Evaluation of the repeatability of a crude adult indirect Ostertagia ostertagi ELISA and methods of expressing test results

Epizootiology and Pathology of Sarcoptic Mange in Two Species of Fox (Lycalopex spp.) in Human-Dominated Landscapes of Central Chile

Sarcoptic mange caused by Sarcoptes scabiei can have catastrophic consequences for wildlife. We inspected 122 Andean foxes (Lycalopex culpaeus), collected by active (n=66) or passive (n=56) surveillance, and 28 South American gray foxes (Lycalopex griseus; all from passive surveillance) for mange in Chile (2015-19). In Andean foxes, gross lesions of mange were diagnosed in 24% of passively and 9% of actively collected foxes, although observed prevalences might be underestimated. Seroprevalence was 37 and 18%, respectively, indicating that some individuals recovered from infection or were developing the disease. No differences were found between age and sex groups. Comparing data from passive surveillance, occurrence of gross lesions was lower in gray foxes (5%). Body condition was significantly better in Andean foxes without lesions than in diseased foxes, which had significantly lower albumin concentrations than healthy individuals. Among the 12 foxes with gross lesions, four, six and two individuals were categorized as having type I, type II, and type III lesions, respectively, based on clinical severity. Histologic severity correlated with gross lesions and included irregular epidermal hyperplasia with hyperkeratosis, which was marked in type II and III infections. Conventional PCR targeting of the cox1 gene fragment revealed four nucleotide sequence types, showing 99-100% identity among them and between 99% and 100% identity with previously published sequences of S. scabiei. A significant association between the occurrence of mange in foxes and distance to the nearest house was found. We speculate that diseased foxes tended to approach human settlements, perhaps in search of food. Visual inspection of 211 rural dogs from the study area did not reveal gross mange lesions in any animal. Sarcoptic mange is enzootic in the Andean fox in the study area and should be considered in the management of the species.

Advances in diagnosis of gastrointestinal nematodes in livestock and companion animals

Diagnosis of gastrointestinal nematodes in livestock and companion animals has been neglected for years and there has been an historical underinvestment in the development and improvement of diagnostic tools, undermining the undoubted utility of surveillance and control programmes. However, a new impetus by the scientific community and the quickening pace of technological innovations, are promoting a renaissance of interest in developing diagnostic capacity for nematode infections in veterinary parasitology. A cross-cutting priority for diagnostic tools is the development of pen-side tests and associated decision support tools that rapidly inform on the levels of infection and morbidity. This includes development of scalable, parasite detection using artificial intelligence for automated counting of parasitic elements and research towards establishing biomarkers using innovative molecular and proteomic methods. The aim of this review is to assess the state-of-the-art in the diagnosis of helminth infections in livestock and companion animals and presents the current advances of diagnostic methods for intestinal parasites harnessing (i) automated methods for copromicroscopy based on artificial intelligence, (ii) immunodiagnosis, and (iii) molecular- and proteome-based approaches. Regardless of the method used, multiple factors need to be considered before diagnostics test results can be interpreted in terms of control decisions. Guidelines on how to apply diagnostics and how to interpret test results in different animal species are increasingly requested and some were recently made available in veterinary parasitology for the different domestic species.

Variation in the Performance of Different Batches of Two Mycobacterium avium Subspecies paratuberculosis Antibody ELISAs Used for Pooled Milk Samples

Simple Summary

This article explores variation in the performance of different batches of tests for the detection of antibodies against the ruminant pathogen Mycobacterium avium subspecies paratuberculosis (MAP) in milk. The results indicate that variation is present and that it has sources mainly in the manufacturing process of the test kits and, to a lesser degree, in the test laboratories.

Abstract

Regionally, the monitoring of paratuberculosis at the herd level is performed by the detection of specific antibodies in pooled milk samples by ELISA. The negative/positive cut-off S/P values applied for pooled milk samples are low and particularly vulnerable to variation in the test performance. In this study, a batch variation in the test performance of two ELISA tests was assessed to identify consequences for sample classification. A total of 72 pooled milk samples (50 from MAP-infected herds, 22 from one MAP-non-infected herd) were analyzed using three different batches, each of two different MAP antibody ELISA tests (A and B). Receiver operating characteristic (ROC) analysis was performed, with the results of each batch, S/P values of the samples and optical density (OD) readings of the negative and positive control samples included in the kits being compared between the batches of one test. ROC analysis revealed a considerable variation in the test performance of the batches of the two individual tests, caused by differences in the S/P values of the samples and resulting in different sensitivities at a specificity of 100%. Major sources of variation originate from the manufacturing processes of test batches. These sources have to be better controlled, and the test performance has to be revisited regularly.

Development and evaluation of an indirect ELISA for detection of Teladorsagia circumcincta infection in sheep

Background

The gastrointestinal helminth, Teladorsagia circumcincta, is one of the major health risks and production-limiting diseases in small ruminant populations, particularly in temperate regions. With the increasing importance of disease management and recruited anthelmintic resistant types, accurate approaches are needed for the diagnosis of the infection in the host. Due to uncertain results using faecal examinations, the ELISA method was indicated for the detection of nematode antigenic materials. Despite some promising results, problems were described in terms of test specificity and cross-reactions. Therefore, this study aimed to evaluate the IgG response to worm somatic and excretory/secretory (ES) products using western blot analysis and an indirect ELISA for the detection of T. circumcincta infection in sheep.

Results

Based on the immuno-reactivity analysis, immunogenic fractions with molecular weights (MWs) of approximately 60, 75 and 100 kDa were detected in somatic content and two antigens of about 63 and 75 kDa in ES material. Accordingly, a specific product at 75 kDa had the strongest reaction and appeared as the most common antigenic protein. In ELISA, all the sera from the infected sheep revealed the OD rates above the calculated cut-off value with about two-fold greater average. Negative control samples were also specifically recognized with the mean OD rate of about 1/3 of the estimated cut-off value. The cross-reaction test, using rabbit anti-T. circumcincta IgG, did not show reactivity with the ES antigens of other prevalent nematodes including Haemonchus contortus, Protostrongylus rufescens and Marshallagia marshalli. In contrast, a strong positive reaction was observed with the somatic antigens of M. marshalli.

Conclusions

The results of this study indicated that the indirect ELISA method using the ES content enables distinguishing the T. circumcincta infected sheep with high specificity. Those antigenic ES peptides with 63 and particularly 75 kDa MWs should be further investigated due to the potential for serological diagnostic methods and immunoprotective targets in the host.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-03042-1.

