Andrew S. Peregrine

Clostridium difficile PCR Ribotypes in Calves, Canada

C. difficile, including epidemic PCR ribotypes 017 and 027, were isolated from dairy calves in Canada.

Genotype and subtype analyses of Cryptosporidium isolates from dairy calves and humans in Ontario

To assess the importance of dairy cattle as a source of human Cryptosporidium infections in Ontario, Canada, 44 Cryptosporidium isolates from neonatal dairy calves and 11 from sporadic human cases of cryptosporidiosis in the province were genotyped by PCR-RFLP analyses of the Cryptosporidium oocyst wall protein (COWP) and 18S rRNA genes. Isolates were also subtyped by sequence analysis of the 60-kDa glycoprotein (GP60) gene. All bovine isolates successfully subtyped belonged to Cryptosporidium parvum subtype family (allele) IIa. Seven subtypes of this family were identified among the bovine isolates. Four human isolates were Cryptosporidium hominis, of alleles Ia, Id, and Ie. Of the remaining seven human specimens, four were C. parvum allele IIa, two were C. parvum of an undetermined subtype, and one was identified as Cryptosporidium cervine genotype. Three of the C. parvum isolates from humans were the same subtypes as isolates from the calves. These findings suggest that cattle and other ruminants may be a source of sporadic human infections in Ontario. This is the first published description of Cryptosporidium genotypes and subtypes in Ontario, and is the second published report of human infection with Cryptosporidium cervine genotype.

Identification of foals infected with Parascaris equorum apparently resistant to ivermectin

During September 2002, routine fecal examinations performed on 16 Thoroughbred foals residing on a farm outside Toronto, Ontario, Canada, revealed low to moderate numbers of Parascaris equorum eggs in feces from 9 of the 16. All foals were then treated with ivermectin at a dose of 220 to 280 microg/kg (100 to 127 microg/lb), p.o., and fecal egg counts were repeated 12 days later. Fecal P. equorum egg counts increased between the first and second fecal examination in 7 foals, were unchanged in 1, and decreased in 5. Fecal samples were collected 13 days after treatment from 21 additional foals that had been treated with ivermectin at the same dose, and P. equorum eggs were detected in 12 of the 21. For all 37 foals, high P. equorum egg counts (> or = 100 eggs/g of feces) 12 to 13 days after ivermectin treatment were significantly more likely in foals that had been regularly treated with ivermectin since birth and permanently resided on the farm, compared with foals that had been treated with other anthelmintics or had an unknown deworming history. Collectively, these data suggested that P. equorum in these foals was resistant to ivermectin administered at the recommended dose.

Passive Immunity in Ontario Dairy Calves and Investigation of Its Association with Calf Management Practices

Adequate passive transfer of maternal immunoglobulin is important for optimal health and performance in newborn dairy calves. From June to October 2003 and January to April 2004, blood samples were collected from 961 dairy calves 0 to 8 d of age on 11 farms in southwestern Ontario. This was followed by a second study conducted from May to October 2004, in which similar samples were taken from 422 calves up to 8 d of age on 119 dairy farms throughout southern Ontario. For each sample collected, serum refractometry was used to evaluate serum total protein (TP) as a measure of passive transfer of maternal immunity. During each study, producers were asked to provide information on calf management practices, including details of colostrum feeding. Data were analyzed to assess the levels of maternal immunity present in the calves, and to investigate whether these were associated with any calf management or colostrum feeding practices used on the farms. Serum TP readings ranged from 3.5 to 9.8 g/dL. Controlling for any effects of variation between farms, we found no statistically significant difference in serum TP levels, or risk of failure of passive transfer (FPT), between heifer and bull calves. The odds of FPT in calves on farms where more than 75% of cows were usually allowed to remain with their calves for more than 3 h after calving were significantly higher than the odds of FPT in calves on farms where dams and calves were separated within 3 h of the birth. Furthermore, an increased volume of colostrum given to calves within 6 h of birth was significantly associated with a reduced risk of FPT in calves. Information from this work provides valuable insight into the efficiency of passive transfer in newborn dairy calves in southern Ontario.

