D. J. Prattley

Descriptive epidemiological study of the use of antimicrobial drugs by companion animal veterinarians in New Zealand

Abstract AIM: To describe the patterns of use of antimicrobial drugs by veterinary surgeons treating commonly presented bacterial infections in companion animals in New Zealand. METHODS: A postal survey of 800 randomly selected companion animal veterinarians practicing in New Zealand was conducted between August and December 2008. Data were collected regarding the antimicrobials prescribed for recent cases of skin, ear and urinary tract infections; the use of culture and susceptibility testing; and veterinarian characteristics such as proportion of time spent treating companion animals and recent attendance at continuing professional development (CPD) events. Potential associations within the data were explored using extended mosaic plots and multivariable regression models. RESULTS:Completed surveys from 393 respondents were available for analysis, providing data on systemic antimicrobial drug use for 1,799 cases of presumptive bacterial infections. The most frequently prescribed drugs were amoxicillin-clavulanic acid (864 cases, 48%), cephalexin (558, 31%), and fluoroquinolones (198, 11%). Of 359 cases of canine superficial pyoderma, 157 (44%) were treated with amoxicillin-clavulanic acid and 155 (43%) were treated with cephalexin with median reported treatment durations of 7 and 10 days, for these two drugs respectively. Culture and susceptibility tests had been used in 376 of 1,984 (19%) of all reported cases and 160 (43%) of these were suspected urinary tract infections. Practitioners that spent 100% of their time treating companion animals and who had attended a CPD course related to companion animals within the 12 months prior to completing the survey were more likely to submit a sample for culture and susceptibility testing and to prescribe longer courses of antimicrobials for the treatment of canine pyoderma than practitioners who spent less than 100% of their time treating companion animals and had not attended a CPD course in the last 12 months. CONCLUSIONS: Broad-spectrum drugs considered by the World Health Organisation to be critically important for human health, such as fluoroquinolones and amoxicillin-clavulanic acid, are amongst the most frequently prescribed antimicrobials in companion animal medicine, and these drugs are often prescribed without submitting a sample for culture and susceptibility testing. CLINICAL RELEVANCE: Many cases of superficial pyoderma were treated for less than the recommended duration of 21 days, which may contribute to a higher rate of recurrent pyoderma and the development of drug resistance within the causal bacteria. Veterinarians should be aware that the use of fluoroquinolones, in particular, should be based upon the results of a culture and susceptibility test.

Prevalence of endemic enteropathogens of calves in New Zealand dairy farms

AIM: To conduct a country-wide prevalence study of bovine group A rotavirus, coronavirus, Cryptosporidium parvum, Salmonella spp. and enterotoxigenic K99+ Escherichia coli (K99) in calves on New Zealand dairy farms. METHODS: Faecal samples (n=1,283) were collected during the 2011 calving season from calves that were 1–5 and 9–21 days-old on 97 dairy farms, and were analysed for the presence of bovine group A rotavirus, coronavirus, Cryptosporidium and Salmonella spp., and K99. Farm-level prevalences were calculated and relationships between demographic variables and the presence of enteropathogens were examined using logistic regression models. RESULTS: Of the 97 farms, 93 (96%) had at least one sample infected with enteropathogens. The standardised farm prevalences of bovine group A rotavirus, bovine coronavirus and C. parvum were 46, 14 and 18%, respectively, in calves that were 1–5 days-old, and 57, 31 and 52%, respectively, in calves that were 9–21 days-old. The farm-level prevalence of K99 was 11% in calves that were 1–5 days-old. Salmonella spp. were found in three and four samples, from calves that were 1–5 and 9–21 days-old, respectively. No associations between explanatory variables and the presence of the enteropathogens were identified at the farm level. At the calf level, the odds of C. parvum shedding and of co-infection with any combination of pathogens were greater in calves that were 9–21 than 1–5 days-old. CONCLUSIONS AND CLINICAL RELEVANCE: This study provides epidemiological estimates of the prevalence of calves’ enteropathogens in New Zealand, which could be used for infection risk assessment or estimation of the environmental loads of pathogens shed in cattle faeces.