Electrochemical enzyme-linked immunosorbent assay (e-ELISA) for parasitic nematode Ostertagia ostertagi (brown stomach worm) infections in dairy cattle

A sensitive electrochemical immunoassay (e-ELISA) has been developed for the detection of the gastrointestinal parasitic nematode Ostertagia ostertagi (brown stomach worm) in infected and control serum samples. An antigen-indirect immunoassay format was employed to detect the presence of O. ostertagi antibodies, coupled with an anti-species monoclonal horseradish peroxidase (HRP) conjugate. ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid)) and TMB (3,3',5,5'-tetramethylbenzidine/hydrogen peroxide) were investigated as both chromogenic visualising reagents for optical ELISA and electroactive substrates for electrochemical ELISA in the HRP catalysed oxidation reaction. Coulometry was applied for the detection of O. ostertagi antibodies (via TMB electrochemistry) and compared with the commercial optical ELISA (ABTS based SVANOVIR® O. ostertagi-Ab ELISA kit). Cost-effective in-house sensors were designed and fabricated using polyester and chemical adhesive materials with the aid of stencil printing and laser machining techniques. The performance of the electrochemical ELISA and sensor was evaluated by investigating redox mediators (ABTS vs. TMB), stop solutions (sodium dodecyl sulfate vs. sulfuric acid) and incubation times (150 min vs. 70 min vs. 25 min). For a total assay incubation time of 70 minutes, the TMB/H2SO4 based e-ELISA was able to differentiate between positive (P) and negative (N) control serum samples, with a P/N70 control ratio 1.6 times higher than that of optical ELISA (TMB/H2SO4 combination) and 2.9 times higher than that of the commercial ELISA kit (ABTS/SDS combination). Furthermore, the e-ELISA approach is quicker and required only 25 min (total incubation time) with even better response (P/N25 = 14.7), which is approximately 4-fold higher than the optical immunoassay (P/N25 = 3.8). The proposed e-ELISA is specific (selective Ab-Ag interactions) and highly sensitive - capable of detecting up to 16-fold dilutions of a positive control serum sample. The electrochemical ELISA approach has the potential for rapid sample screening in a portable, disposable format, contributing to the quest for effective prevention and control of parasitic Ostertagia ostertagi infections in cattle.

First description of sarcoptic mange in the endangered Iberian lynx (Lynx pardinus): clinical and epidemiological features

A 6-month-old female Iberian lynx (Lynx pardinus) cub that was severely affected by mange died in September 2016 in the Montes de Toledo (Spain) with crusts and fissures on its face, outer ears, nipples and footpads. The body condition of the cub was very poor, and it also had a mandibular abscess and a severely ankylosed luxation on its left knee. After confirming that the origin of the deceased cub’s dermal lesions was Sarcoptes scabiei, the subsequent search for ectoparasites and a comparison of histopathological and immunohistochemical findings in all sympatric lynxes handled (n = 30) and submitted for necropsy (n = 4) during 2016 and 2017 revealed the presence of S. scabiei mites and/or milder mange compatible lesions in five members of her family group, which was treated against mange together with two exposed contiguous family groups. An ELISA developed by the authors showed the presence of antibodies against S. scabiei in the deceased female cub and one brother. The presence of concomitant immunosuppressive factors in the dead female cub and the results obtained for the other sympatric lynxes studied since 2016 suggest that S. scabiei had a limited effect on immune-competent Iberian lynxes in the local population of the Montes de Toledo. However, a different evolution and relevance of sarcoptic mange in different populations—or even in the same one in the presence of immunosuppressive factors—cannot be ruled out, thus confirming the need for further research in order to attain a complete comprehension of the epidemiology and the real threat that this ectoparasitic disease may imply for L. pardinus.

Longitudinal monitoring of anti-saliva antibodies as markers of repellent efficacy against Phlebotomus perniciosus and Phlebotomus papatasi in dogs

A 2-year longitudinal study of enzyme-linked immunosorbent assay (ELISA) antibodies against Phlebotomus perniciosus and Phlebotomus papatasi (Diptera: Psychodidae) sandfly saliva was performed in 32 Beagle dogs treated preventively with an imidacloprid-permethrin topical insecticide in an endemic area in Spain. Dogs were grouped into three sandfly exposure groups according to the time of inclusion in the study. Assays analysed immunoglobulin G (IgG) against salivary gland homogenates (SGH) of both species and recombinant P. papatasi rSP32 and P. perniciosus rSP03B proteins in serum. The dogs were participating in a Leishmania infantum (Kinetoplastida: Trypanosomatidae) vaccine trial and were experimentally infected with the parasite in the second year. No dog acquired natural L. infantum infections during the first year, but most developed anti-saliva antibodies, and median log-transformed optical densities (LODs) were seasonal, mimicking those of local sandflies. This indicates that the repellent efficacy of the insecticide used is below 100%. Multi-level modelling of LODs revealed variability among dogs, autocorrelation and differences according to the salivary antigen and the dog's age. However, dog seroprevalence, estimated using pre-exposure LODs as cut-offs, was relatively low. This, and the fact that dogs did not become naturally infected with L. infantum, would support the efficacy and usefulness of this imidacloprid-permethrin topical insecticide in canine leishmaniasis control.

Seasonal dynamics of canine antibody response to Phlebotomus perniciosus saliva in an endemic area of Leishmania infantum

Background

Canine leishmaniosis (CanL) is an important zoonotic parasitic disease, endemic in the Mediterranean basin. In this region, transmission of Leishmania infantum, the etiological agent of CanL, is through the bite of phlebotomine sand flies. Therefore, monitoring host-vector contact represents an important epidemiological tool, and could be used to assess the effectiveness of vector-control programmes in endemic areas. Previous studies have shown that canine antibodies against the saliva of phlebotomine sand flies are specific markers of exposure to Leishmania vectors. However, this method needs to be further validated in natural heterogeneous dog populations living in CanL endemic areas.

Methods

In this study, 176 dogs living in 12 different locations of an L. infantum endemic area in north-east Spain were followed for 14 months. Blood samples were taken at 5 pre-determined time points (February, August and October 2016; January and April 2017) to assess the canine humoral immune response to whole salivary gland homogenate (SGH) and to the single salivary 43 kDa yellow-related recombinant protein (rSP03B) of Phlebotomus perniciosus, a proven vector of L. infantum naturally present in this region. Simultaneously, in all dogs, L. infantum infection status was assessed by serology. The relationship between anti-SGH and anti-rSP03B antibodies with the sampling month, L. infantum infection and the location was tested by fitting multilevel linear regression models.

Results

The dynamics of canine anti-saliva IgG for both SGH and rSP03B followed the expected trends of P. perniciosus activity in the region. Statistically significant associations were detected for both salivary antigens between vector exposure and sampling month or dog seropositivity to L. infantum. The correlation between canine antibodies against SGH and rSP03B was moderate.

Conclusions

Our results confirm the frequent presence of CanL vectors in the study area in Spain and support the applicability of SGH- and rSP03B-based ELISA tests to study canine exposure to P. perniciosus in L. infantum endemic areas.

