Multigeneric resistance to benzimidazole anthelmintics in four sheep flocks

Clinical parasitism associated with multigeneric resistance to benzimidazole anthelmintics was investigated in four sheep flocks during February and March 1989. The genera considered resistant were Haemonchus and Nematodirus spp. on all four farms and Trichostrongylus and Ostertagia spp. on three of the four farms. It is suggested that when investigating cases of suspected drench resistance, postdrenching worm counts are useful to help identify the resistant worm species present.     

The distribution of Nematodirus spp. occurring in sheep in New Zealand

Extract

Most outbreaks of parasitic gastro-enteritis in sheep in New Zealand have been ascribed to the presence of nematodes of the family Trichostrongylidae, and in particular the genera, Haemonchus, Ostertagia, and Trichostrongylus. However, during the period 1956–58, a number of outbreaks of disease occurred in lambs and the condition was associated with heavy Neniatodirus infestation. Although Neinatodirus spp. are commonly foundin sheep in this country, only moderate numbers of worms are usually present in any individual and the worm has been regarded as non-pathogenic. Similar views were held in the British Isles until about 1951, when an acute disease condition of lambs, associated with heavy Neniatodirus burdens, caused serious losses.     

Multigeneric Resistance to Benzimidazole Anthelmintics in Sheep

Benzimidazole resistance involving several gastrointestinal nematode genera on a single sheep farm in New Zealand is reported for the first time. A controlled slaughter trial showed that at the recommended dose rate of 12.5 mg/kg, mebendazole had efficacies of 0, 60, 66, 90, 54 and 38% against Haemonchus contortus, Ostertagia spp., Nematodirus spp., intestinal Trichostrongylus spp., Strongyloides spp. and Oesophagostomum venulosum, respectively. The relevance of such multigeneric resistance to possible future options for controlling anthelmintic resistant sheep trichostrongylids is briefly discussed.     

Delay in timing of the oxfendazole pulse release bolus in calves in the Netherlands

Summary

The efficacy of the oxfendazole pulse release bolus (OPRB) was tested in a grazing experiment at the University of Utrecht. Three groups of four OPRB‐treated calves and one group of four untreated control calves were grazed on separate pastures between 18 May and 21 October 1987. Based on faecal egg counts for strongyle‐type eggs and Nematodirus eggs, embryonation of Nematodirus eggs and faecal larval counts for lungworm, the first pulse of oxfendazole was released after 28 to 63 days, which was later than the period of approximately three weeks indicated by the manufacturer and others. As far as could be detected, the second to fifth pulses were not as delayed, but generally the three‐week period was also exceeded.

This delayed release of the pulse resulted in a build‐up of pasture infectivity for gastrointestinal nematode larvae and lungworm larvae. Nevertheless, this did not result in clinical gastrointestinal helminthiasis and husk in the treated groups of calves, whereas severe husk and mild gastrointestinal helminthiasis were seen in the control group.     

Dose confirmation studies for monepantel, an amino-acetonitrile derivative, against fourth stage gastro-intestinal nematode larvae infecting sheep

Monepantel is the first compound from the recently discovered amino-acetonitrile derivative (AAD) class of anthelmintics to be developed for use in sheep. Nine dose confirmation studies were conducted in Australia, New Zealand and Switzerland to confirm the minimum therapeutic oral dose of monepantel to control fourth stage (L4) gastro-intestinal nematode larvae in sheep (target species were Haemonchus contortus, Teladorsagia (Ostertagia) circumcincta, Teladorsagia trifurcata, Trichostrongylus axei, Trichostrongylus colubriformis, Trichostrongylus vitrinus, Cooperia curticei, Cooperia oncophora, Nematodirus battus, Nematodirus filicollis, Nematodirus spathiger, Chabertia ovina and Oesophagostomum venulosum). In each study, sheep infected with a defined selection of the target nematodes were treated with 2.5 mg monepantel/kg liveweight. Following euthanasia and worm counting, efficacy was calculated against worm counts from untreated control groups. The results demonstrate high (95 < 100%) efficacy of monepantel when administered orally to sheep at 2.5 mg/kg for most species tested. Efficacy levels against N. spathiger and O. venulosum were variable and failed to meet the required regulatory standard (≥90%) in some studies. Efficacy was demonstrated against L4 stages of nematodes known to be resistant to either benzimidazole and/or levamisole anthelmintics (macrocyclic lactone resistant isolates were not available for testing). The broad-spectrum activity of monepantel against L4 larvae of common gastro-intestinal nematodes in sheep and its favorable safety profile represents a significant advance in the treatment of parasitic gastro-enteritis in this animal species. No adverse effects related to treatment with monepantel were observed.     