Geographic divergence of bovine and human Shiga toxin–producing Escherichia coli O157:H7 genotypes, New Zealand.

A historically introduced subset of globally circulating strains continue to evolve and be transmitted between cattle and humans.

Nationwide prevalence and risk factors for faecal carriage of Escherichia coli O157 and O26 in very young calves and adult cattle at slaughter in New Zealand

Nationwide prevalence and risk factors for faecal carriage of Escherichia coli O157 and O26 in cattle were assessed in a 2-year cross-sectional study at four large slaughter plants in New Zealand. Recto-anal mucosal swab samples from a total of 695 young (aged 4-7 days) calves and 895 adult cattle were collected post-slaughter and screened with real-time polymerase chain reaction (PCR) for the presence of E. coli O157 and O26 [Shiga toxin-producing E. coli (STEC) and non-STEC]. Co-infection with either serogroup of E. coli (O157 or O26) was identified as a risk factor in both calves and adult cattle for being tested real-time PCR-positive for E. coli O157 or O26. As confirmed by culture isolation and molecular analysis, the overall prevalence of STEC (STEC O157 and STEC O26 combined) was significantly higher in calves [6·0% (42/695), 95% confidence interval (CI) 4·4-8·1] than in adult cattle [1·8% (16/895), 95% CI 1·1-3·0] (P < 0·001). This study is the first of its kind in New Zealand to assess the relative importance of cattle as a reservoir of STEC O157 and O26 at a national level. Epidemiological data collected will be used in the development of a risk management strategy for STEC in New Zealand.

Risk factors for neonatal calf diarrhoea and enteropathogen shedding in New Zealand dairy farms.

Abstract To investigate the risk factors for neonatal calf diarrhoea, a cross-sectional study was conducted on 97 New Zealand dairy farms. Faecal specimens from 1283 calves were scored as liquid, semi-solid or solid, and analysed for bovine rotavirus (BRV) and coronavirus (BCV), enterotoxigenic K99+ Escherichia coli (K99), Salmonella spp. and Cryptosporidium parvum. Calf- and farm-level data were collected by means of a questionnaire and the odds of liquid faeces calculated using mixed effects logistic regression models. Among the infectious agents, only C. parvum (odds ratio [OR] = 2.6; 95% confidence interval [CI], 1.3–5.6; P = 0.02), BRV (OR = 2.7; 95% CI, 1.3–5.9; P = 0.01) and co-infection with more than one agent (compared with mono-infection: OR = 2.5; 95% CI, 1.3–4.8; P = 0.01) were associated with increased odds of liquid faeces in calves which were 9 to 21 days old. Housing of calves in open barns so exposing them to the weather was also associated with increased odds of liquid faeces compared with closed barns (OR = 2.1; 95% CI, 1.1–12.2; P = 0.03). Vaccinating cows against calf enteropathogens (OR = 0.2; 95% CI, 0.1–0.9; P = 0.03), administering waste milk (from mastitis and/or containing antibiotics; OR = 0.4; 95% CI, 0.1–0.8; P = 0.01), the sex of calves (females compared to males OR = 0.2, 95% CI, 0.07–0.7; P < 0.01), and the use of straw for bedding (OR = 0.2; 95% CI, 0.03–0.9; P = 0.03) decreased the odds of liquid faeces. Conversely, in calves that were 1 to 5 days old, only K99 was associated with liquid faeces (OR = 4.6; 95% CI, 1.2–16.1; P = 0.02). In this age group, the odds of liquid faeces were smaller on farms where females took care of the calves, compared with males (OR = 0.4; 95% CI, 0.01–0.9; P = 0.04).

