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Biomedical subjects

B J Losson

Publications and source records attributed to B J Losson.

15 recordsLinked to original sources
PubMed2001

Diagnosis of psoroptic sheep scab with an improved enzyme-linked immunosorbent assay.

An enzyme-linked immunosorbent assay (ELISA) was developed for the detection of specific antibodies against crude Psoroptes antigen. The diagnostic sensitivity was 93.7% in 191 sheep with clinical signs associated with mange. These animals originated from 29 flocks in which psoroptic mites were detected. All of 59 sheep infested with Psoroptes ovis were seropositive. Additionally, in 49% of 70 clinically unaffected sheep originating from P. ovis-infested flocks, specific antibodies could be detected, suggesting that asymptomatic infestations can be diagnosed by serology. The specificity of the ELISA was 96.5% as determined with 254 sheep originating from 44 flocks without clinical mange. Cross-reactivity in a low range was detected with selected sera of sheep with clinical chorioptic or forage mite infestations. Four sheep seroconverted 2 weeks after experimental P. ovis infestation, i.e. 2 weeks before clinical signs became obvious. After successful doramectin treatment of 14 sheep with naturally acquired P. ovis infestation, the ELISA values declined slowly but remained positive in seven cases beyond 17 weeks.

Animals↗
PubMed1999

The pathology of Psoroptes ovis infestation in cattle with a special emphasis on breed difference.

In cattle, infestations with P. ovis are responsible for a severe dermatitis. The disease is very common in some breeds of beef cattle whereas dairy cattle such as Frisian Holstein are considered as resistant. In order to investigate the factors responsible for this marked breed susceptibility, the immune response to P. ovis under experimental and field conditions has been studied using serology, lymphocyte transformation assay, intradermal tests and passive cutaneous anaphylaxis in susceptible Belgian White and Blue (BWB) and resistant Frisian Holstein (FH) cattle. The results of published studies are reviewed in this paper; original data on specific hypersensitivity reactions to P. ovisare also presented. The use of a sandwich ELISA allowed the detection of specific antibodies as early as 7 days post-infestation and very high titres were observed. There was a clear positive correlation between the antibody titre and the extent of lesions. This antibody response was associated with a marked in vitro lymphocyte proliferation but there was no difference between susceptible and resistant cattle. The passive cutaneous anaphylaxis test revealed the presence of specific Ig E in actively infested animals irrespective of the breed. Specific Ig E were detected fairly late during the course of an experimental infestation with P. ovis. The intradermal injection of P. cuniculi antigenic extract induced an immediate reaction in all animals including the controls; in contrast, a delayed hypersensitivity reaction was observed in infected BWB animals only. It is concluded that immunological as well as non-immunological factors may be responsible for the breed related susceptibility or resistance to P. ovis.

Animals↗
PubMed1999

Histopathological pattern and humoral immune response to a crude exo-antigen and purified keratinase of Microsporum canis in symptomatic and asymptomatic infected cats.

In order to understand better the mechanisms involved in the diverse clinical patterns in Microsporum canis-infected cats, the histopathological features were compared in symptomatic and asymptomatic infected cats. Additionally, the IgG immune response to a crude exo-antigen and purified keratinase of M. canis was studied by ELISA in cats of various clinical and mycological status. Acute and subacute perifolliculitis and folliculitis occurred more frequently in symptomatic than asymptomatic cats. The latter usually displayed signs of chronic inflammation and a marked infiltration of superficial dermis by mast cells, which would suggest that these animals present similarities to chronically dermatophytic humans or animals. When using a crude M. canis antigen, all infected cats were shown to have significantly higher levels of specific IgG when compared to culture negative and mechanical carrier-cats. In these non-infected animals, specific IgG was more frequently detected in adults than in young animals. No difference in anti-crude antigen specific IgG was observed between symptomatic and asymptomatic infected cats, indicating that the presence of IgG is probably unrelated to the clinical status of cats. Anti-keratinase specific IgG was only detected in one of the infected cats.

Animals↗
PubMed1999

Humoral and cellular immune response to a crude exo-antigen and purified keratinase of Microsporum canis in experimentally infected guinea pigs.