Ostertagia ostertagi antibodies in bulk tank milk from dairy cattle in Italy: A nation-wide survey

The objective of this study was to investigate the exposure to Ostertagia ostertagi in dairy cattle herds across Italy through measurement of antibody concentration in the bulk tank milk (BTM) and to evaluate the possible effect of regions, seasons and pasture management practices on the level of exposure to the parasite. The O. ostertagi antibody levels in milk were determined using a commercial ELISA kit (SVANOVIR® O. ostertagi-Ab) and expressed as optical density ratio (ODR). From March 2015 to September 2017, BTM samples were collected in 1209 dairy cattle farms located in 15 regions of Northern, Central and Southern Italy. As reported in previous studies, BTM samples were classified in three different categories according to the level of exposure to O. ostertagi as follows: (i) positive with ODR values >0.60; (ii) negative with ODR values <0.30 and (iii) grey zone with ODR values between 0.30 and 0.60. Finally, differences in ODR values between regions, seasons and herd management practices were studied using the one-way analysis of variance. The overall mean ODR revealed a value of 0.49 in Italy; in particular, dairy cattle farms located in Southern Italy showed the highest O. ostertagi BTM ODR values than the other regions (p < 0.05). The ODR values ranged from 0.45 in autumn to 0.53 in spring and the seasonal difference was significant (p < 0.05). Furthermore, a positive association was found between the ODR values and the access to pasture; herds with access to pasture showed significantly higher titres (p < 0.0001) of O. ostertagi antibodies in milk (mean ODR = 0.63) than in those in total-confinement housing (mean ODR = 0.42). This study, the first of its kind in Italy, will provide a quantitative assessment exposure to O. ostertagi of Italian dairy herds and represents a significant step forward in evidence-based medicine for dairy veterinarians, advisors and farmers.

Serodiagnostic Potential of Alpha-Enolase From Sarcoptes scabiei and Its Possible Role in Host-Mite Interactions

Infestation of the epidermis with the highly contagious ectoparasite, Sarcoptes scabiei, causes scabies, which is characterized by intense itching, pruritus, and secondary infection. This condition affects humans, livestock, and wildlife worldwide, incurring large economic losses and reducing the quality of human life. In the present study, we cloned the alpha-enolase, a key enzyme in the glycolytic and gluconeogenesis pathways, from S. scabiei var. cuniculi, characterized it and produced soluble recombinant enolase protein (rSsc-eno). We determined the localization of Ssc-eno in isolated mites and mites in lesioned skin. The results showed that native enolase was intensely localized in the tegument of the mouthparts, the entire legs, and the whole mites' body, as well as in the gut and reproduction system. Interestingly, we found that native enolase was widely distributed in mites in lesioned skin, with obvious high protein intensity compared with isolated mites. Building on good immunoreactivity, an indirect enzyme-linked immunosorbent assay (ELISA) based on rSsc-eno showed 92% sensitivity and 95.8% specificity, compared with other indirect ELISA in this study, rSsc-eno based ELISA is better in detecting scabies in rabbits. Besides, this method can detect S. scabiei infection as early as 1 week post infection. Compared with other detection methods, such as traditional microscopic examination and recently published universal conventional PCR, rSsc-eno ELISA was more effective to detect early infection in rabbits. Additionally, in vitro incubation experiments demonstrated the concentration-dependent acaricidal activity of rabbit anti-rSsc-eno sera against larval mites, suggested its potential as a vaccine candidate.

Identification of a novel PYP-1 gene in Sarcoptes scabiei and its potential as a serodiagnostic candidate by indirect-ELISA

Scabies is a parasitic disease caused by the ectoparasite Sarcoptes scabiei, affecting different mammalian species, including rabbits, worldwide. In the present study, we cloned and expressed a novel inorganic pyrophosphatase, Ssc-PYP-1, from S. scabiei var. cuniculi. Immunofluorescence staining showed that native Ssc-PYP-1 was localized in the tegument around the mouthparts and the entire legs, as well as in the cuticle of the mites. Interestingly, obvious staining was also observed on the fecal pellets of mites and in the integument of the mites. Based on its good immunoreactivity, an indirect enzyme-linked immunosorbent assay (ELISA) using recombinant Ssc-PYP-1 (rSsc-PYP-1) as the capture antigen was developed to diagnose sarcoptic mange in naturally infected rabbits; the assay had a sensitivity of 92·0% and specificity of 93·6%. Finally, using the rSsc-PYP-1-ELISA, the Ssc-PYP-1 antibody from 10 experimentally infected rabbits could be detected from 1 week post-infection. This is the first report of S. scabiei inorganic pyrophosphatase and the protein could serve as a potential serodiagnostic candidate for sarcoptic mange in rabbits.

Indirect ELISA (iELISA) for routine detection of antibodies against Minute Virus of Mice (MVM) in mice colonies

In this study we developed an indirect ELISA to detect antibodies against Minute Virus of Mice (MVM) using an antigen produced from BHK-21 cells infected with a prototype strain of the virus. The optimal antigen concentration and serum dilutions were established. In order to analyze variability in the laboratory, reproducibility and repeatability within and between plates were determined. Then, a panel of 460 sera from conventional facilities and previously classified as positive or negative by the indirect fluorescent antibody assay was analyzed. The cutoff value was determined by a receiver operating characteristic (ROC) curve. The results of the indirect ELISA were compared with those of the indirect fluorescent antibody assay. The ELISA assay showed 100% sensitivity and 99% specificity. ELISA is a useful tool to be developed in standard virology laboratories and can be used for screening animals faster than the traditional indirect fluorescent antibody assay.

Vaccination of rabbits with immunodominant antigens from Sarcoptes scabiei induced high levels of humoral responses and pro-inflammatory cytokines but confers limited protection

BACKGROUND

Vaccination is an attractive ecological alternative to the use of acaricides for parasite control. However, effective anti-parasite vaccines against sarcoptic mange have not yet been developed. The purpose of this study was first to identify Sarcoptes scabiei immunodominant antigens and second to evaluate them as vaccine candidates in a rabbit/S. scabiei var. cuniculi model.

METHODS

The S. scabiei Ssλ15 immunodominant antigen was selected by immunoscreening of a S. scabiei var. hominis cDNA. The full-length cDNA was sequenced and cloned into the pGEX vector and the recombinant protein expressed in BL21 (DE3) cells and purified. A vaccination trial was performed consisting of a test group (n = 8) immunised with recAgs (a mix of two recombinant antigens, Ssλ15 and the previously described Ssλ20∆B3) and a control group (n = 8) immunised with PBS. All analyses were performed with R Statistical Environment with α set at 0.050.

RESULTS

The full-length open reading frame of the 1,821 nt cloned cDNA encodes a 64 kDa polypeptide, the sequence of which had 96 % identity with a hypothetical protein of S. scabiei. Ssλ15 was localised by immunostaining of skin sections in the tegument surrounding the mouthparts and the coxa in the legs of mites. Rabbit immunisation with recAgs induced high levels of specific IgG (P < 0.010) and increased levels of total IgEs. However, no significant clinical protection against S. scabiei challenge was detected. Unexpectedly, the group immunised with the recAgs mix had significantly higher lesion scores (P = 0.050) although lower mean mite densities than those observed in the control group. These results might indicate that the lesions in the recAgs group were due not only to the mites density but also to an exacerbated immunological response after challenge, which is in agreement with the specific high levels of pro-inflammatory cytokines (IL-1 and TNFα) detected after challenge in this group.

CONCLUSIONS

The selected antigens delivered as recombinant proteins had no clinical protective efficacy against S. scabiei infestation although immunisation reduced mite density. However, these results pave the way for future studies on alternative production systems, adjuvants, delivery methods and combinations of antigens in order to manage stimulation of clinical protective immune responses.

