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.
Tecles F, Cerón JJ.Whole blood cholinesterase was measured using acetyl-, butyryl- and propionylthiocholine as substrates in 10 healthy adult dogs, cats, horses, pigs, goats, sheep and cows, in order to determine and characterise the cholinesterase activity in whole blood of the main domestic animals. An in vitro exposure test with two anticholinesterase compounds, the organophosphate insecticide coumaphos and the carbamate insecticide imidocarb, was also performed. In whole blood of ruminants and pigs, acetylthiocholine yielded the highest cholinesterase activity and other substrates were poorly hydrolysed; in ...
McTaggart C, Yovich JV, Penhale J, Raidal SL.Flow cytometric assays were used to compare phagocytic and oxidative burst activity of neutrophils from healthy foals less than 7 days of age with the activity of cells from healthy adult horses. The phagocytosis of Staphylococcus aureus by foal neutrophils was less than that observed for adult neutrophils when autologous serum was used as the source of opsonins in the assay. The use of adult serum did not significantly improve the ability of foal neutrophils to attach bacteria. The oxidative burst activity of foal neutrophils was equivalent to that of adult cells. However, when serum or plasm...
Frees KE, Gaughan EM, Lillich JD, Cox J, Gorondy D, Nietfeld JC, Kennedy GA, Cash W.Formalin was injected into an ethmoidal hematoma in an 18-year-old Arabian gelding. Abnormal neurologic signs were observed within minutes of the injection. The horse did not respond favorably to medical treatment of the neurologic signs and was euthanatized. Postmortem examination revealed erosion and necrosis of the ventral cribriform plate, which appeared to have allowed the injected formalin to reach the rostral portion of the frontal lobe of the brain. Endoscopy and radiography had been performed prior to euthanasia, but neither delineated the cribriform lesion. Before treating large prog...
Matthews S, Dart AJ, Dowling BA, Hodgson JL, Hodgson DR.To review the clinical findings, diagnosis and treatment of 51 horses with peritonitis attributed to Actinobacillus equuli. Methods: Retrospective study of clinical cases. Methods: Breed, age and gender of horse, history, physical examination findings, treatment and outcome were determined from the hospital records of 51 horses in which a diagnosis of peritonitis attributed to A. equuli was made between January 1993 and June 1999. Results of abdominal fluid cytology and bacteriology, antimicrobial sensitivity patterns, haematology and faecal egg counts, when performed, were also retrieved. Res...
Varrasso A, Dynon K, Ficorilli N, Hartley CA, Studdert MJ, Drummer HE.To develop and validate specific, sensitive and rapid (< 8 hour) diagnostic tests using polymerase chain reaction (PCR) for the diagnosis of abortion and respiratory disease caused by equine herpesvirus 1 (EHV1; equine abortion virus) and EHV4 (equine rhinopneumonitis virus). Methods: Primer sets based on nucleotide sequences encoding glycoprotein H (gH) of EHV1 and gB of EHV4 were designed and used in single round and second round (seminested) PCRs, and in a multiplex PCR for the diagnosis of EHV1 and EHV4 infections. Methods: Oligonucleotide primers were designed for each virus, PCR condi...
Latimer FG, Colitz CM, Campbell NB, Papich MG.To determine the pharmacokinetics of fluconazole in horses. Methods: 6 clinically normal adult horses. Methods: Fluconazole (10 mg/kg of body weight) was administered intravenously or orally with 2 weeks between treatments. Plasma fluconazole concentrations were determined prior to and 10, 20, 30, 40, and 60 minutes and 2, 4, 6, 8, 10, 12, 24, 36, 48, 60, and 72 hours after administration. A long-term oral dosing regimen was designed in which all horses received a loading dose of fluconazole (14 mg/kg) followed by 5 mg/kg every 24 hours for 10 days. Fluconazole concentrations were determined i...
Nicolaiewsky TB, Richter MF, Lunge VR, Cunha CW, Delagostin O, Ikuta N, Fonseca AS, da Silva SS, Ozaki LS.We describe a nested polymerase chain reaction (PCR) for the detection of Babesia equi in equine infected erythrocytes using oligonucleotides designed on the published sequence of a B. equi merozoite antigen gene (ema-1). A 102bp DNA fragment is specifically amplified from B. equi but not from Babesia caballi, Babesia bovis or Babesia bigemina DNA. In a mock infection we were able to detect down to six infected cells in 10(8) equine erythrocytes or to detect the parasite in blood with an equivalent parasitemia of 0.000006%. Furthermore, gene polymorphism was found by performing a PCR-RFLP (PCR...
