The Dairy Dilemma: Part 6: Pathogens and Environmental Hazards

Though milk is a natural product, it can pick up very unnatural substances during the course of the life of its source, a milking cow.


Milk, even after it is pasteurized, can contain dangerous microorganisms

Food Poisoning
Microorganisms such as Salmonella, Listeria, Campylobacter, Brucella, Shigella and E. coli
are some of the foodborne pathogens that human beings can be exposed to through contaminated food. Outbreaks caused by these pathogens have occurred after ingestion of dairy foods.

Milk that has been pasteurized, which means it has been treated with a heating process that is assumed to kill any microbes present in the milk, can still harbour potentially dangerous microorganisms and can be a source of food poisoning. Pasteurized milk has been the confirmed source of poisonings caused by Salmonella, Campylobacter, Staphylococcus, Novovirus, Clostridia, Listeria and Shigella species of microorganisms (1,2,3,4,5).

Improperly handled raw milk is responsible for nearly three times more hospitalizations than any other food-borne disease source, making it one of the world’s most dangerous food products (1,4).

Bovine Leukemia Virus (BLV)
Perhaps even more disturbing is the presence of Bovine Leukemia Virus (BLV) in the milk of dairy cows. In Canada 78% of dairy herds contain animals that have antibodies to BLV, indicating its presence at some point in the life of the cow (6). Mammary gland tests show that 83% of dairy herds in the US are infected (7).

Why is this important for human beings? The International Agency on Research for Cancer states that up to 20% of all cancers are linked to infections and particularly to infections caused by viruses (8). In one study, 74% of human blood samples tested showed antibodies to BLV. This does not necessarily mean that these human beings were infected with BLV, however it does suggest that exposure to BLV may be widespread (9). Later tests that examined breast tissue samples from surgeries on women found the BLV virus itself present in 44% of the samples tested (10).

The next question is whether or not the presence of this virus is causing harm to humans. A 2015 study found BLV in 59% of breast cancer patients, a significantly higher level than the 29% rate observed in the healthy control patients in this study. Researchers observed that the presence of bovine leukemia virus DNA in breast tissue was strongly associated with diagnosed and confirmed breast cancer and they calculated that 37% of breast cancer cases may be attributable to BLV exposure (11). It is not known yet whether the presence of BLV in healthy women is an indication higher breast cancer risk in the future.

Mycobacterium Paratuberculosis and Diabetes
Type-1 diabetes is an autoimmune disease. It has been known for decades that exposure to cow’s milk is associated with the development of type-1 diabetes, increasing the risk by 150% (12). The mechanism for this is thought to be “molecular mimicry” where a foreign body such as a virus or a bacterium causes an immune response that spreads to a similar protein in our bodies. For example, if that similar protein is part of the make-up of pancreatic tissue, the immune system will not only attack pathogenic microbes, but also the pancreas itself, with development of type-1 diabetes as the devastating result (13).

During the 1980’s and 1990’s a protein in the human pancreas was identified that closely resembled bacteria of the Mycobacteria family. A member of this family, Mycobacterium avium paratuberculosis (MAP), has been found in significant numbers in the milk and milk products from dairy cows (14,15,16). The last national survey of dairy herds in the U.S. shows that 68% of US dairy herds are infected with this bacterium (17). Contaminated milk and milk products, along with contaminated meat, appear to be the largest contributors of MAP in human beings (18). Compounding the problem is that current methods of milk pasteurization are not sufficient to kill all MAP microorganisms (15). Research has found that the immune systems of children with newly-diagnosed type-1 diabetes react to MAP (DA) and that the DNA of MAP is present in the blood of autoimmune (type-1) patients but not in non-autoimmune (type-2) diabetics (DJ). It is theorized that genetics are also involved in this process, with some genes affecting the susceptibility of humans to mycobacterium infections and their subsequent development of type-1 diabetes (19).

Multiple studies have shown the association between the consumption of milk from cows and the prevalence of type-1 diabetes (12,33,34). The relationship between MAP in dairy products with type-1 diabetes is still controversial but the evidence linking these two factors is becoming more compelling as further research results are gathered. Future investigation is needed to connect all these factors, proving that ingesting milk will increase the risk of developing type-1 diabetes.

Ear infections in children
Scientists have long acknowledged an association between cow milk exposure and recurrent ear infections in children. It is thought that an allergy to milk is the mechanism for this effect. Studies have found that children with cow milk allergy experience significantly more recurrent ear infections (otitis media) than children not suffering from an allergy to cow’s milk (20). Researchers recommend that all children with recurrent ear infections be tested for allergy to milk or other foods (21,22). Despite many studies pointing to this link, definitive proof is lacking and more research is needed (23).


Dairy products contain environmental pollutants

Many of the pollutants in our environment are present in the milk of dairy cattle. The chemicals enter the animals through the contaminated plants that they eat.

