THIS SECTION on zoonoses that people acquire from our closest companions would not be complete without considering two of the oldest and deadliest diseases associated with domestic livestock: Bang’s disease (brucellosis) and the white plague (tuberculosis).
Diseases caused by mycobacteria, a family that includes leprosy as well as various forms of tuberculosis, are among the most ancient of zoonoses. Spinal damage typical of some forms of tuberculosis has been found in Egyptian mummies from as far back as four thousand to five thousand years ago.
When leprosy all but disappeared from Europe after the Black Death swept through in the mid-fourteenth century, its sister, tuberculosis, appeared to rise up in a wave and displace it, peaking among the ill-housed and ill-fed industrial workers in the nineteenth century, dropping well before Robert Koch discovered the tubercle bacillus, and continuing to drop as nutrition and housing improved in the early twentieth century, partly in response to the bacteriological discoveries of people like Koch and Louis Pasteur.
Drugs and vaccines provided the tools to finally get rid of it, but TB dug in and held on in areas of poverty and overcrowding, saved in part by misguided politicians and physicians, who now saw diseases as only medical problems and therefore saw no need to work for improving social conditions as a fundamental condition for good health. More recently, concurrent with the collapse of the Soviet Union and the general skepticism among international financial institutions and development donors toward government-sponsored health-and-welfare programs, and along with the spread of AIDS in fragmented economies and marginalized populations, the old white plague is making a comeback.
Now, every year, some eight million people—many in subSaharan Africa, many with concurrent HIV infection—come down with tuberculosis; a couple of million people a year die.
Tuberculosis has a complex social and ecological history. The disease conjures for some the romantic “consumption” of nineteenth-century wraiths and doe-eyed poets. Others think of sanitariums where tubercular people retreated for fresh air in the first part of the twentieth century—now long gone or used as retreats for aspiring writers. Others recall the image of a foolhardy and compassionate Dr. Norman Bethune, kissing a woman with tb so that she could feel some human warmth before she died.
Except for veterinarians, few people think of tuberculosis as a zoonosis. In 1901, Koch stated absolutely that tuberculosis could never be transmitted from cattle to people, and that public health measures to prevent such transmission were ill-advised. He held to this position in the face of a great deal of contrary evidence. Much to the dismay of some veterinary scientists, such as Daniel Elmer Salmon (after whom Salmonella was named), who was the director of the U.S. Bureau of Animal Industry, Koch’s arguments were used to support the sale of meat and milk from animals with tb.
In the next few decades, investigators from the Ministry of Agriculture in the United Kingdom demonstrated that 40 percent of dairy cattle in that country were tuberculous, and that 2,500 people per year, most of them children under five, were dying from bovine tuberculosis.
The pulmonary form of the disease with which many of us are familiar, in which the lungs are invaded and victims cough and spit blood, is transmitted by people spraying bacteria at each other. However, tuberculosis of the bones and intestinal tracts, which is more common in younger people and in developing countries, probably comes from ingestion of organisms through food and could well be from cattle. Scientists don’t usually know which tb is coming from people and which from other animals; even when tb is diagnosed, the countries where it is most common don’t have the facilities to differentiate among the various strains.
The findings from the U.K. in the early twentieth century stimulated disease eradication programs in cattle. Along with test-and-slaughter programs, in which infected animals (or infected herds) were slaughtered, the advent of pasteurization all but eliminated this route of infection in industrialized countries. However, the disease is still widespread in cattle (and other species) in many poor southern countries.
Mycobacteria are still pretty much everywhere, albeit in scattered pockets of poverty or wilderness. In North America, bison and elk are known to be infected. Besides Mycobacterium bovis and M. tuberculosis, M. avium occurs in a wide range of birds, as well as in pigs, cattle, deer—and in people with AIDS. One strain, M. marinum, is found in fish. In the United Kingdom and Ireland, badgers are infected with M. Bovis, and in New Zealand, brushtail possums (Trichosurus vulpecula), ferrets, wild deer, and wild pigs. There is also evidence that dogs, cats, and parrots can get tb from people or cattle.
Given the widespread wildlife reservoirs, the difficulty in treating tb (six months of daily, expensive treatments with some potentially toxic drugs), the pandemic of AIDS (about 10 percent of tb globally is in people with AIDS), and the lack of political will to tackle difficult problems of economic disparity, tb is likely to be with us just about as long as we ourselves manage to stay around. The vaccine, bcg—bacillus Calmette-Guérin, named for the French scientists who developed it—is of uncertain efficacy; originally derived from cattle tb by a veterinarian and a physician, ironically it is even less effective in cattle than in people.
Brucellosis is probably not as old as tb, but a disease that causes abortion in animals and fevers in people is difficult to distinguish from the background noise of the aches and pains of our normal mortal coil. There is archaeological evidence of brucellosis cases going back to the fourth millennium BC in Italy, Egypt, and the Near East, and to 400–230 BC in pre-Roman Britain. Since goats—one of the animal reservoirs for this disease—have been domesticated for about nine thousand years, this news should not be surprising. Also, since the disease was known locally in many areas before anyone knew exactly what caused it, we should not be surprised that it goes by many names: Cyprus fever, undulating fever, Malta fever, Mediterranean fever, relapsing fever, rock fever, and Bang’s disease.
