Individual-level life-history strategies are the rails that guide population dynamics. Due to the difficulty of conducting long-term, individual-based studies, current management practices often focus on estimating and controlling demographic rates with little consideration for the individual-level responses that guide them. This approach cannot account for important factors such as age-specific responses to changes in population density or long-term impacts of conspecific density and resource limitation. As such, population-level approaches may fail to predict age structure or the rate of population growth. Recent studies of mammals and birds have shown that short-term changes in factors such as population density can have lasting impacts on vital rates of individuals. These results highlight the importance of long-term individual-based analyses in understanding population dynamics. However, very few researchers have thus far been able to isolate and study interacting effects of density and resources on life histories apart from processes such as predation, interspecific competition, and management of anthropogenic disturbance. The feral horses (Equus ferus caballus) of Sable Island, Nova Scotia, Canada, exist in a natural though simplified system without predation, human interference, or interspecific competition (they are the island’s only terrestrial mammal, numbering approximately 500 individuals). Here I determined the roles of local conspecific density and an interacting resource gradient in guiding the reproduction and survival of adult female Sable Island horses (2008–2012). I used body condition (estimates of subcutaneous fat) as an indication of resource allocation towards the often conflicting purposes of reproduction and maintenance. Reproduction was best predicted by body condition (reproducing females were in relatively poorer condition) but there was also evidence of density-dependence in reproductive success. Survival was predicted by and positively related to body condition. Survival was also predicted by an interaction between conspecific density and location on the island consistent with expectations of a known east-west resource gradient that occurs on Sable Island (in available water and forage). Greater variability in fitness estimates in resource-poor, eastern Sable Island suggests that regions of low density and resources may be high risk/high reward habitats. Such habitats may be disproportionately avoided by young animals and exploited by senescent animals. All feral horses are descended from domesticated animals and recent work has found evidence of artificially selected life-history traits in unmanaged populations of domestic mammals like cattle, sheep, and horses (e.g., reproducing even at high densities and earlier in life than expected). I therefore attempted to determine if effects of artificial selection existed in the Sable Island population by examining age-based contributions to population growth and the relationship between reproduction (foaling) and female mortality. Perhaps due to the population’s long history of low management (>250 years), I failed to find any strong evidence of artificially selected life-history traits in Sable Island horses. That is, life history trade-offs in survival and reproduction in Sable Island horses were more similar to wild species of large herbivores inhabiting natural environments, than other populations of feral ungulates. My research suggests a rarely documented but fascinating instance of reversal of artificial selection by natural selection for a domesticated species like the horse.

Os herpesvírus equinos do tipo 1 (EHV-1) e do tipo 4 (EHV-4) são considerados os principais agentes infecciosos para a espécie equina. Dentre as doenças causadas por estes agentes, destacam-se a rinopneumonite em animais jovens, o abortamento em fêmeas no terço final da gestação, a mortalidade perinatal em potros e a mieloencefalopatia. Estudos anteriores relatam ampla disseminação do EHV-1 na população eqüina no Estado de São Paulo, entretanto a ocorrência de infecção pelo EHV-4 não possui registro. Devido à similaridade antigênica entre os dois tipos virais, a diferenciação pelos métodos de sorodiagnóstico tradicionais, como a Soroneutralização e a Reação de Fixação de Complemento, não é possível. Assim, este trabalho avaliou, pela primeira vez no Estado de São Paulo, através de um teste