Evaluation of an ELISA using recombinant Ssλ20ΔB3 antigen for the serological diagnosis of Sarcoptes scabiei infestation in domestic and wild rabbits

An ELISA, based on the Sarcoptes scabiei Ssλ20ΔB3 inmunodominant antigen, was evaluated for the detection of antibodies to S. scabiei in experimentally infested (n=10), farm (n=109), and wild (n=78) rabbit sera. The S. scabiei antigen Ssλ20ΔB3, a major structural protein present over the entire mite's body, was produced as a recombinant protein in Escherichia coli and purified for its use in the ELISA. The resulting ELISA showed, in experimentally infested domestic rabbits, detectable specific antibody responses (IgG) above the cut off level from week three post-infestation indicating that the assay is able to detect positive rabbits very early during the course of the infestation. The ELISA was validated on a panel of 109 domestic breeding rabbit sera collected from 26 Spanish farms, of which 41 were obtained from rabbits with skin lesions compatible with sarcoptic mange, 26 with skin lesions compatible with psoroptic mange, and 42 from unexposed individuals from mange-free farms. The ELISA in this group was characterized by 95% sensitivity, 97% specificity, and a high degree of repeatability. In the psoroptic mange compatible lesions group, included in the study as control group for cross-reactivity with the closely related mite Psoroptes cuniculi, cross-reacting antibodies to Ssλ20ΔB3 S. scabiei antigen were detected in 42.30% of the rabbit sera. However, mean% OD values of the sarcoptic-mange group (55.61 ± 39.20%) were significantly higher (p<0.001) than OD values of the psoroptic-mange (3.64% ± 5.4%) and also of the free-mange (0.21% ± 0.67%) groups. In addition, the ELISA was also evaluated in serum samples obtained from both naturally infested and non-infested wild rabbits from Mallorca Island. The sensitivity of the assay for this group was 100% (4 out of the 4 rabbits with sarcoptic mange compatible lesions and presence of S. scabiei mites were seropositive) and the specificity was 90% (67 out of 74 wild rabbits without detectable mange lesions were seronegative). Although, the total number of tested samples from experimentally infested, farm and wild rabbits was limited, our study showed that the ELISA is able to differentiate between infested and non-infested animals in all tested groups with very high sensitivity and specificity indicating that recombinant Ssλ20ΔB3 is a reliable diagnostic antigen. This assay might be a cost-effective tool for detecting the presence of mangy animals and therefore helping prevent spread of mange among domestic rabbits, reducing potential transmission from female breeding rabbits to other farms, and detecting infestation with sarcoptic mange in the wild.

Canine Antibodies against Salivary Recombinant Proteins of Phlebotomus perniciosus: A Longitudinal Study in an Endemic Focus of Canine Leishmaniasis

Background

Phlebotomine sand flies are vectors of Leishmania parasites. During blood feeding, sand flies deposit into the host skin immunogenic salivary proteins which elicit specific antibody responses. These anti-saliva antibodies enable an estimate of the host exposure to sand flies and, in leishmaniasis endemic areas, also the risk for Leishmania infections. However, the use of whole salivary gland homogenates as antigen has several limitations, and therefore, recombinant salivary proteins have been tested to replace them in antibody detection assays. In this study, we have used for the first time sand fly salivary recombinant proteins in a longitudinal field study on dogs.

Methodology/Principal Findings

Sera from dogs naturally exposed to P. perniciosus bites over two consecutive transmission seasons in a site endemic for canine leishmaniasis (CanL) were tested at different time points by ELISA for the antibodies recognizing whole saliva, single salivary 43 kDa yellow-related recombinant protein (rSP03B), and a combination of two salivary recombinant proteins, 43 kDa yellow-related protein and 35.5 kDa apyrase (rSP01). Dogs were also tested for Leishmania infantum positivity by serology, culture, and PCR and the infection status was evaluated prospectively. We found a significant association between active CanL infection and the amount of anti-P. perniciosus saliva antibodies. Importantly, we detected a high correlation between IgG antibodies recognizing rSP03B protein and the whole salivary antigen. The kinetics of antibody response showed for both a whole saliva and rSP03B a similar pattern that was clearly related to the seasonal abundance of P. perniciosus.

Conclusions

These results suggest that P. perniciosus rSP03B protein is a valid alternative to whole saliva and could be used in large-scale serological studies. This novel method could be a practical and economically-sound tool to detect the host exposure to sand fly bites in CanL endemic areas.

Canine leishmaniasis (CanL) is a widespread zoonosis caused by protozoan parasite Leishmania infantum. CanL is endemic in more than 70 countries, including regions of southwestern Europe, where the main vector is Phlebotomus perniciosus. Saliva inoculated into the host during blood feeding provoke species-specific antibody response. They could be used as a serological marker of exposure to sand flies and, in leishmaniasis endemic areas, also as an indication of Leishmania infection risk. However, in case of large-scale serological studies, it is difficult to obtain appropriate amounts of crude salivary antigen from laboratory-reared sand flies. Therefore, we studied if specific salivary recombinant proteins could be suitable to replace whole saliva as an antigen for serological assays. Antibodies recognizing recombinant salivary protein in naturally bitten dogs were highly correlated with antibody response against whole saliva. Seasonal exposure of dogs to sand flies led to antibody response fluctuations related to the period of activity and abundance of vectors. In a context of high CanL endemicity, we found a significant association between progressive CanL infections and antibodies against sand fly saliva. Thus, salivary recombinant proteins could be used as suitable tool for investigations host exposure to sand flies in endemic settings.

Prevalence and seasonality of bulk milk antibodies against Dictyocaulus viviparus and Ostertagia ostertagi in Irish pasture-based dairy herds

Infections with Dictyocaulus viviparus and Ostertagia ostertagi nematode parasites are of importance to bovine health and production in temperate areas across the world. Losses due to these parasites in dairy herds can be considerable due to decreased milk productivity and fertility. However, information on current epidemiological patterns in Irish dairy herds is limited. Bulk milk samples were collected from a total of 319 dairy farms across the Republic of Ireland. The D. viviparus samples were tested with an ELISA based on recombinant major sperm protein, while the O. ostertagi samples were tested with an ELISA based on crude saline extract, whole worm O. ostertagi antigen. Management data were collected from the farms using a questionnaire. Logistic regression was used to find significant associations between the presence of antibodies against D. viviparus and O. ostertagi and management factors. The overall prevalence of D. viviparus infection was 62.8%, while over 98% of herds had antibodies to O. ostertagi at the specified cut-off. Both D. viviparus and O. ostertagi antibodies were highest in November, which could be explained by the accumulated uptake of larvae through the grazing season. In herds of farmers that dosed their in-calf heifers with anthelmintics were significantly more likely to be positive for antibodies against D. viviparus infection. This study highlights that both D. viviparus and O. ostertagi infections are widespread in dairy herds in Ireland throughout the grazing season.