Molecular epidemiology of Mycobacterium avium subsp. paratuberculosis isolated from sheep, cattle and deer on New Zealand pastoral farms

The present study aimed to describe the molecular diversity of Mycobacterium avium subsp. paratuberculosis (MAP) isolates obtained from sheep, cattle (beef and dairy) and deer farms in New Zealand. A total of 206 independent MAP isolates (15 beef cattle, 89 dairy cattle, 35 deer, 67 sheep) were sourced from 172 species-mobs (15 beef cattle, 66 dairy cattle, 31 deer, 60 sheep). Seventeen subtypes were identified, using a combination of variable number of tandem repeats (VNTR) and short sequence repeat (SSR) methods. Rarefaction analysis, analysis of molecular variance (AMOVA), Fst pairwise comparisons and proportional similarity index (PSI) were used to describe subtype population richness, genetic structure and potential associations between livestock sectors and New Zealand two main islands (North and South). The rarefaction analysis suggests a significantly higher subtype richness in dairy cattle herds when compared to the other livestock sectors. AMOVA results indicate that the main source of subtype variation is attributable to the livestock sector from which samples were sourced suggesting that subtypes are generally sector-specific. The pairwise Fst results were similar, with low Fst values for island differences within a livestock sector when compared to between sector analyses, representing a low subtype differentiation between islands. However, for a given island, potential associations were seen between dominant subtypes and specific livestock sectors. Three subtypes accounted for 76% of the isolates. The most common of these was isolated from sheep and beef cattle in the North Island, the second most frequent subtype was mainly isolated from dairy cattle (either island), while the third most common subtype was associated with deer farmed in the South Island. The PSI analysis suggests similarities in subtypes sourced from sheep and beef cattle. This contrasted with the isolates sourced from other livestock sectors, which tended to present sector-specific subtypes. Sheep and beef cattle were mainly infected with MAP Type I, while dairy cattle and deer were almost exclusively infected with MAP Type II. However, when beef cattle and deer were both present at farm level, they harboured similar subtypes. This study indicates that cross-species transmission of MAP occurs on New Zealand farms although close contact between species appears to be required, as in the case of sheep and beef cattle which are commonly grazed together in New Zealand.

Utility of halofuginone lactate for the prevention of natural cryptosporidiosis of calves, in the presence of co-infection with rotavirus and Salmonella Typhimurium.

Abstract Halofuginone lactate (HL) is registered in several countries for the prevention of calf cryptosporidiosis, but the compounds utility in the presence of co-infection with other enteropathogens is not well understood. We performed a randomized controlled field trial of the efficacy of HL for the prevention of natural calf cryptosporidiosis, in the presence of co-infection with rotavirus and Salmonella Typhimurium. Newborn calves on one farm were sequentially enrolled and allocated to a full dose (n =15), half dose (n =15), or a placebo control group (n =15), using a randomized block design. The Cryptosporidium oocysts in fecal specimens collected on Days 6, 8, 10, 14 and 20 were counted and the severity of the diarrhea was assessed using fecal consistency scores (solid, semisolid, or liquid). The oocyst numbers and fecal consistency scores were statistically compared between the groups. Ninety one percent of the calves shed Cryptosporidium parvum oocysts during the trial. The full dose group had a longer prepatent period than the control group, but no statistical difference in the number of oocysts was identified between the groups after controlling for the effects of sex and breed. The fecal consistency scores and mortality rates did not differ between the groups. These results indicated that the anti-Cryptosporidium activity and clinical benefit of HL were limited. It is concluded that in order to maximize the clinical efficacy of HL in the field, diagnostic efforts should aim to rule out the presence of other enteropathogens.