Parasites of Chamois in New Zealand

Sir, — Andrews’⁽²⁾ checklist of helminth parasites of wild ruminants in New Zealand recorded the presence of 10 species of gastrointestinal nematodes in chamois (Rupicapra rupicapra rupicapra L.) from “Central South Island”. In October 1978 we examined 28 freshly-shot chamois cadavers from the Harper-Avoca watershed in the headwaters of the Rakaia River. Six of the nematode species reported by Andrews were found again; viz. Ostertagia ostertagi, O. circumcincta, O. trifurcata, Nematodirus filicollis, Oesophagostomum venulosum and Trichuris ovis. The 4 species found by Andrews that were not recovered by us from the animals we examined were: Trichostrongylus axei, T. vitrinus, Spiculotragia spiculoptera and S. asymmetrica. On the other hand we found 4 helminths not encountered by Andrews: 3 nematodes: Nematodirus spathiger (Railliet, 1896), N. abnormalis (May, 1920), and Chabertia ovina (Fabricius, 1794), and 7 specimens of the cestode Moniezia expansa (Rud., 1805). Nematodirus spathiger was the most commonly encountered Nematodirus species, but generally the numbers of all 3 species encountered were low as might be expected in a sample of adult and almost year-old animals. It is probable that most of the adults had acquired some measure of immunity⁽³⁾, and the most susceptible group, the kids, would not be born until late November. Because peptic digestion was not used to recover juveniles from the intestinal submucosa, only small numbers of adults were obtained.     

The availability of ovine infective trichostrongyle larvae on forested paddocks

A study was made to compare the numbers of infective ovine nematode parasite larvae on an open pastured block and an adjacent block forested with Pinus radiate at 200 stems per hectare. Each block consisted of two paddocks which had similar nematode parasite egg contamination. Infective larvae of six genera were recovered over a 12 month period viz., Trichostrongylus spp., Ostertagia spp., Cooperia spp., Nematodirus spp., Chabertia/Oesophagostomum spp. and Haemonchus sp. A significantly higher recovery of Trichostrongylus spp. (p<0.01) and Ostertagia spp. (p<0.05) from the pine forested block was probably due to the more favourable climatic environment under the pines.

The lower mean body weights of sheep grazing the pine block was considered to be due to the greater exposure to infective larvae and marginal undernutrition.     

Susceptibility of Australian Redfin Perch Perca fluviatilis Experimentally Challenged with Epizootic Hematopoietic Necrosis Virus (EHNV)

The ranavirus epizootic hematopoietic necrosis virus (EHNV) is endemic to Australia and is listed by the Office International des Epizooties. Clinical outbreaks have only been observed in wild populations of Redfin Perch Perca fluviatilis (also known as Eurasian Perch) and farmed populations of Rainbow Trout Oncorhynchus mykiss. The initial outbreaks of EHNV describe all age-classes of Redfin Perch as being susceptible and can lead to epidemic fish kills. Subsequently, experimental challenge studies using either cohabitation with the virus or injection exposures resulted in mixed susceptibilities across various age-groupings of Redfin Perch. We used an experimental bath challenge model to investigate the susceptibility of Redfin Perch collected from areas with and without a history of EHNV outbreaks. The median survival time for fish from Blowering Dam in New South Wales, a zone with a history of EHNV outbreaks, was 35 d, compared with fish from other areas, which had a median survival between 12 and 28 d postexposure. Redfin Perch from Blowering Dam demonstrated an increased mortality associated with epizootic hematopoietic necrosis up to approximately day 14 after exposure, and then there was a significantly reduced risk of mortality until the end of the trial compared with all other fish. Redfin Perch from Blowering Dam had markedly decreased susceptibility to EHNV, and less than 40% became infected following a bath challenge. In contrast, Redfin Perch from neighboring (e.g., Bethungra Dam and Tarcutta Creek) and distant water bodies (e.g., in Western Australia) with no previous history of EHNVdisplayed moderate to high susceptibility when given a bath challenge. Potential factors for the observed changes in the host–pathogen relationship include intense positive selection pressure for resistant fish following epizootic hematopoietic necrosis outbreaks and subsequent attenuation of the virulence of the virus in resistant fish.