de ELISA indireto que emprega uma região da glicoproteína G para diferenciar o EHV-1 do EHV-4 (iELISAgG),a presença de anticorpos específicos para os dois tipos de herpesvírus equino em 512 animais de 20 municípios de 8 mesoregiões do Estado de São Paulo, dentre equinos, muares e asininos, de ambos os sexos, diferentes faixas etárias, vacinados e não vacinados. As mesmas amostras foram testadas para o EHV através do teste de soroneutralização, tradicionalmente empregado para a pesquisa de anticorpos contra o vírus. Os resultados obtidos com a soroneutralização revelam 205/512 (40,03%) animais soropositivos. Através do teste de ELISA obteve-se 3/512 (0,59%) animais positivos para o EHV-1, 347/512 (67,77%) animais positivos para o EHV-4 e 108/512 (21,09%) animais positivos para ambos. O grupo de animais não vacinados apresentou 127/352 (36,07%) soropositivos pelo teste de soroneutralização; enquanto 4/352 (1,14%) foram positivos para o EHV-1, 237/352 (67,33%) foram positivos para o EHV-4 e 69/352 (19,6%) foram positivos para ambos, pelo teste de ELISA. O grupo de animais vacinados apresentou 78/160 (48,75%) soropositivos pelo teste de soroneutralização; enquanto 1/160 (0,63%) foram positivos para o EHV-1, 112/160 (70%) foram positivos para o EHV-4 e 37/160 (23,13%) foram positivos para ambos, pelo teste de ELISA. Os resultados sugerem baixa circulação de EHV-1 e alta circulação de EHV-4, de acordo com os resultados encontrados nos animais não vacinados. A análise de correlação entre os dois testes empregados mostrou baixa concordância. / The equine herpesvirus type 1 (EHV-1) and type 4 (EHV-4) are considered the major infectious agents for the equine species. Among the diseases caused by these agents, we highlight the rinopneumonite in young animals, abortion in females in the final third of pregnancy, perinatal mortality in foals and encefalopathy. Previous studies have reported wide spread of EHV-1 equine population in the State of São Paulo, however the occurrence of infection with EHV-4 is not registered. Due to the antigenic similarity between the two virus types, the differential serodiagnosis by traditional methods such as neutralization and complement fixation reaction, it is not possible. Thus, this study evaluated the first time in São Paulo, through an indirect ELISA employing a region of glycoprotein G to differentiate EHV-1 EHV-4 (iELISAgG), the presence of specific antibodies to the two types of equine herpesvirus in 512 animals from 20 municipalities in 8 regions the State of São Paulo, among horses, mules and donkeys of both sexes, different age groups, vaccinated and unvaccinated. The same samples were tested for EHV through the neutralization test, traditionally used for the detection of antibodies against the virus. The results obtained with the neutralization revealed 205/512 (40.03%) seropositive animals. By ELISA we obtained 3/512 (0.59%) animals positive for EHV-1, 347/512 (67.77%) animals positive for EHV-4 and 108/512 (21.09% ) animals positive for both. The group of unvaccinated animals showed 127/352 (36.07%) HIV-positive by serum neutralization test, while 4/352 (1.14%) were positive for EHV-1, 237/352 (67.33%) were positive for EHV-4 and 69/352 (19.6%) were positive for both ELISA. The group of vaccinated animals showed 78/160 (48.75%) seropositive by neutralization test, while 1 / 160 (0.63%) were positive for EHV-1, 112/160 (70%) were positive for EHV-4 and 37/160 (23.13%) were positive for both ELISA. The results suggest low circulation of EHV-1 and high circulation of EHV-4 according to the results found in unvaccinated animals. The correlation analysis between the two tests employed showed poor agreement

Os herpesvírus equinos do tipo 1 (EHV-1) e do tipo 4 (EHV-4) são considerados os principais agentes infecciosos para a espécie equina. Dentre as doenças causadas por estes agentes, destacam-se a rinopneumonite em animais jovens, o abortamento em fêmeas no terço final da gestação, a mortalidade perinatal em potros e a mieloencefalopatia. Estudos anteriores relatam ampla disseminação do EHV-1 na população eqüina no Estado de São Paulo, entretanto a ocorrência de infecção pelo EHV-4 não possui registro. Devido à similaridade antigênica entre os dois tipos virais, a diferenciação pelos métodos de sorodiagnóstico tradicionais, como a Soroneutralização e a Reação de Fixação de Complemento, não é possível. Assim, este