Equine Granulocytic Anaplasmosis

Equine granulocytic anaplasmosis is a clinically significant and common disease of equids that has a broader prevalence than was once thought. The most common clinical signs include high fever and edema, with mild to mderate thrombocytopenia and lymphopenia typically noted on complete blood count. Subclinical cases are reported and many are self-limiting. Rare clinical presentations include neurologic disease, vasculitis, dysphagia, rhabdomyolysis, or bicavitary effusion. Most cases resolve rapidly with appropriate antimicrobial intervention.

Prevalence of Anaplasma phagocytophilum and Borrelia burgdorferi infection in horses from Pennsylvania (2017-2019) using antibody and organism-based detection

OBJECTIVE

To determine the prevalence of Anaplasma phagocytophilum and Borrelia burgdorferi infections in Pennsylvania horses.

ANIMALS

271 horses.

PROCEDURES

A survey was conducted with PCR and serology to evaluate anaplasmosis and Lyme disease infections in horses from Pennsylvania that were suspected for tick-borne infection.

RESULTS

A phagocytophilum was detected in 19/271 (7.0%) Pennsylvania horses tested by the duplex PCR. B burgdorferi was not detected in any horse blood tested by PCR. Overall, 120/271 (44.3%) horses tested positive for presence of A phagocytophilum antibodies by at least the IDEXX SNAP 4Dx Plus lateral flow immunosorbent (SNAP) or indirect fluorescent antibody (IFA) assay, with 69 (25.5%) testing positive by both SNAP and IFA; 43 (15.9%) tested positive by IFA only, and 8 (3.0%) tested positive by SNAP only. Similarly, 209/271 (77.1%) horses tested positive for the presence of B burgdorferi antibodies by at least 1 test, with 139 (51.3%) testing positive by both SNAP and IFA; 45 (16.6%) tested positive by SNAP only, and 25 (9.2%) tested positive by IFA.

CLINICAL RELEVANCE

Both A phagocytophilum and B burgdorferi are important tick-borne infections. The study provides prevalence data for both A phagocytophilum and B burgdorferi and compares test performance. For serologic detection, IFA detected antibodies to A phagocytophilum in a higher proportion (41.3%) of horses compared to SNAP (28.4%), while SNAP detected antibodies to B burgdorferi in a higher proportion (67.9%) of horses compared to IFA (60.5%). Both diseases showed a high seroprevalence in all areas surveyed.

Evaluation of 2 ELISAs to determine Borrelia burgdorferi seropositivity in horses over a 12-month period

The blacklegged tick (Ixodes scapularis), which transmits Borrelia burgdorferi, the causative agent of Lyme disease, has undergone rapid range expansion in Ontario. In horses, Lyme disease remains an enigmatic disease, with limited understanding of the pathogenesis and many issues pertaining to selection and interpretation of laboratory tests. We evaluated B. burgdorferi seropositivity in naturally exposed horses over a 12-mo period and compared paired samples with 2 common serologic tests. Serum samples were collected in 2017, ~1 y after initial testing, from a cohort of 22 horses that were seropositive in a 2016 seroprevalence study. Samples were tested using a C6 ELISA and a multiplex ELISA targeting outer surface proteins A, C, and F. 1 y after initial testing, 14 of 22 (64%) horses remained seropositive; 7 (32%) were positive on the multiplex ELISA, 2 (9%) on C6 ELISA, and 5 (23%) on both tests. Repeatability was 100% for the C6 ELISA, and 95% for the multiplex ELISA, with no significant difference between paired sample multiplex titer values. Our results indicate strong intra-test reliability, although further investigation is required to determine the clinical significance of serologic testing.

Seroprevalence of Antibodies Against Anaplasma Phagocytophilum and Borrelia Burgdorferi in Horses (Equus Caballus) from Northern Algeria

Introduction

Horses (Equus caballus) are susceptible to tick-borne diseases. Two of them, Lyme borreliosis due to Borrelia burgdorferi and granulocytic anaplasmosis due to Anaplasma phagocytophilum were investigated in Algerian horses. The diseases have been less extensively studied in horses and results pertinent to Algeria have not been published.

