Serological reactions against Leptospira interrogans serovars in New Zealand horses

Extract

In October 1989, we received a blood sample from a horse which had recently aborted. The sample showed a very high titre against Leptospira interrogans serovar copenhageni and lower titres against several other tested serovars. Two in-contact horses showed high titres against serovar hardjo.     

A study of cattle-to-cattle transmission of Mycobacterium bovis infection

Twenty steers, positive to the single intradermal comparative tuberculin test (SICTT), were selected fromherds with a recent history of Mycobacterium bovis infection. Ten steers, negative to SICTT, were selected from herds with no history of M. bovis infection and served as in-contact animals. The animals were divided into 10 groups, each consisting of two SICTT-positive (reactor) animals and one in-contact animal. Each group was housed in an individual loose-box for a period of 1 year. Five of the groups were fed a restricted diet for part of the experiment. All cattle were slaughtered at the end of the study period and examined at post mortem. Transmission of infection to an in-contact animal occurred in four of the 10 groups. One of the four in-contact animals, which became infected, had a retropharyngeal lymph node tubercle and M. bovis was isolated from lymph nodes without visible lesions from the other three. Two of the infected in-contact animals without visible lesions did not show any detectable cell-mediated immune response. There was no evidence that dietary, restriction had any effect on transmission of disease.     

Evaluation of different diagnostic methods for diagnosis of Lumpy skin disease in cows

Viral isolation, polymerase chain reaction (PCR), dot blot hybridization (DBH), and indirect enzyme-linked immunosorbent assay (iELISA) were used for the diagnosis of lumpy skin disease in clinically infected, fevered, and apparently normal dairy cows. Lumpy skin disease virus (LSDV) was isolated from skin biopsies and blood samples collected from clinically infected cows in percentages of 72% and 20%, respectively. The virus recovered from blood samples collected from fevered cows in percentage of 33.3%. Both PCR and DBH detected viral DNA in 100% of skin biopsies collected from clinically infected cows whereas the detection rates in blood samples collected from clinically infected animals were 100% and 84% using PCR and DBH, respectively. Viral DNA was detected in blood samples collected from fevered cows using PCR and DBH in percentages of 77.8% and 66.6%, respectively. Only 19.1% of blood samples collected from in-contact cows was positive for both of PCR and DBH. Detection rates of antibodies against LSDV using iELISA in serum samples collected from clinically infected and fevered cows were 56% and 11.1%, respectively, whereas all in-contact cows had no antibodies against the virus.     

Transmission studies of Hendra virus (equine morbilli-virus) in fruit bats, horses and cats

Objective To determine the infectivity and transmissibility of Hendra virus (HeV). Design A disease transmission study using fruit bats, horses and cats. Procedure Eight grey-headed fruit bats (Pteropus poliocephalus) were inoculated and housed in contact with three uninfected bats and two uninfected horses. In a second exper iment, four horses were inoculated by subcutaneous injection and intranasal inoculation and housed in contact with three uninfected horses and six uninfected cats. In a third experi ment, 12 cats were inoculated and housed in contact with three uninfected horses. Two surviving horses were inoculated at the conclusion of the third experiment: the first orally and the second by nasal swabbing. All animals were necropsied and examined by gross and microscopic pathological methods, immunoperoxidase to detect viral antigen in formalin-fixed tissues, virus isolation was attempted on tissues and SNT and ELISA methods were used to detect HeV-specific antibody. Results Clinical disease was not observed in the fruit bats, although six of eight inoculated bats developed antibody against HeV, and two of six developed vascular lesions which contained viral antigen. The in-contact bats and horses did not seroconvert. Three of four horses that were inoculated devel oped acute disease, but in-contact horses and cats were not infected. In the third experiment, one of three in-contact horses contracted disease. At the time of necropsy, high titres of HeV were detected in the kidneys of six acutely infected horses, in the urine of four horses and the mouth of two, but not in the nasal cavities or tracheas. Conclusions Grey-headed fruit bats seroconvert and develop subclinical disease when inoculated with HeV. Horses can be infected by oronasal routes and can excrete HeV in urine and saliva. It is possible to transmit HeV from cats to horses. Transmission from P poliocephalus t o horses could not be proven and neither could transmission from horses to horses or horses to cats. Under the experimental conditions of the study the virus is not highly contagious.     

Comparative serologic study of equine piroplasmosis, with card and complement-fixation tests.

