Biomedical subjects

P R Torgerson

Publications and source records attributed to P R Torgerson.

At least 19 recordsLinked to original sources

PubMed2006

Avermectin-resistance in gastrointestinal nematodes of Boer goats and Dorper sheep in Switzerland.

Anthelmintic resistance in gastrointestinal nematodes among small ruminants is widespread in South Africa and Dorper sheep and Boer goats have been imported into Switzerland from this country on a number of occasions. Therefore, this study aimed to investigate the occurrence of avermectin (AVM) resistant gastrointestinal nematodes (GIN) in these breeds in Switzerland. A total of 24 Boer goat farms and 12 Dorper sheep farms participated in the study. According to the faecal egg count reduction test (FECRT) AVM-resistant GIN populations were confirmed in 7 of the 24 Boer goat farms and suspected in a further 8 farms. Likewise AVM-resistance was confirmed in 2 of 12 Dorper sheep farms and suspected in a further 6 farms. Haemonchus contortus and Trichostrongylus spp. were the dominant resistant species according to larval cultures. In the farms with detected AVM-resistance the animals were additionally treated with levamisole after natural reinfection. With the exception of one farm with a 'close-to cutoff-result' the FECRT gave no indication for resistance against levamisole. The results indicate that AVM-resistance is widespread in Swiss small ruminant farms keeping Boer goats and Dorper sheep. The common tradition of grazing animals from different farms on prealpine and alpine pastures could favour the spread of resistant populations within the country.

Animal Husbandry↗

PubMed2006

Epidemiology of flea infestation of ruminants in Libya.

The results of an epidemiological and clinical study of flea infestations of farm animals in northern Libya is reported. Of 12,130 sheep examined from 124 flocks, 150 sheep were found to be infested with fleas from 50 different flocks. Likewise 23 goats from 2981 examined, and 11 calves from 1124 cattle examined were infested No fleas were recovered from camels or horses. Of 1861 fleas recovered from farm livestock, 1857 were Ctenocephalides felis strongylus and 4 were Pulex irritans. Dogs from farms and local clinics were also examined. Eight farms dogs were found to be infested with P. irritans. Of 79 infested dogs examined in veterinary clinics, 53 were found infested with P. irritans, 11 with Ctenocephalides felis felis, 12 had a mixed infestation of P. irritans and C. felis felis. Single dogs had mixed infestation of P. irritans and C. canis; C. felis felis and C. canis; and P. irritans, C. felis felis and Echidnophaga gallinacia. C. felis felis was also found on 15 infested cats. C. felis felis was never found on large farm animals despite frequently sharing their environment with dogs or cats. Likewise C. felis stongylus was never isolated from dogs or cats. This is consistent with the hypothesis that C. felis strongylus has become adapted to large farm animals, whilst C. felis felis is better adapted to dogs and cats. However, four stockmen were found infested with a total of 176 C. felis strongylus, which suggests that this subspecies is also a potential zoonosis. A significantly higher proportion of intensive farms had animals with flea infestation compared to semi-intensive farms. Fleas were not found in nomadic herds. Infested farm animals often presented with excoriation, alopecia, pruritus and hyperkeratitis particularly on the lower limbs. These signs are consistent with the generation of flea-bite hypersensitivity.

Animal Husbandry↗

PubMed2006

Estimating the true prevalence of Fasciola hepatica in cattle slaughtered in Switzerland in the absence of an absolute diagnostic test.

