Rhodococcus equi causes severe pneumonia, resulting in disease and sometimes death of foals. Infection is thought to occur by inhalation of dust contaminated with virulent R equi. A recent study of 3 horse breeding farms in Ireland found airborne concentrations of virulent R equi to be significantly higher in stables than in paddocks. More importantly, another study from Australia established an association of airborne concentrations of virulent R equi with the prevalence of R equi pneumonia at 28 farms. The extent to which these associations extend to other farms in different parts of the world is not known. Two farms in central Kentucky with recurrent R equi pneumonia in foals were studied from February through July 2008. Air samples were collected and environmental factors were measured hourly for a 24-hour period each month from stalls and paddocks used to house mares and their foals at each farm. In 2009, samples were collected from 47 foals from stalls at a single horse-breeding farm in central Kentucky on days 1-2, days 7-9, and days 14-16 of life. Concentrations of airborne virulent R equi were determined via a modified colony immunoblot technique. Airborne concentrations of virulent R equi were significantly higher (P = 0.016) from 6:00 A.M. through 11:59 P.M. than for the period from midnight through 5:59 A.M. Presence of the mare and foal at the time of sampling was significantly (P < 0.001) associated with increased airborne concentrations of virulent R equi in stalls. The presence of virulent R equi in stalls was significantly (P = 0.045) more likely at 7 days of age for foals subsequently found to be affected by rhodococcal pneumonia. These findings suggest that recovery of airborne virulent R equi is less likely between 12:00 A.M. and 5:59 A.M., relative to other times, that airborne concentrations of virulent R equi are significantly increased when horses are present at the site for collection of air samples, and that environments containing airborne virulent R equi during the first week of life may influence the risk of subsequent disease for a foal.

No / Streptococcus equi is the causative agent of strangles, a prevalent and highly contagious disease of horses. Despite the animal suffering and economic burden associated with strangles, little is known about the molecular basis of S. equi virulence. Here we have investigated the contributions of a specific lipoprotein and the general lipoprotein processing pathway to the abilities of S. equi to colonize equine epithelial tissues in vitro and to cause disease in both a mouse model and the natural host in vivo. Colonization of air interface organ cultures after they were inoculated with a mutant strain deficient in the maturase lipoprotein ( prtM138-213, with a deletion of nucleotides 138 to 213) was significantly less than that for cultures infected with wild-type S. equi strain 4047 or a mutant strain that was unable to lipidate preprolipoproteins ( lgt190-685). Moreover, mucus production was significantly greater in both wild-type-infected and lgt190-685-infected organ cultures. Both mutants were significantly attenuated compared with the wild-type strain in a mouse model of strangles, although 2 of 30 mice infected with the lgt190-685 mutant did still exhibit signs of disease. In contrast, only the prtM138-213 mutant was significantly attenuated in a pony infection study, with 0 of 5 infected ponies exhibiting pathological signs of strangles compared with 4 of 4 infected with the wild-type and 3 of 5 infected with the lgt190-685 mutant. We believe that this is the first study to evaluate the contribution of lipoproteins to the virulence of a gram-positive pathogen in its natural host. These data suggest that the PrtM lipoprotein is a potential vaccine candidate, and further investigation of its activity and its substrate(s) are warranted.

Made available in DSpace on 2014-08-20T14:37:54Z (GMT). No. of bitstreams: 1 tese_clairton_marcolongo_pereira_resumo.pdf: 10803 bytes, checksum: 3f7507f184a7adb5ceb1296595a35eca (MD5) Previous issue date: 2014-02-21 / This thesis is a study developed in period of 34 years about equine diseases diagnosed through out 34 municipalities of Southern Rio Grande do Sul, which includes de influence area of the Laboratório Regional de Diagnóstico of the Veterinary School of the Federal University of Pelotas. There is a general paper about the diseases diagnosed in this specie related by etiologic agent. This paper establishes the importance of dermatological diseases, including equine sarcoid and squamous cell carcinoma as a cause of economic losses in equines. It also demonstrates that leucoencephalomalacia, rabies, thromboembolism by Strongylus vulgaris and equine monocytic ehrlichiosis are the leading causes of death in horses in the region. Other three papers are presented: two related to the causes of abortion and the one about the epidemiology of pythiosis. These conditions are important causes of economic losses in the breeding of horses in the region. / Esta tese trata-se de um estudo das enfermidades de equinos diagnosticadas em 34 municípios da região Sul do Rio Grande do Sul, que compreende a área de influência do Laboratório Regional de Diagnóstico da Faculdade de Veterinária da Universidade Federal de Pelotas, em um período de 34 anos. É apresentado um trabalho geral das enfermidades diagnosticadas nesta espécie animal, relacionadas por agente etiológico tendo sido estabelecida a importância das doenças dermatológicas, dentre elas o sarcoide equino e o carcinoma de células escamosas como causas de prejuízos econômicos nesta espécie animal. Com este estudo foi possível, ainda, demonstrar que a leucoencefalomalacia, a raiva, o tromboembolismo por Strongylus vulgaris e a erliquiose monocítica são as principais causas de morte de equinos na região. São apresentados, também, dois trabalhos científicos referentes às causas de aborto e um à epidemiologia da pitiose, respectivamente, que são importantes causas de prejuízos econômicos na criação de equinos na região, identificadas neste estudo.