Infections in horses encompass a range of diseases caused by various pathogens, including bacteria, viruses, fungi, and parasites. These infections can affect different systems within the horse, such as the respiratory, gastrointestinal, and integumentary systems, leading to a variety of clinical signs depending on the pathogen and the severity of the infection. Common infectious diseases in horses include equine influenza, strangles, and equine herpesvirus. Diagnosis often involves clinical examination, laboratory testing, and sometimes imaging, to identify the causative agent and assess the extent of the disease. Treatment strategies may include antimicrobial therapy, supportive care, and preventive measures such as vaccination and biosecurity practices. This page aggregates peer-reviewed research studies and scholarly articles that explore the pathogenesis, diagnosis, treatment, and prevention of infectious diseases in equine populations.
Wilson JH, Olson EJ, Haugen EW, Hunt LM, Johnson JL, Hayden DW.Progressive multisystemic disease caused by Blastomyces dermatitidis was diagnosed in a 17-year-old Quarter horse broodmare. The mare had been treated unsuccessfully with antibiotics for mastitis 3 months postpartum. The disease progressed to exudative cutaneous lesions affecting the ventrum, pectoral region, and limbs accompanied by weight loss across several months. Yeast bodies were observed in swabs of the cutaneous exudate, suggesting a clinical diagnosis of blastomycosis. Following referral, pleural effusion, cavitated lung lesions, and hyperproteinemia were identified, and the mare was ...
Bryant UK, Lyons ET, Bain FT, Hong CB.A 13-week-old Thoroughbred colt from central Kentucky was euthanized after an acute onset of ataxia, blindness, head tremors, leaning to the right, recumbency, and seizures. Microscopically, there was a verminous meningoencephalitis characterized by an eosinophilic and granulomatous inflammatory reaction primarily affecting the cerebellum. Dispersed within regions of inflammation were numerous cross and longitudinal sections of intact and degenerative small nematodes. The nematodes had dorsoflexed ovaries and ventroflexed vulvas, which are distinguishing features of Halicephalobus gingivalis. ...
Amusategui I, Sainz A, Tesouro MA.A total of 1,098 serum samples were analyzed against Anaplasma phagocytophilum by immunofluorescent antibody (IFA) test. These serum samples belonged to four different populations distributed throughout two provinces of Galicia (Ourense and Pontevedra) located in northwestern Spain: bovine population (456 samples); ovine population (389 samples); caprine population (207 samples); and equine population (46 serum samples, all from Pontevedra). The seroprevalence against A. phagocytophilum within the bovine population was 3.07%. On the other hand, two of 389 (0.51%) sheep and one of 207 (0.48%) g...
du Toit N, McGorum BC, Pemberton AD, Brown J, Dacre KJ.Cyathostomins (Cyathostominae) are regarded as the most pathogenic equine nematode worldwide. These nematodes are difficult to control in equine populations due to emerging anthelmintic resistance and evasion of encysted larval cyathostomins to regular modern anthelmintics. Mast cells and their proteinases have been shown to play a role in the mammalian immune response to nematode infections. Involvement of mast cells and mast cell proteinases in the equine immune response to cyathostomin infection is proposed. A technique was established to perform immunohistochemical staining using polyclona...
von Samson-Himmelstjerna G, Fritzen B, Demeler J, Schürmann S, Rohn K, Schnieder T, Epe C.In 2003 and 2004, on a total of 63 different German horse farms, a survey using the faecal egg count reduction (FECR) test was performed to investigate the efficacy of ivermectin (IVM, Ivomec) and pyrantel (PYR, Banminth) treatment against gastro-intestinal nematodes in a total of 767 horses. IVM treatment resulted in 100% reduction of the cyathostomin egg production 14 and 21 days post-treatment (d.p.t.) on 37 farms. On the remaining five farms, the mean faecal egg count reduction ranged between 97.7 and 99.9%. The mean cyathostomin FECR following PYR treatment ranged between 92.2 and 100% on...
Piza AS, Pereira AR, Terreran MT, Mozzer O, Tanuri A, Brandão PE, Richtzenhain LJ.We used a p26 recombinant protein (p26r) from equine infectious-anemia virus (EIAV) expressed in Escherichia coli as antigen to standardize an agar-gel immunodiffusion (AGIDp26r) test and an indirect ELISA (ELISAp26r) for the detection of antibodies against EIAV in 720 equine sera from Brazil. We evaluated the tests's relative diagnostic sensitivities (relSe) and relative diagnostic specificities (relSp) against a commercial AGID kit (Idexx, USA). We used three sera panels: panel A--196 AGID-negative sera from an AIE non-endemic controlled area; panel B--194 AGID-negative sera from an AIE ende...