An agglutinating antigen and a rapid card test (CT) for equine piroplasmosis was developed. The antigen for the CT was prepared from lyophilized Babesia caballi complement-fixation (CF) antigen. Serum and plasma samples for testing were obtained from known B caballi-infected horses and clinically normal horses maintained at the laboratory. Serum samples also were obtained from horses outside the continental United States, in areas where piroplasmosis is endemic. Comparative CT and CF tests were done on all samples. The CT correctly identified 85% of 192 plasma samples from known infected and normal horses and 92% of 188 serum samples from these same horses. The CT results agreed closely with CF results. There was good agreement between CT and CF results. There was good agreement between CT and CF results on serum samples from horses outside the United States. Of 19 CF-positive samples, 90% were also CT-positive and 92% of 177 CF-negative samples were also CT-negative.     

Prevalence of leptospiral titres in normal horses

SUMMARY Serum samples were collected from 479 clinically normal horses from 11 different locations in Queensland. Using a microscopic agglutination test, 157 serums (33%) reacted to one or more serovars of Leptospira interrogans at a minimum serum dilution of 1/30. The prevalences of reactors among all horses to the serovars tested were pomona 30.5%icterohaemorrhagiae 23.9%, tarassovi 18.8%, hardjo 12.2%, canicola 8.6%, grippotyphosa 3.6%, and australis 2%. There was a significantly higher prevalence of reactors in tropical areas than in sub-tropical areas, but no difference in prevalence between coastal and non-coastal areas.     

Indirect hemagglutination test in equine infectious anemia.

An indirect hemagglutination was developed for the diagnosis of equine infectious anemia using sheep red blood cells coated with group specific virus antigen which had been highly purified by affinity chromatography. The presence of indirect hemagglutination antibodies was demonstrated in horses with equine infectious anemia since the cells were specifically agglutinated by all the serum samples obtained from experimentally infected horses. Antibodies appeared within 35 days after inoculation, and development of which coincided well with that of precipitating and complement fixing antibodies. Titer of indirect hemagglutination antibodies were ten to 320 times greater than those of precipitating antibodies. Test results could be read more clearly by the indirect hemagglutination test especially in weakly positive cases. Ninety-six samples from suspected field cases collected from every region of Japan which were positive on the immunodiffusion test were also positive on indirect hemagglutination test. Serum samples from 420 horses in one race track were examined by both the indirect hemagglutination and immunodiffusion tests to determine the reliability of the indirect hemagglutination test for diagnosis of equine infectious anemia. The same result was obtained on both tests. Based on this evidence, the indirect hemagglutination test can be employed as a very sensitive serological test for the diagnosis of equine infectious anemia.     

A glycogen synthase 1 mutation associated with equine polysaccharide storage myopathy and exertional rhabdomyolysis occurs in a variety of UK breeds

Reasons for performing study: A glycogen synthase (GYS1) mutation has been described in horses with histopathological evidence of polysaccharide storage myopathy (PSSM) in the USA. It is unknown whether the same mutation is present in horses from the UK. Objectives: To determine whether the GYS1 mutation occurs in UK horses with histopathological evidence of PSSM and exertional rhabdomyolysis. Hypothesis: The R309H GYS1 mutation is present in a variety of UK horse breeds and that the mutation is commonly associated with exertional rhabdomyolysis. Methods: DNA was extracted from 47 muscle or blood samples from UK horses with histories of exertional rhabdomyolysis in which muscle biopsy diagnosis had been pursued. The proportions of GYS1 mutation positive cases were compared among histopathologically defined groups. In addition, breeds that carried the GYS1 mutation were identified from a total of 37 grade 2 (amylase‐resistant) PSSM cases. Results: Of 47 horses with exertional rhabdomyolysis in which a muscle biopsy diagnosis was pursued, 10 (21%) carried the GYS1 mutation. The mutation was only found in horses with grade 2 PSSM (i.e. not in horses with normal, idiopathic myopathy or grade 1 PSSM biopsy samples). In total, the GYS1 mutation was found in 24/37 (65%) of grade 2 PSSM cases. A variety of breeds, including Quarter Horse, Appaloosa, Warmblood, Connemara‐cross, Cob, Polo Pony and Thoroughbred cross carried the mutation. Conclusions: The GYS1 mutation is an important cause of exertional rhabdomyolysis of UK horse breeds but does not account for all forms of PSSM. Potential relevance: Genotyping is recommended in cases of exertional rhabdomyolysis, prior to or in combination with, muscle biopsy. However a significant proportion of horses with histopathological evidence of PSSM and/or exertional rhabdomyolysis have different diseases.     