Comparison of the performance of two spontaneous sedimentation techniques for the diagnosis of human intestinal parasites in the absence of a gold standard

Performance evaluation of diagnostic tests is critical in the search for accurate diagnoses. A gold standard test is usually absent in parasitology, thus rendering satisfactory assessment of diagnostic accuracy difficult. Moreover, reliability (assessed by the study of repeatability) is a rarely studied characteristic of diagnostic tests. This study compared and evaluated the performance (repeatability, concordance and accuracy) of the spontaneous sedimentation technique (SST) and the Paratest for the diagnosis of Giardia lamblia, Entamoeba histolytica complex, Blastocystis spp., Ascaris lumbricoides, hookworm, Trichuris trichiura and Calodium hepaticum. Fecal samples of 143 individuals were separated into three replicates for each test. Concordance and homogeneity of the results between replicates of each test and between tests were evaluated. Proportions of positives, sensitivity and specificity were estimated using a Bayesian Latent Class Model. High repeatability of both tests was found for the detection of intestinal parasites, except for Blastocystis spp. and hookworm. Concordance between tests was generally high (concordance correlation coefficient, 0.72-0.88), except for Blastocystis spp., hookworm and T. trichiura. The Paratest detected more cases of Blastocystis spp. and fewer of hookworm than the SST. The tests were quite discordant in the detection of T. trichiura. A low sensitivity (39.4-49.2% for SST, 35.8-53.8% for Paratest) and a high specificity (93.2-97.2%) were found for both tests. The Paratest presented a slightly higher sensitivity for the diagnosis of Blastocystis spp. (53.8%), and SST did so for hookworm (49.2%). This is the first study on repeatability and accuracy (using a Bayesian approach) of two spontaneous sedimentation techniques. These results suggest underdiagnosis of little dense parasitic forms due to technical limitations in both tests. We conclude that the combined study of repeatability, concordance and accuracy is a key strategy for better evaluation of the performance of tests and is also useful for the identification of technical limitations.

Variable performance of a human derived Sarcoptes scabiei recombinant antigen ELISA in swine mange diagnosis

The performance of an indirect ELISA test based on Sarcoptes scabiei var hominis recombinant antigen Ssλ20ΔB3 (rec-ELISA), to diagnose pig mange was investigated in 15 experimentally infected and non-infected pigs and 692 commercial pigs from 16 herds in southeast Spain. These latter animals included 6-7 month old fatteners (13 herds), 11-12 month old replacement sows (1 herd) and ≥24 month old breeding sows (7 herds). All pigs were examined for mites in ear skin scrapings and the presence of S. scabiei-associated macroscopic dermatitis; moreover, fatteners were also tested for antibodies against porcine viruses including: Aujeszky disease virus (ADV), swine influenza virus (SIV), type 2 porcine circovirus (PCV2) and porcine respiratory and reproductive syndrome virus (PRRSV). S. scabiei and chronic hyperkeratotic dermatitis were detected in breeding sows from 6 herds. Mite prevalence in other pigs was 83% in replacement sows, 0% in 7 fattener's herds and 3-82% in other fattener's herds. All fattener herds had pigs with acute hypersensitivity dermatitis and the percentage of affected pigs and lesion area was significantly greater in S. scabiei infected ones. Rec-ELISA relative optical densities (RODs) were greater in older than in young pigs, as well as in infected compared to non-infected pigs. However, RODs differed significantly between infected individuals, regardless of age and origin (commercial or experimental) and the herd prevalence of S. scabiei. Low repeatability between ELISA microtiter plates, suggesting variable specific antibody binding to antigen, are likely partly responsible for ROD variation. Other potential causes of variation were examined in fatteners using random effects logistic regression analysis, after defining a seropositivity threshold value with receiver-operating characteristics (ROC) analysis. The logistic model indicated that seropositivity was associated with large dermatitis areas and with the only herd with low PCV2 seroprevalence. Pigs with more extensive dermatitis may have older infections and more rec-ELISA detectable antibodies. The possibility that PCV2, a recognized immunosupressor, depresses antibody production against S. scabiei infection merits further attention. In summary, results indicate some potential of the studied rec-ELISA as a complementary tool for herd-level swine mange diagnosis, and that work to reduce internal and external sources of assay variation is essential.

Explaining patterns of infection in free-living populations using laboratory immune experiments

The host response to different helminth species can vary and have different consequences for helminth persistence. Often these differences are generated by changes in the dynamics and intensity of the immune components against parasites with distinct life history strategies. We examined the immune response of rabbits to primary infections of the gastrointestinal nematodes Trichostrongylus retortaeformis and Graphidium strigosum under controlled conditions for 120 days post-challenge. Results showed that rabbits developed a robust and effective immune response against T. retortaeformis and abundance quickly decreased in the duodenum and was completely cleared in the remaining sections of the small intestine within 4 months. Infected individuals exhibited an initial strong inflammatory response (IFN-γ), IL-4 expression also increased and was coupled to a rapid serum and mucus IgG and IgA and eosinophilia. Strong IL-4, serum IgA and IgG responses and eosinophilia were also observed against G. strigosum. However, parasite abundance remained consistently high throughout the infection, and this was associated with relatively low mucus antibodies. These findings suggest that immunity plays a key role in affecting the abundance of these nematodes, and different immune mechanisms are involved in regulating the dynamics of each infection and their long-term persistence in free-living host populations.

Seasonal breeding drives the incidence of a chronic bacterial infection in a free-living herbivore population

Understanding seasonal changes in age-related incidence of infections can be revealing for disentangling how host heterogeneities affect transmission and how to control the spread of infections between social groups. Seasonal forcing has been well documented in human childhood diseases but the mechanisms responsible for age-related transmission in free-living and socially structured animal populations are still poorly known. Here we studied the seasonal dynamics of Bordetella bronchiseptica in a free-living rabbit population over 5 years and discuss the possible mechanisms of infection. This bacterium has been isolated in livestock and wildlife where it causes respiratory infections that rapidly spread between individuals and persist as subclinical infections. Sera were collected from rabbits sampled monthly and examined using an ELISA. Findings revealed that B. bronchiseptica circulates in the rabbit population with annual prevalence ranging between 88% and 97%. Both seroprevalence and antibody optical density index exhibited 1-year cycles, indicating that disease outbreaks were seasonal and suggesting that long-lasting antibody protection was transient. Intra-annual dynamics showed a strong seasonal signature associated with the recruitment of naive offspring during the breeding period. Infection appeared to be mainly driven by mother-to-litter contacts rather than by interactions with other members of the community. By age 2 months, 65% of the kittens were seropositive.

Immune regulation of a chronic bacteria infection and consequences for pathogen transmission

Background

The role of host immunity has been recognized as not only playing a fundamental role in the interaction between the host and pathogen but also in influencing host infectiousness and the ability to shed pathogens. Despite the interest in this area of study, and the development of theoretical work on the immuno-epidemiology of infections, little is known about the immunological processes that influence pathogen shedding patterns.

Results

We used the respiratory bacterium Bordetella bronchiseptica and its common natural host, the rabbit, to examine the intensity and duration of oro-nasal bacteria shedding in relation to changes in the level of serum antibodies, blood cells, cytokine expression and number of bacteria colonies in the respiratory tract. Findings show that infected rabbits shed B. bronchiseptica by contact up to 4.5 months post infection. Shedding was positively affected by number of bacteria in the nasal cavity (CFU/g) but negatively influenced by serum IgG, which also contributed to the initial reduction of bacteria in the nasal cavity. Three main patterns of shedding were identified: i- bacteria were shed intermittently (46% of individuals), ii- bacteria shedding fell with the progression of the infection (31%) and iii- individuals never shed bacteria despite being infected (23%). Differences in the initial number of bacteria shed between the first two groups were associated with differences in the level of serum antibodies and white blood cells. These results suggest that the immunological conditions at the early stage of the infection may play a role in modulating the long term dynamics of B. bronchiseptica shedding.