A survey of 1,331 cattle presented for slaughter at two abattoirs in Switzerland was used to estimate the true prevalence of Fasciola hepatica infection and the diagnostic parameters of visual meat inspection, coproscopy after sedimentation technique, a commercial ELISA test for specific antibody detection in serum and the post mortem microscopic detection of eggs in bile. Faeces, blood and the gall bladder were taken from most cattle presented for slaughter. In addition, livers that were rejected by the meat inspectors were also dissected to examine for the presence of liver fluke. Bayesian techniques (Markov Chain-Monte Carlo) were used to estimate the diagnostic parameters of each of these procedures and the true prevalence of bovine fasciolosis. The true prevalence of F. hepatica infection was estimated at 18.0% (95% credible intervals 15.9-20.3%). The diagnostic sensitivity of coproscopy, bile examination, antibody ELISA and meat inspection were estimated at 69.0% (57.3-79.7%), 93.4% (88.0-97.5%), 91.7% (87.2-95.2%) and 63.2% (55.6-70.6%), respectively. The diagnostic specificity of the ELISA test was estimated at 93.7% (91.7-95.2%). These results demonstrate that the prevalence of bovine fasciolosis is higher than previously thought due to the low sensitivity of meat inspection. They also demonstrate that traditional coproscopy can be very efficient if there is repeated sampling, resulting in sensitivity of approximately 92%.

Abattoirs↗

PubMed2006

Clinical findings and treatment of 94 cattle presumptively diagnosed with listeriosis.

The clinical findings and treatment of 94 cattle with listeriosis are described. The general behaviour and condition of the animals were mostly moderately to severely disturbed. A common abnormality in posture was an exaggerated forward or sideward stance, and 11 of the animals were recumbent. More than half of the animals were ataxic and 22 circled. The most frequent cranial neurological signs observed were facial nerve paralysis, salivation, strabismus, reduced or absent pupillary light reflex, reduced or absent tongue movement and head tilt. The haematological and biochemical findings did not contribute to the diagnosis of listeriosis, but they were useful indicators of dehydration and the acid-base status of the animal. Forty-four of 57 of the animals had high leucocyte counts in the cerebrospinal fluid (CSF), mostly mononuclear cells. Eighty-seven of the animals were treated with various antibiotics (penicillin G, oxytetracycline, amoxicillin, and amoxicillin and gentamicin combined), but there was no significant difference in the success rate of the different treatments. Only two of the nine recumbent animals that were treated survived. Univariable analysis suggested that animals that were recumbent, excited, with an absent or weak menace reflex, nystagmus, high numbers of leucocytes in the CSF, high serum concentrations of urea and calcium and high serum activities of aspartate aminotransferase and creatine kinase, and an acid-base deficit, had a smaller chance of surviving. When a logistic regression model was constructed, only recumbency, excitement and a weak or absent menace reflex remained significant factors affecting the likelihood of survival.

Animals↗

PubMed2006

Agricultural restructuring and gastrointestinal parasitism in domestic ruminants on the rangelands of Kazakhstan.

In order to evaluate the epidemiology of parasitism in farmed ruminants in the changed agricultural context in Kazakhstan, 505 cattle, sheep and goats were surveyed for gastrointestinal parasitism using coprological examination, and a further thirty sheep and four goats using post mortem extraction of helminths. The dominant helminth genera were Marshallagia, Nematodirus and Trichostrongylus. Haemonchus was also present. Faecal egg counts were low (mean abundance 0-115 eggs per gram in different groups), and there was no relationship between faecal egg density and body condition score. Eggs of Nematodirus spp. were more common in sheep less than 1 yr of age, whereas those of the Trichostrongylidae were generally more common in adult sheep. Based on faecal egg counts, sheep grazing on common land close to permanent human settlements were generally no more heavily infected than those grazing the remote open plains. This could be due to a non-linear relationship between livestock numbers and stocking density. We suggest that cessation of strategic nematode control in the region following post-Soviet agricultural reform was offset by a general reduction in stocking density, such that parasite burdens remained low. However, recovery in livestock numbers is likely to lead to increased levels of infection and production loss unless sustainable control strategies are put in place.

Age Factors↗

PubMed2006

Przhevalskiana silenus myiasis among slaughter goats in northern Jordan.