Received August 22, 2015; accepted February 13, 2016     

Clostridium Infection (Jisizheng) in Yaks in Qinghai,China

Since the mid-1980s, outbreaks of a disease characterized by a sudden onset, acute deaths and extensive haemorrhages in the viscera and digestive tract of yaks have been prevalent in Qilian, Qinghai, China. The disease is known as jisizheng by local people. Virulent Clostridium perfringens type A and Clostridium haemolytica were isolated from yaks that had died of jisizheng. In 1996 and 1997, yaks were immunized with a polyvalent inactivated vaccine against C. perfringens and with an inactivated vaccine against C. haemolyticum, and this prevented the occurrence of jisizheng.     

A report on the prevalence of gastrointestinal parasites in yaks (<Emphasis Type="Italic">Bos poephagus</Emphasis>) in the cold desert area of North Sikkim,India

Faecal samples were collected from 348 yaks(Bos poephagus) in and around Gurudogmer Plateau, a cold desert area in North Sikkim, India. The prevalence of gastrointestinal parasitic infection was recorded at 10.05% in both the organized and traditionally managed farms of yak. The pattern of infection was either single (2.58%) or mixed (7.47%) with a faecal egg count range of 100–200 eggs per gram of faeces in positive animals. Among the helminths, Haemonchus spp. infection was predominant (6.89%) followed by Nematodirus spp. (1.72%), Cooperia spp. (1.43%) and Dicrocoelium spp. (0.29%).     

Outbreaks of Salmonella enterica infections linked to animal contact: Demographic and outbreak characteristics and comparison to foodborne outbreaks—United States, 2009–2014

In the United States, multistate Salmonella outbreaks are most commonly linked to a food source; however, contact with live animals can also result in outbreaks of human illness. To characterize Salmonella outbreaks linked to animal contact and examine differences compared to foodborne outbreaks, we analysed data reported to the Centers for Disease Control and Prevention through the National Outbreak Reporting System (NORS) from 2009 to 2014 with a primary mode of transmission listed as “animal contact” or “food.” Four hundred and eighty‐four outbreaks with animal contact or foodborne transmission were reported through NORS; of these outbreaks, 99 (20.5%) resulted from Salmonella transmission through animal contact and 385 (79.5%) resulted from foodborne transmission, which resulted in 3,604 (19.8%) and 13,568 (80.2%) illnesses, respectively. A higher proportion of illnesses among children aged <1 year and children aged 1–4 years were linked to animal contact outbreaks compared to foodborne outbreaks (15.2% vs. 1.4%, p < 0.01 and 24.5% vs. 5.6%, p < 0.01, respectively). Illnesses resulting in hospitalizations (OR: 1.81, 95% CI: 1.62, 2.02) were more likely to be associated with animal contact compared to food. Animal contact outbreaks reported to NORS were more likely to be multistate compared to foodborne outbreaks (OR: 5.43, 95% CI: 3.37, 8.76) and had a longer median duration (99.0 days vs. 9.0 days, p < 0.01). Characterizing the differences between outbreaks of illness linked to animal contact and outbreaks linked to food provides useful information to investigators to improve public health response.     

On the Persistence of Infective Ostertagia ostertagi, Cooperia oncophora and Nematodirus helvetianus on Pastures

By grazing parasite-free susceptible calves on naturally infected paddocks for eighteen day periods, Nematodirus helvetianus was shown to survive over two winters on marshland pastures under Maritime climatic conditions in three successive years although the numbers surviving the second winter in two of the three years were low. Climatic conditions of below normal temperatures and little snowfall would appear to have a detrimental effect on the survival of Nematodirus over a second winter although large numbers did survive one winter of such adverse weather. However, under certain conditions, large numbers of Nematodirus can overwinter two years on pastures since over 12,000 worms were picked up by individual calves grazing paddocks in 1969 which had been vacant since 1967.

The findings indicated that few, if any, Ostertagia ostertagi and Cooperia oncophora survive over a second winter under Maritime conditions. The sharp decline in numbers of infective Ostertagia and Cooperia on pastures during the first grazing season following pasture contamination observed in this and previous investigations indicate that few worms of these species survive longer than a year under Maritime conditions.

     

Prevalence of anthelmintic resistance on sheep farms in New Zealand

AIM: To establish the prevalence of anthelmintic resistance in parasitic nematodes on sheep farms in New Zealand.