Borromeo V, Berrini A, Gaggioli D, Secchi C.Heterophile antibodies (HAs) present in serum recognize animal immunoglobulins and are one of the most unpredictable causes of false results in immunoassays. However, no study has yet reported their interference on the diagnostic reliability of immunochemical analyses on horse plasma. Recently, we developed a sandwich ELISA for detection of equine growth hormone (eGH) in plasma. In a pilot study to measure basal eGH levels (blood samples were drawn from 13 horses every 10 min for 1h), we noted one horse with abnormally high eGH (>100 ng/mL). We demonstrate here that this plasma eGH level wa...
Howerth EW, Mead DG, Mueller PO, Duncan L, Murphy MD, Stallknecht DE.Horses were inoculated with Vesicular stomatitis New Jersey and Indiana viruses by routes simulating contact and vector transmission. Clinical signs, lesions, antibody development, viral shedding and persistence, and viremia were monitored. Horses were infected with both viruses by all routes as confirmed by seroconversion. Salivation, primary lesions at inoculation sites, and secondary oral lesions were the most common clinical findings. Viral shedding was most often from the oral cavity, followed by the nasal cavity; titers were highest from oral cavity samples. Virus was rarely isolated fro...
Hobo S, Niwa H, Anzai T.The reactivity of synthesised peptide sets for the M-like proteins SeM and SzPSe with sera from horses infected with Streptococcus equi or Streptococcus zooepidemicus, or control horses, was investigated by an ELISA. Seventeen horses were infected experimentally with S equi or S zooepidemicus, convalescent sera were obtained from 25 horses and control sera were obtained from 1945 horses. The serum antibody responses of individual horses to the peptide sets were highly variable. Some of the peptide sets for SeM reacted strongly with the sera from the horses infected experimentally with S equi, ...
Womble A, Giguère S, Murthy YV, Cox C, Obare E.The objectives of this study were to determine the serum and pulmonary disposition of tilmicosin in foals and to investigate the in vitro activity of the drug against Rhodococcus equi and other common bacterial pathogens of horses. A single dose of a new fatty acid salt formulation of tilmicosin (10 mg/kg of body weight) was administered to seven healthy 5- to 8-week-old foals by the intramuscular route. Concentrations of tilmicosin were measured in serum, lung tissue, pulmonary epithelial lining fluid (PELF), bronchoalveolar lavage (BAL) cells, and blood neutrophils. Mean peak tilmicosin conc...
Tsujimura K, Yamanaka T, Kondo T, Fukushi H, Matsumura T.To develop a live vaccine for equine herpesvirus type 1 (EHV-1), two EHV-1 mutants containing no heterogeneous DNA, DeltagI and DeltagE, were constructed with deletions in the open reading frame of either glycoprotein I (gI) or E (gE), respectively. In equine cell culture, deletion mutants formed smaller plaques than the parental and revertant viruses, but the one-step growth patterns of the deletion mutants and the parental strain were approximately the same. These results suggest that both gI and gE contribute to the ability of EHV-1 to spread directly from cell-to-cell, but that these glyco...
Infernuso T, Watts AE, Ducharme NG.Septic epiglottic chondritis with abscessation diagnosed in 2 Thoroughbred racehorses. Infected cartilage removed videoendoscopically followed by systemic antibiotics. The infectious process was successfully controlled, but permanent dorsal displacement of the soft palate (DDSP) with a shortened, deformed epiglottic cartilage developed. Surgery for the DDSP using bilateral partial sternothyroidectomy or laryngeal tie-forward failed. Chondrite septique abcédée de l’épiglotte chez 2 jeunes chevaux de course Thoroughbred. Une chondrite septique abcédée de l’épiglotte a été diagnostiqu...