During the period December 1998-May 2000, 900 local goats slaughtered at the Irbid Abattoir (northern Jordan) were examined for the larval instars of Przhevalskiana silenus. Of 900 goats, 10% (95% CI: 9,13) were infested with P. silenus larvae. Only the second and third larval instars were seen. A multiple-regression analysis (with the error variance described by the negative-binomial function) suggested that infestation depended on the month of sampling, and that infestation with live larvae was associated with a poorer carcass. The percentage of infested goats and the mean monthly total number of larvae per goat peaked in samples taken in the autumn and winter. Larval numbers were highly aggregated: most animals had no larvae but the maximum was 69. Analysis of the pattern of aggregation suggested that the best model fit was one in which the larvae counts per goat varied with the monthly prevalence.

Abattoirs↗

PubMed2006

Canid immunity to Echinococcus spp.: impact on transmission.

The canid intestinal immune system recognizes the cestode parasite Echinococcus following infection, but it is still unclear the extent to which protection against reinfection occurs. An increasing number of studies have shown that there are convex age-related abundance or prevalence rates in naturally infected populations of dogs with E. granulosus and foxes infected with E. multilocularis. Data from dogs naturally infected with E. granulosus give a better fit to a model that incorporates herd immunity compared to competing models of age-related changes in infection pressure. A theoretical framework suggests that such herd immunity will act as a stabilizing force for Echinococcus populations. Hence a decrease in infection pressure to dogs or foxes will not result in a corresponding decrease in infection pressure to intermediate hosts or to humans. In addition the age structure of the canid population could affect transmission.

Animals↗

PubMed2005

A method for sheep scab control by applying selective treatment based on flock serology.

Sheep scab, caused by Psoroptes ovis, is a severe and debilitating disease that can be treated and controlled by the use of acaricidal dips or the use of broad-spectrum avermectins. In Switzerland, control measures are state regulated. In particular, sheep should be routinely treated with ectocide dips or avermectin injections before they are moved onto common alpine pasture in late spring. However, a substantial part of the sheep population remains untreated and represents a potential reservoir for the mite population. Untreated sheep that are not moved to alpine pasture may infest treated sheep when flocks are reassembled in autumn. In an attempt to identify infested sheep, all flocks in the Canton of Schwyz (Switzerland) were serologically tested in 2001 and in 2002 (587 and 565 flocks, respectively). In 2003, a representative number (182 of the 531 flocks) was again investigated. Seropositive flocks were treated with doramectin (0.3 mg kg(-1) body weight, intramuscularly) from 2001 to 2003. In spring 2002, no chemo-methaphylaxis was given to seronegative flocks before movement onto common alpine pastures. Of the 587 flocks surveyed in spring 2001, 34 were seropositive (5.8%). These consisted of 21 infested with P. ovis, 1 with P. cuniculi, 4 with Chorioptes spp. and 8 of seropositivity of unknown origin; there was a decrease of seropositive flocks in spring 2002 (4.4%) with 15, 0, 2 and 8, respectively. Of the 182 flocks surveyed in spring 2003, just 4 flocks (2.2%) were seropositive. All the seropositive reactions in these flocks were the result of Chorioptes spp. infestations. There was a corresponding decrease in the proportion of seropositive animals from 6.3% in spring 2001 to 2.1% in spring 2003. These results corroborate the concept that it may be possible to target chemo-metaphylaxis and hence decrease the use of endectocides as well as of ectocides to control sheep scab. This would be of great benefit in reducing the likelihood of development of anthelmintic resistance against avermectins, decreasing the extent of environmental and human contamination with potentially toxic products and diminishing potential drug residues in meat and milk.

Animals↗

PubMed2005

Reproductive potential of Echinococcus multilocularis in experimentally infected foxes, dogs, raccoon dogs and cats.