METHODS: A cross-sectional prevalence study was conducted, using a standardised faecal nematode egg count (FEC) reduction (FECR) test (FECRT) for ivermectin, at a full (0.2 mg/kg) and half (0.1 mg/kg) dose rate, and albendazole, levamisole and albendazole-levamisole in combination, on 60 lambs (n=10 per group) on farms selected from throughout New Zealand. Farms that conformed with selection criteria were chosen at random (n=80) or with a history of suspected resistance to macrocy- clic lactone (ML) anthelmintics (n=32). Resistance to an an- thelmintic was inferred when there was <95% reduction in FEC 7-10 days after treatment. Larval cultures were performed for all control groups and for treated groups for which resistance was evident.

RESULTS: Of the farms randomly selected, 36% showed ≥95% FECR for all anthelmintics tested; resistance to ivermectin at 0.1 and 0.2 mg/kg liveweight was evident on 36% and 25% of these farms, respectively. Resistance to both ivermectin (0.2 mg/kg) and levamisole was evident on 8/80 (10%) farms, to ivermectin and albendazole on 10/80 (13%) farms, and to iver- mectin, levamisole and albendazole on 6/80 (8%) farms. The prevalence of resistance to a half dose of ivermectin tended to be more prevalent on farms with a history of suspected ML resistance (p=0.06). Resistance to albendazole was seen across all the main parasite genera, and to levamisole in Nematodirus, Ostertagia (= Teladorsagia) and Trichostrongylus species. Resistance to ivermectin was dominated by Ostertagia spp, although Cooperia, Nematodirus and Trichostrongylus species were also implicated.

CONCLUSION: Anthelmintic resistance in parasitic nema-todes of sheep is common in New Zealand. Not only was resistance to albendazole and levamisole common, but resistance to the ML, ivermectin, was at a higher prevalence than expected. Sheep farmers and advisors in New Zealand need to re-evaluate the way they manage parasites, and more research is urgently needed if the steady decline in anthelmintic susceptibility is to be halted.     

Occurrence and Distribution of Aeromonas salmonicida Infections on Swedish Fish Farms, 1951–1987

Abstract

The occurrence of typical and atypical Aeromonas salmonicida infections on Swedish fish farms was surveyed, and the methods for controlling the disease are described here. This review is based on data for a period of 36 years from fish health control studies conducted by the National Veterinary Institute and the Salmon Research Institute. The epizootiology and routes of transmission of the pathogens are described, and policy and methods for disease control are discussed. The distribution of atypical A. salmonicida infections was entirely different from that of typical infections. There was also circumstantial evidence of different routes of transmission for typical and atypical A. salmonicida infections. Although subclinical carriers of atypical A. salmonicida occurred among Atlantic salmon Salmo salar and rainbow trout Oncorhynchus mykiss on fish farms, acute disease outbreaks were most frequent among Arctic char Salvelinus alpinus and brown trout Salmo trutta. On the other hand, acute outbreaks of typical A. salmonicida infections were frequent among Atlantic salmon and rainbow trout.     

Risk Factors Associated with Enteric Septicemia of Catfish on Mississippi Commercial Catfish Farms

Abstract

A gram-negative bacterium, Edwardsiella ictaluri, is the cause of enteric septicemia of catfish (ESC), which is one of the most prevalent bacterial diseases in farm-raised catfish. The objective of this study was to identify risk factors associated with ESC mortalities and are reported by farm personnel. To identify risk factors a catfish management database was developed. The odds ratios (OR) of the final multivariable logistic regression model were: (1) volume of the pond (OR, 0.56), (2) interval from harvest until a mortality event (OR, 1.49), (3) interval from stocking until a mortality event (OR, 0.52), (4) nitrite measured within 14 d of a mortality (OR, 3.49), (5) total ammonia measured within 14 d of a mortality (OR, 20.48), and (6) sum of feed fed for 14 d prior to the disease outbreak (OR, 1.02), all of which were significantly (P ≤ 0.05) associated with ESC occurrence. This study showed that some commonly recorded production variables were associated with ESC outbreaks and if monitored could help identify “at risk” ponds prior to disease outbreaks.

Received September 18, 2013; accepted December 17, 2013     

On the Immunological Response of Young Calves to Light Nematodirus helvetianus Infection

Infecting parasite-free eight week old calves with 8,000 infective Nematodirus helvetianus larvae did not modify appreciably their response to a later heavy field challenge with N. helvetianus, Ostertagia ostertagi and Cooperia oncophora, although two of six animals did have smaller Nematodirus burdens.     