Material and Methods

Blood samples were obtained from 128 horses. IgG antibodies directed against Anaplasma phagocytophilum and Borrelia burgdorferi were detected by an indirect immunofluorescence antibody test (IFAT) and ELISA. The potential effects of age, gender, breed, and health status on seropositivity were also evaluated.

Results

Using IFAT, 28 (21.8%) and 25 (19.5%) animals were positive for B. burgdorferi and A. phagocytophilum, respectively. Using ELISA, 19 (14.8%) and 33 (25.9%) animals were positive for these bacteria.

Conclusion

The study shows that horses in Algeria are exposed or co-exposed to tick-transmitted zoonotic bacterial species.

Modelling the probability and impact of false-positive serology for Borrelia burgdorferi sensu lato: A case study

Background

Serological screening tests for Lyme borreliosis have poor specificity, with potential for misdiagnosis and unnecessary antimicrobial treatment.

Objectives

To evaluate the impact of Lyme borreliosis seroprevalence and serologic test characteristics on the probability of obtaining a false‐positive result and impact on antimicrobial use.

Study design

Cross‐sectional serological survey and modelling.

Methods

Sera from 303 horses in southern Belgium were analysed by enzyme‐linked immunosorbent assay (ELISA). Apparent seroprevalence was derived from serological data and a Bayesian estimate of true seroprevalence was computed. These were a starting point to model the impact of test and population characteristics on the probability of obtaining false‐positive results and consequently unnecessary treatments and complications.

Results

Apparent and true seroprevalence were 22% (95% CI 18%‐27%) and 11% (credible interval with 95% probability 0.6%‐21%) respectively. We estimate that two‐thirds of positive samples are false positive in southern Belgium, with one in five of tested horses potentially misdiagnosed as infected. Around 5% of antimicrobial use in equine veterinary practice in Belgium may be attributable to treatment of a false‐positive result.

Main limitations

There was uncertainty regarding the ELISA's sensitivity and specificity.

Conclusions

This study highlights the importance of appreciating the poor diagnostic value of ELISA screening for Lyme borreliosis as demonstrated by this case study of seroprevalence in southern Belgium where we demonstrate that a nontrivial number of horses is estimated to receive unwarranted treatment due to poor appreciation of screening test characteristics by practitioners, contributing substantially to unnecessary use of antimicrobials.

Point-of-Care Diagnostics in Equine Practice

Point-of-care testing (POCT) refers to benchtop diagnostic modalities that have been translated into portable and easy-to-use formats suitable for patient-side use. Recent advances in diagnostic technology have allowed the development of a growing collection of POCT assays available to equine practitioners. Advantages include rapid results that reduce initial guesswork and promote diagnosis-targeted patient care, which may ultimately provide better clinical outcomes. Small handheld devices comprise most POCT technologies, providing qualitative or quantitative determination of an increasing range of analytes, including critical care analyzers and, more recently, hematology and immunology analyzers. This article discusses commercially available equine POCT.

Borreliosis in Sport Horse Practice

Given the variable clinical signs attributed to Borrelia burgdorferi, including infectious arthritis, neurologic disease, and behavioral changes, B burgdorferi is an important differential for decreased performance in sport horses. The primary vectors (Ixodes tick species) are expanding their range and thus Borrelia species are located in a wider area, making exposure more likely. Due to regionally high seroprevalence and vague clinical signs, diagnosis of Lyme disease in the horse is believed overestimated. Antibiotics are first-line treatment of confirmed Lyme disease. A single positive serologic test, by itself, is not conformation of Lyme disease but is evidence of current or past infection.

