Press Release: Department of Community Health Confirms Human Case of Bovine TB

[Fierkej]

FOR IMMEDIATE RELEASE CONTACTS: Geralyn Lasher (517) 241-2112
April 10, 2002 Bridget Patrick (517) 324-3438

Department of Community Health Confirms Human Case of Bovine TB
Michigan Department of Community Health officials today announced that an elderly individual was diagnosed with bovine Tuberculosis (TB), but died from unrelated causes in February. DNA fingerprinting conducted by the Department of Community Health laboratory has determined the strain of Mycobacterium bovis found in the individual is the same found in cattle and deer in Northern Lower Michigan. The source of infection is under investigation.
“Bovine tuberculosis is a serious bacterial disease that affects primarily the lungs and sometimes the digestive tract of livestock, deer and other wildlife,” said Michigan Department of Community Health Director James K. Haveman, Jr. “Due to the fact that it is slow growing, it has taken some time to culture the bacterium and conduct the appropriate DNA testing.” The individual lived in a rural area within the Northeast Lower Peninsula. The patient was not coughing and was not likely to transmit disease, Haveman said.
“This patient had underlying health problems and any form of tuberculosis is a risk for persons with history of chronic illness or the elderly,” said Haveman. “In this case, tuberculosis was not the cause of death, but was discovered as part of the patient’s diagnostic workup.”
Physicians and laboratories in Michigan are required by law to report communicable disease cases, including tuberculosis, to local health departments. Rapid and complete reporting assures that timely public health investigations and interventions prevent the spread of disease.
The Michigan Department of Community Health, in conjunction with the state’s Bovine TB Eradication Project, continues to emphasize standard bovine TB prevention practices. Because the bacterium is most often found in lung tissues the disease is primarily spread through breathing or coughing but can also be spread by drinking unpasteurized milk or eating improperly cooked meats from infected animals.
Decades ago, unpasteurized milk served as a major source of human infections. Milk in Michigan has been required for years to be pasteurized to assure the safety of Michigan’s milk supply. Farm families and others are reminded not to drink unpasteurized milk.
“The possibility of humans contracting bovine TB from animals continues to be extremely remote,” said Michigan bovine TB eradication coordinator Bob Bender. “However, hunters or individuals who come into contact with TB-infected animals are encouraged to take extra precautions and contact their physicians concerning the need to have regular TB skin tests.”
(More)
Bovine TB—Page 2

Extra precautions while handling animals include wearing disposable latex gloves and washing your hands afterward. TB skin tests are offered at local health departments or private physicians' offices. A positive skin test reveals infection, not disease, and does not identify the type or source of the exposure. Bovine TB can be effectively treated in humans, so it is crucial to contact a physician if an individual thinks they have been exposed or have symptoms of tuberculosis including persistent cough, night sweats and unexplained weight loss.
Local health departments in the rural counties where bovine tuberculosis has been confirmed have offered tuberculin skin testing to all persons who feel they may have been exposed to bovine tuberculosis (custom processors, camp personnel, hunters) in their areas free of charge. They are also providing testing to all persons on farms with affected herds.
All meats, including hunter-harvested deer, should be thoroughly cooked to an internal temperature of 165 degrees F for 15 seconds to kill bacteria. If the lungs, ribcage or internal organs from wild deer look abnormal (multiple tan or yellow lumps), the meat should not be eaten and the deer should be taken to a Michigan Department of Natural Resources check station.
Livestock in Michigan destined for consumer use are cooperatively scrutinized by the Michigan Department of Agriculture and the US Department of Agriculture to assure that meat products meet stringent requirements that guard the safety of the food supply.
Consumers also play an important food safety role once meat leaves the retail counter. Prudent handling such as proper hand and utensil washing, proper refrigeration, and using a meat thermometer to cook meat to the proper temperature are all very important.
Since bovine TB was re-discovered in Michigan in the mid-1990’s, the state has moved aggressively to develop and implement a comprehensive and stringent TB testing strategy and protocol. Since 1995 more than 760,000 TB tests have been conducted on Michigan cattle, bison and goats and 16,500 privately owned cervids have been tested or are under a herd surveillance plan. In 1997, one privately owned cervid herd was identified with TB and was depopulated. To date, 19 cattle herds have been diagnosed with bovine TB. Two dairy herds are under plans that remove animals responding to TB skin tests, and 17 beef herds have been depopulated.
In addition, over 88,373 TB tests have been conducted on wild white-tailed deer and elk, with 397 deer and two elk confirmed with the disease. Carnivore tests for 2001 revealed two TB positive coyotes, two bobcats and three probe-positive bear, bringing the total number of carnivores that have tested positive for bovine TB to 30.
The Bovine TB Eradication Project is a multi-agency team of experts from the Michigan Departments of Agriculture, Community Health, and Natural Resources, Michigan State University and the U.S. Department of Agriculture. Information on the Michigan Bovine TB Eradication Project can be found at www.bovinetb.com

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[Shoes]

:confused: Okay, now that we have evidence contrary to the perceptions painted previously by all agencies, the next question is, "How vulnerable are humans to exhibit the symptoms and experience the outcome of the disease as compared to deer?"