Martin-Downum K, Yazwinski T, Tucker C, Fincher M, Ralph J, Hamilton J.Commercial preparations of fenbendazole (Safe-Guard, Intervet), ivermectin (Eqvalan, Merial) or moxidectin (Quest, Fort Dodge) were administered once to horses scheduled for routine parasiticide treatment. In total, 93 horses from six cooperating farms were used in the study. Computer generated, random allocation of horses to treatment group was conducted at each farm. Fecal egg counts were determined for all horses on trial days 0, 56, 84 and 112, with corresponding calendar dates that were unique to each farm. Only strongyle egg counts from animals which were positive at day 0 were used for ...
Faye D, Pereira de Almeida PJ, Goossens B, Osaer S, Ndao M, Berkvens D, Speybroeck N, Nieberding F, Geerts S.In a study of the prevalence and incidence of trypanosomosis in horses and donkeys in two regions of the Gambia, surveys were carried out at Niamina east and Bansang south with a high and low to moderate tsetse challenge, respectively. Eleven horses and 67 donkeys were sampled monthly from August 1997 to September 1998. Blood samples were examined for trypanosomes using the buffy-coat (BC) method and polymerase chain reaction (PCR). Three primer sets were used, specific for either Trypanosoma vivax (TVW), Trypanosoma congolense (GOL) or Trypanosoma brucei (ORPHON5J). The BC results showed that...
Johnson DJ, Ostlund EN, Pedersen DD, Schmitt BJ.A traditional single-stage reverse transcription-polymerase chain reaction (RT-PCR) procedure is effective in determining West Nile (WN) virus in avian tissue and infected cell cultures. However, the procedure lacks the sensitivity to detect WN virus in equine tissue. We describe an RT-nested PCR (RT-nPCR) procedure that identifies the North American strain of WN virus directly in equine and avian tissues.
Nordengrahn A, Klingeborn B, Lindholm A, Merza M.A blocking enzyme-linked immunosorbent assay (ELISA) was developed to detect antibodies to equine herpesvirus 2 in serum samples of horses. By measuring the binding to a single epitope, this blocking ELISA gives a good picture of the antibody status in the animal. The test is based on a monoclonal antibody with neutralizing activity and had a sensitivity of 94% and a specificity of 100%. Antibodies due to newly acquired infection in foals were successfully detected with this blocking ELISA.
Jang HK, Albrecht RA, Buczynski KA, Kim SK, Derbigny WA, O'Callaghan DJ.The sole immediate-early (IE) gene of equine herpesvirus 1 encodes a 1,487-amino-acid (aa) regulatory phosphoprotein that independently activates expression of early viral genes. Coimmunoprecipitation assays demonstrated that the IE protein physically interacts with the general transcription factor TFIIB. Using a variety of protein-binding assays that employed a panel of IE truncation and deletion mutants expressed as in vitro-synthesized or glutathione S-transferase fusion proteins, we mapped a TFIIB-binding domain to aa 407 to 757 of the IE protein. IE mutants carrying internal deletions of ...
Schmidtmann ET, Lloyd JE, Bobian RJ, Kumar R, Waggoner JW, Tabachinick WJ, Legg D.The blood feeding of mosquitoes and black flies from Hereford cattle and ponies treated with commercial formulations of permethrin was evaluated using an animal enclosure trap sample system that allowed comparison of insect blood-feeding levels between treated and nontreated animals. Blood feeding of both Aedes dorsalis Meigen and A. melanimon Dyar from heifers treated with pour-on concentrate and whole body spray treatments was reduced significantly by 79-88% at 4 d posttreatment, with apparent but not significant reductions of 61-68% at 11 d posttreatment. Simulium bivittatum Malloch and S. ...
