Background: Reduction or elimination of vector populations will tend to reduce or eliminate transmission of vector-borne diseases. One potential method for environmentally-friendly, species-specific population control is the Sterile Insect Technique (SIT). SIT has not been widely used against insect disease vectors such as mosquitoes, in part because of various practical difficulties in rearing, sterilization and distribution. Additionally, vector populations with strong density-dependent effects will tend to be resistant to SIT-based control as the population-reducing effect of induced sterility will tend to be offset by reduced density-dependent mortality.

Mating by male Anopheles mosquitoes (Diptera: Culicidae) was evaluated in the laboratory to assess fitness effects of radio-sterilization applied during different life stages of the malaria vectors An. stephensi Liston and An. gambiae Giles sensu stricto. After reproductive sterilization by gamma-irradiation (120 Gy), equal proportions of sterile and fertile (unirradiated) male adults were released into cages with virgin females and allowed to compete for matings. Radio-sterilization was applied when the males were pupae aged 0-7 h or 24-32 h, or adults aged <24 h or 24-55 h. After being radio-sterilized in the adult stage, males of both species competed effectively with unirradiated males, whereas those sterilized in the pupal stage obtained significantly fewer matings than unirradiated males from the same cohort. There was no evidence of females obtaining multiple inseminations. These findings emphasize the need to radio-sterilize males as adults in order to minimize the fitness cost. Such males may be intended for sterile insect technique population suppression or for trial releases of transgenic anophelines.

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In 2010, the "yellow card scheme" which was adopted by the Danish Veterinary and Food Administration imposed restrictions on pig farmers who used more antimicrobials than twice the average. To study the potential impact on pig health, we looked into antimicrobial consumption and vaccine use data from the monitoring programme Vetstat, covering all treatments conducted on Danish pigs between January 2010 and July 2011. The decrease in antimicrobial consumption was pronounced for all age groups (sows/piglets, weaners and finishers) treated for either gastro-intestinal or respiratory disease. Evaluated over 12 months, use of vaccines increased in general: PCV2-related infections (+31%), gastro-intestinal disease (27%), respiratory infections (21%) whereas use of vaccines against other infections remained almost constant (-18%). Data from meat inspection of finisher pigs from before and after introduction of the scheme were compared. This included 1.7 million finisher pigs originating from 2765 pig farms, slaughtered on one large Danish abattoir and covered the first 9 weeks in 2010 and 2011, respectively. Nine lesions of chronic nature and infectious origin and the code "condemned" were selected. The prevalence of these lesions was calculated. Logistic regression models with year and week as explanatory variables were used to identify whether the prevalence of a lesion changed from 2010 to 2011. Possible clustering due to correlation within herds and between weekly shipments of animals originating from the same herd was taken into account in the models. The most common lesion seen was chronic pleuritis (∼23%) while the other lesions occurred less-commonly (<1%). For osteomyelitis, pleuritis, chronic arthritis and condemnation, no differences were observed between the 2 years. The prevalence of chronic peritonitis (OR=1.5), umbilical hernia (OR=1.2) and chronic enteritis (OR=1.2) were statistically higher in 2011 compared to 2010, whereas it was lower for tail bite infection (OR=0.6), chronic pericarditis (OR=0.6), and chronic pneumonia (OR=0.7) (P<0.001). Moreover, in the condemned carcasses, chronic pneumonia plummeted as a lesion found in 2011 compared to 2010 (OR=0.07, P<0.0001). Our results indicate that marked reduction in use of antimicrobials is associated with a short-term increase in the prevalence of specific lesions found during meat inspection and higher coverage of vaccines against respiratory diseases might impact the prevalence of chronic pneumonia positively. Other factors that impact on pig health were not included in the study. Moreover, effect of productivity was not evaluated.

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