Scientists have cured macaques infected with a worst-case scenario strain of Lassa fever virus.
Lassa fever is a viral disease native to West Africa where it affects around 300,000 people each year. In severe cases, patients may develop seizures or enter a coma.
It’s hard to get accurate figures about Lassa fever infection and survival rates due to poor record keeping. It is, however, thought that most people infected with Lassa fever have no symptoms, meaning they can unwittingly spread the disease.
The infrequent studies that have been done on Lassa fever indicate that when patients are sick enough to seek medical attention, nearly 70% die and, of those that survive, 25% become deaf.
It’s no surprise then, that the USA’s Centers for Disease Control and Prevention classifies the Lassa virus as a “Category A” agent on its bioterrorism diseases and agents list. Such agents are considered the biggest threats to public health and national security.
Professor Thomas Geisbert at the University of Texas describes how this is more than the premise of a Hollywood blockbuster as “the former Soviet Union explored the use of a number of viral fevers, including Lassa, as bioweapons during the cold war.”
Geisbert warns that “there are currently no licensed vaccines or treatments available for Lassa fever”, meaning that the USA would be vulnerable to pandemics caused by the virus.
Geisbert led a multinational team to develop “medical countermeasures” against the Lassa virus. They started by looking for memory B cells in the blood of people who had survived the fever.
Memory B cells play a protective role in your body’s immune system. After you overcome an infection, memory B cells patrol the blood looking out for the same invader.
If they meet the same intruder then they will produce unique antibodies that stick to the intruder’s surfaces, alerting the rest of the immune system to the attack. Once the immune system is aware of the threat, it can begin to fight off the infection.
Geisbert’s hypothesis is that they could take these memory B cells from humans who had survived Lassa fever and use their antibodies to mark the virus in other people, enabling their immune systems to fight the fever.
Geisbert’s team started with over 100 different potential antibodies and narrowed it down to 5 candidates.
Published this week in Nature Medicine, Geisbert’s and colleagues showed how treating cynomolgus macaques, infected with the Lassa virus, with a combination of three of the antibodies, saved 100% of the animals. The macaques were infected with the nastiest strain of the virus, meaning that all untreated animals died.
The scientists found that they could cure all the primates if they started treating them eight days after they had been infected. Primates that have been infected for eight days are really sick - Geisbert explains how some of the untreated animals started dying after day ten and that their work mimics the real world, where “when someone has Lassa fever, they don't come to a clinic or hospital until they are very ill.”
When describing a new therapy that's proven effective in animals, scientists will normally caution that it will be many years of clinical trials before it’s approved for human use.
However, the Food and Drug Administration of the USA has a special “animal rule” that allows medical countermeasures to bioterror threats to skip some of the human trial steps as long as they have proved effective and safe in animals.
Many West African nations, however, don’t have time to wait for a horror story where the USA experiences Lassa Fever bioterror and proves the therapy safe and effective in humans. They are already greatly affected by this virus and need treatments now.
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