Furr M, Pontzer C, Gasper P.The percentages of T-lymphocytes, lymphocyte subsets CD4+ and CD8+ T-cells, and lymphocyte adhesion molecule CD11a/CD18 were determined in the peripheral blood and cerebrospinal fluid (CSF) of seven normal horses and four horses with equine protozoal myeloencephalitis (EPM) using flow cytometry. There was a greater percentage of CD5+ cells in the CSF (79.0%) than in peripheral blood (67.0%), although this did not achieve statistical significance. Furthermore, the lymphocyte population in CSF comprises a significantly greater (P = .01) percentage of CD8+ T-cells, resulting in a decrease of the ...
Johnson JS, Hibler CP, Tillotson KM, Mason GL.An adult horse was euthanatized following a clinical diagnosis of cauda equina neuritis. Significant gross postmortem and histopathologic findings were limited to the sacral spinal cord and cauda equina. The sacral spinal cord, meninges, and spinal nerve roots were expanded and partially effaced by sclerosing granulomatous inflammation with necrosis. The lesion contained numerous nematode larvae and fewer adults with a rhabditiform esophagus having a corpus, isthmus, and valved bulb. Female nematodes were amphidelphic and didelphic with reflexed ovaries. These morphologic features confirm Hali...
Wells D, Krecek RC.Structured interviews using a questionnaire were conducted to gather information on socioeconomic aspects, health, nutrition, breeding and management of working equids in 3 study areas of Moretele 1 near Hammanskraal, North West Province, South Africa. The questionnaire addressed questions about the role of animals with a focus on donkeys used for work in these areas. Extension and animal health officers and donkey owners participated. The analysis highlights the use of donkeys for transport of water, wood and people; that ticks, wounds and harness sores are the conditions reported most freque...
Wollanke B, Rohrbach BW, Gerhards H.To measure antibody titers against Leptospira interrogans in serum and vitreous humor and determine the prevalence of L interrogans in vitreous humor of horses with recurrent uveitis. Methods: Cross-sectional study. Methods: 242 horses (270 eyes) with recurrent uveitis undergoing vitrectomy and 39 control horses (54 eyes) without any history or clinical signs of recurrent uveitis undergoing euthanasia or enucleation for unrelated reasons. Methods: Serum and vitreous humor were tested for antibodies against 13 serovars of L interrogans. Vitreous humor was submitted for leptospiral culture; isol...
Magnarelli LA, Ijdo JW, Van Andel AE, Wu C, Oliver JH, Fikrig E.To test serum samples of dogs and horses by use of class-specific recombinant-based ELISA for establishing a diagnosis of granulocytic ehrlichiosis attributable to infection with organisms from the Ehrlichia phagocytophila genogroup. Methods: Serum samples from 43 client-owned dogs and 131 horses (81 with signs of acute illness and 50 without signs of disease). Methods: Serum samples were analyzed, using ELISA with a recombinant 44-kd protein antigen for IgM and IgG antibodies to the human granulocytic ehrlichiosis (HGE) agent (NCH-1 strain). Western blot analyses, using infected human promyel...
Jose-Cunilleras E, Hinchcliff KW.Listeria monocytogenes rarely causes disease in horses
(Emerson and Jarvis 1968; McCain and Robinson 1976; Clark et
al. 1978; Welsh 1983; Wallace and Hathcock 1995; Larochelle et
al. 1999; Wilkins et al. 2000). It is described as a cause of
abortion, septicaemia in equine neonates, mature horses and
ponies and neurological disease in a foal (Emerson and Jarvis
1968; McCain and Robinson 1976; Clark et al. 1978; Welsh
1983; Wallace and Hathcock 1995; Larochelle et al. 1999;
Wilkins et al. 2000). Most cases of listeriosis in other species
arise from the ingestion of contaminated food and...
Martens A, De Moor A, Demeulemeester J, Peelman L.To examine apparently normal skin around equine sarcoids for evidence of bovine papilloma virus (BPV) DNA, and to relate this finding to the observed recurrence after surgery. Methods: Prospective study. Methods: Forty-one equine sarcoids from 19 horses. Methods: The tumors were surgically excised at a measured distance of 8, 12, or 16 mm. Samples from the tumor and of the entire surrounding skin were taken at 4, 8, 12, and 16 mm from the tumor border and analyzed for the presence of BPV DNA using polymerase chain reaction (PCR) amplification. The samples were grouped per examined sarcoid, and...
