Assessment of factors contributing to changes in the incidence of antimicrobial drug resistance in Salmonella enterica serotypes Enteritidis and Typhimurium from humans in England and Wales in 2000, 2002 and 2004.

An investigation into changes in the occurrence of antimicrobial resistance in Salmonella enterica serotypes Enteritidis and Typhimurium from human infection in England and Wales in 2000, 2002 and 2004 has shown that the incidence of strains of S. Enteritidis with resistance to nalidixic acid coupled with decreased susceptibility to ciprofloxacin has more than doubled between 2000 and 2004, whereas the overall levels of resistance in S. Typhimurium have fallen by ca. 25%. In relation to published data on veterinary sales of antimicrobials in the UK, the findings demonstrate that changes in the incidence of resistance do not correlate with changes in veterinary usage. For S. Enteritidis, important factors in the increased incidence of resistance were foreign travel and the consumption of imported foods contaminated with drug-resistant strains. For S. Typhimurium, the most important factor has been an overall decline in the occurrence of multiple drug-resistant S. Typhimurium definitive phage type 104. These studies have demonstrated that changes in the incidence of resistance in predominant salmonellas in humans in England and Wales from 2000 to 2004 are multifactorial. The findings also demonstrate that, in order to combat drug resistance in zoonotic salmonellas causing infections in humans, controls on the use of antibiotics in food animals analogous to those in operation in the UK should be implemented in countries that regularly import food into the UK.

Use of veterinary antiprotozoal products in the UK, 1998-2002.

The Veterinary Medicines Directorate, an agency of the Department for Environment, Food and Rural Affairs, collates and publishes reports detailing the quantities of veterinary antimicrobial products sold in the UK by the pharmaceutical companies. For the most part, these reports have focussed on antibacterials. This paper reports, for the first time, the sales of antiprotozoal products (as base active ingredients) in the UK over a five-year period, 1998-2002, to act as a baseline. Trends and patterns in sales of different groups of the antiprotozoal products are also evaluated. It is hoped that knowledge of sales of these products will fill the knowledge gap of the potential for overall development of antimicrobial resistance in the veterinary field and also reinforce the commitment of the UK Government to promote responsible use of antimicrobial products in the veterinary field.

Use of veterinary antimycotic products in the UK, 1998-2002.

The UK Government is committed to promoting the responsible use of antimicrobial products. As part of this commitment, the Veterinary Medicines Directorate (VMD), an agency of the Department for Environment, Food and Rural Affairs, collates and publishes reports detailing the quantities of veterinary antimicrobial products sold by the pharmaceutical companies in the UK. To date, these reports have focussed on antibacterials and antiprotozoals. This paper acts as a baseline by summarising, for the first time, the sales of veterinary antimycotic products in the UK over a five-year-period, 1998-2002, and looks at trends in sales of different groups of products. It is hoped that information of sales of these products will contribute to knowledge of the potential for overall development of antimicrobial resistance in the veterinary field.

The effects of stage-specific selection on the development of benzimidazole resistance in Haemonchus contortus in sheep.

Resistance to the benzimidazole (BDZ) class of anthelmintics in nematodes of sheep has become a common and global phenomenon. The rate at which the selection process and development of resistance occurs is influenced by a number of factors. Of these, the effects of stage-specific exposures to anthelmintic were investigated with a BDZ-resistant strain of Haemonchus contortus (HCR) over five parasite generations. Sheep were infected at each generation with the HCR strain and were treated with thiabendazole (TBZ), either 5 days post-infection (p.i.) (larval line), 21 days p.i. (adult line), or left untreated (no selection line). Additionally eggs from each generation were exposed to TBZ (egg line). Geometric worm burdens were calculated from post-mortem worm counts, both at the start of the study, and after the final selection studies for each of the selection lines. Egg hatch assays (EHAs) were also conducted throughout the study. All data relating to worm burdens and EHAs for each generation were analysed by linear regression to produce dose titration curves and lethal dose(50) (LD(50)) values for each of the selection lines. Over the five generations, LD(50) values on dose-response were increased and worm survival occurred at higher dose rates of TBZ irrespective of the parasite stage exposed to treatment. A similar picture was seen with ED(50) values, which showed a fluctuating but generally upward trend for each of the three selection lines. In contrast, LD(50) and ED(50) values were decreased in the no selection line, indicating some degree of reversion albeit to levels still considered to be BDZ-resistant.

Anthelmintic resistance detection methods.

The development of species and populations of parasitic helminths with resistance to one or more anthelmintics is an increasing problem world-wide. The majority of currently available anthelmintics used to control parasitic nematodes of cattle and sheep belong to only three main groups, the benzimidazoles, imidazothiazoles and the avermectins/milbemycins. The successful implementation of helminth control programmes designed to limit the development of resistance in nematode populations depends to some degree on the availability of effective and sensitive methods for its detection and monitoring. A variety of in vivo and in vitro tests have been developed for the detection of nematode populations resistant to the main anthelmintic groups, but each suffers to some degree from reliability, reproducibility, sensitivity and ease of interpretation. This review covers those tests that have been reported and described and highlights some of their strengths and weaknesses.