Conclusions

We propose that IgG influences the threshold of bacteria in the oro-nasal cavity which then affects the intensity and duration of individual shedding. In addition, we suggest that a threshold level of infection is required for shedding, below this value individuals never shed bacteria despite being infected. The mechanisms regulating these interactions are still obscure and more studies are needed to understand the persistence of bacteria in the upper respiratory tract and the processes controlling the intensity and duration of shedding.

Development and field evaluation of a new serological test for Taenia saginata cysticercosis

Cattle infected with the tapeworm cyst, Taenia saginata metacestode (synonym: Cysticercus bovis) are a source of human infection if affected beef is eaten raw or undercooked. Control measures targeted at individual cattle rather than all animals in a T. saginata-exposed herd should help reduce costs and alleviate current constraints associated with managing an outbreak. To that end, we have developed a reliable diagnostic test for use in live animals that would enable veterinary regulators to focus disease control strategies. The test detects bovine anti-T. saginata immunoglobulin G1 antibodies using an enzyme-linked immunosorbent assay (ELISA) which relies on the excretory-secretory antigens of T. saginata. Animals were inoculated with 10, 100 or 1000 viable T. saginata eggs in order to simulate the parasite burden of field-infected animals (parasite load=1-86; n=28). By testing sera obtained from the inoculated animals 84 days post-inoculation, test sensitivity was estimated to be 92.9% (95% confidence interval or CI=83.4-100.0%). Another 17 animals inoculated with 5000 or 10,000 viable eggs of T. saginata and shown to harbour metacestodes at post-mortem, all tested positive in the ELISA. Test specificity estimated from a herd of field animals with no historical, epidemiological, or post-mortem evidence of infection was 90.6% (95% CI=87.0-94.2%; n=256 field cattle). Using the test on samples (n=347) from a T. saginata-infected feedlot, the Bayesian approach estimate of seroprevalence was 4.6% (95% probability intervals=0.5-10.3%). The test performance characteristics of the ELISA suggest that it will be adequate for field application in bovine cysticercosis outbreaks.

The impact of milk handling procedures on Ostertagia ostertagi antibody ELISA test results

The impact of various milk handling stressors were analyzed using a commercially available enzyme-linked immunosorbent assay (ELISA) test measuring Ostertagia ostertagi antibodies in milk from dairy cattle (Svanovir). An indirect ELISA has the ability to determine the amount of milk production losses related to intestinal parasitism. The ELISA test recommends fresh defatted milk, however, milk collected from Dairy Herd Improvement (DHI) programs in North America undergo many stressors, including, heating, freezing and are not defatted. Normalized optical density ratios (ODRs) were compared between fresh defatted milk and milk subjected to one or more stressors with a linear mixed model accounting for differences in variation between the fresh and the frozen samples. Concordance correlation coefficients were also analyzed for comparisons to other similar studies. After accounting for random cow and container effects, the treatment factors interacted with each other (p<0.001). Biologically interesting contrasts were created to explain the interaction. The estimated difference in ODR between the milk samples handled according to recommendations of the manufacturers of Svanovir and the whole milk samples that were subjected to the most extreme treatment (heated, frozen, thawed, and re-frozen for 4 weeks) was 0.062 (p<0.001). This difference represented less than 5% of the range, and was thus considered biologically negligible. Frozen whole milk processed by DHI programs, the most likely method of collecting on-farm samples in North America, will likely yield reliable results for the indirect ELISA tests, particularly, Svanovir.

Assessment of the within- and between-laboratory repeatability of a commercially available Ostertagia ostertagi milk ELISA

The objectives of this study were (1) to assess the within- and between-laboratory repeatability of a commercially available antibody-detection Ostertagia ostertagi ELISA (SVANOVIR(O). ostertagi-Ab, Svanova, Uppsala) and (2) to investigate if the assay could be further simplified by reading optical density at a single instead of double wavelength. A total of 80 bulk-tank milk samples were divided into aliquots and tested in duplicate per ELISA plate on 3 different days in 4 different laboratories (Bristol, Ghent, Hannover, Uppsala). The within- and between-laboratory repeatability of the ELISA was assessed by random effect models and the amount of variance attributable to each source of variation (duplicate within plate, day, laboratory and sample) was expressed as a proportion of the total between-sample variance. Overall, the within-laboratory repeatability was good in each laboratory with a proportion of total between-sample variance that could be attributed to assay variability of 5% in Ghent to 27% in Bristol. The between-laboratory repeatability was high: 15% of the total between-sample variance was attributable to the duplicate, 1% to the day, 2% to the laboratory and 82% to the sample. The range of deviations expected to include 95% of the observations when the same sample is tested in different laboratories was -0.23 to 0.23. The mean difference between the ODR values when the optical density was read at a single or double wavelength was -0.002 and the 95% confidence interval included zero. This study demonstrates that the SVANOVIR(O). ostertagi ELISA has a good repeatability and can be further simplified by reading optical density at a single instead of double wavelength. However, the observed variations in the within-laboratory repeatabilities suggest that regular ring testing is necessary when different laboratories cooperate in a same monitoring programme.

Effect of eprinomectin pour-on treatment around calving on reproduction parameters in adult dairy cows with limited outdoor exposure

The objective of this study was to investigate if treatment of cows with eprinomectin around calving had any beneficial effects on the calving to first artificial insemination interval, calving to conception interval, and number of services per conception in totally- and semi-confined dairy herds. In totally-confined herds lactating- and dry-cows were housed throughout the summer and had no access to pasture. In semi-confined herds lactating- and dry-cows had limited outdoor exposure to a small pasture or paddock but were still fed a ration that met all their nutritional requirements. The study was carried out between February 2002 and February 2003 in 35 herds (2381 cows) located in Quebec, Ontario and Minnesota (USA) participating in a larger clinical trial. The herds kept electronic reproduction records. Cows were randomly allocated to receive eprinomectin or a placebo, with treatment being administered on or close to the day of calving. Monthly bulk tank milk samples from each farm were tested with an indirect ELISA using a crude Ostertagia ostertagi antigen and these data were averaged over the study year. The optical density ratio (ODR) values were then dichotomized into high and low using a cut-point of 0.50. Treatment effects were analyzed using Cox proportional hazards survival models with herd frailty effects for calving to conception and calving to first service intervals. Aalen's linear hazards model was used to investigate time-varying effects in the Cox models. A random effects poisson regression model was used to model the number of services per conception. Other predictor variables tested in the models were lactation number, calving season, study site, peak milk production, ODR and the lactating- and dry-cow housing variables. Overall, there was no significant effect of treatment on the three indices of reproductive performance. The effect of season of calving depended on how much time had passed since calving. Presumably this effect reflected a seasonal effect at the time of breeding. Hazard of conception in younger cows was higher than in older cows. Early bred cows tended to have a higher number of inseminations per conception than those bred late. The results of the study suggested that eprinomectin treatment at calving was not beneficial to reproduction.