A total of 15 red foxes, 15 raccoon dogs, 15 domestic dogs and 15 domestic cats were each infected with 20,000 protoscolices of Echinococcus multilocularis. At 35, 63, and 90 days post inoculation (dpi), five animals from each group were necropsied and the worm burdens determined. The highest worm burdens in foxes (mean of 16,792) and raccoon dogs (mean of 7930) were found at 35 dpi. These declined to a mean of just 331 worms in foxes and 3213 worms in raccoon dogs by day 63 with a further decline to 134 worms in foxes and 67 worms in raccoon dogs by day 90. In dogs, there was no significant difference between worm burdens recovered at days 35 (mean of 2466) and day 90 (mean of 1563), although reduced numbers were recovered on day 63 (mean of 899). In cats, worms were found in four animals 35 dpi (mean of 642), in three at 63 dpi (mean of 28) and in two at 90 dpi (mean of 57). Faecal egg counts were determined at 3 day intervals from 25 dpi. A mathematical model of egg excretion dynamics suggested that the mean biotic potential per infected animal was high in foxes (346,473 eggs); raccoon dogs (335,361 eggs) and dogs (279,910 eggs) but very low for cats (573 eggs). It also indicated that approximately 114, 42 and 27 eggs per worm were excreted in the faeces of dogs, raccoon dogs and foxes, respectively. The fecundity of worms in cats was low with an average of less than one egg per worm. The peak levels of coproantigen were detected earlier in foxes and raccoon dogs than in dogs. Eggs recovered from foxes, raccoon dogs and dogs resulted in massive infections in experimental mice. However, metacestodes did not develop from eggs originating from infected cats. It is concluded that foxes, raccoon dogs and dogs are good hosts of E. multilocularis. In contrast, the low worm establishment, the very few excreted eggs and the lack of infectivity of eggs strongly indicate that cats play an insignificant role in parasite transmission.

Animal Diseases↗

PubMed2005

Estimating the financial losses due to bovine fasciolosis in Switzerland.

In dairy cattle in Switzerland, the prevalence of infection with Fasciola hepatica is over 16 per cent. Previous studies have suggested that even subclinical infections with liver fluke may induce significant reductions in the performance of cattle. The financial losses attributable to F hepatica were estimated using a simple spreadsheet model to sum the individual losses that have been suggested in the literature. Because there is substantial variability in these production losses, Monte Carlo sampling techniques were used to model this variability. Each cost item and each data item related to the prevalence of F hepatica was assigned a mathematical distribution which took account of the variability of the experimental data and/or the sample size of the data. A total of 10,000 simulations were undertaken, with each item randomly varied through its mathematical distribution on each simulation. The results suggest that the median financial loss due to bovine fasciolosis in Switzerland is approximately 52 million, with probable 95 per cent confidence limits ranging from 22 million to 92 million per annum, which represents a median loss of 299 per infected animal. Most of the losses arise from reduced milk yield and reduced fertility, and smaller losses are due to reduced meat production and the condemnation of livers.

Animals↗

PubMed2005

Milk amyloid A: correlation with cellular indices of mammary inflammation in cows with normal and raised serum amyloid A.

This study compared concentrations of amyloid A in bovine milk with the cell-based indicators of intramammary inflammation, somatic cell count and California Mastitis Test. Mammary quarter data pertaining to 180 cows were categorised according to concentrations of serum amyloid A in the cow of origin. Ranked correlation, ranked regression and receiver operator characteristics all demonstrated acceptable agreement between milk amyloid A concentrations and cell-based indices. There were some indications of reduction in this agreement, in cows with raised concentrations of serum amyloid A. However, there were also indications that serum amyloid A did not significantly influence milk amyloid A. The results of the current study indicate that milk amyloid A exhibits good correlation with established cell-based indicators of intramammary inflammation.

Animals↗

PubMed2005

Detection of anthelmintic resistance: a comparison of mathematical techniques.