Borrelia burgdorferi Infection and Lyme Disease in North American Horses: A Consensus Statement

Borrelia burgdorferi infection is common in horses living in Lyme endemic areas and the geographic range for exposure is increasing. Morbidity after B. burgdorferi infection in horses is unknown. Documented, naturally occurring syndromes attributed to B. burgdorferi infection in horses include neuroborreliosis, uveitis, and cutaneous pseudolymphoma. Although other clinical signs such as lameness and stiffness are reported in horses, these are often not well documented. Diagnosis of Lyme disease is based on exposure to B. burgdorferi, cytology or histopathology of infected fluid or tissue and antigen detection. Treatment of Lyme disease in horses is similar to treatment of humans or small animals but treatment success might not be the same because of species differences in antimicrobial bioavailability and duration of infection before initiation of treatment. There are no approved equine label Lyme vaccines but there is strong evidence that proper vaccination could prevent infection in horses.

Comparison between available serologic tests for detecting antibodies against Anaplasma phagocytophilum and Borrelia burgdorferi in horses in Canada

To investigate the agreement between available serologic tests for the detection of antibodies against Anaplasma phagocytophilum and Borrelia burgdorferi, 50 serum samples from horses of unknown clinical status and at low risk for infection were tested. In addition to a point-of-care enzyme-linked immunosorbent assay (pocELISA), the evaluated tests included 2 indirect fluorescent antibody tests (IFATs) for antibodies against A. phagocytophilum and an IFAT, an ELISA confirmed with Western blot, and the Lyme multiplex assay for antibodies against B. burgdorferi. For each pair-wise comparison between serologic tests, the difference in the proportion of seropositive results as well as kappa and the prevalence-adjusted, bias-adjusted kappa were calculated. The proportion of seropositive results differed significantly in each pairwise comparison of tests for detection of antibodies against A. phagocytophilum, and between the pocELISA and IFAT as well as between the pocELISA and Lyme multiplex assay for detection of antibodies against B. burgdorferi. Agreement based on kappa varied from poor to fair while agreement was improved when evaluating prevalence-adjusted, bias-adjusted kappa. Lack of agreement may be explained by differences in methodology between the evaluated tests, cross-reactivity or false-positive and false-negative tests. In addition to the limitations of serologic test interpretation in the absence of clinical disease, this data suggest that screening of horses for exposure to tick-borne diseases in nonendemic areas may not be warranted.

Serological survey of Ehrlichia species in dogs, horses and humans: zoonotic scenery in a rural settlement from southern Brazil

The aims of this study were to determine the seroprevalence of Ehrlichia spp. and risk factors for exposure in a restricted population of dogs, horses, and humans highly exposed to tick bites in a Brazilian rural settlement using a commercial ELISA rapid test and two indirect immunofluorescent assays (IFA) with E. canis and E. chaffeensis crude antigens. Serum samples from 132 dogs, 16 horses and 100 humans were used. Fifty-six out of 132 (42.4%) dogs were seropositive for E. canis. Dogs > one year were more likely to be seropositive for E. canis than dogs ≤ one year (p = 0.0051). Ten/16 (62.5%) and 8/16 (50%) horses were seropositive by the commercial ELISA and IFA, respectively. Five out of 100 (5%) humans were seropositive for E. canis and E. chaffeensis. Rhipicephalus sanguineus (n = 291, 97.98%) on dogs and Amblyomma cajennense (n = 25, 96.15%) on horses were the most common ticks found. In conclusion, anti-Ehrlichia spp. antibodies were found in horses; however, the lack of a molecular characterization precludes any conclusion regarding the agent involved. Additionally, the higher seroprevalence of E. canis in dogs and the evidence of anti-Ehrlichia spp. antibodies in humans suggest that human cases of ehrlichiosis in Brazil might be caused by E. canis, or other closely related species.

Antibodies to OspC, OspF and C6 antigens as indicators for infection with Borrelia burgdorferi in horses

REASONS FOR PERFORMING STUDY

Lyme disease is caused by Borrelia burgdorferi, which is transmitted by infected ticks (Ixodes spp.). Reports on Lyme disease in horses have increased in recent years. Nevertheless, the diagnosis of Lyme disease in horses is still challenging owing to its vague clinical presentation and the limitations of diagnostic tests.