The effect of an experimentally induced acute mastitis on the test results of an Ostertagia ostertagi milk ELISA

Antibody levels against Ostertagia ostertagi in the milk are a promising parameter to identify dairy cows or herds with production losses due to gastrointestinal nematodes. However, milk antibody levels can be influenced by udder-related factors. In this study, the effect of an experimentally induced mastitis on the test results (ODR) of a milk O. ostertagi ELISA was investigated. Twenty-five cows that were naturally infected with gastrointestinal nematodes, were inoculated in their left udder quarters with Escherichia coli P4:O32 and quarter milk samples were collected at several intervals from 24 h before until 144 h after experimental infection. The effect of the contribution of milk from one or more infected quarters on the bulk tank milk ODR was estimated, based on a titration experiment. The mean O. ostertagi antibody levels of the infected udder quarters were significantly (P < 0.001) higher than those of the uninfected udder quarters at each sampling time post-infection. The largest difference was observed at 24 h post-infection with a mean difference of 0.251 ODR (95%CI: 0.172; 0.330). There was also a significant increase (P < 0.001) in total IgG levels with the largest difference being observed at 24 h post-infection. Highly significant (P < 0.005) correlation coefficients were observed between O. ostertagi ODR, total IgG ODR, Na+ and Cl- ion concentration and log transformed somatic cell counts at 24 h post-infection. The results demonstrate that an acute mastitis causes a flow of specific and non-specific antibodies from serum to milk with a subsequent increase in the O. ostertagi ODR values. The effect of the contribution of milk from infected quarters on the bulk tank milk O. ostertagi ODR was estimated to be minor if the relative number of infected quarters is small (< 3%).

Evaluation of the stability of Ostertagia ostertagi ELISA microtitre plates over time using cow milk samples

The objective of this study was to assess the stability of ELISA plates prepared with one of three blocking agents and used with one of two conjugates at various time intervals after preparation of the plates. Two of the blocking agents used were commercially available: one termed stabilgaurd (stab) and one manufactured by SVANOVA Biotek AB Inc. (svan). The third blocking agent used was bovine serum albumin (bsa). A polyclonal rabbit anti-bovine IgG (poly) and an anti-bovine IgG monoclonal (mono) conjugate were used. Eighteen composite individual cow milk samples collected late in lactation (200-400 days in milk) were used in this study. An indirect microtitre plate ELISA that used the Ostertagia ostertagi antigen was used to quantify antibodies against the parasite, present in the milk samples. Each of six blocking agent/conjugate combinations (called systems) were used to test 18 milk sub-samples at 1, 4 and 24 weeks after blocking the plates. Plates blocked with stab and svan were kept at room temperature and an additional set were incubated at 37 degrees C so as to mimic long term storage (about 1 year) and tested only once at 4 weeks. Those blocked with bsa were frozen at -20 degrees C. Concordance correlation coefficients (CCC) and reproducibility were used to assess the agreement between test results conducted on the same milk sample at the various test-times using a particular system. Generally, there was good agreement between tests conducted at different times for all systems. However, the svan-mono and bsa-poly systems had the best agreement with overall CCC values of 96% and 93%, respectively. The svan-poly system had the lowest CCC of 75%. The CCC and reproducibility ranked the systems in a similar way. The high CCC between tests done using plates kept at room temperature and ones incubated at 37 degrees C, suggested that plates would be stable up to a year after blocking. The storage of plates blocked with svan and stab agents under room temperature, makes them more convenient to use and transport relative to bsa-blocked plates that have to be frozen.

Assessing the agreement between Ostertagia ostertagi ELISA tests performed using the crude adult antigen and the adult and larval stage 4 excretory/secretory antigens

The objective of this study was to determine the agreement between ELISA tests conducted using three O. ostertagia antigens: crude adult worm, larval stage 4 (L4) excretory/secretory (ES) and adult ES. This study was carried out on 289 Holstein cows from five herds in Prince Edward Island and one herd in Nova Scotia. Composite milk samples of these cows were collected (between May and September 2002) from the respective provincial laboratories and sent to the Atlantic Veterinary College where each sample was tested for antibodies to O. Ostertagi using an indirect microtitre ELISA test. Results were expressed as optical density ratio (ODR) values. Each milk sample was tested with three ELISA tests, with each test using a different O. ostertagi antigen. There was a slight rise in ODR values of both adult antigens, between May and August, with higher values obtained using the adult ES antigen. L4 ES ODR values were generally higher than those for both adult antigens during the study period, except for May. There was a more dramatic rise in L4 ES ODR values between May and August. Rises in ODR in May and end of July coincided with periods of mass maturation of L4 to adult worms. The results of the study showed that the concordance correlation coefficient (CCC) between tests performed using both ES and the crude antigens were low (crude adult versus adult ES=0.31, crude adult versus L4 ES=0.30). The highest CCC was observed between tests done using both ES antigens (CCC=0.56). Generally, the study results suggest that the antibody response (detectable by the ELISA) is mainly directed against ES antigens (especially L4) than the crude adult worm antigen.

The use of an indirect Ostertagia ostertagi ELISA to predict milk production response after anthelmintic treatment in confined and semi-confined dairy herds

An indirect Ostertagia ostertagi ELISA was used in late lactation milk samples from cows in confined and semi-confined dairy herds to determine if it could predict milk production response after endectocide treatment at calving. Holstein cows from 9 dairy farms from Prince Edward Island (PEI), 5 from central Nova Scotia and 16 from southern Ontario that were participating in a clinical trial of endectocide treatment around calving were used in this study. The cows were randomly treated with either eprinomectin pour-on endectocide or a placebo solution. Milk samples were obtained from cows late in the lactation before treatment was applied. These samples were tested for antibodies to gastrointestinal nematodes (GIN) using the indirect ELISA with the results expressed as optical density ratios (ODR). Production records were obtained from a computerized database of dairy herd improvement data. Pre-calving ODR showed a seasonal pattern. They were higher in the summer and fall and lower during the winter months. Older animals had higher pre-calving ODR values compared with younger cows. Similarly, cows from semi-confined herds had higher parasite antibody levels compared with cows from confined herds. The endectocide treatment did not affect the milk production response in the overall study population. However, the interaction effect between treatment and pre-calving ODR on milk production response after endectocide treatment was significant (P = 0.02), with some evidence of positive treatment response in cows with an ODR > 0.4. The relationship between pre-calving ODR and production response appeared to be quadratic rather than linear.