Luque I, Fernández-Garayzábal JF, Blume V, Maldonado A, Astorga R, Tarradas C.The anti-microbial susceptibility and genetic diversity of 65 strains of Streptococcus equi ssp. zooepidemicus (Sez) isolated from mares presenting clinical signs of endometritis was determined by disk agar diffusion and pulsed field gel electrophoresis (PFGE) methods, respectively. Overall, Sez isolates were susceptible to beta-lactams, enrofloxacin, trimethoprim-sulfamethoxazole and gentamicin. These anti-microbials could be recommended as empiric anti-microbial therapy in cases of endometritis caused by Sez. Pulsed field gel electrophoresis typing revealed a great genetic diversity (56 diff...
Salinas-Mélendez JA, Galván de la Garza S, Riojas-Valdés VM, Wong González A, Avalos-Ramírez R.The aim of the present study was to determine the presence of Borrelia burgdorferi antibodies in horses from the metropolitan area of Monterrey, Nuevo León, México. Blood serum was obtained from a total of 100 horses residing at different counties in the area. From each animal data was obtained on age, sex, county of residence, presence of ectoparasites and clinical signs. All sera samples were analyzed by indirect immunofluoresence and the sera that resulted positive to this test was analyzed by Western blot. The serological test yielded 34 positive sera at 1:64 dilution, and from them 6 we...
Arroyo LG, Staempfli H, Weese JS.Clostridium difficile is an important cause of diarrhea in horses, causing sporadic and epidemic disease of varying severity. This study evaluated the molecular characteristics of 48 C. difficile isolates recovered from diarrheic horses admitted to a veterinary hospital by using PCR-ribotyping and toxin gene profile. Additionally, feces were tested for the presence of C. difficile toxin A/B via enzyme immunosorbant assay (EIA) in 38 horses. The toxin genes tcdA, tcdB and cdtB were present in 27 (56.25%), 35 (72.91%) and 2 (4.1%) strains, respectively. Eight isolates (16.6%) were A(-)B(+) varia...
Ibrahim ES, Kinoh M, Matsumura T, Kennedy M, Allen GP, Yamaguchi T, Fukushi H.Equine herpesvirus 1 was isolated from an onager in 1985, a zebra in 1986 and a Thomson's gazelle in 1996 in USA. The genetic relatedness and pathogenicity of these three viruses were investigated based on the nucleotide sequences of the glycoprotein G (gG) gene, experimental infection in hamsters, and comparison with horse isolates. The gG gene sequences of EHV-1 from onager and zebra were identical. The gG gene sequences of the gazelle isolate showed 99.5% identity to those of onager and zebra isolates. The gG gene sequences of EHV-1 isolated from horses were 99.9-100% identical and 98, 98 a...
Capobianco G, Cherchi PL, Ambrosini G, Cosmi E, Andrisani A, Dessole S.Alobar holoprosencephaly is a rare and severe brain malformation due to early arrest in brain cleavage and rotation. Methods: We report a congenital anomalous fetus with alobar holoprosencephaly, prenatally diagnosed by two-dimensional (2D) sonography at the 40 weeks of gestation. The mother was affected by gestational diabetes mellitus and was obese (BMI > 30 kg/m(2)). 2D Ultrasound depicted the cerebral malformation, cyclopy, proboscis, cardiac defects (atrial septal defect, hypoplastic left heart, anomalous communication between right ventricle and aorta) and extremities defects. The new...
Bell SA, Balasuriya UB, Nordhausen RW, MacLachlan NJ.Horses are commonly infected by herpesviruses, but isolation of equine herpesvirus-5 (EHV-5) has only infrequently been reported. We describe the isolation and characterization of a strain of EHV-5 from the blood mononuclear cells of a healthy adult horse in California. The virus was initially identified by EHV-5 specific polymerase chain reaction (PCR), and it caused lytic infection of cultured rabbit kidney cells only after repeated serial passage. Virions with characteristic herpesvirus morphology were readily demonstrated in cell culture lysate by transmission electron microscopy. A portio...
Nunes J, Mackie JT, Kiupel M.A 3.5-year-old Thoroughbred mare presented at necropsy with a large mass at the root of the mesentery and multiple smaller mesenteric masses. The mucosa of the small intestine contained numerous raised nodules. Histologic examination revealed severe granulomatous mesenteric lymphadenitis and enteritis. Epithelioid macrophages and multinucleated giant cells frequently contained numerous intracytoplasmic yeast organisms, which were strongly positive on immunohistochemical staining when using a polyclonal antibody against Histoplasma spp. A diagnosis of abdominal histoplasmosis was made based on ...
