CONICET | Buscador de Institutos y Recursos Humanos

Ticks from the Ixodida order act as vectors for an extensive list of animal and human pathogens, including the infection of cattle with Anaplasma marginale (Am) and Babesia bovis or bigemina (Bb). Assessment of the nature and extent of the interaction between tick-borne disease agents is important due to the consequences that such interaction may have for disease prevention and control (1-3). However, the interaction between Am and Bb infection in cattle has never been demonstrated (4-7). Here, molecular techniques were applied on an extensive collection of samples from Argentine livestock in order to assess the hypothesis that Bb-positive cattle are more likely to be Am-positive than Bb-negative animals and that the intensity of the association is influenced by epidemiological conditions of the environment. Samples (n=348) were collected from 22 herds located in two ecologically distinct regions of the country, referred to as North-eastern (NE) and North-western (NW) Argentina, respectively. DNA was extracted and Am and Bb were detected using a reverse line blot hybridization (RLBH) technique (8, 9). Association between Bb and Am was quantified using a hierarchical Bayesian logistic regression model (10). In this model, Bb-positive and negative cattle were considered cases and controls, respectively, status to Am infection (infected, uninfected) was introduced as a risk factor for Bb status, and herd of origin was modeled as a hierarchy to account for lack of independence at the intra-herd level. In NW, the odds of being Bb-positive was 8.8 times higher for Am-positive cattle than for Am-negative animals; conversely, in NE, Am-negative cattle had 2.3 higher chances of being Bb-positive than Am-positive animals (P<0.05). Results suggest that the nature and strength of the association between Bb and Am infections are spatially heterogeneous and likely influenced by epidemiological differences of the settings.

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