OBJECTIVES

This study used a new serological Lyme multiplex assay to examine antibody responses to 3 antigens of B. burgdorferi, outer surface protein (Osp) C, OspF and C6, and to verify their use as markers for early and late infection stages in horses.

METHODS

Multiplex analysis of antibodies to OspC, OspF and C6 in equine patient sera (n = 191) was performed. A subset of the sera (n = 90) was also tested using a commercial C6-based Lyme test.

RESULTS

Antibodies to OspF and C6 highly correlate as reliable markers of infection with B. burgdorferi in horses. Antibodies to OspC, which have been confirmed as early infection markers in man and dogs, were only detected in some patient sera, suggesting that OspC antibodies are indicators of early infection in horses. Commercial C6 testing identified most infected horses but also resulted in false positive and false negative interpretations.

CONCLUSIONS

Serological multiplex testing is a rapid and quantitative diagnostic method to confirm infection with B. burgdorferi and to identify the stage of infection. In horses with risk of exposure and clinical signs, multiplex testing supports the diagnosis of Lyme disease.

POTENTIAL RELEVANCE

Antimicrobial treatment of B. burgdorferi is time sensitive. Treatment success decreases with time of persistent infection, while the risk of developing chronic disease increases. The ability to identify early infection with B. burgdorferi provides practitioners and clinicians with a tool to improve the diagnosis of equine Lyme disease and make treatment decisions.

Changes in Borrelia burgdorferi ELISA antibody over time in both antibiotic treated and untreated horses

Changes in ELISA serology are frequently used to determine antibiotic treatment success for Lyme disease in horses. This concept was based upon a previous report showing a marked decline in ELISA values in experimentally infected and antibiotic-treated ponies. Changes in Lyme serology following antibiotic treatment in naturally infected horses have not been reported. The objective of this study was to compare Borrelia ELISA antibody concentrations in naturally exposed horses both before and following antibiotic treatment for Lyme disease. A retrospective study was performed comparing oxytetracycline- or doxycyclinetreated (n = 68) and untreated (n = 183) horses from a single equine practice and their change in Borrelia ELISA values over a similar time period. Antibiotictreated horses had a decline in ELISA values in comparison to control horses (P ≤ 0.05) and untreated horses were twice as likely to have their ELISA values increase (OR = 0.5; 95% C.I. = 0.3-0.9) compared to treated horses. The magnitude of the decline in ELISA units following treatments was small compared to that previously reported in experimentally infected and treated ponies. Field-exposed horses with high Borrelia burgdorferi ELISA values who are treated with either oxytetracycline or doxycycline can be expected to have only a small decline in ELISA values following treatment. Persistently high ELISA titres following appropriate treatments for Lyme disease may not, without appropriate clinical signs, be a reason for more prolonged treatment.

Occurrence of Borrelia lusitaniae infection in horses

The aim of the study was to investigate Borrelia burgdorferi sensu lato (s.l.) infection in horses exposed to heavy tick infestations. Blood samples of 98 healthy horses from 5 stud farms were examined by SNAP(®) 4D× and PCR to detect antibodies against B. burgdorferi s.l. and Borrelia DNA, respectively. Ten samples (15.3%) were antibody positive and 5 samples (5.1%) were both antibody and PCR positive. Sequence analysis showed the highest homology with the B. lusitaniae genospecies. No differences were found between sexes and stud farms, while age was significantly related to seropositivity (p<0.05). Our data confirms the presence of B. lusitaniae infection in horses, previously not clearly demonstrated.