A retrospective study on the epidemiology of foot-and-mouth disease in Bhutan

A retrospective study on the outbreaks of foot-and-mouth disease (FMD) in Bhutan, between the years 1996 and 2008, based on the data collected through passive surveillance, was undertaken. A total of 230 outbreaks of FMD at sub-district level were recorded in 299 villages located in 19 out of the 20 districts in the country. There were no significant differences between the years (P = 0.998) or months (P = 0.989) on the incidence of FMD. The sub-districts in the north (altitude >1,000 m above mean sea level) had significantly (P = 0.008) higher incidences of outbreaks in winter than in summer. The sub-districts that shared border with India had significantly more outbreaks than those that didn't (P = 0.001). Cattle were the most predominant species affected being involved in all of the outbreaks reported. Serotype O, which constituted 70.6% of the outbreaks typed was the most predominant serotype prevalent in Bhutan followed by A (16.7%), Asia 1 (8.8%), and C (3.9%). Cattle density was significantly positively correlated (P = 0.023) with the incidence of disease. Three waves of outbreaks of epidemic proportions were reported in 1997/1998, 2002/2003, and 2007/2008 due to the PanAsia strain of the O serotype. The study highlights the incursion of the PanAsia strain of the O serotype into the country, possibly, through the transboundary movement of animals and the need for active surveillance of FMD, especially at the border areas. The study also highlights the significance of the O serotype and cattle as the main indicator species in the epidemiology of FMD in Bhutan. The findings from this study can be used as baseline epidemiological data for further research to understand the epidemiology of FMD in Bhutan.     

The haematological and biochemical effects of the gastrointestinal nematodes prevalent in camels (Camelus dromedarius) in central Saudi Arabia

Coprological examinations on 1200 Najdi camels (Camelus dromedarius) in the Gassim region of central Saudi Arabia between October 1992 and September 1993 revealed the presence of strongyletype, Nematodirus and Strongyloides eggs. In addition, examination of the gastrointestinal tracts of 240 camels slaughtered in different abattoirs in the Gassim region from March to August 1994 revealed 11 species of helminths. Infection with gastrointestinal trichostronglyes resulted in normocytic, normochromic anaemia. Adult infected camels showed leukocytosis, a decrease in total serum protein concentration and increases in blood urea concentration and in serum creatine phosphokinase activity.Abbreviations ALP alkaline phosphatase - AST aspartate aminotransferase - CPK creatine phosphokinase; epg, eggs per gram - GGT gamma-glutamyl transferase - Hb haemoglobin - MCV mean corpuscular volume - MCHC mean corpuscular haemoglobin concentration - PCV packed cell volume - RBC red blood cell     

Increased prevalence of Mycoplasma bovis in the Netherlands

Summary

The epidemiology, therapy, and prevention of M. bovis infections are briefly reviewed In a survey begun in 1982 M. bovis was found frequently in the respiratory of veal calves and beef cattle with respiratory problems. In replacement calves infected with respiratory disease in dairy herds, however, the organism has only been detected since 1986. Respiratory tract specimens collected from calves with respiratory disease were submitted for examination for M. bovis from 1986 to 1991 and originated from 83 herds. Mycoplasma bovis was detected in specimens from 59 of the herds, 20% of which were dairy herds and 80% fattening herds. Arthritis caused by M. bovis was observed in 12 herds until July 1991. Since 1976 when the first mastitis outbreak caused by M. bovis was diagnosed M. bovis has caused 14 more outbreaks. The number of diseased cattle varied from 1 tot 16 per farm, and clinical signs of mastitis varied from mild to severe. In all instances the infection has been eradicated from the herds. Because M. bovis can cause great losses in intensively reared cattle herds, it is advisable to separate purchased veal calves and beef cattle from dairy cattle to prevent further spread of M. bovis.     

The identity of nematode genera involved in cases of ovine anthelmintic resistance in the southern North Island of New Zealand

Larval cultures and faecal egg count reductions were used to determine the identities and frequencies of occurrence of nematode genera involved in cases of ovine anthelmintic resistance submitted to the Batchelar Animal Health Laboratory between 1992 and 1994. Based on an examination of 102 cases, it was found that, while there were some differences relating to the method of assessment, the genera most frequently involved were Trichostrongylus, Ostertagia and Nematodirus. Also implicated, although less commonly, were infections of Oesophagostomum/Chabertia, Haemonchus and Cooperia. The majority of cases involved resistance in two or more genera, with resistance in a single nematode genus occurring in 45% of cases. Most such monogeneric resistances comprised infections of Trichostrongylus (52%), Ostertagia (17%) or Nematodirus (11%). Anthelmintic resistance involving Haemonchus alone was found in only three cases. These results suggest that the potential role of narrow-spectrum drenches in the management and control of anthelmintic-resistant worms in New Zealand sheep is likely to be strictly limited.