Davis E, Rush BR, Herr LG, Ewert KM.Successful clinical management of bacterial pneumonia in horses depends on the administration of an appropriate antimicrobial agent at an adequate dosage and frequency, given by the correct route of administration for an adequate duration. Empiric antimicrobial therapy should be based on the clinician's experience and current veterinary literature. Based on the frequency of Gram-positive bacterial pathogens isolated from horses with bacterial pneumonia, every effort should be made to provide antimicrobial coverage for this class of pathogens. Gram-negative pathogens may co-exist; therefore, br...
Saad MD, Hussein HA, Bashandy MM, Kamel HH, Earhart KC, Fryauff DJ, Younan M, Mohamed AH.Hepatitis E virus (HEV) is an important cause of hepatitis among young Egyptian adults with high seroprevalence rates seen in both rural areas of the Nile Delta and in suburban Cairo. Because natural antibodies to HEV have been detected in animals and zoonotic transmission is postulated, we surveyed work horses in Cairo for evidence of HEV exposure and viremia. Sera from 200 Cairo work horses were tested by ELISA for the presence of IgG anti-HEV antibody revealed a seropositivity of 13%. Among 100 samples processed for detection of viral genome by means of nested polymerase chain reaction (N-P...
Fiala SM, Pimentel CA, Mattos AL, Gregory RM, Mattos RC.Our objective was to determine whether the concentration of cooled sperm inseminated influenced sperm transport and intensity of the uterine inflammatory reaction 2, 4 and 24h after insemination. Experimental subjects were 189 estrous mares with a dominant follicle > or =35 mm in diameter and no bacterial growth or neutrophils detected in uterine smears. Each mare was randomly assigned to receive one of the following intrauterine treatments (volume, 20 mL): insemination with 5x10(6) mL(-1) or 25x10(6) mL(-1) or 50x10(6) mL(-1) sperm diluted in 3 mL seminal plasma (SP) and 17 mL skim milk; s...
Nagy AD, Simhofer H.To report use of mandibular condylectomy for treatment of advanced degenerative joint disease of the temporomandibular joint (TMJ) caused by sepsis. Methods: Clinical case report. Methods: Two-year-old Noriker filly. Methods: Computed tomography (CT) was used to confirm advanced degenerative joint disease of the left TMJ and for follow-up after mandibular condylectomy and removal of necrotic meniscus. Results: Painful swelling (3 weeks duration) with drainage located just caudal to the left lateral canthus of the eye was associated with atrophy of the left masseter muscle, masticatory problems...
Moodley A, Stegger M, Bagcigil AF, Baptiste KE, Loeffler A, Lloyd DH, Williams NJ, Leonard N, Abbott Y, Skov R, Guardabassi L.Region X of the protein A gene (spa) was sequenced from methicillin-resistant Staphylococcus aureus (MRSA) isolates originating from animals, humans and the environment at veterinary hospitals in the UK and Ireland. MRSA transmission between animals and veterinary staff was assessed on the basis of spa typing, PFGE and epidemiological data. Methods: MRSA isolates from dogs (n = 27), horses (n = 9), cats (n = 6), staff (n = 22) and environmental surfaces (n = 3) were analysed by PFGE and spa typing. Known contacts between human and animal MRSA carriers were ascertained from the veterinary hospi...
Yamanaka T, Tsujimura K, Kondo T, Hobo S, Matsumura T.We investigated the efficacy of the oral administration of oseltamivir phosphate (OP) in horses experimentally infected with equine influenza A virus (H3N8). Nine horses were divided into three horses each of control, treatment and prophylaxis groups. An administration protocol for the treatment group (2 mg/kg of body weight, twice a day for five days) was started immediately after the onset of pyrexia (above 38.9 degrees C). An administration protocol for the prophylaxis group (2 mg/kg of body weight, once a day for five days) was started on a day before viral inoculation. In the treatment gr...
Parra-Sanchez A, Lugo J, Boothe DM, Gaughan EM, Hanson RR, Duran S, Belknap JK.To evaluate the pharmacokinetic-pharmacodynamic parameters of enrofloxacin and a low dose of amikacin administered via regional IV limb perfusion (RILP) in standing horses. Methods: 14 adult horses. Methods: Standing horses (7 horses/group) received either enrofloxacin (1.5 mg/kg) or amikacin (250 mg) via RILP (involving tourniquet application) in 1 forelimb. Samples of interstitial fluid (collected via implanted capillary ultrafiltration devices) from the bone marrow (BMIF) of the third metacarpal bone and overlying subcutaneous tissues (STIF), blood, and synovial fluid of the radiocarpal joi...