In order to understand better the host-parasite relationship and to compare with previous observations in Microsporum canis naturally infected cats, the humoral and cellular immune responses to both a crude exo-antigen and a 31.5 kDa purified keratinase were evaluated in 12 M. canis experimentally infected guinea pigs. Humoral and cellular responses were assessed by ELISA from days 0 to 56 postinfection (PI) and by measurement of delayed-type hypersensitivity (DTH) responses on days 14 and 57 PI, respectively. Additionally, immunohistochemical staining was performed and demonstrated that the keratinase was produced in infected guinea pig skin, as previously reported in cats. Despite a marked interindividual variation, all the guinea pigs produced specific IgG to the crude exo-antigen from day 21 PI onwards, but no anti-keratinase IgG was detected. Strongly positive DTH responses to the exo-antigen were observed on both dates, whereas the keratinase elicited no and weak DTH on days 14 and 57 PI, respectively. These results are in agreement with those previously described for naturally infected cats, and indicate that the 31.5 kDa keratinase is not a major antigen in M. canis infection.

Animals↗
PubMed1998

The relationship between parasite counts, lesions, antibody titres and daily weight gains in Psoroptes ovis infested cattle.

Psoroptes ovis counts, extent of lesions (clinical index: ClinI), daily weight gains (DWGs) and anti-P. cuniculi antibody titres in ELISA were recorded during seven therapeutic field trials. Relationship between these different data were studied. The differences between the mean DWG of treated and untreated control animals of the different trials ranged from 39 to 1206 g/day. Data were pooled for statistical analysis and the influence of trial conditions (management of the herd, farm, treatment) was extracted from each individual data by subtracting, from the DWG of each animal, the mean DWG of its trial. Such data were called daily weight gain over the trial mean (DWG/TM). Multiple regression of DWG/TM, calculated over the period between the clinical examinations in control animals (n = 40), on clinical indices and sex demonstrated a significant DWG/TM reduction per percentage of affected body surface according to the following equation: DWG/TM (in g/day)= 135-22 ClinI(0)-13 ClinI(28/35)-70 (if male) (R2 adjusted = 0.39), where ClinI(0) and ClinI(28/35) are the clinical indices recorded respectively at the beginning (day 0) and at the end (day 28 or 35) of the experimental period during which the animals were left untreated. A nonsignificant relationship (R2 adjusted = 0.07) was found between the antibody titres on day 28 or 35 and the individual DWG/TM This would suggest that serology could be used to estimate the prevalence of the disease on a local or national basis but not to calculate its economic impact.

Animals↗
PubMed1998

Field efficacy of injectable doramectin against Chorioptes bovis in naturally infected cattle.

A single subcutaneous injection of doramectin at a dose rate of 200 micrograms/kg bodyweight was effective in controlling an infection of Chorioptes bovis mites in naturally infected cattle. From 14 days after treatment, the geometric mean number of live mites was significantly lower (P < 0.001) in the doramectin-treated cattle than in the control group at each sampling until day 35. The percentage efficacy (treated versus controls) of doramectin against C bovis at day 35 was 99.9 per cent and the percentage reduction (day 35 versus day 0) in the treated animals was 99.3 per cent. At day 35, all seven controls were still positive for C bovis whereas five of the eight doramectin-treated animals were free of live mites.

Animals↗
PubMed1998

The in vitro and in vivo production of a 31.5-kD keratinolytic subtilase from Microsporum canis and the clinical status in naturally infected cats.

BACKGROUND: Microsporum-canis-infected cats, especially the asymptomatic infected ones, are mainly responsible for the zoonotic disease. The important variability of the clinical signs in cats is poorly understood. Recently, a 31.5-kD keratinolytic subtilase was found to be a putative virulence factor. OBJECTIVE: To investigate the possible relationship between the clinical status of dermatophytic cats and the production of the keratinase. METHODS: Seven M. canis strains isolated either from clinically affected, asymptomatic infected or mechanical carrier cats were tested for the in vitro production of the enzyme. The immunohistochemical detection of the enzyme was also assessed in skin biopsies of 4 symptomatic and 7 asymptomatic naturally infected cats. RESULTS: All the strains produced in vitro a 31.5-kD keratinolytic subtilase. The enzyme was present in all but 1 of the infected cats. CONCLUSION: The production of the keratinase is not a factor directly responsible for the clinical picture seen in M.-canis-infected cats.

Animals↗
PubMed1997

Efficacy of pour-on and injectable formulations of moxidectin and ivermectin in cattle naturally infected with Psoroptes ovis: parasitological, clinical and serological data.