The bacterium that causes brucellosis was isolated in 1887 by David Bruce in Malta. Bruce, also of Trypanosoma brucei fame, was investigating Mediterranean fever, first described by Hippocrates in 450 BC and in the nineteenth century a problem for the Royal Navy. The disease was a chronic, debilitating condition affecting Royal Navy seamen (and other local people, but, as ever, it was the warriors who “mattered”). Themistocles Zammit, a Maltese physician-archaeologist and a member of the British government commission run by Bruce, discovered the natural host for the disease. In the fashion of all good scientists, Zammit made his discovery serendipitously: He was planning to use goats as experimental animals, since they didn’t seem to get sick from the organism. Raw goats’ milk had, until then (and in many places, until now), sometimes been used to help patients in the hospital get well. Zammit demonstrated the organism in the milk of apparently healthy goats. Bruce called the bug Micrococcus melitensis. This organism, later renamed Brucella melitensis, is found almost entirely in goats and in people who handle aborted goat fetuses or drink raw milk or eat fresh cheese made from milk from infected goats. Aging cheese kills a lot of bacteria, as the cheese gets more acidic over time.
In 1897, Danish veterinarian Bernhard Bang found a similar organism, which eventually was christened with the somewhat less mellifluous name Brucella abortus. At least two others are now recognized: B. suis, found in pigs, hares, reindeer, musk oxen, and caribou, and B. canis, found in, well, canines.
The disease in people can start weeks to months after they have ingested the organisms and can include any or all or none of fever, sweats, depression, headache, backache, vomiting, diarrhea or constipation, certain kinds of arthritis—especially sacroileitis—and heart, lung, and urinary tract problems. In animals, the organism causes abortion in females and inflammation of the joints and genital organs in males. It can settle into udders and lymph nodes and be excreted with the animal showing few signs of illness.
The tactics used to get rid of brucellosis have been very similar to those for TB. In this case, the eradication programs had the head start of a good live vaccine—good enough not only to protect cows, but also to infect a lot of veterinarians who accidentally injected themselves while trying to jab the unhappy cattle. Once the level of disease had been decreased through vaccination, livestock farmers could push through with a test-and-slaughter policy.
As for TB, pasteurization all but eliminated brucellosis in people except for abattoir workers, farmers, veterinarians, and all those hundreds of millions of people around the world who like raw goats’ milk and fresh goat cheese, or who can’t afford or who don’t have access to pasteurization or firewood for cooking the milk. Also, as for TB, wildlife reservoirs persist.
In Canada and the United States, from at least the late 1980s on, various scientists, advocacy groups, and politicians wrestled with what to do about infections with B. abortus in wild wood bison in Wood Buffalo National Park in northern Alberta and bison and elk in Yellowstone National Park. “Solutions” have ranged from killing all the bison and putting in “clean” ones, to carrying out some kind of test-and-slaughter program, to building fences around areas the size of Switzerland, to doing nothing. The kill-all-and-repopulate strategy (which many cattle ranchers supported) raises a lot of hackles, given how poorly we understand even the simplest ecosystems. First Nations groups in Canada are skeptical of government intentions and suspect the disease problem is being exaggerated. Up to 2006, the do-nothing side seemed to be winning. It is not clear that brucellosis has any impact on the bison populations; although a female may abort in her first year, she is okay (and immune) in years after that.
In the U.S., hunters and outfitters have supported the setting up of feeding grounds for elk, but those also provide increased opportunity for diseases to spread. Bison and cattle don’t mix much, and some have suggested that vaccinating the bison could get rid of the disease, as long as the elk populations were allowed to fall back to “natural” numbers (no feeding grounds).
When the issue first hit the headlines, I remember some people arguing that we absolutely had to do something, and we had to do it soon, or else . . . I don’t remember where the “or else” led, but probably to reinfected cattle herds and loss of international trade, plus dire public health consequences. But no politician could stomach a public massacre of bison, so the “problem” was left. Both TB and brucellosis shuffle around in these populations, spread, and probably infect some people—hunters, mostly.
How important is brucellosis? It depends on what criteria you are using. Who gets sick is as important as how many. As historian William McNeill points out in Plagues and Peoples, epidemics among armies have changed the course of political and military history. So the British had good cause to be concerned.
Sometimes one case has amazing implications. I recently visited the Sagrada Familia (“Holy Family”) basilica in Barcelona, Spain, the organic, wildly celebratory work by the Catalan modernist architect Antoni Gaudí. According to some of his associates, Gaudi lived on a spartan diet of olive oil, nuts, lettuce, chard, bread with honey, and a few splashes of goats’ milk. In 1911, the splashes of milk caught up with him in the form of a severe bout of brucellosis. This chronically debilitating disease was one of the influences that led him to set aside all other projects and focus exclusively on what was to become his (unfinished) masterpiece, the Sagrada Familia. Without the disease, would the world be culturally poorer?
In the U.S., there are maybe a hundred human cases a year. In Canada, there are far fewer. Brucellosis is described as being “endemic” in parts of Africa, Latin America, the Mediterranean, and Asia, but “endemic” in this case can refer to anything from less than 0.01 sick people per 100,000 to over 200 per 100,000.
No doubt the effects outside North America are far greater than within. It seems to me that the angry passion attached to the debate in North America and the drastic “solutions” proposed are in inverse proportion to the seriousness of the disease. There are programmatic costs—maintaining a surveillance system and trained laboratory personnel—to maintaining a situation where there is always some risk, where the disease is not eradicated, where the bacteria live on in pockets of wildlife, but those are the costs of living in a complex, beautiful, amazing, heartbreaking planet. That’s gotta be worth a few bucks.