Research is currently underway by Defra (Department for Environment, Food & Rural Affairs) to develop a female oral contraceptive for badgers. Ideally, the contraceptive would be available to female badgers through oral baits and would aid in reducing population growth by preventing these females from reproducing. Mathematical models have predicted that fertility control alone would not be effective in eradicating bTB, but would need to be used in combination with other strategies such as vaccination or culling (Swinton et al., 1997).
Badger sneaking into cattle housing while foraging for food, as possible route of transmission
While management strategies alone are not likely enough to eradicate bTB, cattle management practices can be used to greatly reduce the probability of badger-to-cattle transmission.
Possible Management Practices:
Prevent badgers from accessing cattle housing
Keep buildings and gates closed, secured
Raising cattle feed off the ground to exclude badger access
Rotational grazing system
To reduce exposure of cattle to potentially badger-contaminated pasture
Currently there is no bTB vaccine available legally for cattle.
While the Bacillus Calmette-Guérin(BCG) vaccine could potentially be used to vaccinate cattle, the current test available to detect bTB known as the Single Intradermal Comparative Cervical Tuberculin (SICCT) skin test cannot differentiate between vaccinated and infected animals. Thus, BCG vaccines for cattle are not yet approved by the European Union for use. For now, new diagnostic tests for bTB are being developed, known as the Differentiate Vaccinated from Infected Animals (DIVA) tests. Vaccinations are expected to be available for use once these diagnostic tests are fully approved in cattle, which is estimated to be within the next 10 years.
Vaccinations are the major alternative to badger culling to control bTB. While the use of vaccines is not effective if the animal is already infected, vaccinations are able to provide protective immunity against bTB. This is especially important in limiting the spread of bTB in susceptible populations. The following posts will describe current vaccines available to use for badgers and cattle, effectiveness, and the associated costs.
While cattle are the main animals to be infected with bTB, various scientific reports such as by Krebs (1997) suggest that Eurasian badgers (Meles meles) act as a wildlife reservoir and can transmit bTB to cattle.
Badger infection rate is estimated to be ~4-6% (RSPCA), and badger to cattle transmission may account for 5.7% of the total bTB infections in Great Britain cattle. The rest of the cattle infections are thought to derive from cattle-to-cattle transmission (McDonald, 2014).
Percentage of bTB transmission source to cattle, according to McDonald (2014)
In order for badger to cattle transmission, certain criteria must be met:
susceptible cattle
badgers must be excreting bacteria such that cattle can encounter it
cattle must encounter min. infectious dose of bacteria (5 bacilli through aerosols)
While transmission is thought to occur through aerosols, feces, or urine, the exact mechanism of transmission from badger to cattle is unknown and controversial (Lodge and Matus, 2014).
Potential transmission mechanisms include:
Contaminated pasture (urine/feces from badger encountered by cattle)
Unlikely since cattle avoid contaminated feed (Benham and Broom, 1991)
Badger visits to cattle housing while foraging for food
Enhanced transmission with low ventilation housing
Badgers would tend to visit cattle feed stores -> possible contamination
Direct contact with cattle
When bTB in late, terminal stage, badger behaviour changes (more active and less fearful of cattle)
Cattle very curious
When combined… increased contact between badgers and cattle
WARNING:The following post contains graphic images!
Bovine tuberculosis is often identified and characterized by large lesions on affected organs, primarily on lymph nodes and throughout the respiratory tract. These lesions greatly impair respiratory function and the overall health of the infected animals.
Diseased vs. normal lung:
bTB-infected vs. normal lungs from possums
Granulomatous lesions:
bTB Lesions on cattle lung
Infected alpaca lungs illustrate loss of respiratory function during bTB
Bovine tuberculosis can potentially infect humans, resulting in lesions across the respiratory tract and body. Humans can contract bTB from cattle primarily through drinking milk contaminated with Mycobacterium bovis. However the overall risk to humans is LOW since milk is now routinely pasteurized.
Child with facial lesions from bTB, infected from drinking contaminated milk
Other animals can potentially also spread bTB to humans during close contact such as through slaughter or veterinary care. Accidental exposure in laboratories is another possible route of infection. These routes of infection are highly unlikely though.
Bovine tuberculosis progresses from initial infection, subclinical symptoms, to a severe disease state riddled with numerous lesions. Death may eventually result.
Step 1: Infection
Bacteria enters respiratory system
Engulfed by immune cells
Carried to lymph nodes and throughout respiratory tract
Step 2: A silent danger
Symptoms often do not appear for long periods of time following infection (subclinical infection)
Step 3: Lesions!
Development of numerous lesions on infected organs