Lessons learned from a strangles outbreak on a large Standardbred farm

Streptococcus equi subspecies (ssp.) equi infection (strangles) remains one of the most frequently diagnosed and costly infectious diseases of horses. Large breeding herds, where a disease outbreak competes for personnel and financial resources needed for foaling management, present a special challenge for equine practitioners. A 15‐month outbreak involving 62 clinical cases of strangles occurred on a large Standardbred breeding farm (average population of 1400 horses). Sixteen asymptomatic horses were found to be PCR (polymerase chain reaction)‐positive for S. equi ssp. equi. During the outbreak, serological samples from 48 clinically normal horses were found to be seropositive for S. equi ssp. equi, confirming herd‐wide exposure. After several clinical cases of strangles had been diagnosed, an intranasal S. equi ssp. equi vaccine was administered to clinically normal horses (n = 558) considered to be at risk of exposure. Strangles complications included 7 fatalities (none in vaccinated horses) and 6 cases of purpura haemorrhagica (4 in vaccinated horses). Midway through the outbreak, injectable, sustained release ceftiofur crystalline free acid (CCFA), given as an initial dose followed by a second dose 4 days later, was used exclusively for systemic antimicrobial treatment of clinically affected and PCR‐positive horses. This antimicrobial regimen coincided with a reduction in disease incidence and eventual resolution of the outbreak. Two horses with persistent guttural pouch infection were endoscopically confirmed as carrier horses. The herd history demonstrated that a strangles outbreak will often result in asymptomatic carrier horses and that identification and treatment of these horses are necessary to eliminate long‐term sources of infection. Ceftiofur crystalline free acid was found to be a suitable antimicrobial due to its activity against S. equi ssp. equi and the efficiencies associated with twice parenteral dosing during a 10‐day treatment period. Occurrence of purpura in 4 vaccinated horses suggests that vaccination should be reserved for healthy seronegative horses and avoided during an active outbreak.     

Nuclear scintigraphic assessment of the thoracolumbar synovial intervertebral articulations

Reasons for performing study: The results of nuclear scintigraphic examination of the thoracolumbar synovial intervertebral articulations (facet joints) have to date been poorly documented. Objectives: To establish an objective scintigraphic grading system for the facet joints; to investigate the relationship between the presence or absence of clinical signs of back pain and increased radiopharmaceutical uptake (IRU); and to compare the results of scintigraphy and radiography. Methods: Nuclear scintigraphic images of the 13th thoracic (T13) to first lumbar (L1) vertebrae were graded subjectively (visual assessment of the image) and objectively (using region of interest analysis) from 31 clinically normal horses in full work (Group N) and 65 horses with clinical evidence of thoracolumbar region pain and osteoarthritis of ≥1 facet joint (Group B). Sensitivity and specificity of IRU for detection of back pain and radiographic abnormalities were assessed. A Spearman correlation was performed to test for an association between the grade of IRU and the classification of radiographic abnormality. Results: The objective scintigraphic grades were matched by 96.7% of subjective grades. IRU was seen more commonly in Group B (61.5%) than in Group N (25.8%), and moderate or intense IRU was only seen in Group B. The strongest association between radiographic abnormalities and scintigraphy was seen in horses with intense IRU. Conclusions: Moderate or intense IRU in a facet joint is more likely to be seen in horses with back pain than in clinically normal horses. Potential relevance: Nuclear scintigraphy is a potentially useful tool in the evaluation of a horse with thoracolumbar region pain.     

Leptospirosis: II. Investigation of clinical disease in dairy cattle in the Waikato district of New Zealand

Investigations were carried out in 1975, 1976 and 1977 in 16 dairy herds where leptospiral abortions were suspected and in five other herds where clinical disease was not present. Both Leptospira interrogans serovars pomona and hardjo were isolated from cattle in herds with leptospirosis, but only pomona was recovered from those that had aborted. There was no evidence that hardjo caused clinical disease in dairy cattle in the Waikato district.

