Sticky plant sap may cause the most common deadly cancer affecting children in sub-Saharan Africa, researchers have discovered. White sap from the African milkbush is used by children as a gooey toy or as glue in their schoolbooks, while adults use it to make herbal remedies. But scientists have now found that even tiny amounts of the plant sap can boost the activity of a cancer-causing virus in human cells. The Epstein-Barr virus is thought to be a major cause of Burkitt’s lymphoma, a cancer of the immune system that is rare in Western countries.
In countries like Kenya and Tanzania, it is common for people to use the milkbush as fencing, and the gooey sap as medicine or a toy, says Rosemary Rochford, a virologist at the University of Michigan in Ann Arbor, Michigan. “Yet we’ve found evidence that they may unknowingly be putting themselves in danger,” she says.Nobel laureate Paul Nurse, of Cancer Research UK, says a “depressingly high” proportion of children in Africa with the lymphoma receive almost no treatment and die. “This study could be important, if avoiding exposure to the plant reduced the number of children suffering from the disease,” he says. But he adds that more research is needed to confirm the link.Up to 10 children in every 100,000 suffer from Burkitt’s lymphoma in sub-Saharan Africa, where it is characterised by tumours in the jaw, says Rochford. This compares with only 0.1 cases in every 100,000 children in the Western world.Kick-start Epstein-Barr virus is an extremely common microbe that is harmless in most cases. It sits as a “quiet passenger” in most people’s cells, Rochford told New Scientist. In the West it is commonly picked up in adolescence and can cause glandular fever. In Africa, most children have the virus, transmitted through saliva, by the age of three.However, in certain circumstances the virus can kick-start cancer by driving immune cells called B-cells to proliferate. A link between the cancer and malaria was already known, and exists because the virus multiplies more in a person with a suppressed immune system.In the 1980s, sap from the milkbush (Euphorbia tirucalli) had been suggested by scientists as a third factor causing the lymphoma, following anecdotal reports. But no one had tested its effects until now.Rochford and colleague Adam MacNeill visited Kenya to investigate the reports. “We found the kids playing with the plant a lot because it’s really sticky. And what do kids do with their hands? – they put them in their mouths,” she says.On/off switchBack in their US laboratory, the team tested how the virus responded to various concentrations of sap in human cells. “It actually switched how the virus was replicating in cells. And if you diluted it out a million-fold, it still had the same effect,” says Rochford.She says the sap acts like an “on/off switch” for the virus, activating three crucial genes and leading to rapid replication. The researchers believe they have identified the chemical in the sap that causes this effect.Rochford says the team now hopes to study children with Burkitt’s lymphoma in Kenya to see if they have been exposed to milkbush sap. If a link is established, parents could be educated to keep their children away from the sticky plant.(Source: Journal reference: British Journal of Cancer (vol 88, p 1566): NewScientist.com News Service: Shaoni Bhattacharya: 13 May 2003)