Dioxins and furans are common names for a group of chemicals formed during combustion processes such as waste incineration, power generation, fuel burning and metal production. They are very persistent in the environment. Human exposure to these chemicals is mainly through the diet. Health effects associated with these substances include liver problems; impairment of the immune system, endocrine system and reproductive system; certain types of cancers; effects on developing nervous systems; and skin problems. Dioxins and furans accumulate in the fatty portions of animal-derived foods so, if you do consume dairy products, avoid high-fat milk and cheese and choose products low in fat such as skim milk (24).

Polychlorinated Biphenyls (PCBs) are man-made chemicals. Though they were banned in North America in 1977 they are very persistent and are still found throughout our environment. Humans continue to be exposed to low levels of PCBs through the foods we eat. Once PCBs get into the environment, they accumulate in the cells of animals. Animals at the top of the food chain, including humans, harbour the highest concentrations of PCBs.

Health effects of low-level environmental exposure to PCBs are complex and further investigation is needed. High levels of PCBs, such as those which occur in people who work in industries that use or manufacture PCBs, include liver damage, respiratory problems and skin lesions. Animal studies show toxic responses such as cancer development, liver abnormalities, immunosuppression, neurotoxicity, reproductive and developmental toxicity and thyroid injury (25). PCBs tend to accumulate in the fatty portions of animal-derived foods so you may want to avoid high-fat dairy products (26,27).

Organochlorine pesticides (OCPs) such as DDT are synthetic pesticides that are derived from chlorocarbon and were once widely used in the chemical industry and agriculture. They are now banned in most countries of the world. OCPs are highly toxic, take a long time to breakdown and contaminate both water and agricultural land. OCPs are associated with endocrine disorders, effects on embryo development, lipid metabolism disorders and alterations in blood and liver process with unverified carcinogenic effects (28). Once again, these chemicals accumulate in fatty tissues with animals such as dairy cows concentrating these substances in their body fat and in their milk. Pesticides such as DDT that were banned decades ago still appear in dairy products (29,30,31).


In summary…

Milk can be contaminated in many ways. Poor agricultural and veterinary practices, inferior hygienic and industrial systems, direct contact with pesticides or the inevitable exposure to environmentally persistent chemicals can all pose a potential threat to human health (32). Such contamination is an invisible and insidious threat to our health. Awareness of this situation must be incorporated into the decision to include dairy products in our diet.



1 Langer, A.J., Ayers, T., Grass, J., Lynch, M., Angulo, F.J., Mahon. B.E. Non-pasteurized Dairy Products, Disease Outbreaks and State Laws – United States, 1993-2006. Emerg Infect Dis. 2012 Mar; 18(3): 385–391.

2 Comparing the Food Safety Record of Pasteurized and Raw Milk Products

3 Anand, S. Corralling milk microbes that survive pasteurization. South Dakota State University. ScienceDaily. 8 April 2014.

4 Sarkar, S. Microbiological Considerations: Pasteurized Milk. International Journal of Dairy Science. 2015; 10: 206-218.

5 Food safety of raw milk. 8 April 2014.

6 Nekouei, O., VanLeeuwen, J., Sanchez, J., Kelton, D., Tiwari, A., Keefe, G. Herd-level risk factors for infection with bovine leukemia virus in Canadian dairy herds. Prev Vet Med. 2015 May 1; 119(3-4):105-113.

7 Frie, M.C., Sporer, K.R.B., Benitez, O.J., Wallace, J.C., Droscha, C.J., Bartlett, P.C., Coussens, P.M. Dairy Cows Naturally Infected with Bovine Leukemia Virus Exhibit Abnormal B- and T-Cell Phenotypes after Primary and Secondary Exposures to Keyhole Limpet Hemocyanin. Front. Vet. Sci., 14 July 2017.

8 Alibek, K., Kakpenova, A., Mussabekova, A., Sypabekova, M., Karatayeva, N. Role of viruses in the development of breast cancer. Infect Agent Cancer. 2013 Sep 2;8:32.

9 Buehring, G.C., Philpott, S.M., Choi, K.Y. Humans have antibodies reactive with Bovine leukemia virus. AIDS Res Hum Retroviruses. 2003 Dec;19(12):1105-1113.

10 Buehring, G.C., Shen, H.M., Jensen, H.M., Choi, K.Y., Sun, D., Nuovo, G. Bovine leukemia virus DNA in human breast tissue. Emerg Infect Dis. 2014 May;20(5):772-782.

11 Buehring, G.C., Shen, H.M., Jensen, H.M., Jin, D.L.. Hudes, M., Block, G. Exposure to Bovine Leukemia Virus Is Associated with Breast Cancer: A Case-Control Study. PLoS One. 2015 Sep 2;10(9):e0134304.