Development of a multiplex assay for the detection of antibodies to Borrelia burgdorferi in horses and its validation using Bayesian and conventional statistical methods

Lyme disease is a zoonotic, vector-borne disease and occurs in mammals including horses. The disease is induced by infection with spirochetes of the Borrelia burgdorferi sensu lato group. Infection of mammalian hosts requires transmission of spirochetes by infected ticks during tick bites. Lyme disease diagnosis is based on clinical signs, possible exposure to infected ticks, and antibody testing which is traditionally performed by ELISA and Western blotting (WB). This report describes the development and validation of a new fluorescent bead-based multiplex assay for the detection of antibodies to B. burgdorferi outer surface protein A (OspA), OspC and OspF antigens in horse serum. Testing of 562 equine sera was performed blindly and in parallel by using WB and the new multiplex assay. Because a true gold standard is missing for Lyme antibody testing, we performed and compared different statistical approaches to validate the new Lyme multiplex assay. One approach was to use WB results as a 'relative gold standard' in ROC-curve and likelihood-ratio analyses of the new test. Cut-off values and interpretation ranges of the multiplex assay were established by the analysis. The second statistical approach used a Bayesian model for the calculation of diagnostic sensitivities and specificities of the multiplex assay. The Bayesian analysis takes into consideration that no true gold standard exists for detecting antibodies to B. burgdorferi and estimated sensitivities and specificities of both tests that were compared. Therefore, the Bayesian analysis also resulted in an evaluation of diagnostic sensitivity and specificity of WB. Overall, the new assay was characterized by low background values and a wide dynamic quantification range for the detection of antibodies to OspA, OspC and OspF antigens of B. burgdorferi. The diagnostic sensitivity and specificity for the OspA bead-based assay were calculated as 49% and 85%, respectively, and by a standard ROC curve analysis only because the Bayesian model could not be run on this parameter. The Bayesian-derived diagnostic sensitivities of the OspC and OspF assays were 80% and 86%, respectively. For comparison, the Bayesian-derived estimates for WB resulted in sensitivities of 72% for OspC and 80% for OspF. The Bayesian diagnostic specificities of the multiplex assay were 79% and 69% for OspC and OspF, respectively. WB analysis had specificities of 92% for OspC and 77% for OspF. Although the analysis of a new assay in the absence of a true gold standard remains challenging, the approach used here can help to address this problem when new technologies and traditionally used test standards differ significantly in their analytical sensitivities, which consequently causes problems in the calculation of diagnostic sensitivity and sensitivity values for the new assay. In summary, the new multiplex assay for the detection of antibodies to B. burgdorferi OspA, OspC and OspF antigens in horse serum has improved analytical and diagnostic sensitivities compared to WB analysis. Multiplex analysis is a valuable quantitative tool that simultaneously detects antibodies indicative for natural infection with and/or vaccination against the Lyme pathogen.

Antibody profiling of Borrelia burgdorferi infection in horses

Infection with Borrelia burgdorferi is common in horses and ponies from the New England and mid-Atlantic regions of the United States. Here, we evaluated luciferase immunoprecipitation systems (LIPS) for profiling antibody responses against three different antigenic targets for the diagnosis of equine B. burgdorferi infection. LIPS testing of horse serum samples suspected of Lyme infection revealed that approximately 75% of the horse samples (114/159) were seropositive against the synthetic VOVO antigen, comprising repeated immunodominant C6 epitopes as well as OspC immunodominant epitopes. A comparison of VOVO and immunofluorescence assays (IFA) showed that 51% of the samples were positive in both assays (VOVO(+)/IFA(+)), 13% were VOVO(-)/IFA(+), 21% were VOVO(+)/IFA(-), and 15% were negative in both. To further understand humoral responses to B. burgdorferi and reconcile the diagnostic differences between IFA and VOVO, two additional B. burgdorferi LIPS tests were performed with DbpA and DbpB. Robust seropositive antibody responses against DbpA and/or DbpB were detected in 98% (79/81) of the VOVO(+)/IFA(+) and 93% (50/54) of the discrepant samples. Additionally, some of the samples negative by both VOVO and IFA showed immunoreactivity against DbpA and/or DbpB. Overall, 94% of the suspected horse samples were seropositive by LIPS, and heat map analysis revealed that seropositive samples often were immunoreactive with at least two of the three antigens. These results suggest that LIPS tests employing multiple recombinant antigens offer a promising approach for the evaluation of antibody responses in Lyme disease.

