A single case of Mad Cow disease on a dairy farm in the United States last month has sent shock waves through the nation's $175 billion beef industry. But as journalist and veterinarian Mark Jermone Walters claims in his book Six Modern Plagues: and How we Are Causing Them Mad Cow is just part of a wave of new global infections. Since the Washington state mad cow incident was first reported last month, 36 countries have banned the import of U.S. beef and a study by the National Cattlemen's Beef Association reports a 15 percent drop in cattle prices, a significant shock to the U.S. farm economy.

A CNN-Time poll released last week says 27 percent of Americans have either reduced their consumption of beef or stopped eating it altogether. Since the mad-cow epidemic emerged in Europe in the early 1990s much has been learned about the brain-wasting disease. At its peak in England approximately one million cows were slaughtered. New international rules, including a ban on feed rendered from potentially tainted animal parts have worked to curb the infection. Author Mark Jerome Walters says old diseases like malaria and tuberculosis, once thought to be controlled, are re-surging. Others like Mad Cow, Lyme disease, Salmonella, SARS, Hantavirus and HIV-AIDS the six epidemics discussed in his new book - are imposing new public health risks.

"And so you find this whole range of new infections, from old to new that is reconfiguring itself. It is mutating," said Mr. Walters. "There is some reason that this is all happening together. And the reason is that we have made radical changes in the environment and thereby put humans in the way of diseases that evolutionarily did not tend to mess [bother] us very much."

Mr. Walters says in his introduction to the book that the larger story is not simply that humans and other animals are falling victims to new diseases, but that humans and animals are causing these diseases or making them worse.

"One of the points that I wanted to make in my book was to begin to get past the old human archetype of [that] 'we are in a war against Nature and if we don't watch out, Nature is going to victimize us,'" he added. "How often we hear about human beings being victimized by disease as if we had absolutely nothing to do with it. We have made changes to the environment, to the ecology, to the natural systems that support us, that has caused the emergence and spread of these new diseases."

"It falls into several categories and sometimes several overlap: for example, agriculture," replied Mr. Walters when asked: How do you connect the emerging health risks to human-imposed environmental changes? "We have seen that industrialized agriculture is clearly responsible for the spread of mad cow disease," he said. "Cattle were never meant to eat meat, let alone each other. You find with industrialized production that the traditionally discarded parts of cattle were ground up and rendered into pellets and fed back to cattle. They were being fed their pasture mates.

"This was a disruption of the natural food chain," continued Mr. Walters. "Consequently mad cow spread very rapidly. That's just one example. We even see [this] in West Nile Virus. Currently Colorado is being hit very badly by this virus which is new to the Western hemisphere as of 1999 [and] there have been over 40 deaths there. One of the reasons it has hit so hard there is that the mosquito that transmits it in that part of the west breeds very well in irrigated fields. And, because of the farming there it has created an ideal habitat for these mosquitoes. So, time and time again with antibiotic resistant disease, salmonella food poisoning, which is common in the U.S. and elsewhere. We feed antibiotics to cattle, not because they are sick, we feed antibiotics to cattle to make them grow faster or to prevent disease because they are kept in naturally unsanitary crowded conditions. And so here we see essentially a public health tool being used to make money at the expense of public health." Twenty three thousand cases of Lyme disease were reported in the United States in 2002. Infected deer ticks are the culprits. Mark Jerome Walters says rapid forest fragmentation has led to an increase in mice and deer, two species that help spread the disease. But, he says, other environmental factors come into play. "The spread of this tick seems to be correlated with temperature rise in the mid-Atlantic [states] and higher humidity and that has permitted the tick apparently to spread further," said Mark Jerome Walters. Now you add to that to have people move from cities to have their 'little kingdoms' homes] at the edge of the woods and you have a perfect confluence of events that have resulted in a very big, serious public health problem."

"I see frequently that reaction to the arguments," answered Mr. Walters, when asked how does he answer critics that deny, for example, the human impact of climate change and by extension, the connection between disease and the environment. "I think that the only way to answer those critics is to point out time and time again how this is occurring and in time will become an undeniable lesson," he said. "We see that many of the large organizations or institutions, that were not critical of the concept, but certainly did not 'but it' [incorporate] into their day to day operations, are now beginning to include in their conversations, veterinarians, ecologists, even ornithologists.

"And you find, what I think has been a very positive evolution on the part of the Centers for Disease Control and Prevention," he continued. 'After West Nile Virus, that organization began to really expand its efforts to bring into the conversation about emerging diseases, people outside the human health field. I think that you are beginning to see changes, and that to me is really one of the most positive signs in this scary phase of epidemics that we are going through. People are beginning to widen their perspective and see that people are a dependent part in a much larger system."

"One of the things that they tell us is that humans beings don't take their place in nature," said Mark Jerome Walters, when it comes to what these diseases tell us about how we live, who we are and our assumptions about modern medicine. "Our place has been given to us, by and large. It is a piece of advice that is word heeding. They [the diseases] tell us that we are a dependent part of a larger system of natural things. 75 percent of these new epidemics have a non-human animal in the picture, as a carrier of it transmitted to people. It tells us that humans are part of the disease grid as [are] other animals. We exit on that same grid, and in part depending on what we do, the viruses, the bugs and bacteria can move across that grid and infect us when they normally might not have."

"It seems to me one of the great possibilities arising from this surge [in the] series of epidemics that we have seen over the last 30 years is that we are going to learn in many ways a dark and necessary lesson," said Mr. Walters, answering what sense of optimism does he bring to this subject, and if it is in our power to understand and control future epidemics. "And it has to become a fundamental assumption of how we do business, how we formulate policy, how we live our daily lives," he added. "And it is that we have to preserve the larger world around us if we wish to remain healthy. That realization in and of itself would be a huge positive outcome of this."

Mark Jerome Walters, author of Six Modern Plagues: And How We Are Causing Them. He says, "human health does not belong to us alone. Nor, unfortunately," he adds, "do the plagues we are all now experiencing."