trabalho avaliou, pela primeira vez no Estado de São Paulo, através de um teste de ELISA indireto que emprega uma região da glicoproteína G para diferenciar o EHV-1 do EHV-4 (iELISAgG),a presença de anticorpos específicos para os dois tipos de herpesvírus equino em 512 animais de 20 municípios de 8 mesoregiões do Estado de São Paulo, dentre equinos, muares e asininos, de ambos os sexos, diferentes faixas etárias, vacinados e não vacinados. As mesmas amostras foram testadas para o EHV através do teste de soroneutralização, tradicionalmente empregado para a pesquisa de anticorpos contra o vírus. Os resultados obtidos com a soroneutralização revelam 205/512 (40,03%) animais soropositivos. Através do teste de ELISA obteve-se 3/512 (0,59%) animais positivos para o EHV-1, 347/512 (67,77%) animais positivos para o EHV-4 e 108/512 (21,09%) animais positivos para ambos. O grupo de animais não vacinados apresentou 127/352 (36,07%) soropositivos pelo teste de soroneutralização; enquanto 4/352 (1,14%) foram positivos para o EHV-1, 237/352 (67,33%) foram positivos para o EHV-4 e 69/352 (19,6%) foram positivos para ambos, pelo teste de ELISA. O grupo de animais vacinados apresentou 78/160 (48,75%) soropositivos pelo teste de soroneutralização; enquanto 1/160 (0,63%) foram positivos para o EHV-1, 112/160 (70%) foram positivos para o EHV-4 e 37/160 (23,13%) foram positivos para ambos, pelo teste de ELISA. Os resultados sugerem baixa circulação de EHV-1 e alta circulação de EHV-4, de acordo com os resultados encontrados nos animais não vacinados. A análise de correlação entre os dois testes empregados mostrou baixa concordância. / The equine herpesvirus type 1 (EHV-1) and type 4 (EHV-4) are considered the major infectious agents for the equine species. Among the diseases caused by these agents, we highlight the rinopneumonite in young animals, abortion in females in the final third of pregnancy, perinatal mortality in foals and encefalopathy. Previous studies have reported wide spread of EHV-1 equine population in the State of São Paulo, however the occurrence of infection with EHV-4 is not registered. Due to the antigenic similarity between the two virus types, the differential serodiagnosis by traditional methods such as neutralization and complement fixation reaction, it is not possible. Thus, this study evaluated the first time in São Paulo, through an indirect ELISA employing a region of glycoprotein G to differentiate EHV-1 EHV-4 (iELISAgG), the presence of specific antibodies to the two types of equine herpesvirus in 512 animals from 20 municipalities in 8 regions the State of São Paulo, among horses, mules and donkeys of both sexes, different age groups, vaccinated and unvaccinated. The same samples were tested for EHV through the neutralization test, traditionally used for the detection of antibodies against the virus. The results obtained with the neutralization revealed 205/512 (40.03%) seropositive animals. By ELISA we obtained 3/512 (0.59%) animals positive for EHV-1, 347/512 (67.77%) animals positive for EHV-4 and 108/512 (21.09% ) animals positive for both. The group of unvaccinated animals showed 127/352 (36.07%) HIV-positive by serum neutralization test, while 4/352 (1.14%) were positive for EHV-1, 237/352 (67.33%) were positive for EHV-4 and 69/352 (19.6%) were positive for both ELISA. The group of vaccinated animals showed 78/160 (48.75%) seropositive by neutralization test, while 1 / 160 (0.63%) were positive for EHV-1, 112/160 (70%) were positive for EHV-4 and 37/160 (23.13%) were positive for both ELISA. The results suggest low circulation of EHV-1 and high circulation of EHV-4 according to the results found in unvaccinated animals. The correlation analysis between the two tests employed showed poor agreement

