TB in deer hunters

For a country that still proclaims, we enjoy the safest food supply in the world in U.S. Department of Agriculture missives, when we’ve been arguing reduced risk is a better message for 25 years and that there are so many countries with the self-proclaimed title of safest food in the world they can’t all be right – it’s alarming that Mycobacterium bovis has been transmitted from deer to a human.

Hello zoonoses.

Deer hunting season in Ontario (that’s in Canada) begins about today.

I never had any interest.

Not a Bambi thing, just thought it was boring.

My dad went a few times but I’m not sure if he enjoyed it or not.


The U.S. Centers for Disease Control reports that in May 2017, the Michigan Department of Health and Human Services was notified of a case of pulmonary tuberculosis caused by Mycobacterium bovis in a man aged 77 years. The patient had rheumatoid arthritis and was taking 5 mg prednisone daily; he had no history of travel to countries with endemic tuberculosis, no known exposure to persons with tuberculosis, and no history of consumption of unpasteurized milk. He resided in the northeastern Lower Peninsula of Michigan, which has a low incidence of human tuberculosis but does have an enzootic focus of M. bovis in free-ranging deer (Odocoileus virginianus). The area includes a four-county region where the majority of M. bovis–positive deer in Michigan have been found.

Statewide surveillance for M. bovis via hunter-harvested deer head submission has been ongoing since 1995; in 2017, 1.4% of deer tested from this four-county region were culture-positive for M. bovis, compared with 0.05% of deer tested elsewhere in Michigan. The patient had regularly hunted and field-dressed deer in the area during the past 20 years. Two earlier hunting-related human infections with M. bovis were reported in Michigan in 2002 and 2004. In each case, the patients had signs and symptoms of active disease and required medical treatment.

Whole-genome sequencing of the patient’s respiratory isolate was performed at the National Veterinary Services Laboratories in Ames, Iowa. The isolate was compared against an extensive M. bovis library, including approximately 900 wildlife and cattle isolates obtained since 1993 and human isolates from the state health department. This 2017 isolate had accumulated one single nucleotide polymorphism compared with a 2007 deer isolate, suggesting that the patient was exposed to a circulating strain of M. bovis at some point through his hunting activities and had reactivation of infection as pulmonary disease in 2017.

Whole-genome sequencing also was performed on archived specimens from two hunting-related human M. bovis infections diagnosed in 2002 (pulmonary) and 2004 (cutaneous) that were epidemiologically and genotypically linked to deer (3). The 2002 human isolate had accumulated one single nucleotide polymorphism since sharing an ancestral genotype isolated from several deer in Alpena County, Michigan, as early as 1997; the 2004 human isolate shared an identical genotype with a grossly lesioned deer harvested by the patient in Alcona County, Michigan, confirming that his infection resulted from a finger injury sustained during field-dressing. The 2002 and 2017 cases of pulmonary disease might have occurred following those patients’ inhalation of aerosols during removal of diseased viscera while field-dressing deer carcasses.

In Michigan, deer serve as maintenance and reservoir hosts for M. bovis, and transmission to other species has been documented. Since 1998, 73 infected cattle herds have been identified in Michigan, resulting in increased testing and restricted movement of cattle outside the four-county zone. Transmission to humans also occurs, as demonstrated by the three cases described in this report; however, the risk for transmission is understudied.

Similar to Mycobacterium tuberculosis, exposure to M. bovis can lead to latent or active infection, with risk for eventual reactivation of latent disease, especially in immunocompromised hosts. To prevent exposure to M. bovis and other diseases, hunters are encouraged to use personal protective equipment while field-dressing deer. In addition, hunters in Michigan who submit deer heads that test positive for M. bovis might be at higher risk for infection, and targeted screening for tuberculosis could be performed. Close collaboration between human and animal health sectors is essential for containing this zoonotic infection.

Notes from the Field: Zoonotic mycobacterium bovis disease in deer hunters—Michigan, 2002-2017

James Sunstrum, MD1; Adenike S hoyinka, MD2; Laura E. Power, MD2,3; Daniel Maxwell, DO4; Mary Grace Stobierski, DVM5; Kim Signs, DVM5; Jennifer L. Sidge, DVM, PhD5; Daniel J. O’Brien, DVM, PhD6; Suelee Robbe-Austerman, DVM, PhD7; Peter Davidson, PhD5


NZ: Tb testing important for food safety

Dr Paul Livingstone, research leader for TBfree New Zealand, writes in this op-ed that the small but rising number of New Zealanders drinking unpasteurised milk supplied directly from dairy herds need to have as much protection from being infected with bovine Tb as it is possible to provide.

symptoms-for-tuberculosis-in-cattleWhen an animal in the Mt Cargill area reacted positive to a Tb test in May, the Ministry for Primary Industries – New Zealand’s food safety regulator – halted the supply of raw milk.

