, and partner with global health organisations for expertise and logistical support. 

How do we travel safely?

Travellers’ health is a crucial aspect of public safety, especially for Indian citizens travelling to regions with high risks of infectious diseases. Areas known for diseases like Lassa fever, yellow fever, and malaria pose significant health challenges. Ensuring proper pre-travel health measures, including vaccinations, preventive medications, and awareness of local disease outbreaks, is essential. The Indian government emphasises the importance of travellers obtaining up-to-date health advice, following safety precautions, and maintaining hygiene to minimise risks. This includes enhancing surveillance measures at entry points, including airports, and recommending post-travel health checks for early detection and management of imported cases.

(Dr. C. Aravinda is an academic and a public health physician. aravindaaiimsjr10@hotmail.com)

Published - November 06, 2024 02:19 pm IST