Plant sap may cause Africa's commonest children's cancer
The sticky sap of the African milkbush may be an important cause of Burkitt's lymphoma - the most common childhood cancer in much of Africa - according a new study in the British Journal of Cancer.
Africans use the white sap that gives the plant its name to make glue and herbal medicines, while children use it as a gooey toy.
But scientists in the US have found that exposure to the sap may make children more susceptible to the effects of a cancer-causing virus.
Burkitt's lymphoma is a tumour of the immune system and is the most common childhood cancer in Central Africa, although in Western countries it is rare. While scientists think infection with Epstein-Barr virus is the major cause, they have struggled to identify other risk factors.
But several teams of researchers have noticed that rates of Burkitt's lymphoma are much higher in areas of Africa where the milkbush is common than where it is rare.
In the new study, scientists from the University of Michigan grew milkbush plants in the laboratory and studied how the sap affected the behaviour of Epstein-Barr virus.
The virus often lies low within human cells, without causing much harm, but scientists found that even very low concentrations of sap seemed to switch it into a more active state, in which it was much more likely to trigger cancer.
In particular, milkbush sap seemed to make Epstein-Barr virus switch on three genes crucial for its ability to replicate and infect new cells - processes vital for the virus's cancer-causing effects.
Lead researcher Dr Rosemary Rochford, of the School of Public Health at the University of Michigan, says: "In countries like Kenya and Tanzania, it is common to see people growing the milkbush as fencing around their homes, making it into medicine, or children using the gooey sap as a toy. Yet we've found evidence that they may unknowingly be putting themselves in danger."
Nobel Laureate Sir Paul Nurse of Cancer Research UK says: "In Africa a depressingly high proportion of children die with almost no treatment, so it is particularly important to identify the factors that may be increasing their risk, in order to help prevent the disease.
"Further research is necessary to confirm the link between exposure to milkbush sap and Burkitt's lymphoma. But this study could be important, if avoiding exposure to the plant reduced the number of children suffering from the disease."
Note to Editors:
Cancer Research UK is Europe's largest cancer charity and owns the British Journal of Cancer.
The milkbush (Euphorbia tirucalli) is a tropical plant that grows in many parts of Africa and in the Amazon rainforest of South America.
Researchers found that milkbush sap turns up the levels of three viral genes - BZLF1, EAD and gp350. These play key roles during different stages of the virus's lytic cycle, in which it replicates, kills cells and moves out to infect new ones.
Scientists believe that the chemical 4-deoxyphorbol ester may be responsible for switching up the levels of viral genes.