The cheap food policy in this country is probably most evident in livestock raising systems. The vast majority of animals raised for milk, meat or eggs in the United States these days are housed in CAFOs (Concentrated Animal Feeding Operations) on factory farms. As a result, they are crowded inside buildings or into feedlots where conditions are conducive to the spread of disease.
Once an infectious agent (germ) is introduced into a host animal in such an environment, the potential for that infection to spread to other nearby animals is significant. The animals are close together (indoor space is expensive and factory farms try to minimize expenses), manure and urine are omnipresent, and ventilation is costly (especially on cold days when it requires extra heat for the buildings). The sterilizing effects of bio-diverse soil, fresh air, and sunshine, which still exist on small family farms (especially among NOFA members), are too expensive for CAFOs to make available.
Accompanying the growth of this confinement system, naturally enough, has been the growth of outbreaks of disease at American CAFOs. Most notable have been cases of avian flu at large poultry operations — which are located, naturally enough, primarily in the grain-growing breadbasket states. Despite the administration of antibiotics in most of the feed at these facilities, health conditions are so deplorable that when an outbreak occurs it rapidly overwhelms the facility and the response is usually to kill all the birds immediately, dispose of the bodies, sanitize the place as best they can, and start over.
In the six months from mid December to mid June, 2015, an astonishing total of almost 50 million birds died this way, primarily in Iowa (31.7 million), Minnesota, Nebraska, Wisconsin, and South Dakota. Despite repeated warnings from government circles about the dangers to backyard home flocks from wild birds, only 6 small flocks reported deaths. The remaining 217 outbreaks were in large flocks, averaging over 220,000 birds each.
Such a level of outbreaks and death is called a disease epidemic. Many people are familiar with the term when used relating to human health, but the same exact science prevails whether the victims are people or livestock. I thought readers might be interested in learning a little more about the science of epidemics, or epidemiology.
An epidemic is defined as the spread of an infectious disease to a large number of host organisms in a given population within a short period of time. An example of a famous human epidemic is the bubonic plague, caused by a bacterium called Yersinia pestis and carried by fleas. It caused the “black death” in fourteenth century Europe as well as in parts of Africa and Asia, killing an estimated 50 million people. Another human ex-ample is the 1918 influenza pandemic or “Spanish flu” which killed 20 to 40 million people worldwide.
Why are epidemics rare?
What is particularly useful to understand about epidemics, whether among people or among animals, is the answer to the question: Why don’t they happen all the time? Infectious agents (germs) exist everywhere, and so do large populations of potential hosts. Why are epidemics so rare?
The answer is that there are two natural ‘firewalls’ which prevent epidemics from occurring very often.
The first firewall is that of resistance or host immunity. As living creatures we all evolved in the presence of countless parasites and pathogens whose livelihoods depend on infesting or infecting us. As healthy hosts we have developed defenses such as immune systems which normally at-tack such agents and soon prevent them from disabling us. We may feel sick for a few days during the struggle, but if healthy we usually emerge victorious with stronger defenses than before.
The second firewall is that of self-defeating virulence. Parasites and pathogens are most successful if they do not kill — they need a living host’s resources to multiply. A roundworm egg needs to be excreted by the host before it can develop into an adult roundworm. An infestation virulent enough to kill the host pig or sheep will also end the worm’s cycle of life. Similarly, viruses and bacteria need to multiply using the host’s energy and then trigger episodes of sneezing, coughing, diarrhea, etc. to be expelled and infect again. Dead hosts don’t cough. Thus pathogens unwisely virulent enough to kill their host will themselves die off, leaving their less virulent brethren to carry on their infective mission.
What causes an epidemic?
Hosts and diseases usually coexist in a kind of equillibrium. Epidemics, then, are caused by a sudden change in the host, the agent, or the environ-ment. A genetic mutation in the pathogen reservoir can introduce a new, virulent strain of an existing pathogen. If a susceptible host is present, one which has not yet developed resistance to the new strain, an epidemic can result. Similarly, if a host population suddenly becomes weakened – by poor nutrition, overcrowding, stress – its resistance can drop and it can fall prey to infection. Finally, if something changes in the environment – flea-infested rats show up in the Mediterranean aboard ships from the orient, or millions of men are transported from all over the globe to fight a European war in the rain and cold of filthy, overcrowded trenches – infectious agents can suddenly find plentiful hosts with weakened defenses.
The ‘etiology’ of a disease is its cause. In epidemiology, several lines of evidence together are required to infer causation since events may occur together simply due to chance, bias or confounding, instead of one event being caused by the other. Sometimes several symptoms regularly appear together more often than what could be expected, though it is known that one cannot cause the other. These situations are called ‘syndromes’ and normally it is assumed that an underlying condition must exist that explains all the symptoms.
Transmission
Transmission usually refers to the transfer of infectious microorganisms directly from one individual to another by one or more of the fol-lowing means:
• droplet contact – coughing or sneezing on another individual
• direct physical contact – touching an infected individual, including sexual contact
• indirect physical contact – usually by touching a contaminated surface or soil
• airborne transmission – if the microorganism can remain in the air for long periods
• fecal-oral transmission – usually from unwashed hands or contaminated food or water sources due to lack of sanitation and hygiene, an important transmission route in pediatrics, veterinary medicine and developing countries.
Transmission can also be indirect, via another organism, either a vector (e.g. a mosquito or fly) or an intermediate host (e.g. tapeworm in pigs can be transmitted to humans who ingest improperly cooked pork).
Nothing new here!
The risk to animals of harm from sickness is not new. Long before science possessed knowledge of microbiology, ancient thinkers were aware of the role of disease and infectious organisms in threatening the success of a livestock farm. The Roman Marcus Terentius Var-ro (116 BC – 27 BC) wrote three books on agriculture. In Book I, speaking about the ‘steading’ (farmstead), he says:
Especial care should be taken, in locating the steading, to place it at the foot of a wooded hill, where there are broad pastures, and so as to be exposed to the most healthful winds that blow in the region. A steading facing the east has the best situation, as it has the shade in summer and the sun in winter. If you are forced to build on the bank of a river, be careful not to let the steading face the river, as it will be extremely cold in winter, and unwholesome in summer.
Precautions must also be taken in the neighborhood of swamps…because there are bred certain minute creatures which cannot be seen by the eyes, which float in the air and enter the body through the mouth and nose and there cause serious diseases. “What can I do,” asked Fundanius, “to prevent disease if I should inherit a farm of that kind?” “Even I can answer that question,” re-plied Agrius; “sell it for the highest cash price; or if you can’t sell it, abandon it.”
Scrofa, however, replied: “See that the steading does not face in the direction from which the infected wind usually comes, and do not build in a hollow, but rather on elevated ground, as a well-ventilated place is more easily cleared if anything obnoxious is brought in. Furthermore, being exposed to the sun during the whole day, it is more wholesome, as any animalculae (tiny animals, meaning the germs which bring sickness) which are bred near by and brought in are either blown away or quickly die from the lack of humidity.
Perhaps we should learn from the wisdom of the ancients when it comes to how we house and care for our animals?