Chemotherapy and delivery systems: haemoparasites.

Chemotherapy of haemoparasitic diseases in domestic animals is dependent on a limited number of compounds, many of which are chemically closely related. In this review, a summary is given of each of the drugs currently available for treatment and prophylaxis of trypanosomosis and the tick-borne diseases theileriosis, babesiosis, anaplasmosis and cowdriosis. In contrast to the situation with the drugs used for tick-borne diseases, drug resistance appears to be becoming an increasing problem associated with the compounds used for trypanosomosis. The literature that has been reviewed, therefore, is that which relates to the methods used to identify and quantify drug resistance in trypanosome populations, reports of resistance to trypanocides, and cross-resistance between trypanosome populations, reports of resistance to trypanocides, and cross-resistance between trypanocides. The possible reason(s) for the apparent lack of development of resistance to the compounds used for treatment of tick-borne diseases is also discussed. Local toxicity at the site of injection is a problem that is particularly associated with many of the trypanocides when used on a long-term basis in individual animals. Various alternative preparations of the currently used trypanocides therefore have been evaluated in an attempt to reduce this toxicity, and are summarised. Finally, future developments in haemoparasitic chemotherapy are considered and, for trypanosomosis, highlight the importance of integrating chemotherapeutic and chemoprophylactic programmes with control of the vector when drug resistance becomes a significant constraint.

Guidelines for animal-assisted interventions in health care facilities.

Many hospitals and long-term care facilities in North America currently permit animals to visit with their patients; however, the development of relevant infection control and prevention policies has lagged, due in large part to the lack of scientific evidence regarding risks of patient infection associated with animal interaction. This report provides standard guidelines for animal-assisted interventions in health care facilities, taking into account the available evidence.

Calf-level risk factors for neonatal diarrhea and shedding of Cryptosporidium parvum in Ontario dairy calves.

Abstract This work was conducted to investigate calf-level factors that influence the risk of neonatal diarrhea and shedding of Cryptosporidium parvum oocysts in calves, on dairy farms in Ontario with histories of calf diarrhea or cryptosporidiosis. Fecal samples were collected weekly for 4 weeks from each of 1045 calves under 30 days of age on 11 dairy farms in south-western Ontario during the summer of 2003 and the winter of 2004. A questionnaire designed to gather information on calf-level management factors was administered on farm for each calf in the study. Samples were examined for C. parvum oocysts by microscopy, and a subset of specimens was also tested for enterotoxigenic Escherichia coli, Salmonella, bovine rotavirus and bovine coronavirus. The consistency of each sample was scored and recorded at the time of collection in order to assess the presence or absence of diarrhea. In addition, a blood sample was taken from each calf upon enrolment in the study, for assessment of maternal antibody transfer and for polymerase chain reaction testing for persistent bovine viral diarrhea virus infection. Using the GLLAMM function in Stata 9.0, multilevel regression techniques were employed to investigate associations between management practices and the risk of C. parvum shedding or diarrhea. C. parvum oocysts were detected in the feces of 78% of the 919 calves from which all four fecal samples had been collected. Furthermore, 73% of the 846 calves for which all four fecal consistency scores had been recorded were diarrheic at the time of collection of at least one sample. Significant predictors of the calf-level risk of C. parvum shedding included the use of calf diarrhea prophylaxis in pregnant cows, and the type of maternity facilities in which the calves were born. Factors associated with an increased risk of diarrhea were leaving the calf with the dam for more than an hour after birth, and the birth of a calf in the summer as opposed to winter. Calves shedding C. parvum oocysts had 5.3 (95% CI 4.4, 6.4) times the odds of diarrhea than non-shedding calves, controlling for other factors included in the final multivariable model. Furthermore, infected calves shedding more than 2.2×105 oocysts per gram of feces were more likely to scour than infected calves shedding lower numbers of oocysts (OR=6.1, 95% CI 4.8, 7.8). The odds of diarrhea in calves shedding oocysts that had been allowed to remain with their dams for more than an hour were higher than the odds of diarrhea in shedding calves that had been separated from their dams within an hour after birth.