On the basis of Psoroptes ovis counts performed on day -7, 32 animals were randomly allocated to a control group of five animals or to four groups comprising six or seven animals which were treated, respectively, with pour-on ivermectin (IPO), injectable ivermectin (II), pour-on moxidectin (MPO) and injectable moxidectin (IM). Living mites were counted in skin scrapings on days 0, 7, 14, 28, 42 and 56 post-treatment (PT). Lesions were recorded on a standardized map on days 0 and 56 PT. Antibody kinetics were studied using ELISA on serially diluted sera. The antibody titres were expressed as the dilution giving the positive/negative cut-off. Until their treatment on day 28, the control animals remained parasitologically positive and their antibody titres increased. In treated groups, all living mite counts were negative on days 28 and 42 PT but some animals were still infected on days 7 and 14 PT. On day 56, living P. ovis were found in one animal of the IPO group. An equation of regression describing the antibody decrease was calculated with each individual data set. In most of the treated animals, the coefficient of determination R2, which describes the closeness of fit to the linear model, was above 0.9. The linear model could not be applied (low R2) to the antibody kinetics of four animals: the day 56 positive animal and its two neighbours in the IPO group and one animal from the MPO group. In the treated groups, the differences between the numbers of infected animals, the mean daily weight gains or the mean antibody titres were not statistically significant. Mean daily weight gains of the treated groups were higher than in control animals.

Animals↗
PubMed1996

A sandwich enzyme-linked immunosorbent assay to study the antibody response against Psoroptes ovis in cattle.

A sandwich enzyme-linked immunosorbent assay (ELISA) was developed using polyclonal antibodies from Psoroptes cuniculi infested rabbit and a crude P. cuniculi antigen. Sera from 133 Psoroptes ovis infested and 137 uninfested cattle were serially diluted from 1:100 to 1:102,400 and analyzed. Curves obtained by plotting log dilution versus optical densities (OD) were used and a working dilution of 1:400 was selected. Positive/negative cut-off values were calculated using the mean OD percentage (6%) of all negative sera plus 3 standard deviations. Sensitivity and specificity according to the resulting cut-off (25%) were 98.5% and 97.8% respectively. Expressed as the dilution giving the cut-off value, results in ELISA revealed a wide range of antibody titres (from 1:19 up to 1:2,240,000) with a geometric mean value of 1:35,480, and this is probably related to the well-described hyperglobulinemia in P. ovis infestations. In two trials performed at a 1 year interval, 19 Belgian White and Blue and six Fresian-Holstein calves were experimentally infested, and sensitivity and specificity were calculated throughout the experimental period. Sensitivity reached 78% on day 70 in trial 1 and 100% on day 49 in trial 2 (sensitivity was calculated using data from three control animals, three infected Fresian-Holstein animals and seven (trial 1) or six (trial 2) infected Belgian White and Blue animals). Specificity on day 0 was 100% in trial 1 and 92% in trial 2. At the end of both trials, specificity decreased in 80%. The development of the serum antibody activity to Psoroptes antigens was correlated with the development of lesions: in trial 1, the coefficient of correlation between the percentage of body surface with lesions and antibody titre was 0.82 (probability of no relationship P < 0.005) on day 56 post-infection (PI) and in trial 2, 0.83 (P < 0.025) and 0.87 (P < 0.025) on days 35 and 63 PI respectively.

Animals↗
PubMed1996

Efficacy of a phyto-aromatic gel against auricular manage in rabbits and carnivores.

The efficacy of a phyto-aromatic gel (Canidor) was evaluated, in vitro against Psoroptes cuniculi and in vivo against P cuniculi and Otodects cynotis, in experimentally and naturally infested rabbits and domestic carnivores respectively. At a 1/1 dilution the gel was 100 per cent active in vitro against P cuniculi after less than six hours of contact. In experimentally infested rabbits the gel was administered daily during two periods of five consecutive days, six days apart. A clinical cure was achieved in all the animals, but two harboured a few eggs and mites at the end of the trial. In dogs and cats the active formulation was given for two periods of four consecutive days, seven days apart. Clinical and parasitological examinations 10 and 30 days after initiating the treatment regiment revealed an excellent acaricidal effect.

Animals↗
PubMed1994

The efficacy of moxidectin 0.5% pour-on against Hypoderma bovis in naturally infested cattle: parasitological and serological data.

