On surveillance systems and surveys for bluetongue and zoonotic diseases of ruminants

Abstract

Health of livestock populations is a concern for all communities. This concern arises from the consequences of animal diseases on public health, economy and societal development but also from animal welfare and environmental considerations. The marked differences in economies, environments, husbandry systems and veterinary service capabilities amongst countries, shape the impacts of livestock diseases on societies and priorities that need to be addressed. Effective surveillance is essential to understand pathogen epidemiology and consequently pivotal to the development of disease control programmes. It is increasingly recognized that the oldest known zoonotic infections are one of the most important public health priorities in low-income countries. By using existing data from a population-based survey brucellosis, leptospirosis and Q fever seroprevalences and distributions of seropositive animals and herds were investigated in the Adamawa Region of Cameroon. The estimates were ~20% of herds seropositive for Brucella spp. compared to ~95% for Leptospira spp. and ~68% for Q fever. The within-herd seroprevalences were ~16%, ~35% and ~39% respectively. There was statistical evidence of clustering of seropositive brucellosis and Q fever herds. Multivariable mixed-effects logistic regression models in this study revealed potential risk factors associated with the aforementioned pathogens in cattle, with wildlife, cattle mixing with other herds, transhumance practice and age (>2yrs), playing a major role in either pathogen seropositivity. Over the last decades, arboviral diseases once confined to the southern parts of the world, are emerging beyond the well-known pathogen-vector geographical ranges, particularly at the northern incursional limits. The bluetongue and its recent emergence in northern Europe represent a clear example. Data from the active vector-sampling programme conducted during the 2006-2008 epidemic of bluetongue in The Netherlands, were used to gather information on the presence/absence, abundance and seasonality of Culicoides biting midges, and to study how the presence and activity of bluetongue virus vectors are susceptible to weather and environmental conditions. Proven and potential vectors for bluetongue virus comprised almost 80% of the midges collected: the Obsoletus Complex (C. obsoletus and C. scoticus) (44.2%), C. dewulfi (16.4%), C. chiopterus (16.3%) and C. pulicaris (0.1%). Half of the 24 commonest species of Culicoides captured completed only one or two generations annually, whereas bluetongue virus vectors cycled through 5-6 generations. The relative role of meteorological parameters on vector abundances were quantified within a hurdle modeling framework and showed a broadly consistent association across species, with larger catches linked to temperature related variables and lower wind speed. Moreover, the influence of edaphic factors, likely related to the species-specific breeding habitat preferences, differed markedly amongst species. A series of field experiments aimed at studying the relation between the number of biting midges caught by a standardized surveillance sampling tool and the number attracted by the host. Although the black-light suction trap remains a practical and valid method to study the Culicoides resident population (presence and abundance), this study suggests that it could not be used as a reliable measure of the vectors activity in the field and that species-specific and location specific variations in sampling efficiency deserve further studies.