The project was undertaken to monitor a group of 30 foals on a farm both clinically and microbiologically from birth until one year of age, to determine the aetiology of upper respiratory tract infections and to establish immune profiles of some of the known respiratory viral pathogens. One to two months prior to the birth of their foals, blood for serology was collected from the mares. The same specimens were collected from the foals just after birth, prior to suckling and a day after suckling. Thereafter the foals were examined monthly for the presence of respiratory disease and specimens taken. The following specimens were collected from each foal: three nasopharyngeal swabs, (one for virus isolation, one for bacteria and fungus isolation, and one for mycoplasma isolation) and blood that was allowed to clot. Blood was collected in heparin from sick foals with elevated rectal temperatures. Virus isolation was done on roller tube cultures of equine embryonic lung (EEL), Vero cells and rabbit kidney 13 (RK13) cells. The bacteria (including mycoplasmas) and fungi were cultured from the swabs and identified using a variety of traditional methods. The serum neutralization test (SNT) was used to detect antibodies to equid herpesvirus 1 (EHV-1), equid herpesvirus 4 (EHV-4), equine rhinovirus 1 (ERV-1), equine rhinovirus 2 (ERV-2) and equine adenovirus 1 (EAdV-1). The complement fixation test (CFT) was used to detect antibodies to EHV-1 and EHV-4 and the haemagglutination inhibition test (HIT) antibodies to equine influenzavirus (EIV). Only EHV-4 was cultured from the nasopharyngeal swabs of nine foals when they were 5 to 6 months of age and from one foal two months later. A wide variety of bacteria and fungi were cultured and it was established that coagulase-negative staphylococci, viridans streptococci, Moraxella spp. and Flavobacterium spp. predominated in most of the samples. Several potential bacterial pathogens were isolated but the most common were Streptococcus equi subsp. zooepidemicus, Actinobacillus equuland Staphylococcus aureus. Colostrum-derived antibodies were detected for all the viruses in all but two of the foals. It was found that the foals had similar or slightly higher titres than their mothers. The levels declined in direct proportion to what they initially were and were depleted by the time the foals were 2 to 7 months of age. Antibodies to natural infection was detected to EHV-4, ERV-2 and EAdV-1. A rise in antibody titres occurred when the foals were 5 to 6 months of age, two months later and when they were one year of age. Antibodies resulting from immunization was detected to EHV-1, EHV-4 and EIV. It was established that the most important virus causing upper respiratory tract disease of the foals from 5 to 12 months of age was EHV-1 with EAdV-1 playing a minor role. These viruses caused repeated bouts of infection with a two to five months interval. Streptococcus equi subsp. zooepidemicus was considered to be the most important secondary pathogen. Prior to this period most of the foals were healthy with only a few suffering from upper respiratory disease. The aetiology was not determined in these cases, but based on the bacteriology results, it was suspected that some of them were suffering from bacterial infections. / Dissertation (MSc (Veterinary Science))--University of Pretoria, 2005. / Veterinary Tropical Diseases / unrestricted

Equine coital exanthema (ECE), caused by equid herpesvirus 3 (EHV-3), is a contagious venereal disease characterised by the formation of painful papules, vesicles, pustules and ulcers on the external genitalia of both mares and stallions. EHV-3 is an alphaherpesvirus, distinct from the other equine herpesviruses, endemic in most horse breeding populations worldwide. EHV-3 is primarily transmitted through coitus, although there is also evidence supporting the possibility of non-coital spreading through infected fomites and contacts other than coitus. The infection does not usually result in systemic illness. Epidemiological observations and serological monitoring suggest the existence of latently infected animals from which EHV-3 is periodically reactivated and transmitted to cohorts but latency of EHV-3 has not been formerly demonstrated. The negative impacts of ECE on equine breeding enterprises are the forced, temporary disruption of the mating activities of mares and stallions, the additional care and supportive treatment in affected horses, and the risk of virus spread by either fresh or frozen semen as well as by artificial insemination and embryo transfer practices. In intensively managed stud operations, which have heavily-scheduled breeding dates for thoroughbred stallions, breeding disruptions may translate into significant end-of-season decreases in the number of entries into the mare book of affected stallions. Also, delayed foaling dates and/or reduced pregnancy rates may occur in mares that miss breeding opportunities due to the disease. Similarly, in the face of an ECE outbreak in artificial insemination