It was found that 73% of the cows that aborted and 19% of other animals in the same herds had microscopic agglutination test titres to pomona of 1:2 000 or greater. By contrast, only 2% of cattle in herds without clinical evidence of leptospirosis had such titres. One cow retained a titre of 1:2 000 or greater to pomona for 7 months; titres of this order had a shorter duration in other cows. Leptospiruria occurred in 50% of cows that had aborted and in 9% of in-contact cows in the same herds. Only 0.7% of cows had leptospiruria in the herds with no clinical disease. Ten of 35 cows shedding pomona still had leptospiruria one month later.

It was concluded that clinical leptospirosis should be diagnosed by testing a sample of the herd, rather than just individual cows, because of the variability and persistence of leptospiruria and serological titres in cows with and without clinical signs. Although hardjo is common in cattle in the Waikato district, it was not found to cause abortion in cattle.     

<Emphasis Type="Italic">Theileria</Emphasis> (<Emphasis Type="Italic">Babesia</Emphasis>) <Emphasis Type="Italic">equi</Emphasis> and <Emphasis Type="Italic">Babesia caballi</Emphasis> Infections in Horses in Galicia,Spain

The control of equine piroplasmosis is becoming increasingly important to maintain the international market open to the horse industry. The purpose of this study was to demonstrate the occurrence of equine piroplasmosis (Theileria equi and Babesia caballi) in Galicia, north-west Spain, and to compare haematological and serum biochemistry parameters between non-parasitaemic horses and horses parasitaemic with T. equi and B. caballi. Sixty serum samples (control group) were taken from healthy horses pastured on two farms, and examined for evidence of equine T. equi and B. caballi infection by indirect fluorescent antibody test (IFAT). Of the 60 samples, 24 (40%) and 17 (28.3%) samples were positive for T. equi and B. caballi, respectively. Twelve (20%) samples were positive for both parasites. Haematology and serum biochemistry were compared between controls and a series of 36 horses clinically affected by T. equi (25) or B. caballi (11). Compared with the healthy group, there was a 43% and 37% decrease in the haematocrit for T. equi and B. caballi infection, respectively. Parasitaemic horses presented an intense anaemia and serum biochemistry signs of liver damage. The anaemia was more severe in T. equi-infected than in B. caballi-infected horses. Our results suggest that equine piroplasmosis is widespread in the region and is a cause for concern.     

Comparison of Immunoperoxidase Plaque Staining and Neutralizing Tests for Canine Distemper Virus

The use of immunoperoxidase plaque staining (IP) in the antibody test for canine distemper virus (CDV) and its diagnostic value were investigated. Antibody titres by the IP test and neutralizing test (NT) against CDV were compared in 114 specific pathogen-free (SPF) dogs, including 84 CDV-vaccinated and 30 unimmunized dogs. All of the unimmunized dogs, which had negative NT titres, also showed negative IP titres, and all of the CDV-vaccinated dogs, which had positive NT titres, showed positive IP titres. Furthermore, the IP titres showed similar changes with time after vaccination to the NT titres in five CDV-vaccinated SPF dogs. These findings indicate that the IP test has similar specificity to the NT.Next, the IP and NT titres were compared in 190 clinically suspected cases of canine distemper (CD), including 107 dogs with neurological signs and 83 dogs without neurological signs, and also in 50 clinically healthy dogs. Among the suspected cases of CD, of 46 dogs with neurological signs and 29 dogs without neurological signs, and which had negative NT titres, 33 (72%) and 19 (66%), respectively, showed positive IP titres. Many suspected cases of CD showed a high IP titre despite a low NT titre. In contrast, among healthy dogs, none of 9 NT-negative dogs showed positive IP titres.The difference in the IP and NT titres (log₁₀ [reciprocal of IP titre] – log₁₀ [reciprocal of NT titre]) was measured to investigate the agreement between IP test and NT. The differences were 1.488±0.867, 1.245±0.833, 0.595±0.351 and 0.594±0.372, respectively, in the suspected cases of CD with neurological signs, the suspected cases of CD without neurological signs, the healthy dogs and the SPF dogs. The differences in the suspected cases of CD were significantly high compared to those for the SPF dogs (p<0.001).Furthermore, in 8 dogs diagnosed as cases of CD from their paired sera, whose initial sera showed a markedly low NT titre compared to the IP titre, 5 dogs without neurological signs developed neurological signs later.These findings suggest that the IP test can detect CD during its early phases and in dogs with low antibody levels, undetectable by NT, and so would be useful for serological diagnosis.     