Also, this seems to open up a whole new can of worms regarding precautionary measures that should be taken while gutting, skinning, and/or butchering a deer. Furthermore, should all successful hunters request TB skin test, since many infected deer will not exhibit the symptoms? Where does one draw the line with respect to the probability of becoming infected?

[Fierkej]

Shoes,

Your questions/comments have been forwarded to the appropriate state agency. We will post their response when we receive it.

[Fierkej]

The following response comes in part from Bridgett Patrick, Communications Coordinator, Bovine TB Eradication Project and from an occupational safety report regarding bovine tb by O'Brien, Raths and Schmitt of the Rose Lake Lab:

From Shoes' previous post: Okay, now that we have evidence contrary to the perceptions painted previously by all agencies, the next question is "How vulnerable are humans to exhibit symptoms and experience the outcome of the disease as compared to deer?"

Bovine tuberculosis (TB) is a disease caused by the bacterium Mycobacterium bovis, which is a different strain of mycobacterium that usually infects humans, but can affect any warm-blooded animal, including humans.

Tuberculosis is capable of infecting anyone, even healthy people. However, decades of studying tuberculosis in humans has shown that some groups of people are at greater risk than others of being infected with TB. These groups include the elderly, injection drug users, prisoners, alcoholics, patients undergoing immunosuppressive chemotherapy, those with cancer, autoimmune diseases (for example, Lupus), or those who have undergone surgical transplantation, and immigrants from countries with a high background prevalence of TB (generally, in Asia, Africa, and Latin America). What these groups have in common are that 1) they either have immune systems that are not functioning well enough to fight off the infection, or 2) they are from areas where there are, relatively speaking, large numbers of TB infected people or animals, and so they simply have a greater chance of coming into contact with the bacteria.
Tuberculosis is different from many other diseases in that it has the ability to infect a person, but then remain undiscovered in the person’s body without causing any noticeable symptoms of sickness. This state is called “latency”. People with latent TB are not infectious to others, and most (about 9 out of 10) stay in the latent state for their entire lives. However, some people with latent disease sooner or later develop “active” TB, that is, they become obviously ill and are capable of spreading their TB to other people and to animals. Groups at greatest risk of progression from latent to active TB include people who have the Human Immunodeficiency Virus (HIV) or Acquired Immune Deficiency Syndrome (AIDS); those with silicosis (a type of lung disease), sugar diabetes, some blood disorders and cancers; people who have had their stomachs or portions of bowel surgically removed, or who are on high dose cortisone or immunosuppressive chemotherapy; those at least 10% below their ideal body weight; kidney failure patients undergoing dialysis; and children less than 4 years old.

When people develop active TB, they generally have one or more of a characteristic set of symptoms. These include persistent (greater than 3 weeks duration) cough, which often produces bloody phlegm (called “sputum”), unexplained weight loss, loss of appetite, persistent fever, and night sweats. Depending on the place in the body affected by the TB infection, other symptoms specific to body site can also occur (swollen lymph glands, skin sores, bone and joint pain, kidney and bladder infections, and others).

About 2 to10 weeks after a person is initially infected, a normal immune response in that person generally limits further spread of the bacteria in the body. However, the tuberculosis bacteria can survive for long periods in immune cells called macrophages. This state is referred to as “latent TB”. A person in this state, while she/he usually has a positive skin test, has no symptoms of the disease and is not infectious to others. TB can remain latent in a person for a lifetime, or progress to active disease at some future date when the person’s immune system is weakened sufficiently. The risk of this progression is greatest in the first 2 years post-infection. So, people with latent tuberculosis usually require periodic monitoring to allow health care professionals to make sure they are not progressing to active disease.



From Shoes' previous post: Also this seems to open up a whole new can of worms regarding precautionary measures that should be taken while gutting, skinning and/or butchering a deer. Furthermore, should all successful hunters request TB skin test, since many infected deer will not exhibit the symptoms? Where does one draw the line with respect to the probability of becoming infected?