The ministry made the decision to prevent raw milk sales from Tb-infected dairy herds until they had tested free from Tb for five years. MPI’s decision was based on historical data that showed there is a very low risk of a previously infected herd being found with latent infection up to five years after being Tb-free.

The TBfree New Zealand programme run by Ospri uses Tb testing, animal movement and possum control towards the goal of eradicating bovine Tb. It employs a small range of diagnostic tests to detect tuberculosis infection in our cattle herds.

All tests are based on measuring an animal’s immune response to tuberculin, which is a standardised protein extract derived from killed Tb bacteria (Mycobacterium bovis). In general, this response is measurably different between infected and non-infected animals.

Tuberculin tests can be applied directly to an animal with an injected skin test, or can be carried out in a laboratory using a blood sample taken from the animal.

The Tb skin test on average detects 85% of infected cattle. Thus, if there is one infected animal in a herd, there is an 85% chance that the herd will be found infected and subjected to further testing. If there are two infected cattle in a herd, then there is a 98% chance of detecting the herd as infected and subjecting it to further Tb testing.

Once a herd is infected, it is subject to a regime of increased skin and blood testing to clear infection from the herd as fast as possible. This has proven to be very effective. About 60% of infected herds are clear of infection within two Tb tests and 95% of herds clear infection within five Tb tests. However, in rare instances, a cow may be infected with Tb, yet appear clinically normal and not respond to any of the Tb tests.

Following a chronic stressful event, usually associated with a combination of events such as feed shortage or introduction of new herd mates during late pregnancy or early lactation, a latently infected animal may quickly convert into one that becomes a major shedder of Tb bacteria. This can happen via a number of routes including the udder, leading to Tb infected milk.

Hence the importance of requiring five years of testing freedom before allowing raw milk sales, to guard against such an event.

The Tb testing programme for cattle in New Zealand is based on long and thorough research, proven in the field. In any one year, a large proportion of the national cattle population (4.41million animals in 2014-15) is skin tested for Tb.

During the decade to 2013-14, about 52,850,000 cattle were Tb tested nationally and 52,840,000 of these gave negative test results. That is a 99.98% accuracy (what we term “specificity”) rate.

Of about 9650 cattle that were taken nationally as Tb reactors out of that nearly 53million, 2630 showed gross lesions of Tb at slaughter. A further proportion of those not showing gross lesions (anywhere between 10% and 20%) will be infected but not showing visible lesions, due to early stages of infection. Such gross lesion rates are generally within the ranges seen in overseas countries.

There is high confidence that the testing regime is working.

New Zealand is getting into the latter stages of its Tb eradication programme, where a more intensive approach to eradicating Tb in herds is required to clear infection quickly. It is, therefore, not surprising in the latter stages of a programme that lesion rates in Tb reactors fall as the overall amount of Tb in the population is reducing.

As part of the Tb-free programme we are constantly looking at ways to improve how we our work, and Tb testing is no exception.

Research is under way into a new tuberculin used in the reactor that is much more specific at targeting bovine Tb. The research is now 18 months into a trial and is looking promising in helping to reduce the false positive incidence.

First cases documented of TB caught from cats

There was this one time, I went to the U.S., and when I returned there were two Persian furballs in the house.

I vacuumed this morning and reminded Amy, you wanted fluffy cats, right?

jacques.salamader.2.14She laughed as she went out the door.

The New York Times reports the first documented cases of people catching tuberculosis from their cats were revealed in England this week, but TB experts there and in the United States reassured pet owners that they had virtually nothing to fear.

The four human cases were all related to a rare cluster of sick cats in southern England, and all were instances of bovine tuberculosis, which is carried by cows.

Public Health England, which released the report, said the risk to cat owners was “very low.”

The English medical report was a follow-up to a veterinary TB outbreak, in which one veterinarian diagnosed the illness in nine very sick cats from different households within a few miles of one another in or around Newbury, England, from late 2012 to early 2013. Twenty-four people connected to those cats were screened; two had latent TB without symptoms, and two had active infections. DNA testing showed that all four had the same strain as all the cats.

The cats roamed through local woods, the report said, and probably got infected either by eating rodents that had picked up the disease from cows or by fighting with badgers, which also carry it. They may have passed it among themselves through bites.

Bovine TB is more common in England than in the United States, said Dr. Paul P. Calle, chief veterinarian for the Wildlife Conservation Society at the Bronx Zoo.

“This may very well have happened before, in the days before milk was pasteurized and cats were kept in barns for mouse control,” he said. “But for an apartment cat, the risk is nil.”

Although there could be a Salmonella risk from hunting salamanders and skinks, and the little ones enter the townhouse routinely.