and embryo transfer centres, both donor and recipient affected mares show such discomfort that they are reluctant to be inspected, inseminated or transferred, with the consequent loss of opportunity to become pregnant. The additional time and necessary precautions required to manage the donor and receptor mares due to the presence of the disease also have a substantial negative impact. Because ECE is a not a notifiable disease and the diagnosis is made on the basis of typical clinical signs, most cases and outbreaks of ECE remain unnoticed and its true prevalence and economic impact is difficult to assess and is probably underestimated. Therefore, as several aspects of EHV-3 infection are largely unknown and it has severe economic consequences to the horse industry, the general aim of this doctoral study was to increase the knowledge about the biology of EHV-3 infection. The specific objectives were to investigate the iatrogenic transmission of infection and to set up a protocol for experimental reproduction of the disease, to study the reactivation and re-excretion patterns from latency, to evaluate the epidemiological importance of subclinical infections, and to hypothesise about the ECE economic consequences in the current context of the equine industry. During the occurrence of an outbreak of ECE in an embryo transfer centre, approximately 32% (n=35) of the donor mares and 25% (n=125) of the recipient mares showed typical ECE lesions around the anus and on the perineal skin, discomfort, and anorectal lymphadenopathy. EHV-3 was detected in 7 (58%) of the affected mares and specific antibodies in 23 (88%) of the convalescent mares. Since no natural breeding had taken place on the affected mares, it could be hypothesised that the virus spread was a consequence of contamination by means of the gloves or the ultrasonography scanner used. Lymphadenopathy provides a new concern associated with ECE. EHV-3 was isolated from nasal swabs obtained during an outbreak of unilateral rhinitis affecting approximately 40 out of 2000 thoroughbred horses. The fact that an endoscopic examination had been performed in the week previous to the onset of the lesions to evaluate the respiratory tract function was a common finding in all the horses affected. EHV-3 was demonstrated as the etiologic agent of the unilateral rhinitis observed in those 40 thoroughbred horses. The endoscope used for respiratory tract examination was identified as the most likely cause of the spread of the infection. This case is an example of non-genital iatrogenic transmission and reinforces the importance of strict application of hygienic measures in order to reduce the risk of spread of infectious diseases. The virus isolated from this field outbreak as well as that isolated from others were characterized by means of restriction endonuclease (RE) fragment patterns, plaque size and gG gene partial nucleotide sequencing. In the 25 isolates included in the study, different RE patterns were found: two with BamHI (one of them identical to the one of the reference strain), two with Hind III (both different from the one of the reference strain) and one with Eco RI (different from the one of the reference strain). The plaque size was homogeneous between the isolates, and 1.64 and 2.88 times larger than that of the reference strain. Three base substitutions in the gG gene were found at positions 904, 1103 and 1264, which resulted in strains CAT (Australia), AAT (the United States and Brazil), CAG (Argentina) and ACT (Argentina). The RE pattern and the nucleotide sequence of the gG gene obtained revealed that there are genetically distinguishable EHV-3 strains in circulation. Not only the RE patterns, as previously described, but also the nucleotide sequence of the gG gene, could be useful tools for epidemiological studies. The biological implications of these changes are still unknown. Two sets of experimental infection with EHV-3 were carried out under controlled conditions. In the first experiment, two seronegative mares were topically inoculated in the vagina and perineal area with EHV-3. The same protocol was followed in the second experiment in two seronegative and two seropositive mares (the mares which had been included in the first experiment were used six months later). Clinical samples consisted of swabs from the vagina and perineal area, and blood samples were obtained for