Extra precautions while handling animals include wearing disposable latex gloves and washing your hands afterward. TB skin tests are offered at local health departments or private physicians' offices. A positive skin test reveals exposure, not infection, and does not identify the type or source of the exposure.

It is very important to understand that becoming infected with tuberculosis is not just something that happens out of the blue. There are a number of separate events that have to happen in order for the disease to be transmitted. If this chain of events is interrupted at any point, the disease can be prevented from passing from an infected animal to people.

First of all, in order to be infected, an individual must be exposed to an animal infected with M. bovis. That means that the population of animals in the area has to have a sufficiently high prevalence of the disease in order for them to have contact with an infected animal. This fact alone makes it unlikely that one will be exposed to an animal with TB. In the geographic area at the core of the tuberculosis outbreak (old Deer Management Unit 452) in 2000, the apparent prevalence of TB was 2.3%. That means that in the area of the state most affected by tuberculosis, DNR testing suggests that only about 2 out of every 100 deer are infected with the disease. Even if testing was missing half of the deer actually infected, the prevalence was still less than 5%. In other areas of the state, the prevalence of tuberculosis is even lower, meaning it is even less likely that one will be exposed to a TB infected animal.

Second, even if an animal is infected, it has to have tuberculosis bacteria present in its tissues in high enough numbers to infect a person. Even though, in theory, even a single bacterium could infect a person, in reality, the chances of a person becoming infected are related to the dose (number) of M. bovis bacteria they are exposed to. This means that, in general, animals that have lots of bacteria in their bodies pose a greater risk than those with only a few. High numbers of bacteria are generally present only in abscesses (sometimes called “gross lesions”, meaning signs of disease that can be seen with the naked eye). Deer that have tuberculosis that has spread throughout their bodies (called “disseminated disease”) have many more M. bovis bacteria, and so pose the highest risk for transmitting the disease to people. It is important to understand that these deer are only a very small percentage of the total deer that pass through a check station. For example, in 2000, only 25 deer that tested positive for M. bovis had TB lesions in areas of the body other than the head, out of the nearly 26,000 deer tested for TB and the over 49,000 deer that passed through DNR check stations. The chances of an individual being exposed to one of these deer with widespread disease is very low.

Third, even if a person is exposed to animals with disseminated disease, the tuberculosis bacteria have to have a way to get out of their abscesses and into the air (where a person could inhale them) or onto the skin (where they could get into the body through cuts and scratches). That is, they have to have a route available to get out of the animal’s body, and be dispersed effectively in order to cause infection. M. bovis bacteria that are effectively sealed up in the animal’s body pose a minimal risk of infection for people.

Fourth, even if the bacteria are effectively dispersed, they have to be taken into a person’s body in order to cause infection. That is, there has to be a failure of control measures that are taken to prevent the exposure of people. So, even if M. bovis bacteria are present in the air, or on the skin, if they are prevented from entering a person’s body by wearing a respirator or rubber gloves, or washing of hands after handling animals, human infection can be prevented.

Finally, even if tuberculosis bacteria effectively get into a person’s body, the person’s immune system has to be sufficiently susceptible in order for them to become infected. Even if a person becomes infected, while it is certainly nothing to take lightly, it does not mean that they will ever actually get sick with tuberculosis. In fact, the vast majority of people who have latent tuberculosis infections will never go on to develop active disease in their lifetimes.

To recap, then, a number of separate events need to happen in order for Wildlife Division staff to become infected with tuberculosis while working on the job, and steps that are taken to interrupt the chain of transmission at any point can prevent people from getting the disease.


People who come into contact with TB-infected animals are encouraged to take extra precautions and contact their physicians concerning the need to have regular TB skin tests.

Bovine TB can be effectively treated in humans, so it is crucial to contact your physician if you have been exposed.

[Shoes]

Fierkej - Thanks for the detailed information. I surmise the risk is low, but there is a risk. Also, there is a need to evaluate the circumstances on a case-by-case basis, and react accordingly.

[sadocf1]

An excellent professional description of the epidemiology of TB in humans. The World Health Organization estimates that 1/3 of the human population, 2,000,000,000 people are infected with TB, 2% of that number with active transmissable disease.
I believe MDCH reported 20 odd human cases in Michigan, 2 of which were of the bovine strain - found in Mexican transients.
One cannot help wondering why the public was not informed of this helpful information 5 or 6 years ago, when all releases to the media screamed of the HIGHLY INFECTIOUS DEADLY DEVASTATING DISEASE!!!
It is also interesting to note that none of the cattle that were found to be infected showed any symptoms of the disease, were apparently healthy, some were high producing dairy cows.