Anthelmintic resistance has become an increasing problem particularly to gastrointestinal tract nematodes and appropriate methods are required to detect this phenomenon so the correct action can be taken. This paper compares a number of mathematical techniques that are used to analyse data. The negative binomial distribution is a mathematical distribution used to model aggregated data and hence is suitable to model the intensity of parasite burden and the magnitude of the faecal egg counts. Maximum likelihood techniques are utilised to exploit this mathematical distribution to analyse the magnitude of the faecal egg count reduction and decline in the worm burden in response to anthelmintic treatment. Data from experimental groups of sheep described in the accompanying paper are used. In addition, simulated data sets of faecal egg counts were created using a random number generator following appropriate negative binomial distributions. The results demonstrate this statistical model can detect evidence of anthelmintic resistance with a faecal egg reduction test that otherwise might require a slaughter trial to demonstrate. In addition, the simulated data sets confirm that there is a significant probability of failure to detect low anthelmintic efficacy with commonly used mathematical techniques. Consequently, the use of maximum likelihood mathematical techniques with a negative binomial statistical model would aid in the early detection of anthelmintic resistance using faecal egg count reductions and result in a lower probability of inappropriately assigning an anthelmintic as effective.

Animals↗

PubMed2005

Multiple anthelmintic resistance in Haemonchus contortus isolated from South African Boer goats in Switzerland.

A suspected case of multiple anthelmintic resistance on a farm in the canton of Zurich, Switzerland, into which South African Boer goats had previously been imported, was confirmed in a controlled test. Twenty sheep were allocated into one control group and three treatment groups to determine the efficacy of mebendazole, ivermectin and moxidectin applying the faecal egg count reduction test (FECRT). The sheep were slaughtered 1 week later and post-mortem worm counts were performed. Benzimidazole and ivermectin resistance were found in Haemonchus contortus with an efficacy of 55 and 61%, respectively. Moxidectin appeared to be effective when the data was analysed according to the recommended analytical techniques with an efficacy of 96%. This is the first description of resistance of gastrointestinal nematodes to one of the macrocyclic lactones in small ruminants in Switzerland. The results are discussed in relation to the importance of controlling livestock before importation.

Abomasum↗

PubMed2004

Transmission dynamics of the Echinococcus granulosus sheep-dog strain (G1 genotype) in camels in Tunisia.

Cystic echinococcosis, caused by Echinococcus granulosus, is highly endemic in North Africa and the Middle East. This paper examines the abundance and prevalence of infection of E. granulosus in camels in Tunisia. No cysts were found in 103 camels from Kébili, whilst 19 of 188 camels from Benguerden (10.1%) were infected. Of the cysts found 95% were considered fertile with the presence of protoscolices and 80% of protoscolices were considered viable by their ability to exclude aqueous eosin. Molecular techniques were used on cyst material from camels and this demonstrated that the study animals were infected with the G1 sheep strain of E. granulosus. Observed data were fitted to a mathematical model by maximum likelihood techniques to define the parameters and their confidence limits and the negative binomial distribution was used to define the error variance in the observed data. The infection pressure to camels was somewhat lower in comparison to sheep reported in an earlier study. However, because camels are much longer-lived animals, the results of the model fit suggested that older camels have a relatively high prevalence rate, reaching a most likely value of 32% at age 15 years. This could represent an important source of transmission to dogs and hence indirectly to man of this zonotic strain. In common with similar studies on other species, there was no evidence of parasite-induced immunity in camels.

Animals↗

PubMed2004

Short report: the use of a polymerase chain reaction to detect Echinococcus granulosus (G1 strain) eggs in soil samples.

Cystic echinococcosis is a re-emerging disease in central Asia. A total of 120 soil samples taken from 30 gardens of rural homesteads in southern Kazakhstan were analyzed for the presence of taeniid eggs using a concentration technique. Of these, 21 (17.5%) were shown to be contaminated with taeniid eggs. These isolated taeniid eggs were further analyzed using a polymerase chain reaction specific for the G1 (sheep) strain of the tapeworm Echinococcus granulosus, and five samples were shown to be positive. This study demonstrates the widespread contamination of the environment with E. granulosus eggs in an Echinococcus-endemic area and thus the potential for indirect transmission of E. granulosus to humans from such sources.