virological, serological and haematological studies. A scoring system was designed and used for daily clinical evaluation and rectal temperature records from each mare. Neither hyperthermia nor haematological changes were recorded in the mares analyzed. Typical ECE lesions were observed in seronegative animals: the clinical score was 172 and 90 (average score: 131) for the mares included in the first experiment and 160 and 92 (average score: 124) for the mares included in the second experiment. Only slight lesions were observed in the seropositive mares, being the clinical score 53 and 41 (average score: 47). Also, differences were detected in the duration and intensity of virus shedding, being 15 and 9 days (duration) and 105 versus 104 (the highest virus load detected) in the seropositive and seronegative mares, respectively. In one study designed to demonstrate EHV-3 latency and to study reactivation and re-excretion patterns, virus shedding, seroconversion and the presence of a small ECE lesion were observed in one out of two previously naturally infected mares after corticosteroid treatment. EHV-3 was isolated from perineal vaginal swabs of one of the mares, both on day 14 after corticosteroid treatment and along the following 10 days. A small and rounded area of erosion was observed on the left labia of the vulva of the same mare on day 19 after corticosteroid treatment and 5 days after the virus shedding was detected. A significant (four-fold) increase in the antibody titre was found in the mare which shed the virus 28 days after corticosteroid treatment and 14 days after the beginning of virus re-excretion. In concordance with epidemiological observation and serological studies, and in common with other members of the subfamily Alphaherpesvirinae, this study indicates that a state of latency is established after natural infection of EHV-3. A study was carried out to estimate the prevalence of excretion of EHV-3 under field conditions. The virus was detected in perineal-vaginal swabs by real time PCR and specific antibodies were identified by seroneutralization in 14 (6%) and 105 (48%) respectively of 220 thoroughbred mares without clinical signs at the time of breeding. In order to assess the re-excretion patterns of spontaneous reactivation, two seropositive (presumably latently infected) polo mares were kept in isolation for 11 months. Virological investigations on perineal vaginal swabs obtained on a daily basis revealed re-excretion of EHV-3 on two occasions, 3 months apart (each for a 3-day interval) in one of the mares, and on only 1 day in the other mare. Antibodies against EHV-3 were detected with only slight variation during the entire period in both mares. Clear evidence of the existence of EHV-3 shedders in a healthy mare population under both field and isolation conditions is provided. Furthermore, despite the small number of animals included (only two), the study in mares kept in isolation demonstrated that at least two periods of EHV-3 spontaneous reactivation and re-excretion in the presence of serum antibodies were possible in the same animal in an 11-month interval. In conclusion, EHV-3 infections and ECE are still a threat for the equine industry. In the present study, EHV-3 was found in several field outbreaks of ECE in thoroughbred breeding farms; the disease was reported by the veterinarians as a true sanitary problem and thus demands additional preventive measures. In addition, EHV-3 was detected as a not rare event in clinically healthy mares, which constitutes the most relevant finding from an epidemiological perspective. ECE is also a sanitary problem of concern for embryo transfer and routine veterinary practices. The population of EHV-3 latently infected mares which reach up to 50% at the time of breeding deserves special attention. Reactivation of the latent virus is not preventable and those mares can spontaneously reactivate the virus and become a source of infection for highly valuable horses like « shuttle stallions », with the consequent economically negative impact on the equine enterprises. Finally, there is an important need for finding out additional preventive measures including « pen side » diagnostic tools that allow the detection of subclinically EHV-3 shedding mares in order to segregate them from natural breeding and give them an appropriate antiviral treatment before being covered by stallions.