Betbeze CM, Wu CC, Krohne SG, Stiles J.To evaluate the in vitro antifungal properties of silver sulfadiazine (SSD) and natamycin against filamentous fungi isolated from eyes of horses with keratomycosis. Methods: Filamentous fungal isolates obtained from eyes of keratomycosis-affected horses. Methods: Fungal culture of ocular samples yielded 6 Fusarium spp; 7 Aspergillus spp; and 1 isolate each of Curvularia, Scopulariopsis, Penicillium, and Chrysosporium. For each fungal isolate, minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of SSD and natamycin were determined. Results: For all 17 fungal isolat...
Burger NC, Nesvadba J, Nesvadba Z, Busato A, Gottstein B.A cross-sectional field study on the prevalence of Dicrocoelium dendriticum was performed in the Emmental. The study included 211 bovines, 170 equines, 20 ovines, 46 caprines and 23 rabbits (from 119 farms). In addition, laboratory routine diagnostic data obtained from 2.840 animals--all originating from the same area of investigation--were assessed in the same way. The infection extent concerning the different animal species were the following: bovines 46%, equines 12%, ovines 30%, caprines 48% and rabbits 9%. Univariate analyses of baseline epidemiological data identified no significant risk...
Patterson-Kane JC, Donahue JM, Harrison LR.Actinobacillus equuli is a rare cause of peritonitis in adult horses. Septicemia and peritonitis due to A. equuli were diagnosed at necropsy in an 8-year-old Saddlebred mare. The origin of the infection was not known; however, small necrotic colonic mucosal lesions presumed to have been caused by phenylbutazone treatment may have allowed bacterial invasion. A good response to antimicrobial treatment has been documented in the small numbers of previously reported acute cases of peritonitis. Because it is potentially treatable, it is important for pathologists and clinicians to identify horses w...
Huang H, Zhang K, Shao C, Wang C, Ente M, Wang Z, Zhang D, Li K.The dominant Gasterophilus species in the desert steppe (Xinjiang, China) Gasterophilus pecorum poses a serious threat to the reintroduced Przewalski's horses. We investigated the distribution pattern of G. pecorum eggs in June 2017. Two sampling methods, transect and grid, were used, and the results were analyzed via geostatistics by semivariance. The nest quadrat was used to determine the optimal quadrat size. Eggs were found in 99 quadrats (63.1%) and 187 clusters (1.5%) of Stipa caucasica on the steppe. The mean oviposition count of a cluster was 3.8 ± 1.6. Three-eggs is the mode of w...
Hurni JI, Kaiser-Thom S, Gerber V, Keller JE, Collaud A, Fernandez J, Schwendener S, Perreten V.A total of 100 nasal swabs were collected from healthy horses in Switzerland between January 2020 and August 2020. The samples were taken from horses at 40 different stables in 12 different cantons and screened for both methicillin-resistant (MRSA) and methicillin-susceptible S. aureus (MSSA) using selective agar plates. S. aureus were tested for antibiotic susceptibility by measurement of the minimal inhibitory concentration (MIC) and for virulence factors, antibiotic resistance genes and phylogenetic characteristics using whole genome sequence analysis. Ten horses were found to be positiv...
Madigan JE.This article reviews epizootiology, public health considerations, antibody testing, and molecular biology of Lyme borreliosis. Correlation of clinical signs with titer response is discussed.
Caughman GB, Staczek J, O'Callaghan DJ.Enveloped virions and nucleocapsids of equine cytomegalovirus (ECMV; equine herpesvirus type 2) have been purified from the supernatants and the nuclear extracts of infected rabbit kidney (RK) cells, respectively, and their structural protein compositions have been analyzed. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis revealed that ECMV nucleocapsids were composed of nine proteins (average molecular weights = 148K, 52K, 49.5K, 46K, 43.5K, 38.5K, 27K, 20K, and 18K), which together constituted 89% of the total nucleocapsid protein on the basis of incorporated 3H-labeled am...