Assessment of the repeatability of a milk Ostertagia ostertagi ELISA and effects of sample preparation

An indirect Ostertagia ostertagi ELISA on milk is a promising diagnostic tool in bovine parasitology. Interpretation of the test results requires a good knowledge of the test characteristics. In this study, border effects, the repeatability of the ELISA and the effect of different factors such as storage, skimming and freeze-thaw cycles of the milk samples were investigated. The border effects trial showed that significant border effects can occur. The repeatability trial was conducted over 3 days. An alternative graphical technique to assess the repeatability over a large number of ELISA plates measured over different days was developed. From these graphs, it was obvious that the ODR values obtained on the third day were deviating from the values on the first and second day. On the third day, also abnormal control values were observed. When the control values were normal, 94% of the variability was explained by the milk sample and 6% by assay variability. The expected 95% range of the difference of 2 ODR readings of the same sample on the same plate and the same sample on different plates was -0.14 to 0.14 and -0.16 to 0.16. No extra variability was observed when samples were tested on a different day, however these results are based on the measurement of 2 days. Storage for 2-4 days at 4 degrees C, using whole milk instead of skimmed milk and up to 2 extra freeze-thaw cycles of the milk samples did not significantly affect the test results.

A survey to determine relationships between bulk tank milk antibodies against Ostertagia ostertagi and milk production parameters

In temperate climate regions, gastrointestinal nematodes are still widespread in adult dairy cows, but until now there exists no reliable diagnostic tool that can identify herds where the infection interferes with productivity. The objective of this study was to investigate the relationships between levels of antibodies against Ostertagia ostertagi in bulk tank milk and milk production. Bulk tank milk samples of 2553 dairy herds were obtained in spring and 2104 of these herds were sampled a second time in autumn. The antibody levels against O. ostertagi were determined with a milk ELISA and test results were expressed as an optical density ratio (ODR). The effect of bulk tank milk ODR on three different production parameters, kg milk, % and kg fat, % and kg protein was assessed by a multivariable linear regression model on the herds for which production data were available (n = 1063 and 867 in spring and autumn, respectively). The mean and standard deviation for ODRautumn (0.972+/-0.238) were higher than for ODRspring (0.825+/-0.201). Significant negative relationships were found between ODR and milk yield. An increase in ODRspring and ODRautumn from the 25th to the 75th percentile of the available ODR data was associated with a drop in the annual milk yield of 1.1 kg/cow/day, respectively 0.9 kg/cow/day. When a herd's ODR increased between spring and autumn with 0.142, it produced on average 0.4 kg/cow/day less in September than in April, in comparison with herds where the ODR did not increase. A significant negative association was found between ODRautumn and % protein averaged over the period of a year. No significant associations were found between ODR and % fat averaged over the year. When protein and fat production of September were expressed in kg an increase in ODRautumn from the 25th to the 75th percentile was associated with a decrease of 0.037 kg protein/cow/day and 0.042 kg fat/cow/day.

Effect of Eprinomectin Treatment at Calving on Milk Production in Dairy Herds with Limited Outdoor Exposure

The objective of this study was to determine the effect of anthelmintic treatment at calving in herds that were totally or semiconfined during the summer. In totally confined herds, lactating and dry cows were housed throughout the summer and had no access to pasture. In semiconfined herds, lactating and dry cows had limited outdoor exposure to a small pasture or paddock but were still fed a ration that met all their nutritional requirements. The study was carried out between February 2002 and February 2003 in 65 herds enrolled with DHI and distributed in 4 regions in Canada and 1 state in the United States. Cows were randomly allocated to receive eprinomectin or a placebo, with treatment being administered on or close to day of calving. In May and June 2002, 8 fecal samples were collected from each farm and fecal egg counts (FEC) were determined. Monthly bulk tank milk samples from each farm were tested with an indirect ELISA using a crude Ostertagia ostertagi antigen. Monthly test-day milk production data were recorded for 200 d after calving. In general, FEC were very low (mean = 1 egg per gram, range = 0 to 27). Mean herd bulk milk ELISA optical density ratio (ODR) values for the whole year ranged between 0.22 and 0.80. The ODR values were dichotomized into high and low using a threshold of 0.5. Treatment effects were analyzed using a linear mixed model with herd and cow as random effects. The analysis was restricted to 4789 cows (23,956 test-day records) treated between 21 d before and 7 d after calving. Overall, there was no significant effect of treatment. However, there was a tendency for an interaction between treatment and ODR, as illustrated by a larger numerical difference in treated vs. untreated cows in high-ODR herds than in low-ODR herds. However, the confidence intervals for the treatment effects (kg/d of milk per cow) in high-ODR herds (-0.33 to 1.10) and in low-ODR herds (-0.53 to 0.14) were wide and included zero. Therefore, this study failed to show a beneficial effect of eprinomectin treatment in these totally or semiconfined herds.

Milk antibodies against Ostertagia ostertagi: relationships with milk IgG and production parameters in lactating dairy cattle

The present study was carried out to evaluate the relationship between milk optical density ratios (ODRs) from an indirect Ostertagia ostertagi ELISA, total milk IgG levels and milk production and then establish a correction factor to adjust ODR. Five hundred and sixty composite milk samples collected from 358 cows on four dairy herds in June and August 2002 were used in this analysis. The average ODR was 0.34. A positive correlation was found between ODR and IgG values in milk, days in milk, age and log transformed somatic cell counts (SCC). However, ODR was negatively correlated with milk production. The IgG levels and ODR values were constant from 30 to 200 days in milk. However, ODRs increased from 200 days until the end of the lactation. After controlling for age, season, herd and SCC, an increase in milk production of 13 kg/day was associated with a reduction in ODR values of 0.052. The results of the present study suggest that ODR values are not greatly influenced by production factors. ODR follow the same pattern as the IgG variation across lactation and could be adjusted in order to compare ODR values obtained from high producing cows with those obtained from low producing animals.

The effect of eprinomectin treatment at calving on reproduction parameters in adult dairy cows in Canada

A clinical trial was carried out in two provinces of Canada to investigate the effect of treatment with eprinomectin at calving on production parameters in adult dairy cattle in 1999-2000. One of the objectives of this study was to evaluate the impact of treatment on reproductive performance as measured by: calving-to-conception interval, calving-to-first service interval and number of services per conception. The ability of an indirect ELISA using a crude adult Ostertagia ostertagi antigen to predict response to treatment also was evaluated. All lactating cows in 20 dairy herds were allocated randomly to receive either eprinomectin pour-on or placebo at calving. Information on reproductive parameters was obtained from computerised cow records. Survival models were used to evaluate the effect of treatment on the two intervals and a Poisson model was used to evaluate the number of services to conception. A total of 549 cows were included in these analyses. A marginally significant treatment effect on calving-to-conception interval was observed (hazard ratio=1.24, P=0.06) but not on calving-to-first service interval. A significant reduction in the number of breedings to conception for treated animals also was observed with a longer effect in cows with short interval to first service. Milk samples from a subset of 109 late-lactation cows were tested for antibodies against O. ostertagi. The ELISA optical-density ratio (ODR) values obtained between 120 days before calving and drying off were categorised as high ODR (>or=0.5) and low ODR (<0.5). Among untreated animals, the hazard of conception was lower (hazard ratio=0.38, 95% CI=[0.19,0.75]) for high-ODR cows compared to low ODR cows suggesting that higher parasite burdens had an adverse effect on reproductive performance. Treated high-ODR cows had a hazard of conception equivalent to the hazard for all cows in the low-ODR group (indicating that treatment prevented the negative effect associated with these higher parasite burdens).