Orientador: Clarice Weis Arns / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-05T13:06:28Z (GMT). No. of bitstreams: 1 Carvalho_RodrigoFranco_D.pdf: 1262824 bytes, checksum: 9c044e92e7146ea5bb090e025e656061 (MD5) Previous issue date: 2005 / Resumo: O herpesvírus eqüino do tipo 1 (EHV-1) é um membro da subfamília Alfaherpesvirinae, implicado no surgimento de distúrbios respiratórios, reprodutivos e nervosos em cavalos. A principal forma de contaminação dos animais é através do contato direto com secreções contaminadas pelo vírus. No eqüino, a disseminação do vírus ocorre pela transposição da infecção respiratória a outros órgãos e sistemas através da corrente sanguínea. Pouco se sabe sobre a ocorrência do EHV-1 no Brasil. Dessa forma, este estudo teve por objetivo o isolamento do EHV-1 a partir de material biológico e produção e análise de dados moleculares de isolados brasileiros de EHV-1. Durante este estudo, foi realizado o isolamento de uma amostra de EHV-1 a partir da inoculação de material clínico em células de derme eqüina (ED). Este isolado foi diagnosticado como EHV-1 através da reação em cadeia da polimerase (PCR) para o gene da timidina quinase (tk). Neste trabalho, foram também realizados os seqüenciamentos de fragmentos de PCR derivados do isolado aqui descrito, de uma outra amostra brasileira de EHV-1 e de duas amostras estrangeiras do vírus para análise filogenética. A análise comparativa entre seqüências permitiu inferências sobre o nível de divergência entre os vírus estudados, além da listagem de seqüências regulatórias para atividade gênica em um sítio do genoma localizado próximo ao gene tk. Na região genômica reportada foram contextualizadas ao menos três genes (ORF 38, ORF 37 e ORF 36). Os dados levantados com o seqüenciamento de amostras de EHV-1 de origens geográficas distintas (Brasil, Europa e América do Norte) não mostraram divergências, o que pode estar associado a um processo seletivo constritivo, que impediria a fixação de novas mutações naquela região. A ausência de divergências também pode estar associada à importância dessa região na regulação gênica do EHV-1. Também é um indicativo para a fidelidade dos mecanismos de replicação envolvidos na síntese do DNA viral, o que sugere a importância da região estudada na regulação da expressão gênica do EHV-1 / Abstract: Equine Herpesvirus Type 1 (EHV-1) is a member of Alphaherpesvirinae subfamily implicated with abortions, respiratory and neurological disturbs in horses. The principal mode of viral transmission is through close contact virus-containing secretions of infected horses. Systemic pathogenesis in which this virus is implicated combines primary respiratory infection and spread of viral particles through the circulatory/lymphatic system. Until today, there are only few studies involving the isolation of this virus in Brazil. Thus, the main goal of this study was the isolation of EHV-1 from biological material and the production and analysis of molecular data derived from Brazilian EHV-1 isolates. Clinical samples were screened by inoculation into Equine Dermis (ED) cells monolayers, searching for the characteristic citopathic effect produced by EHV-1. Inoculation of one tissue sample has presented a suggestive citopathic effect. Re-inoculation of the original tissue homogenate in a second, independent experiment reproduced the same positive result. Following these observations, infection agent diagnostic was done by PCR for thymidine kinase (tk) gene. The results demonstrated that sample was EHV-1 positive. In this work, it was done either the sequencing of PCR fragments derived from two Brazilian and two foreign samples of EHV-1 for filogenetic and genomic analyses purposes. It was assigned at least three Open Reading Frames contexts (ORF 38, ORF 37, ORF 36). The data do not show genetic variation between sequences. The high level of genetic conservation for this region, despite the distinct geographic origins (Brazil, Europe and North America) of EHV-1 samples studied, indicates a strong selection process against the fixation of new mutations. It also highlights a high level of fidelity for DNA replication and strongly suggests the importance of the studied region for EHV-1 gene regulation / Doutorado / Microbiologia / Doutor em Genetica e Biologia Molecular