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Study explores cost, effectiveness of M. bovis interventions in Morocco
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Researchers used mathematical modeling to explore the cost and effectiveness of interventions against bovine tuberculosis in Morocco, where Mycobacterium bovis accounts for close to 18% of drug-resistant TB in humans.
People usually contract M. bovis through contaminated milk or close contact with infected cattle, but airborne person-to-person transmission also has been reported. WHO includes bovine TB (BTB) among the seven neglected zoonoses perceived to be severe threats to public health, according to Jakob Zinsstag, DVM, PhD, of the Swiss Tropical and Public Health Institute, and colleagues.
Zinsstag and colleagues’ model demonstrated that BTB could be eliminated in Morocco within 32 years if 40% of cattle were tested annually and infected cows are slaughtered.
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“While BTB has been eliminated in cattle and human populations of most high-income countries, it is still a major health threat in low- and middle-income countries,” Zinsstag and colleagues wrote in PLoS Neglected Tropical Diseases.
These countries include Morocco, where a non-mandatory test and slaughter method is currently used to control M. bovis in cattle. According to Zinsstag and colleagues, slaughtering cattle that test positive for the disease is an effective intervention to reduce BTB among domestic cattle, but the method is not used effectively in Morocco.
To address this, they developed a mathematical model of BTB transmission in cattle and humans to assess the disease cost and simulate interventions in Morocco, where around 18% of cows have the disease.
Assuming a BTB prevalence of 18% and using annual data on cattle collected by the Moroccan Ministry of Agriculture, Zinsstag and colleagues showed the time until less than 1 in 1,000 cattle had BTB — the WHO standard to show elimination of the disease.
When 100% of cattle are tested annually, Zinsstag and colleagues calculated the time to BTB elimination as 12 years. It was under 20 years when more than 60% of cattle are tested, and 75 years when only 20% are tested.
In simulations in which more than 40% of cattle are tested, the cost of the intervention was between 1.47 billion to 1.60 billion euros — or around $1.56 billion to $1.7 billion — with a time frame of 12 to 32 years until elimination, Zinsstag and colleagues wrote.
“The economic assessment presented here is preliminary, and a detailed cost and cost-effectiveness analysis will be published separately,” they wrote. “However, our analysis informs Moroccan bovine tuberculosis control policy on the time horizon, range of cost and optimal levels of intervention. An effective control program will depend on the human resources and technical and logistical capacity of the veterinary services to implement testing and slaughtering of animals.” – by Gerard Gallagher
Disclosure: The researchers report no relevant financial disclosures.
Perspective
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Although BTB was once found worldwide, control programs have eliminated or nearly eliminated this disease from domesticated animals in many industrialized countries. From a public health perspective, its eradication from dairy cattle merits the priority.
Nations currently classified as BTB–free include Australia, Austria, Barbados, Canada, the Czech Republic, Denmark, Estonia, Finland, Iceland, Israel, Jamaica, Latvia, Lithuania, Luxembourg, Norway, Singapore, Slovakia, Sweden and Switzerland. Eradication programs are in progress in other European countries, as well as in Japan, New Zealand, the United States, Mexico, and some countries of Central and South America. Although BTB has been eradicated from the majority of U.S. states, a few infected herds continue to be reported, and a few states may periodically lose their disease-free status. In particular, infection in wild white-tailed deer has complicated eradication efforts in Michigan. Similar problems exist with infected badgers in the United Kingdom and Ireland, and infected brush-tailed opossums in New Zealand. BTB is still widespread in Africa, including the Maghreb, parts of Asia and most Middle Eastern countries.
The suggested BTB control plan in Morocco is very ambitious. The country counts (2011 Ministry of Agriculture figures) 780,000 farmers, of which 300,000 maintain dairy cattle (1.25 million head, 69% cross breeds) and 480,000 maintain beef and fattening cattle (1.78 million heads, 60% cross breeds). Farmers’ education, and gaining their trust by safeguarding immediate payments of the compensation for culled animals in the actual market price, should be regarded sine qua non for any attempt to perform the BTB control project, whichever candidate plan is selected. The efforts should preferably concentrate in the dairy cattle. Needless to remind the elementary requirement for the strict performance of pasteurization covering all drinking milk and dairy products. The odds for success of any attempt to control the disease by the described "test and slaughter" policy depend upon the successful implementation of a reliable and sustainable identification system allowing traceability of each tested animal. Until recently, the identification was carried out mainly by ear-tagging and tattooing, coded to enable the tracing back of the animals to its original region, village and holding. In recent years, additional techniques have become available, including electronic methods that implement radio frequency identification technologies (such as rumen boluses, ear tags and injectable transponders).
The chances for success of the early stages of the Moroccan project are expected to be higher in the commercial dairy farms. The project will encounter less favorable conditions and require an extended effort in the small (backyard) holdings of milking cows and especially in beef cattle, particularly in grazing and nomadic herds. Control upon animal movements and law enforcement will be crucial. However, the role of beef cattle in the epidemiology of the disease is mainly as a reservoir for reinfection in the dairy sector, less as a public health hazard.
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