Seroprevalence and exposure to risk factors for leptospirosis among veterinary students at Massey University

AIMS: To determine the seroprevalence and quantify putative risk factors for exposure to leptospirosis both within and outside the veterinary curriculum among undergraduate veterinary students at Massey University, New Zealand. METHODS: A cross-sectional study was conducted from September 2010 to November 2011. In total, 302 students were blood sampled, with serum tested by microscopic agglutination test (MAT) for antibodies to Leptospira borgpetersenii serovars Hardjobovis, Leptospira interrogans Pomona and Leptospira borgpetersenii Ballum. Information on demographic characteristics, potential exposure within and outside the veterinary curriculum in the previous 18 months, and previous leptospirosis-like clinical history were recorded using an online questionnaire. RESULTS: All students were MAT negative for each serovar, using a cut-point of ≥1:48. Potential exposure to animal urine within and outside the veterinary curriculum was reported by 259/302 (85.8%) and 150/302 (49.7%) of the students, respectively. The median number of potential exposures to animal urine by each student within the veterinary curriculum in the previous 18 months was 63 (min 1, max 155). The other potential exposures among respondents included home slaughter (63/302; 20.9%), hunting (43/302; 14.2%) and outdoor activities involving exposure to fresh water (241/302; 79.8%). CONCLUSIONS: This study demonstrated that these veterinary students were at low risk of contracting leptospirosis, despite frequent exposure to potential sources of infection. The findings in this study contribute to a broader understanding of the occupational risk of leptospirosis. Data describe the level of animal exposure in veterinary students, which can support other zoonotic disease studies in this group.

Distribution of Escherichia coli strains harbouring Shiga toxin-producing E. coli (STEC)-associated virulence factors (stx1, stx2, eae, ehxA) from very young calves in the North Island of New Zealand.

The objective of this study was to determine the distribution of Shiga toxin-producing Escherichia coli (STEC) virulence markers (stx1, stx2, eae, ehxA) in E. coli strains isolated from young calves aged fewer than 7 days (bobby calves). In total, 299 recto-anal mucosal swabs were collected from animals at two slaughter plants and inoculated onto tryptone bile X-glucuronide and sorbitol MacConkey agar supplemented with cefixime and potassium tellurite. Isolates were analysed using multiplex polymerase chain reaction to detect stx1, stx2, eae and ehxA genes. The most common combination of virulence markers were eae, ehxA (n = 35) followed by eae (n = 9). In total, STEC and atypical enteropathogenic E. coli (aEPEC) were isolated from 8/299 (2·6%) and 37/299 (12·3%) calves, respectively. All the isolates could be assigned to 15 genotype clusters with >70% similarity cut-off using XbaI pulsed-field gel electrophoresis. It may be concluded that healthy calves from the dairy industry are asymptomatic carriers of a diverse population of STEC and aEPEC in New Zealand.

Diversity and relatedness of Shiga toxin-producing Escherichia coli and Campylobacter jejuni between farms in a dairy catchment

The aim of this study was to examine the population structure, transmission and spatial relationship between genotypes of Shiga toxin-producing Escherichia coli (STEC) and Campylobacter jejuni, on 20 dairy farms in a defined catchment. Pooled faecal samples (n = 72) obtained from 288 calves were analysed by real-time polymerase chain reaction (rtPCR) for E. coli serotypes O26, O103, O111, O145 and O157. The number of samples positive for E. coli O26 (30/72) was high compared to E. coli O103 (7/72), O145 (3/72), O157 (2/72) and O111 (0/72). Eighteen E. coli O26 and 53 C. jejuni isolates were recovered from samples by bacterial culture. E. coli O26 and C. jejuni isolates were genotyped using pulsed-field gel electrophoresis and multilocus sequence typing, respectively. All E. coli O26 isolates could be divided into four clusters and the results indicated that E. coli O26 isolates recovered from calves on the same farm were more similar than isolates recovered from different farms in the catchment. There were 11 different sequence types of C. jejuni isolated from the cattle and 22 from water. An analysis of the population structure of C. jejuni isolated from cattle provided evidence of clustering of genotypes within farms, and among groups of farms separated by road boundaries.