Standardised tests in mice and cattle for the detection of drug resistance in tsetse-transmitted trypanosomes of African domestic cattle

Resistance to the drugs used to control African animal trypanosomosis is increasingly recognised as a constraint to livestock production in sub-Saharan Africa. The most commonly used tests for detection of trypanocidal drug resistance are tests using mice or ruminants, but these suffer from lack of standardisation and hence it may be difficult to compare the results of different investigators. Tests in mice are less expensive than tests in ruminants, but while tests in mice they may be useful as a general guide to resistance in a geographic area they should not be extrapolated to cattle on an individual trypanosome level. Moreover, the commonly used protocols are too laborious for their application to large number of trypanosome isolates on an area-wide basis. This paper presents guidelines for standardised testing of trypanocidal drugs in vivo, and introduces a simplified single-dose test for use in mice, which is convenient for use in areas with limited laboratory facilities. The single-dose test is appropriate for characterisation of geographic areas in terms of trypanocidal drug resistance using large numbers of trypanosome isolates, for making comparisons between areas, and for monitoring changes in trypanocidal drug resistance over time. Multiple-dose tests may be used to determine the degree of resistance of individual stabilates to be determined precisely in mice are also described, but for logistical reasons these will rarely be conducted on more than a few stabilates, and testing of a larger number of stabilates in the single-dose test will generally provide more useful information. Finally, we describe tests in cattle that may be used to determine the efficacy of recommended curative doses of trypanocidal drugs for the treatment of infection with individual trypanosome isolates, including Trypanosoma vivax, which is rarely infective for mice.

Anthelmintic resistance in important parasites of horses: does it really matter?

Parascaris equorum and cyathostomins are currently considered the most important parasites of horses and have traditionally been controlled with anthelmintics belonging to three drug classes: benzimidazoles, the tetrahydropyrimidine pyrantel, and macrocyclic lactones. Unfortunately, resistance to benzimidazoles, and to a lesser extent pyrantel, is widespread in cyathostomins around the world. Furthermore, resistance to macrocyclic lactones appears to be in the early stages of development in cyathostomins in multiple locations. In contrast, P. equorum populations have remained susceptible to the three anthelmintic drug classes for a considerably longer period of time. However, over the last 10 years, resistance to macrocyclic lactones has been described in multiple countries. In contrast, resistance to pyrantel has only been described in the USA; resistance to benzimidazoles has yet to be reported. Despite the large number of reports of anthelmintic resistance in both cyathostomins and P. equorum, there are presently no reports that definitively link anthelmintic resistance with clinical problems in horses. However, that generally appears to be due to a publication bias toward well managed horse farms and the lack of appropriate diagnostic methods for rapidly quantifying anthelmintic resistance in these parasites. Management-based, and other, reasons likely responsible for this apparent anomaly are also discussed. Finally, future research priorities in this area, identified from a discussion at the 9th International Conference on Equine Infectious Diseases, are summarized.

Macrocyclic lactone resistance in Dirofilaria immitis

Microfilariae were isolated from a Katrina rescue dog that remained microfilariaemic despite successful adulticidal treatments and repeated treatment with high doses of macrocyclic lactones (MLs). The microfilariae were genotyped at two P-glycoprotein single nucleotide polymorphic sites which had been found to correlate with reduced sensitivity to MLs. The genetic polymorphism (GG-GG), previously found to be associated with insensitivity to MLs in vitro, was present at a frequency of 45.3% in microfilariae that survived repeated treatments with high doses of ML anthelmintics. The data show phenotypic and genotypic evidence of ML resistance in Dirofilaria immitis.