An increased risk of colorectal cancer has long been shown for the consumption of undercooked red meat. Fish and chicken do not increase this risk, although comparable or even higher concentrations of potentially cancer-causing chemicals are released during roasting or frying. In Japan and Korea, beef and pork were imported on a large scale after the Second World War and the Korean War. A strong increase in the number of patients with colon cancer was observed after 1970 in Japan and after 1990 in Korea. The consumption of undercooked beef (eg, Shabu-shabu, Korean Yukhoe and Japanese Yukke) became very popular in both countries.
Bovine leukemia virus as a source of colon cancer
A specific beef factor, probably one or more heat-resistant carcinogenic bovine viruses (for example, polyoma, papilloma or bovine leukemia virus BLV) can infect the beef and cause latent and persistent intestinal infections after human consumption (Zur Hausen H).
Polyoma viruses in hamburgersIn chopped beef samples three types of polyoma virus have been shown, which are resistant to BBQ temperatures and are carcinogenic to their natural hosts. Animal viruses are frequently found in meat products and can cause colon cancer in humans. The papilloma and polyoma viruses in particular are resistant to medium-heated steak tartar, in which the central parts of the meat are not heated above 40 - 70 degrees Celsius. These viruses endure 80 degrees Celsius for 30 minutes without losing too much of their ability to cause infections. These viruses are also insufficiently inactivated.
People are exposed to carcinogenic viruses that often occur in animals in the food chain, such as laying hens, eggs, broiler chickens and dairy cows. The Avian Leukemia Virus (ALV) and Bovine Leukemia Viruses (BLV) are RNA viruses and have been shown in breast cancer cells.
Bovine Leukemia Virus in breast cancer cells
Breast cancer and ovarian cancer were rare in Japan, compared with other countries. The mortality rates, however, are increasing. After the Second World War changes in lifestyle took place in Japan. In the past 50 years (1947-1997), mortality rates of breast and ovarian cancer increased 2- and 4-fold, and the respective intake of milk, meat and eggs increased 20, 10 and 7-fold. The increase in death rates from breast cancer and ovarian cancer could be attributed to the increased consumption of animal nutrition, which occurred after 1945. Milk, dairy products and eggs are probably the cause of this (Buehring). Cows are often infected with bovine leukemia virus (BLV), a carcinogenic virus that can be transferred from the cow to the calf via the milk or during birth. Most infected cattle seem healthy and the infection is persistent. Consumption of non-pasteurized dairy products, or cheese made from raw milk, or insufficiently heated beef at the BBQ can transmit this infectious virus to humans. About 38% of the cattle, 84% of the dairy herd, and 100% of factory farm herds in the US are infected with BLV. Less than 5% of these cattle get leukemia. With this condition the animals are not admitted to the US consumer market. The BLV virus circulates with the white blood cells through the blood of infected cattle. The BLV virus also infects the mammary gland cells of the cows and infected cells are found in cow's milk (Lanou AJ). Pasteurization of cow's milk makes the BLV ineffective.
Buehring GC (2015) has shown that 39% of people in a San Francisco Bay Area have antibodies against BLV in the blood, which is an indication of exposure to BLV. Almost all cow's milk contains BLV bovine leukemia virus. In a study of 213 women, BLV-related DNA was found in breast tissue of women with a diagnosis of breast cancer, not in breast tissue of women without a history of breast cancer (Buehring GC).
Both in the hospital case-control study and in the general practice survey in the Hague, lung cancer risk for men under 65 years of age was increased six-fold in those who had kept birds as pets 5 – 14 years before diagnosis of the lung cancer. This finding, coupled with the fact that one household in three or four keeps birds, implies that more than 50% of the total lung cancer rate in men under 65 years of age in The Hague can be attributed to keeping/breeding birds.
The finding of a relation between lung cancer and bird keeping/breeding for men under 65 years of age is supported by a study in West Berlin (Kohlmeier L 1992). Two studies found a relation for lung cancer patients below 55 years of age (Jöckel KH 2002, Kocazeybek B 2003). The study in Scotland (Gardiner AJ 1992) found a significant relation with pigeon keeping for patients 55-64 years of age. And the study in Taipei (Ger LP 1992) found also a significant relation between pigeon keeping and lung cancer. Anttila TI 2003, in a prospective study of Finnish women, found also a significant relation between Chlamydia pneumoniae infection and lung cancer, also among the nonsmoking women.
Experimental induction of lung cancer
Chronic inhalation studies with cigarette smoke machines, in hamsters, dogs and monkeys showed no statistically significant increase in malignant tumors in the airways, although very long exposures and high doses of smoke were used (Coggins CR 2001). These inhalation studies were performed without concomitant infection of the airways of the laboratory animals. The tobacco industry has long cited the studies as evidence for no increase in lung cancer due to smoking.
Recently (Chu DJ 2012) a lung cancer animal model was developed through repeated injection of Chlamydia pneumonia in airways of rats, with or without benzo(a)pyrene. With the combination of benzo(a)pyrene and the bacteria of tropical bird flu in the spray, 44% of the laboratory rats got lung cancer. The bacteria of the bird flu is proven to be an independent risk factor for lung cancer. The combined factors of smoking and Cp chronic infection have superimposed eﬀect and lead to greatly increased lung cancer risk.