Sugiura T, Sugita S, Imagawa H, Kanaya T, Ishiyama S, Saeki N, Uchiyama A, Tanigawa M, Kuwano A.The hemagglutinin (HA) protein of an equine influenza strain, A/equine/La Plata/1/93 (LP/93), was produced using a baculovirus expression system. Silkworm larvae inoculated with recombinant baculovirus expressed high quantities of the HA protein which was then purified to greater than 95% purity by fetuin-affinity chromatography. Purified HA protein was used subsequently in an ELISA for detection of antibodies in horse sera. Two hundred serum samples from vaccinated racehorses were reacted on ELISA plates coated with 40.0 ng/ml of purified HA protein. Subsequent optical density (OD) levels rev...
Warner S, Hartley CA, Stevenson RA, Ficorilli N, Varrasso A, Studdert MJ, Crabb BS.Equine rhinitis A virus (ERAV) is a respiratory pathogen of horses and is classified as an Aphthovirus, the only non-Foot-and-mouth disease virus (FMDV) member of this genus. In FMDV, virion protein 1 (VP1) is a major target of protective antibodies and is responsible for viral attachment to permissive cells via an RGD motif located in a distal surface loop. Although both viruses share considerable sequence identity, ERAV VP1 does not contain an RGD motif. To investigate antibody and receptor-binding properties of ERAV VP1, we have expressed full-length ERAV VP1 in Escherichia coli as a glutat...
Labonville M, Higgins R, Lavoie JP.The aim of the study was to assess the relation between the direct smear observations and bacteriological results carried out on equine tracheal secretions. A total of 304 cases comprising both the direct smear (Gram stain) and the bacteriological culture, over a period of 8 years, were submitted to this retrospective study. Most of the specimens (78%) were obtained using tracheal washings while the rest (22%) originated from tracheal brushings. A total of 96 specimens (32%) were negative for both direct smear and culture. The positive predictive value of direct smears appeared high (81-96%) w...
Hinton TM, Crabb BS.Equine rhinitis B virus (ERBV) has recently been classified as an Erbovirus, a new genus in the Picornaviridae family. ERBV is distantly related to members of the Cardiovirus and Aphthovirus genera which utilize a type II internal ribosome entry sequence (IRES) to initiate translation. We show that ERBV also possesses the core stem-loop structures (H-L) of a type II IRES. The function of the ERBV IRES was characterized using bicistronic plasmids that were analysed both by transfection into BHK-21 cells and by in vitro transcription and translation in rabbit reticulocyte lysates. In both system...
Boerlin P, Eugster S, Gaschen F, Straub R, Schawalder P.Acinetobacter baumannii, Enterococcus faecalis, Enterococcus faecium, and Staphylococcus intermedius isolates from infected surgical wounds and other types of infections in a veterinary teaching hospital were typed by pulsed field gel electrophoresis. A first cluster of infections with a multiresistant A. baumannii strain was observed in dogs and cats in 1998-1999. This strain disappeared after cleaning and disinfection of the companion animals intensive care unit. It was followed in 2000 by a second multiresistant strain, which caused another cluster of infections and was also transmitted to ...
Wang J, Li Y, Ma D, Kalish H, Balch AL, La Mar GN.The highly stereoselective cleavage of hemin in myoglobin by coupled oxidation has been attributed to steric barriers that leave more space near the alpha- than the other meso-positions. The steric barriers near meso positions in myoglobin have been investigated by establishing the thermodynamics and dynamics of possible seatings in the pocket of horse myoglobin of a four-fold symmetric etioheme I modified with a bulky nitro group at a single meso position. The cyanomet complex of this reconstituted myoglobin exhibits three sets of (1)H NMR resonances that are linked dynamically and occur in a...
Oduor-Okelo D.The duodenal glands of cat and horse were studied using PAS, Alcian blue, dialysed iron, aldehyde fuchsin-Alcian blue and high iron diamine stains. It was found that the duodenal glands of the horse reacted positively to Alcian blue, dialysed iron stains and also took the Alcian blue stain in the combined aldehyde fuchsin-Alcian blue and high iron diamine-Alcian blue stains. Those of the cat gave negative results. These results suggest the presence of acidic groups in the mucosubstances secreted by the horse's duodenal glands. A suggestion is put forward on the strength of the high iron diamin...