The field efficacy of moxidectin 0.5% pour-on formulation was assessed in heifers naturally infested with Hypoderma bovis. After their first grazing season in an infested area 34 heifers were selected on the basis of results of an ELISA test performed in January 1992. Twenty-five animals were treated with moxidectin 0.5% pour-on at a dose of 0.5 mg kg-1 bodyweight and nine heifers were left untreated. No local or general side-effects associated with the treatment were noticed. In April, seven of the nine untreated heifers were affected by warble fly, and in May all were infested; none of the treated animals harboured warble fly at any time during the trial. All the extracted larvae were identified as Hypoderma bovis. On the basis of the warble counts, efficacy was 100%. The antibody kinetics, studied on blood samples collected on Days 0 (14 January), 6, 27, 48, 90, 119 and 150, showed that in the untreated animals, the antibody titres increased until May (Day 119) and then declined sharply, whereas in the treated animals there was a drop from Day 30 onwards. The mean ELISA titres of the control and treated groups became significantly different from Day 48 onwards (P < 0.05). In conclusion, moxidectin 0.5% pour-on formulation at a dose of 0.5 mg kg-1 bodyweight can effectively treat cattle naturally infested with Hypoderma bovis first instar larvae.

Administration, Topical↗
PubMed1992

Field efficacy of flumethrin pour-on against Psoroptes ovis in cattle.

The field efficacy of pour-on formulation of flumethrin 1 per cent was assessed in cattle naturally infested with Psoroptes ovis. In a finishing unit, 18 infested animals were selected, left untreated for one month and examined twice to monitor the progress of the infestation. They were treated twice 10 days apart with a pour-on formulation of flumethrin 1 per cent (2 mg/kg bodyweight). Skin samples were collected from the animals on days 0, 7, 14, 28 and 42 and examined for the presence of live mites. The clinical condition of the cattle was evaluated at the beginning and at the end of the trial using a standardised chart. Bodyweights were recorded on days -32, 0, 28 and 50. In addition the 65 cows in a calving unit were given the same treatment regimen and its efficacy was evaluated on days 0, 7, 14 and 28 in 11 P ovis infested animals. On the day of treatment most of the infested animals had a severe pyodermatitis. From day 7 onwards no live mites were found in the treated animals and there was a marked clinical improvement. The percentage efficacy on day 28 was 100 per cent in both units. In the finishing animals treatment was associated with a marked improvement in daily weight gains between day 0 and day 28.

Administration, Topical↗
PubMedDate not supplied

Antibody response after treatment in cattle infected with Psoroptes ovis.

The decline of anti-Psoroptes ovis antibody titres after treatment was studied in six groups of naturally infected cattle. In all trials, using a limiting dilution technique, the specific antibody levels were assessed by ELISA on sera collected at regular intervals up to 78 days post treatment. All individual antibody titres started to decline between day 7 and day 14 post treatment. A linear decrease was observed. In a limited trial, five experimentally infected animals were bled monthly after treatment and seronegativity was reached within four months. The results obtained were in agreement with those obtained in the five field trials. Using a linear regression model, it was estimated by interpolation that most of the animals would have been seronegative within seven months post treatment. These results suggest that the exposure to specific P ovis antigen stops with the end of parasite activity and that dead mites are relatively non-immunogenic.

Animals↗
PubMedDate not supplied

Prevalence and characterization of Microsporum canis carriage in cats.

In order to determine the prevalence and to characterize the carriage of Microsporum canis in cats, different mycological examinations (including a culture obtained by hair brushing and Wood's light examination) were performed on 632 animals of different origins. Group 1 comprised 467 healthy pet cats belonging to veterinary students. In this group, prevalence of carriage was 2.1%: eight cats were asymptomatic transient carriers and one cat was an asymptomatic infected animal presenting discrete Wood's-positive lesions disseminated on the whole body that were visible after sedation and clipping. The carriage prevalence was higher (15.7%) in group 2 comprising 134 European cats destroyed in a pound and kept together. In two additional groups of cats, it was shown that an infected cat was responsible for the dissemination of fungal material into its environment including the other in-contact animals. When the active source of fungus was removed, the dissemination stopped, resulting in a decrease in the amount of infective material recovered from both the animal carriers and the environmental surfaces. This was also observed in two experimental groups of guinea pigs. No association between feline immunodeficiency virus infection and the M. canis carriage was observed in a retrospective case-control study performed on group 2. None of these cats was feline leukaemia virus positive.

Animals↗