Prevalence, molecular characterization, transmission dynamics and cost analysis of bovine tuberculosis in Morocco

Bovine tuberculosis is a chronic disease, caused by M. bovis, mycobacteria which belongs to the mycobacterium tuberculosis complex; it is notable for having one of the broadest spectrum of hosts. The preferred host of M. bovis is cattle, but it has the ability to infect humans and a wide range of domestic animals.
In Morocco, cattle production is one of the most important components of the agricultural economy; a sector which contributes heavily to the development of the Moroccan economy. The development of this sector is faced by many problems, like poor infrastructure, lack of services and climate change, in addition to infectious diseases like bovine tuberculosis
Bovine tuberculosis is a zoonosis which affects the livestock industry, the public health sector and wildlife reservoirs. BTB has also effects like international trade restrictions for countries where BTB is endemic. Tourism and other areas of public and private interest could also be affected indirectly by BTB infection.
The respiratory route is considered to be the primary mode of infection between cattle. In addition, M. bovis is largely transmitted to humans through consumption of unpasteurized milk, but there is also the possibility of inhalation of aerosols due to contact with cattle.
Bovine tuberculosis in endemic in Morocco, the prevalence in Moroccan cattle is estimated at 18% (95% CI: 16.5%-20.3%), and 33% (95% CI: 31%-35%) at the individual and the herd level respectively, but the human burden needs further clarification.
A prevalence study have been conducted in Sidi Kacem province in Morocco in 2012, 1201 cattle were screened using single comparative intradermal tuberculin skin test, the apparent prevalence was 20.4% and 57.7% in the individual and herd level respectively. The individual prevalence found in the present study is in line with the last national survey conducted in 2004 in collaboration with the FAO in Morocco. Consequently, Morocco is in an endemic stable state, similarly to other African countries.
The livestock production sector in Morocco is continuously growing, due to the ambitious “plan Maroc Vert” launched in 2008, and also to the increasing demand of animal protein in Morocco. Consequently, livestock production system in Morocco is moving to intensified and irrigation rearing systems. Those factors in Sidi Kacem have been shown to be associated with higher risk of BTB compared to the extensive livestock system.
In order to investigate BTB molecular epidemiology in Morocco. Bovine tuberculosis samples were collected from two slaughterhouses in Morocco, Rabat and El Jadida, 8658 animals were examined, 3.7% of them showed gross visible lesions suggesting bovine tuberculosis. However this prevalence reflects the prevalence in young bulls and old cows rather than the prevalence in the whole cattle population.
Molecular characterization of the samples collected from the previously reported slaughterhouses has shown grown cultures in 225 isolates, 63.6% (n=143) have been confirmed to be M. bovis (absence of the RD4).
From 134 samples analyzed using spoligotyping, 43 different spoligotypes were found; ten of them were new patterns (23%), they were submitted to the M.bovis database and they were given new reference numbers. The most prevalent spoligotypes were SB0121, SB0265, and SB0120, which were already reported in many other countries, mainly in Algeria, Spain, Tunisia, and also in the United States and Argentina.
Spoligotypes of African 1 and African 2 clonal complexes were not reported among the characterized isolates. Considering the localization of Af 1 and Af 2 in West Central Africa and East Africa respectively, we could consider Sahara as a potential efficient barrier preventing the introduction of BTB to Morocco from West Central and East Africa.
More molecular characterization is needed to investigate the strains circulating in the south and the north of Morocco. In order to investigate more deeply transmission dynamics of BTB in Africa, an overall study using whole genome sequencing and including several African countries is needed.
The present thesis presents the first cattle to cattle and cattle to human compartmental deterministic mathematic model. Bovine tuberculosis reproductive number was consequently calculated, it was found to be equal to 1.375, in the range of both low and high risk areas.
The sensitivity analysis of the model showed that the birth rate and the sensitivity of the single comparative intradermal tuberculin skin test are the most sensitive parameters of the model for the total cost and the time to elimination respectively. High birth rate values lead to an increased cattle population yielding higher costs for elimination. In the other hand, low test sensitivity cases low detection of infected animals and therefore less culling which leads to a longer time to elimination.
Simulation of test and slaughter interventions led to a decline of BTB prevalence depending on the proportion of testing (p). Using a severe cut off (2mm) for the SICTT, the time of freedom from BTB ranged from 75 years for p=20% to 25 years for p=50%. The cumulated cost was largely stable ranging from 1.47*10^9 (p=100%, time to disease freedom of 12 years) to 1.87*10^9 (p=20%, time to disease freedom of 12 years).
Deterministic and matrix models were used to develop a demographic model of Moroccan cattle population based on real data. The cost of bovine tuberculosis was consequently calculated using the established model.
The productivity losses triggered by BTB (5%) were estimated for 18 years, applying Leslie matrix with and without BTB. Cattle Moroccan population was compared with and without the disease, and the loss in term of animal numbers was then calculated. Considering the productivity loss, the asset value of the living animals lost due to BTB in year 18 is 98 Million Euro.
The present thesis informs Moroccan stakeholders involved in bovine tuberculosis regarding the updated prevalence in Sidi Kacem Area, molecular epidemiology of BTB among slaughtered cattle, the time frame, and range of cost and levels of intervention, in addition to the cost of BTB considering productivity losses.
Further research is needed in Morocco, in one hand, investigations of the molecular epidemiology of BTB in the north and the south of the country will give more insight about the dynamics of BTB in Morocco, a broader investigation using whole genome sequencing including several African countries could be even more efficient. In the other hand a herd based transmission model will provide a more realistic cost estimation of BTB intervention in Morocco.
Elimination of bovine tuberculosis is a costly and long process, the achievement of BTB control of Morocco will need the commitment of the different stakeholders involved. In addition, public-private collaborations could be helpful in order to achieve a sustainable control intervention of BTB in Morocco.