Gabriel BitarMundane episodes of life such as a cold sore or greedy Saturday meals at a barbecue restaurant can have serious consequences decades later. Infections caused by viruses, bacteria or parasites, as well as the high consumption of red meat may favor the development of tumors, sometimes through mechanisms as yet unknown. German virologist Harald zur Hausen issued this warning with the authority of someone who discovered the link between the infection caused by the human papilloma virus (HPV) and cancer of the cervix; for this reason he received the Nobel Prize for Medicine in 2008. His presentation marked the beginning of operations of the International Center for Research and Education (CIPE) at the A. C. Camargo Cancer Hospital, in São Paulo, on August 5.
Zur Hausen reiterated the association between infections and cancer. The viruses that cause herpes are linked to skin tumors and to others; HPV is linked to cancer of the cervix, anus, genitals, mouth or pharynx; HIV, which causes AIDS, to skin cancers, such as Kaposi’s sarcoma; and hepatitis B and C viruses to liver cancer. The Helicobacter pylori bacterium can cause ulcers and induce the formation of tumors in the stomach, while the Mycobacteria tuberculosis, in addition to tuberculosis, can cause tumors in lining (epithelial) cells or glands like the adrenal. Among the worms, Zur Hausen remembered Schistosoma haemotobium, which causes schistosomiasis, especially in Africa, which is associated with bladder cancer, and Schistosoma mansoni, which causes schistosomiasis in Brazil and can lead to rectal cancer.
One of the reasons why an infection may favor the formation of tumors, he explained, is the fact that the genetic material of viruses interacts with genes in human cells. Once altered, the genes can change the mechanisms of DNA replication or repair and facilitate the proliferation of abnormal cells. Viruses, bacteria and parasites can also cause chronic inflammation, which deregulates the body’s defenses. Roughly 21% of the cases of cancer worldwide are caused by infections,” said Zur Hausen. Of this total, 71% could be avoided by vaccines, antibiotics or anti-worm drugs. In Brazil, 26% of the cases of cancer could be avoided by preventing infections, according to a recent study by the National Cancer Institute (Inca).
Luckily, the evolution of an infection to a cancer is generally slow. Cervical cancer appears 15 to 20 years after the HPV manifested itself and liver cancer 30 to 60 years after the onset of hepatitis B or C. An exception is the Epstein-Barr virus, which can trigger the formation of tumors in the pharynx in less than a year after the virus has taken hold in the body. Conversely, infections can sometimes prevent cancer, as in the case of leukemia. “Risk factors for childhood leukemia are rare infections and of high socio-economic status,” he said.
Diet can also accelerate or delay the development of tumors. “Argentina, Uruguay, New Zealand and the United States are the countries that have the highest consumption of red meat and those with the highest number of cases of bowel and breast cancer, and lung cancer in non-smokers,” commented Zur Hausen, who presented in graphs and tables showing how red or processed meat increases the incidence of cancer and how the consumption of fruit and vegetables contains it. His hypothesis is that an infection caused by a virus that he calls TT is directly related to bowel cancer.
Not everything is clear. According to zur Hausen, cooking or frying red meat can release substances which are still little known and that combine with compounds in the body, forming molecules that benefit the tumors.”Fried or grilled chicken seems not to release these compounds,” he said. “There are suspicions that cow’s milk can transmit cancer-causing agents from the cow to human beings.” Even so, zur Hausen has not become a vegetarian. “I still like red meat. I’m 74 years old; I’m in the final phase of my life and know my risks.”
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