The Role of Poultry Viruses in Human Cancers

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Does a cancer-causing herpes virus in chickens pose a public health threat?

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Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

The incidence of cancers has been rising for the last half-century, and the question is, why? Well, up to 20% of all cancers are caused by “infectious agents, chiefly viruses”—something we’ve known was a possibility for a century, when a cancer-causing virus was discovered in chickens. It was such heresy that Dr. Rous wouldn’t get his Nobel Prize for this landmark discovery until 55 years later.

If there are cancer-causing chicken viruses, what about people who handle or eat poultry? Concern has been raised about the “potential infectivity” of cancer-causing farm animal viruses for decades. The first question was whether there was any evidence of human exposure. And, indeed, people do have antibodies to these cancer-causing chicken viruses in their bloodstream, indicating that the virus is no stranger to our immune systems. Okay, but is there any evidence that the virus itself can get into our blood? There wasn’t, until 2001.

There’s a cancer-causing herpesvirus in poultry. The question is, does it pose a public health hazard? Researchers used DNA-fingerprinting techniques to test the blood of about 200 people, and 20% had the viral DNA in their bloodstream: one in five.

Okay, but that still doesn’t mean these viruses necessarily can infect human cells. But, indeed, they can. Okay, but do they cause human disease? How are we going to figure that out? Obviously, you can’t just inject people. So, researchers looked at poultry workers. That’s how we figured out how other farm animal diseases jumped to humans—not to mention the discovery of the carcinogenic nature of things like asbestos and benzene. You study the workers who are exposed day in and day out. If they don’t have higher cancer rates, then, presumably, the viruses are harmless. But, unfortunately, they do.

Those at “high exposure to poultry [cancer-causing] viruses” do have “increased risk of dying from several cancers.” So, “the relative ease” by which some of the viruses can infect human cells, and infect and cause tumors in primates in laboratories, may be of public health significance—particularly given the increased risk of cancer among meat workers, and the evidence that we may, indeed, become infected.

Even if poultry workers are at risk, though, doesn’t mean people who just eat chickens or eggs are. Just because those who kill chickens may be “6 times more likely to die from brain cancer,” for example, they’ve got live birds flapping in their face. “The intensity of exposure to these viruses in the general population” is presumably nowhere near that “experienced by poultry workers,” though “the general population is nevertheless widely exposed” to the viruses—just because we do eat so many chickens and eggs.

This is supported by data showing that it’s not only the factory farm workers that are at higher risk for brain tumors, but also butchers or meat-cutters who have no exposure to live birds—especially those that don’t wear gloves, apparently, and who frequently have cuts on their hands. And, for other cancers as well.

Those who handle meat for a living also have higher rates of non-cancer mortality, like increased death from heart disease. Could the viruses be involved there, too? Some of the poultry viruses don’t just cause cancer in chickens, but also atherosclerosis. That cancer-causing herpesvirus also triggers the buildup of cholesterol crystals.

Okay, but that’s in chickens; what about in people? “Because chickens infected with Marek disease virus…develop atherosclerotic lesions after infection[s],” researchers “looked for the presence of [any] herpesvirus…in human artery wall tissue,” and found it—though any role viruses play in human heart disease remains speculative.

But, here we were all along thinking that the substances present in animal foods increasing risk of diseases like cancer and heart disease were like, you know, heme iron, saturated fat, cholesterol, dioxins, cooked meat carcinogens.

But, we didn’t think about the animal viruses, which were “important not only for supermarket workers, but also because the general population is exposed” as well. Indeed, that study that found the chicken cancer virus DNA circulating in people’s bloodstreams found about the same rates in office workers as they did in chicken slaughterhouse workers.

Please consider volunteering to help out on the site.

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

The incidence of cancers has been rising for the last half-century, and the question is, why? Well, up to 20% of all cancers are caused by “infectious agents, chiefly viruses”—something we’ve known was a possibility for a century, when a cancer-causing virus was discovered in chickens. It was such heresy that Dr. Rous wouldn’t get his Nobel Prize for this landmark discovery until 55 years later.

If there are cancer-causing chicken viruses, what about people who handle or eat poultry? Concern has been raised about the “potential infectivity” of cancer-causing farm animal viruses for decades. The first question was whether there was any evidence of human exposure. And, indeed, people do have antibodies to these cancer-causing chicken viruses in their bloodstream, indicating that the virus is no stranger to our immune systems. Okay, but is there any evidence that the virus itself can get into our blood? There wasn’t, until 2001.

There’s a cancer-causing herpesvirus in poultry. The question is, does it pose a public health hazard? Researchers used DNA-fingerprinting techniques to test the blood of about 200 people, and 20% had the viral DNA in their bloodstream: one in five.

Okay, but that still doesn’t mean these viruses necessarily can infect human cells. But, indeed, they can. Okay, but do they cause human disease? How are we going to figure that out? Obviously, you can’t just inject people. So, researchers looked at poultry workers. That’s how we figured out how other farm animal diseases jumped to humans—not to mention the discovery of the carcinogenic nature of things like asbestos and benzene. You study the workers who are exposed day in and day out. If they don’t have higher cancer rates, then, presumably, the viruses are harmless. But, unfortunately, they do.

Those at “high exposure to poultry [cancer-causing] viruses” do have “increased risk of dying from several cancers.” So, “the relative ease” by which some of the viruses can infect human cells, and infect and cause tumors in primates in laboratories, may be of public health significance—particularly given the increased risk of cancer among meat workers, and the evidence that we may, indeed, become infected.

Even if poultry workers are at risk, though, doesn’t mean people who just eat chickens or eggs are. Just because those who kill chickens may be “6 times more likely to die from brain cancer,” for example, they’ve got live birds flapping in their face. “The intensity of exposure to these viruses in the general population” is presumably nowhere near that “experienced by poultry workers,” though “the general population is nevertheless widely exposed” to the viruses—just because we do eat so many chickens and eggs.

This is supported by data showing that it’s not only the factory farm workers that are at higher risk for brain tumors, but also butchers or meat-cutters who have no exposure to live birds—especially those that don’t wear gloves, apparently, and who frequently have cuts on their hands. And, for other cancers as well.

Those who handle meat for a living also have higher rates of non-cancer mortality, like increased death from heart disease. Could the viruses be involved there, too? Some of the poultry viruses don’t just cause cancer in chickens, but also atherosclerosis. That cancer-causing herpesvirus also triggers the buildup of cholesterol crystals.

Okay, but that’s in chickens; what about in people? “Because chickens infected with Marek disease virus…develop atherosclerotic lesions after infection[s],” researchers “looked for the presence of [any] herpesvirus…in human artery wall tissue,” and found it—though any role viruses play in human heart disease remains speculative.

But, here we were all along thinking that the substances present in animal foods increasing risk of diseases like cancer and heart disease were like, you know, heme iron, saturated fat, cholesterol, dioxins, cooked meat carcinogens.

But, we didn’t think about the animal viruses, which were “important not only for supermarket workers, but also because the general population is exposed” as well. Indeed, that study that found the chicken cancer virus DNA circulating in people’s bloodstreams found about the same rates in office workers as they did in chicken slaughterhouse workers.

Please consider volunteering to help out on the site.

Doctor's Note

Other viruses may actually play a role in the obesity epidemic. See, for example, Infectobesity: Adenovirus 36 and Childhood Obesity.

For other potential microbiological hazards in poultry, check out:

And, for potential chemical hazards in poultry, see:

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