Dawson FL, Benson JA, Croxton-Smith P.Serum agglutination tests, anti-globulin tests, and complement fixation tests were carried out on sera taken over a period of 98 days from two fillies experimentally infected with the contagious equine metritis organism. The pattern, and significance in diagnosis, of these results is discussed. All 3 tests showed positive titres in the acute phase of experimental disease; reactions in the complement fixation test persisted longest.
Sanada Y, Noda H, Nagahata H.Serological survey of Rhodococcus equi infection in horses in Hokkaido was performed using ELISA. Of 2,879 horse sera, 318 (11.0%) gave antibody-positive (OD greater than or equal to 0.3) reactions. The antibody-positive rate of female was significantly higher (p less than 0.01) than that of male, and no statistical difference between Anglo-Arab and thoroughbred was detected in the antibody-positive rate. The maximum antibody-positive rate (27.1%) was shown at 14 years of age. The antibody-positive rates on the 160 farms were found to vary widely from 0 to 78.9%. A significant difference (p le...
Finger MA, Villalobos EM, Lara Mdo C, Cunha EM, Barros Filho IR, Deconto I, Dornbusch PT, Ullmann LS, Biondo AW.Toxoplasma gondii, the agent for toxoplasmosis, has worldwide distribution. Horses normally play a secondary role in its life cycle, but movement around urban areas, feeding on grass and the increasing use of carthorses for gathering recyclable material in some urban areas of Brazil may increase their exposure to T. gondii infection. The aim of the present study was to investigate the frequency of anti-T. gondii antibodies in carthorses in the metropolitan region of Curitiba, PR. IgG antibodies against T. gondii were detected using the indirect fluorescence antibody test (IFAT) (titers ≥ 64)...
Arnold CE, Pilla R.The fecal microbiome of the horse is reflective of the large colon and plays an important role in the health of the horse. The microbes of the gastrointestinal tract digest fiber and produce energy for the host. Healthy horses have Firmicutes, Bacteroidetes, and Verrucromicrobia as the most common phyla. During gastrointestinal disease such as colic or colitis, the microbiome shows less diversity and changes in bacterial community composition.
Fielding CL, Rhodes DM, Howard EJ, Mayer JR.OBJECTIVE To identify clinical or clinicopathologic variables that can be used to predict a positive PCR assay result for Anaplasma phagocytophilum infection in equids. ANIMALS 162 equids. PROCEDURES Medical records were reviewed to identify equids that underwent testing for evidence of A phagocytophilum infection by PCR assay between June 1, 2007, and December 31, 2015. For each equid that tested positive (case equid), 2 time-matched equids that tested negative for the organism (control equids) were identified. Data collected included age, sex, breed, geographic location (residence at the tim...
Palmero J, Pusterla N, Cherry NA, Kasten RW, Mapes S, Boulouis HJ, Breitschwerdt EB, Chomel BB.Experimental infection of horses with Bartonella species is not documented. Objective: Determine clinical signs, hematologic changes, duration of bacteremia, and pattern of seroconversion in Bartonella henselae or Bartonella bovis-inoculated horses. Methods: Twelve (2 groups of 6) randomly selected healthy adult horses seronegative and culture negative for Bartonella spp. Methods: Experimental/observational study: Group I: B. henselae or saline control was inoculated intradermally into 4 naïve and 2 sentinel horses, respectively. Group II: same design was followed by means of B. bovis. Daily ...
Wilkins PA.Lower airway problems of the adult horse are commonly encountered by the practitioner. Particularly susceptible populations include horses transported for any significant distance and young horses grouped together for training and/or competition. This article presents some of the commonly encountered problems of this patient population, including bacterial pneumonia/pleuropneumonia and influenza, and some uncommon ones, including pulmonary edema, pneumothorax/hemothorax, and acuterespiratory distress syndrome. Information is presented that should allow the practitioner to diagnose these proble...
Hyera JM, Baipoledi EK.A retrospective serological survey of African horse sickness (AHS) in Botswana covering a 10-year period (1995-2004) is reported. The survey involved horses showing clinical symptoms of the disease; the horses had not been vaccinated against AHS. Over the period surveyed, serological evidence suggestive of infection with AHS virus (AHSV) was found in 99 clinical cases out of which 41.4% (41/99) cases were found during the 1st half (1995-1999) and 58.6 % (58/99) cases were found in the 2nd half of the survey period (2000-2004). These serological findings are discussed in relation to AHSV seroty...