Ehrlichiosis and anaplasmosis in dogs and cats

In the time since canine ehrlichiosis due to Ehrlichia canis was first described in 1935 and first recognized in the United States in 1962, many key advances have been made in our understanding of the diversity of the rickettsial organisms responsible for ehrlichiosis and anaplasmosis in dogs and, occasionally, cats, the vectors capable of transmitting these agents, and the role these organisms play as both important veterinary pathogens and zoonotic disease agents. Despite considerable progress in the field, much remains to be learned regarding mechanisms contributing to pathogenesis, effective treatment modalities, and prevention strategies that best protect pet health. This article highlights current understanding of the transmission, diagnosis, and management of ehrlichiosis and anaplasmosis in dogs and cats.

Seroprevalence survey of equine Lyme borreliosis in France and in sub-Saharan Africa

A precise assessment of the epidemiological extent of equine Lyme disease is not well established in metropolitan France, French Guiana, and Africa (Chad, Djibouti, Ivory Coast, Gabon, and Democratic Republic of Congo). Blood samples were obtained from 570 horses. The samples were tested for Borrelia burgdorferi infection by a commercial ELISA Dot-Blot method (SNAP 4 Dx; IDEXX S. Laboratory). Lyme disease antibodies were only detected in metropolitan France, specifically in the eastern and center-western regions (48% and 31%). The geographical distribution of the disease follows the distribution of the vector.

Distribution of antibodies reactive to Borrelia lonestari and Borrelia burgdorferi in white-tailed deer (Odocoileus virginianus) populations in the eastern United States

Southern tick-associated rash illness is a Lyme-like syndrome that occurs in the southern states. Borrelia lonestari, which has been suggested as a possible causative agent of southern tick-associated rash illness, naturally infects white-tailed deer (WTD; Odocoileus virginianus) and is transmitted by the lone star tick (Amblyomma americanum). To better understand the prevalence and distribution of Borrelia exposure among WTD, we tested WTD from 21 eastern states for antibodies reactive to B. lonestari using an indirect immunofluorescent antibody assay and Borrelia burgdorferi using the IDEXX SNAP 4Dx test. A total of 107/714 (15%) had antibodies reactive to B. lonestari, and prevalence of antibodies was higher in deer from southern states (17.5%) than in deer from northern states (9.2%). Using the SNAP 4DX test, we found that 73/723 (10%) were positive for B. burgdorferi, and significantly more northern deer (23.9%) were positive compared with southern deer (3.8%). Our data demonstrate that WTD are exposed to both Borrelia species, but antibody prevalence for exposure to the two species differs regionally and distributions correlate with the presence of Ixodes scapularis and A. americanum ticks.

Seroprevalence of Borrelia burgdorferi sensu lato and Anaplasma phagocytophilum in Danish horses

Background

Borrelia burgdorferi sensu lato and Anaplasma phagocytophilum are able to infect horses. However, the extend to which Danish horses are infected and seroconvert due to these two bacteria is unknown. The aim of the present study was to evaluate the seroprevalence of B. burgdorferi sensu lato and A. phagocytophilum in Danish horses.

Methods

A total of 390 blood samples collected from all major regions of Denmark and with a geographical distribution corresponding to the density of the Danish horse population were analyzed. All samples were examined for the presence of antibodies against B. burgdorferi sensu lato and A. phagocytophilum by the use of the SNAP^®4DX ^® ELISA test.

Results

Overall, 29.0% of the horses were seropositive for B. burgdorferi sensu lato whereas 22.3% were seropositive for A. phagocytophilum.

Conclusions

Antibodies against B burgdorferi sensu lato and A. phagocytophilum are commonly found among Danish horses thus showing that Danish horses are frequently infected by these organisms.