Differentation of Brucella abortus and Yersinia enterocolitica serotype 09 infections in cattle: The use of specific lymphocyte transformation and brucellin skin tests

Summary

The lymphocyte transformation test (using an in vitro whole‐blood lymphocyte stimulation procedure) and the Brucellin skin test were applied to five heifers infected with virulent Brucella abortus strain 544, five cows inoculated with Yersinia enterocolitica serotype 09, and four non‐exposed cows. Lymphocytes from Brucella‐inoculated animals persistently gave very high blastogenic reactions indicative of active Brucella infection. The test was persistently negative in Yersinia‐infected and non‐exposed cattle. Four of thefive cowsinfected with Yersinia enterocolitica type 09 and allfour control cattle were persistently negative to the delayed hypersensitivity skin reaction with brucellin. All cattle infected with Yersinia enterocolitica type 09 were strongly positive to the Rose Bengal, Serum agglutination, Complement fixation and Antibovine globulin tests using Brucella abortus antigens. One lactating cow infected with Yersinia enterocolitica type 09 was positive to Brucella milk ring test. These results indicate that standard Brucella serological tests are unreliable in differentiating the two infections in cattle and that both the Lymphocyte transformation and brucellin skin tests could be used to differentiate bovine brucellosis from yersiniosis.     

Prevalence and pathogenicity of anoplocephala perfoliata in a horse population in South Auckland

A survey of the prevalence of A noplocephala perfoliata in 65 horses is described. An overall prevalence rate of 82% was found for A. perfoliata infection and 77% of infected horses exhibited ulcerative pathology in the ileo-caecal region directly associated with this parasite. Anoplocephela magna and Paranoplocephala mamillana were not recovered.     

Lawsonia intracellularis infection in horses: 2005-2007

Background: Lawsonia intracellularis is an emerging equine pathogen that is a cause of equine proliferative enteropathy (EPE).
Objective: To describe the signalment, month of presentation, common clinical signs, clinicopathologic values, diagnostic tests used, antimicrobial use, and survival status in horses affected with EPE; to evaluate how affected horses sold at public auction as yearlings; and to determine results of fecal polymerase chain reaction (PCR) and serum immunoperoxidase monolayer assay (IPMA) results in age matched, clinically normal herdmates.
Animals: The study group was 57 horses treated for disease associated with L. intracellularis infection between August 2005 and January 2007.
Methods: Retrospective study examined horses exhibiting evidence of infection with L. intracellularis and testing positive for fecal PCR or serum IPMA.
Results: Horses ranged in age from 2 to 8 months with a median age of 6 months, and all were examined between August and January. Ventral edema was present in 81% of horses and hypoalbuminemia occurred in all horses. Only 50% of horses tested positive on both PCR and IPMA. Ninety-three percent of horses survived, and survival was unrelated to antimicrobial administered. Affected horses sold as yearlings an average of 68% less than other yearlings by the same sire. Age matched, clinically normal herdmates also tested positive for L. intracellularis on fecal PCR (6%) and IPMA (33%).
Conclusion: L. intracellularis infection should be considered in young horses with ventral edema and hypoalbuminemia that are examined between August and January. Both fecal PCR and serum IPMA are needed to help determine disease status. Treated animals usually survive, although they do not sell for as high a price at public auction as other yearlings by the same sire. Age matched, clinically normal herdmates also test positive for L. intracellularis on fecal PCR and serum IPMA.     

IgG antibodies from dourine infected horses identify a distinctive Trypanosoma equiperdum antigenic pattern of low molecular weight molecules

Diagnosis and control of dourine is strongly based on serological evidence, but knowledge of the humoral response of horses during infection is limited. In this study we developed a chemiluminescent immunoblotting (cIB) assay to characterise the Trypanosoma equiperdum antigen pattern recognised by IgGs from naturally or experimentally dourine-infected horses and analyse the kinetics of IgG humoral response following the infection. One compounding factor is that sera from uninfected animals often cross-react with T. equiperdum antigens. Development of the cIB assay was based on the hypothesis that serum IgGs from healthy and infected animals recognise different T. equiperdum antigen patterns. We used sera from 8 naturally infected horses which had recovered from Italian outbreaks and 2 experimentally infected mares. In addition, sera from 10 healthy control animals, eight of which were CFT positive but IFA negative for dourine, were collected from disease free regions. Sera were compared by the complement fixation test (CFT), indirect immune fluorescence (IFA) and the cIB assay.cIB analysis revealed that IgGs from infected horses, in contrast to IgGs from healhty horses, specifically recognise a T. equiperdum antigenic profile with low molecular weight bands ranging between 16 and 35 kDa. A time course experiment indicated that IgGs specific for the 16–35 kDa parasite protein fraction appear 17 days post-infection. The cIB assay confirmed all ten infected animals as positive and all controls as negative. This study demonstrated that analysis of IgGs by cIB can provide clear confirmation of trypanosome infection in horses, suggesting that this technique can be applied as a confirmatory serological test for dourine infection.     