12 Gerstein, H.C. Cow’s milk exposure and type I diabetes mellitus. A critical overview of the clinical literature. Diabetes Care. 1994 Jan;17(1):13-19.

13 The 64K question in diabetes. Lancet. 1990 Sep 8;336(8715):597-8. No authors listed.

14 Sorensen, O., Rawluk, S., Wu, J., Manninen, K., Ollis, G. Mycobacterium paratuberculosis in dairy herds in Alberta. Can Vet J. 2003 Mar; 44(3): 221–226.

15 Marchetti, G., Coccollone, A., Giacometti, F., Riu, R., Serraino, A. Mycobacterium Avium Susp. Paratuberculosis in Dairy Production. Fr Italian Journal of Food Safety, Vol. 1 N. 4 Giugno 2012 .

16 Grant, I.R., Ball, H.J., Rowe, M.T. Incidence of Mycobacterium paratuberculosis in Bulk Raw and Commercially Pasteurized Cows’ Milk from Approved Dairy Processing Establishments in the United Kingdom. Food Microbiology. DOI: 10.1128/AEM.68.5.2428-2435.2002.

17 Aphis. Info Sheet, Veterinary Services, Centers for Epidemiology and Animal Health, April 2008. Johne’s Disease on US Dairies – 1991 to 2007.

18 Atreya, R., Bülte, M., Gerlach, G.F., Goethe, R., Hornef, M.W., Köhler, H. et al. Facts, myths and hypotheses on the zoonotic nature of Mycobacterium avium subspecies paratuberculosis. Int J Med Microbiol. 2014 Oct;304(7):858-867.

19 Dow, C.T., Sechi, L.A. Environmental Triggers of Type 1 Diabetes Mellitus – Mycobacterium Avium Subspecies Paratuberculosis (A peer-reviewed Chapter). Published: November 25th 2011. DOI: 10.5772/20614.

20 Juntti, H., Tikkanen, S., Kokkonen, J., Alho, O.P., Niinimäki, A. Cow’s milk allergy is associated with recurrent otitis media during childhood. Acta Otolaryngol. 1999;119(8):867-873.

21 Arroyave, C.M. Recurrent otitis media with effusion and food allergy in pediatric patients.
Rev Alerg Mex. 2001 Sep-Oct;48(5):141-144.

22 Cheng, X., Sheng, H., Mab, R., Gao, Z., Han, Z., Chi, F. et al. Allergic rhinitis and allergy are risk factors for otitis media with effusion: A meta-analysis. Allergologia et Immunopathologia. Jan/Feb 2017; 45(1): 25-32.

23 Doyle, W.J. The link between allergic rhinitis and otitis media. Curr Opin Allergy Clin Immunol. 2002 Feb;2(1):21-25.





28 Nicolopoulou-Stamati, P., Maipas, S., Kotampasi, C., Stamatis, P., Hens, L. Chemical Pesticides and Human Health: The Urgent Need for a New Concept in Agriculture. Front Public Health. 2016; 4: 148.

29 Waliszewski, S.M., Villalobos-Pietrini, R., Gómez-Arroyo, S., Infanzón, R.M. Persistent organochlorine pesticide levels in cow’s milk samples from tropical regions of Mexico. Food Addit Contam. 2003 Mar;20(3):270-275.

30 Lukina, Maria. Pesticides are accumulated in the fat tissue. Fat Eastern Federal University Marine Pollution Bulletin. Eureka Alert; February 28, 2018.

31 Sala, M., Caminiti, A., Rombolà, P., Volpe, A., Roffi, C., Caperna, O., Miceli, M., Ubaldi, A., Battisti, A., Scaramozzino, P. Beta-Hexachlorocyclohexane Contamination in Dairy Farms of the Sacco River Valley, Latium, Italy, 2005. A Retrospective Cohort Study. Epidemiol Prev. 2012 Sep-Oct; 36 (5 Suppl 4): 34-43.

32 Fischer, W.J., Schilter, B., Tritscher, A., Stadler, R. Contaminants of Milk and Dairy Products: Contamination Resulting from Farm and Dairy Practices. Encyclopedia of Dairy Sciences 2011. 887-897.

33 Dahl-Jørgensen, K., Joner, G., Hanssen, K.F. Relationship between cows’ milk consumption and incidence of IDDM in childhood. Diabetes Care. 1991 Nov;14(11):1081-1083.

34 Virtanen, S.M., Räsänen, L., Aro, A., Lindström, J., Sippola, H., Lounamaa, R., Toivanen, L., Tuomilehto, J., Akerblom, H.K. Infant feeding in Finnish children less than 7 yr of age with newly diagnosed IDDM. Childhood Diabetes in Finland Study Group. Diabetes Care. 1991 May; 14(5)

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My name is Debra Harley (BScPhm) and I welcome you to my retirement project, this website. Over the course of a life many lessons are learned, altering deeply-rooted ideas and creating new passions.

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