Meuten DJ, Price SM, Seiler RM, Krook L.Pseudohyperparathyroidism was diagnosed in a mature stallion presented for anorexia, weight loss, pollakiuria and constipation. Laboratory findings included hypercalcemia, hypophosphatemia, anemia and isosthenuria. Thoracocentesis indicated an exfoliating squamous cell carcinoma. At necropsy, a squamous cell carcinoma of the stomach with metastases to the abdominal and thoracic cavities was diagnosed. No osseous metastases were found. No gross or microscopic renal lesions were noted. Bone tissue showed arrested resorption, and the parathyroid gland was atrophic.
Nelson KM, Darien BJ, Konkle DM, Hartmann FA.A 24-hour-old Hackney ony filly developed signs of weakness, depression and a poor suck reflex, with harsh lung sounds over both fields, and a 48-hour-old Arabian colt from a normal birth which had sucked vigorously developed loose stools and became depressed, weak and anorectic. Both foals had serum IgG concentrations greater than 800 mg/dl, but each had a severe neutropenia with a left shift, and blood cultures from both of them yielded Actinobacillus suis. The A suis isolates had different antimicrobial susceptibility patterns and, in the case of the Arabian, the isolate was resistant to co...
Heath TJ, Perkins NR.The pathways through which lymph flows from terminal afferent lymphatics to the lymph sinuses, and from the sinuses to initial efferent lymphatics, were studied in horse lymph nodes by using Microfil casts and electron microscopy. Terminal afferent lymphatics are continuous with the subcapsular sinus through oval holes, about 3 microns wide, along their length, and through larger openings near their end. Other terminal afferents penetrate into the node within trabeculae and are supported by processes across the lumen. They connect with trabecular and medullary sinuses through oval or round hol...
Anderson GA, Mount ME, Vrins AA, Ziemer EL.Acorn poisoning was diagnosed in an 11-year-old Quarter Horse with signs of severe colic, tachycardia, hyperpnea, abdominal borborygmus, rectal tenesmus, and hemorrhagic diarrhea. The diagnosis was based on history and predisposing factors, clinical signs, laboratory data, acorn husks in the feces, the urinary gallic acid equivalent concentration, and necropsy findings. The most striking pathologic changes were gastrointestinal and mesenteric edema, ulcerative enterocolitis, and nephrosis.
Carman MG, Hodges RT.Nineteen isolates of Actinobacillus suis were recovered from horses during the period October 1978-December 1980. Animals varied in age from a full term foetus to 12 years. One isolate was obtained from the nose of an apparently healthy horse, the remainder were obtained from still-born foetuses (2), foals dying within a week of birth (5), older animals with respiratory (6) or genital infections (3) or abscesses in the jaw (1). One isolate was obtained from the lung of a 2-week-old foal which had shown diarrhoea. The bacteriological characteristics of the isolates and the pathological lesions ...
Newton SA.Bacterial infections (such as meningitis or meningoencephalitis) of the central nervous system are rare in horses. They are most prevalent in neonates as a result of septicaemia. A few cases have been reported in the adult and most have been fatal. Streptococcal species appear to be the organism most commonly identified in these cases. Thus, this disease may be a secondary complication of upper respiratory tract infections. Clinical signs are extremely variable making diagnosis difficult. In most cases, postmortem has been the definite diagnostic procedure. This paper describes the clinical co...
Teixeira WF, Felippelli G, Cruz BC, Maciel WG, Fávero FC, Gomes LV, Buzzulini C, Prando L, Bichuette MA, Lopes WD, Oliveira GP, Costa AJ.With the aim of studying the endoparasite fauna of horses from the Formiga city, located in center-west region of the state of Minas Gerais, 25 animals that were naturally infected with helminths were evaluated. By means of parasitological necropsies, different endoparasites were found. The subfamily Cyathostominae presented the highest incidence, followed by Trichostrongylus axei, Oxyuris equi, Triodontophorus serratus, Strongyloides westeri, Strongylus edentatus, Habronema muscae, Parascaris equorum, Probstmayria vivipara, Strongylus vulgaris, Gasterophilus nasalis, Anoplocephala magna and A...