Experimental Leptospira interrogans Serovar Kennewicki Infection of Horses

Background: Little information is available about experimental induction of leptospirosis in horses. Objectives: Determine serologic, hematologic responses of horses to Leptospira interrogans serovar Kennewicki infection. Animals: Four adult horses seronegative for leptospirosis. Methods: Experimental and observational study. Horses were challenged with an equine isolate of L. interrogans serovar Kennewicki at 2 different doses and different inoculation sites. After challenge, the horses were monitored for 60 days. Blood, urine, and aqueous humor samples were collected at intervals until euthanasia 60 days after infection. Results: Pyrexia (39.3–40°C) occurred as early as 1 day after challenge with 10 × 10⁸Leptospira divided equally between topical ocular and intraperitoneal injection in 2 horses. Leptospires were recovered from the blood and urine but not from the aqueous humor of the 2 febrile horses. The sera of all 4 challenged horses developed microscopic agglutination test antibody after challenge and remained relatively constant for 21 days. Titer to cross‐reacting strains declined earlier than titer to the challenge strain. Conclusions: Clinical disease in experimentally infected horses can be mild or inapparent in Leptospira infected horses. Repeated serologic testing can allow recognition of the infecting serovar. In febrile horses, Leptospira can be isolated from blood while isolation from the urine can occur after fever has subsided.     

Corynebacterium pseudotuberculosis infection in goats. IV. Course of the infection in two recently infected goat herds

Adult animals from 2 herds were examined clinically and serologically, 5 (Herd A) and 4 (Herd B) times during the same period of 3% years.Serum samples were examined for antibodies against Gorynebac-terium pseudotuberculosis using the bacterial agglutination test (BAT) and the hemolysis inhibition test (HIT).The results of the first examination showed that no animal in Herd A was seropositive, while in Herd B 1 animal showed a high positive titre in BAT. The prevalence of animals with superficial swellings was then 2 % in Herd A and 4 % in Herd B. In both herds, the prevalence of animals with superficial swellings and seropositive reactions increased during the following 1–2 yeairs. About 30 % of animals had superficial lesions and close to 100 % were seropositive. The proportion, of animals with superficial swellings and seropositive reactions was almost constant on subsequent examinations.In some of the animals, superficial swellings were found during 2 or more of the examinations, a few animals having such lesions at the same site on both or all occasions.Animals in Herd A became infected through grazing together with goats from infected herds. Caseous lymphadenitis was introduced into Herd B by animals obtained from infected herds.     

A screening test for subclinical liver disease in horses affected by pyrrolizidine alkaloid toxicosis

Objective: To evaluate various biochemical tests as indicators of subclinical liver disease in horses exposed to pyrrolizidine alkaloid toxicosis.
Design: A clinical pathology field study.
Animals: Twenty-two clinically normal horses from four properties in the Kimberley region of Western Australia.
Procedure: Serum samples from each horse were assayed for gamma glutamyltransferase, alkaline phosphatase and aspartate aminotransferase activities, and for serum bile acid concentration, albumin and total protein. Serum protein electrophoresis was performed and their amino acid profiles determined. Bromosulphophihalein halfclearance times were measured. Horses were then subjected to a single liver biopsy. Results were analysed by, variance of group means, the Fisher-Irwin exact test, and by sensitivity and specificity calculation.
Results: Horses were classified into 2 groups, of 10 unaffected and 12 subclinically affected, on the basis of liver histology. Significant differences between the unaffected and subclinical groups were observed for gamma glutamyltransferase and alkaline phosphatase activities (P < 0.01). Gamma glutamyltransferase had sufficient sensitivity (75%) and specificity (90%) to function as a primary screening test for subclinical liver disease in horses exposed to pyrrolizidine alkaloids. Alkaline phosphatase was useful, but with lower sensitivity (58%).
Conclusion: Serum gamma glutamyltransferase activity is a useful screening test for detecting subclinical liver disease in horses exposed to pyrrolizidine alkaloids under field conditions in northern Australia.