Animals↗

PubMed2003

Oestrus ovis larval myiasis among goats in northern Jordan.

From December 1998 to December 1999, heads of 520 local goats slaughtered at the Irbid, Ramtha and Howarra Abattoirs (northern Jordan) were examined for the three larval instars (L(1)-L(3)) of Oestrus ovis. Of 520 heads, 126 (24%) were infested with O. ovis larvae. All three larval instars were observed in both sexes; all age groups were infested in each month of the year. The mean age of the goats sampled was 1.5 years. The numbers of parasites infesting hosts showed a significant (P<0.05) correlation with sheep age (r(sp)=0.31-0.42) for all three larval instars. The numbers of larvae in each host followed an overdispersed distribution, which fit a negative-binomial model (but not a Poisson distribution). There were more parasites recorded in the presence of purulent discharge or laryngitis, fewer in the presence of catarrhal discharge and no association with pharyngitis sinusitis, or rhinitis.

Abattoirs↗

PubMed2003

Modelling the transmission dynamics of Echinococcus granulosus in sheep and cattle in Kazakhstan.

Cystic echinococcosis, caused by Echinococcus granulosus, is an emerging disease in many parts of the world and, in particular, in eastern Europe and the former Soviet Union. This paper examines the abundance and prevalence of infection of E. granulosus in cattle and sheep in Kazakhstan. Observed data are fitted to a mathematical model in order to determine if the parasite population is partly regulated by intermediate host immunity and to define parameters in the model. Such data would be useful to develop simulation models for the control of this disease. Maximum likelihood techniques were used to define the parameters and their confidence limits in the model and the negative binomial distribution was used to define the error variance in the observed data. The results indicated that there are significant variations in the infection pressure to sheep depending on their location. In particular sheep from Almaty Oblast and from central and northern Kazakhstan appeared to have a greater exposure than sheep from Jambyl or South Kazakhstan Oblasts. The infection pressure to cattle was somewhat lower in comparison. In common with other similar studies, there was no evidence of parasite-induced immunity in sheep or cattle in Kazakhstan due to natural infection. The highest abundance and prevalence were seen in the oldest age classes of animals.

Age Factors↗

PubMed2003

The use of mathematical models to simulate control options for echinococcosis.

In many parts of the world Echinococcus granulosus is a widespread infection in sheep and dogs with a consequential spill over into the human population. In the past, mathematical models have been derived to define the transmission dynamics of this parasite, principally in the sheep-dog life cycle. These models have characterized the cycles of infection as lacking in density dependent constraints in both the definitive or intermediate hosts. This suggested that there was little, if any, induced host immunity by the parasite in either host in natural infections. However, recent evidence from both Tunisia and Kazakhstan, where young dogs are the most heavily parasitised, suggests the possibility of significant definitive host immunity. This may have an effect on the control effort needed to destabilize the parasite. A preliminary computer simulation model (based on an Excel spreadsheet) to attempt to predict the results of a control programme has been written. This demonstrates that there could be significantly different results if there is indeed protective immunity in the dog than in the absence of immunity. In the former the parasite needs a greater control effort to push the parasite towards extinction than in the latter. The computer simulation is based on a mathematical model of the parasite's life cycle and is flexible so that different values of parameters can be used in different situations where the transmission of the parasite may be at different levels. Because of the flexibility of the computer simulation it is anticipated that this programme can be applied in most situations, although initial parameters for a particular location or strain of the parasite will have to be first predetermined with base line field surveys and possibly experimental infections. The programme also has an additional flexibility to enable simulations if some parameters cannot be accurately estimated through Monte-Carlo techniques. In the latter situation, worst and best case scenarios can be estimated and likely frequency distributions of the unknown parameters can be included in the model.

Animals↗