Molín J, Asín J, Vitoria A, Sanz A, Gimeno M, Romero A, Sánchez J, Pinczowski P, Vázquez FJ, Rodellar C, Luján L.A 1-month-old Purebred Spanish Horse (PSH) foal presented with progressive hepatic failure culminating in death. Hepatic lesions were consistent with congenital hepatic fibrosis (CHF). Genetic studies in the PKHD1 gene in the affected foal revealed that it was heterozygous for the 2 previously described single-nucleotide polymorphisms (SNPs) linked to CHF in Swiss Franches-Montagnes (SFM) horses. In addition, 2 novel mutations were detected, the foal being homozygous for one of them and heterozygous for the other. Genetic studies in a healthy PSH population ( n = 35) showed a 3-fold higher gen...
Finno C, Pusterla N, Aleman M, Mohr FC, Price T, George J, Holmberg T.A 4-month-old American Paint Horse colt was evaluated because of acute onset of ataxia, left-sided head tilt, and fever and a recently noticed heart murmur. Upper respiratory tract infection caused by Streptococcus equi subsp equi had been diagnosed at 3 months of age. Results: Hematologic abnormalities included leukocytosis, mature neutrophilia, monocytosis, and mild anemia. Analysis of a CSF sample revealed high total protein concentration and total nucleated cell count; nucleated cells consisted mainly of degenerate neutrophils. Results of a real-time PCR assay were positive for S equi subs...
Jeffcott LB.The mechanism of transfer of maternal immunity to the foal is reviewed. Maximal efficiency of macromolecular absorption by specialized cells of the small intestine exists soon after birth. The absorptive cells are progressively replaced by more mature-looking cells incapable of taking up large molecules and the rate of absorption is reduced in a linear decline and ceases completely within 24 hr. Passive antibody levels fall rapidly in the first 4 weeks of life to less than half their original values and have usually completely disappeared by 6 months of age. The foal shows immunological compet...
Copetti MV, Santurio JM, Boeck AA, Silva RB, Bergermaier LA, Lubeck I, Leal AB, Leal AT, Alves SH, Ferreiro L.This article reports an outbreak of intoxication of female horses with Claviceps purpurea in southern Brazil. The outbreak affected twelve pregnant mares which were fed with black oat (Avena strigosa) during the pre-delivery period. Underdevelopment of the mammary gland in the pre-delivery period resulting in post-delivery agalactia was the most pronounced finding. These mares delivered weak and unviable foals, which showed no suckling reflex and died within a few hours of birth. Laboratory analysis of oat samples fed to the animals resulted in the identification of Claviceps purpurea scleroti...
Hurd HS, McCluskey BJ, Mumford EL.To identify management factors affecting the risk of animals developing vesicular stomatitis (VS). Methods: Case-control study. Methods: Horses, cattle, and sheep with suspected vesicular stomatitis on 395 premises in Colorado, New Mexico, Utah, and Arizona. Methods: Data were collected during the VS outbreak of 1997. Diagnosticians interviewed livestock owners and completed a supplemental questionnaire. Cases were defined as those premises that had a completed questionnaire and had > or = 1 animal positive for VS. Control premises were all premises investigated that had a completed questionna...
Ferris RA, Dern K, Veir JK, Hawley JR, Lappin MR, McCue PM.To develop a broad-range 28S ribosomal DNA quantitative PCR (qPCR) assay for detection of fungal DNA in equine endometrial samples. Methods: 12 fungal samples from a clinical diagnostic laboratory and 29 samples obtained from 17 mares. Methods: The qPCR assay was optimized with commercially acquired fungal organisms and validated with samples obtained from the clinical diagnostic laboratory. Subsequently, 29 samples from 17 mares suspected of having fungal endometritis were evaluated via the qPCR assay and via traditional fungal culture and endometrial cytology. Amplicons from the qPCR assay w...
Justines G, Sucre H, Alvarez O.Transplacental passage of Venezuelan equine encephalitis virus, epizootic strain P-676, occurred in four of nine fetuses studied. The mares were infected near term. Virus was recovered in high titer from fetal blood and organs, while no virus was detected in maternal blood but neutralizing antibodies were present. No evidence of in utero infection was found in two fetuses from mares infected with MF-8, another epizootic strain of Venezuelan equine encephalitis virus.