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Page de résumé pour ULgetd-09152011-224004

Auteur : Proano Perez, Freddy
E-mail de l'auteur : fproano@student.ulg.ac.be
URN : ULgetd-09152011-224004
Langue : Anglais/English
Titre : Contribution to the epidemiology of bovine tuberculosis in northern Ecuador
Intitulé du diplôme : Doctorat en sciences vétérinaires
Département : FMV - Département des maladies infectieuses et parasitaires
Jury :
Nom : Titre :
Benitez, Washington Membre du jury/Committee Member
Desmecht, Daniel Membre du jury/Committee Member
Detilleux, Johann Membre du jury/Committee Member
Dufaux-Fauville, Maryse Membre du jury/Committee Member
Guyot, Hugues Membre du jury/Committee Member
Haddad, Nadia Membre du jury/Committee Member
Hornick, Jean-Luc Membre du jury/Committee Member
Mainil, Jacques Membre du jury/Committee Member
Portaels, Françoise Membre du jury/Committee Member
Saegerman, Claude Membre du jury/Committee Member
Linden, Annick Promoteur/Director
Mots-clés :
  • bovine tuberculosis
  • Ecuador
  • M. bovis
  • dairy cattle
Date de soutenance : 2011-10-28
Type d'accès : Public/Internet
Résumé :

In Ecuador, as in other Latin American countries, bovine tuberculosis (BTB) is a major concern in the dairy cattle industry, with economic and public health importance. The increase of peri-urban dairy production associated with the absence of BTB control program in Ecuador are major risk factors in the context of tuberculosis. Furthermore, official data related to the disease are scarce and there is no national veterinary reference laboratory for mycobacteria in Ecuador. The present work was undertaken in this context. The main objectives were to provide data on the epidemiologic situation of BTB among dairy cattle in northern Ecuador, and to compare the performances of the standard diagnostic tools used to identify M. bovis. In a first step, a skin test survey was performed in 2003 in the Mejia canton, the major dairy cattle production region of Ecuador. Randomly selected 1012 cattle from 59 dairy herds, classified according to herd size, were tested for tuberculosis by the single intradermal tuberculin test (SITT) and the comparative intradermal tuberculin test (CITT). Results demonstrated 7.95 % of tuberculin skin-reactors in large herds versus 4.24 % in medium and 0.30 % in small herds. These first results underlined the importance of BTB in dairy cattle in the Mejia canton with herd size as a probable risk factor. A more detailed field investigation was performed in 2007 and 2008 in the same region. A total of 2022 cattle from 20 dairy herds were studied. In 2007, each animal was tested using CITT and a follow-up test was performed in the same herds in 2008. The true annual incidence was 1.70 %. Analysis of CITT results showed significant differences between medium and large herds with a BTB prevalence of 0.27 % and 0.57 % in medium-sized herds compared with 8.63 % and 8.43 % in large herds. Herd size was identified as a significant risk factor, confirming the results of the first study. The number of skin test-positive cases also increased significantly with age, contacts with other animal species and introduction of new cattle into the herd. A third study was carried out in 1390 slaughtered cattle over a two years period. Classical diagnostic tools were compared to detect infected cattle. A total of 33 animals with gross suspected lesions were detected representing 2.3 % and 2.4 % of animals inspected in 2007 and 2008, respectively. From these suspected cases, acid-fast bacilli (direct microscopy) were identified in 33% (11/33) and suggestive microscopic lesions (histopathology) in 27.3 % (9/33) of the cases. Cultures and PCR yielded 36.4 % (12/33) and 27.3 % (9/33) of positives, respectively. Overall, the combined use of microscopy, histopathology, PCR and culture identified infected cattle (at least one positive test) in 51.5 % (17/33) of the suspected animals. Compared to culture, other laboratory procedures displayed a sensitivity of 56.5 % (PCR) and 43.5 % (microscopy and histopathology) and a specificity of 94.4 % (PCR and microscopy) and 97.2 % (histopathology). These results underline that reliable post-mortem laboratory testing either requires the combination of several tests or necessitates the development of improved tools with better performance characteristics. It should be noted that lesions were mainly observed in thoracic lymph nodes suggesting that the respiratory tract is the main route of transmission in dairy cattle inspected at slaughterhouse. In a subsequent step, spoligotyping was used to compare M. bovis strains. All strains (n = 23) isolated from slaughtered cattle from Mejia canton presented the same spoligotype (SB0980). Such homogeneity could be related to the relatively small study area. A more extensive molecular study, at a national level, could be helpful to assess the strain diversity of M. bovis in cattle populations in Ecuador. In countries where BTB controls are lacking, M. bovis is also of public health concern. The last study was undertaken to evaluate the prevalence of Mycobacterium spp. in risk populations by tuberculin skin test (TST). The study was conducted on 157 people (farm and slaughterhouse workers) and TST revealed a high prevalence of reactors (29 %). The main risk factors associated with positive human reactors were consumption of raw milk or handmade cheese. Campaign informations are needed to make rural populations aware of the zoonotic risk related to M. bovis. In conclusion, data presented in this thesis confirm the importance of BTB in dairy cattle in northern Ecuador and highlight the need for a national BTB control program. Ideally, this program should include (1) a reference laboratory for BTB and the training of qualified veterinarians; (2) mandatory skin testing and culling of reactors with official compensations; (3) detailed post-mortem inspection with laboratory-based diagnosis associated with a trace-back system and (4) information campaigns related to the zoonotic risk of M. bovis in rural areas.

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