Formalized epidemiological field investigations were conducted to compare and contrast the transmission dynamics of EHV-1 neurological disease among horses stabled at Churchill Downs Racetrack, Louisville, Kentucky and of EHV-1 respiratory illness among horses stabled in the student barn at Murray State University. Differences were assessed by means of statistical and mathematical modeling techniques applied to survey and biological data collected over the course of the respective disease events. Regression methods applied to survey data enabled the construction of a statistical model to predict a date of onset of illness for horses within each equine cohort. Comparisons of the epidemic curves revealed that the Murray State University outbreak was 4.5 times longer (9 weeks versus 14 days) than the Churchill Downs Racetrack event. Survival analysis was used to explore the relationship between time to infection for each equine cohort. Horses stabled in the affected barn at Churchill Downs racetrack had a 3.02 times greater daily risk (p < 0.001) for contracting EHV-1 infection relative to horses stabled in the student barn at Murray State University. Estimates of the basic R0 number, calculated using mathematical formulae that incorporated the duration of the infectious period for neuropathogenic and nonneuropathogenic strains of EHV-1, were 10.25 and 2.94 for the Churchill Downs racetrack and Murray State University outbreaks, respectively. The generation time for the Churchill Downs outbreak was 6.1 times shorter (0.39 days versus 2.38 days) than for the Murray State University event. An assessment of the temporal occurrence of symptomatic infection is similar for each event and suggests that the appearance of clinical illness is constant over the course of an outbreak. A Reed-Frost model was constructed for each EHV-1 event where values of the transmission parameters (q, p and k) were estimated by fitting a model that most closely matched the observed profile of EHV-1 cases. The value of prophylactic vaccination on the spread of EHV-1 was assessed by making adjustments to these fitted models for varying levels of herd immunity. The results indicate that the prevention of EHV-1 neurological illness requires a higher level of herd immunity than EHV-1 respiratory illness.

Equine Herpesvirus type 1 (EHV-1) is a worldwide threat to the health of horses. It can cause mild respiratory disease, abortions and deaths of newborn foals as well as a potentially fatal neurologic disorder known as Equine Herpesvirus Myeloencephalopathy (EHM). The virus is maintained in populations by stress-induced periodic reactivation of virus in long-term latently infected horses and transmission of the reactivated virus to susceptible individuals. In horses, peripheral blood leukocytes (PBLs) are thought to be an important site for EHV-1 latent genomes. Since the Unfolded Protein Response (UPR) is a cellular response to a variety of stressors that has been linked to reactivation of herpes simplex virus in humans, a virus closely related to EHV-1, I tested the hypothesis that latent EHV-1 relies on the UPR as a pluripotent stress sensor and uses it to reactivate lytic gene expression. Since little work has been done in defining the UPR in horses, I first successfully developed a quantitative real-time polymerase chain reaction (RT-qPCR) assay to detect and quantitate transcripts for selected UPR genes in equine dermal (E.Derm) cells and PBLs. Activation of the UPR was achieved in both cell types using thapsigargin and a difference in gene expression after activation of the UPR in two equine cell types was found. A nested PCR assay to detect and distinguish latent EHV-1 and EHV-4 was evaluated and the sensitivity of the technique to detect EHV-1 was determined. I discovered that the nested PCR technique was not sensitive enough to detect the estimated one latent viral genome in 50,000 PBLs. Lytic EHV-1 infection was characterized by single step growth curve in E.Derm cells and consistent detection of temporal EHV-1 gene expression by RT-qPCR was achieved. The relationship between EHV-1 gene expression and UPR gene expression during lytic infection was investigated. While EHV-1 infection had no effect on UPR gene expression, activation of the UPR appeared to decrease the expression of EHV-1 genes temporarily and reversibly during the first 4 h after infection. Finally, detection of EHV-1 in PBLs from horses presumed to be latently infected by co-cultivation with E. Derm cells permissive to EHV-1 infection was attempted. To detect viral DNA, PBLs were stimulated with thapsigargin or interleukin 2 (IL-2) which was previously reported to induce reactivation of latent EHV-1. I was not able to reproduce previously published experiments of reactivation in vitro of latent EHV-1 by stimulation with IL-2, and virus reactivation did not occur after stimulation of PBLs with thapsigargin. In summary, a RT-qPCR assay to measure the expression of equine UPR genes was developed and activation of the UPR by treatment of E.Derm cells and PBLs with thapsigargin was successfully achieved. A difference in gene expression after activation of the UPR in two equine cell types was found. In contrast to what has been reported for other alphaherpesviruses, there appears to be no, or only little, interaction between the UPR and EHV-1 during viral infection. Detection of latent EHV-1 genomes in PBLs was not achieved by using a nested PCR, as this technique was not sensitive enough to detect the estimated one latent viral genome in 50,000 PBLs. Finally, latent EHV-1 was not detected in presumed latently infected PBLs or reactivated by triggering the UPR in equine PBLs.

Equine herpesvirus-1 (EHV-1) can cause acute upper respiratory tract disease, abortion, neonatal death and neurological disease in horses. Rapid, accurate and timely diagnosis of EHV-1 infection in horses is important to curtail the spread of this pathogen. It has been reported that the neuropathogenic phenotype of EHV-1 can result from a single non-synonymous nucleotide substitution at position 2254 (A→G2254) in open reading frame 30 (ORF30). This was the basis for the development of an allelic discrimination, real-time PCR assay to distinguish between potential neuropathogenic and non-neuropathogenic EHV-1 strains. However, PCR analysis of a panel of EHV-1 abortion isolates revealed that other point mutations within ORF30 could produce false negative results with this previously described assay. Therefore, one of the objectives of this dissertation project was to develop a more sensitive and specific allelic discrimination real-time PCR assay for the detection of EHV-1. This was achieved by redesigning the primers and probes targeting ORF30. The new assay was ten times more sensitive than the original assay, with a lower detection limit of 10 infectious virus particles. While mutations within EHV-1’s genome can hinder diagnosis, they can also impact the virulence of the virus. Objective two, therefore, was to determine if sequential cell passage of T953 would induce sufficient attenuation of the EHV-1 genome to produce a low virulence phenotype. Two separate groups of 28 BALB/c mice were inoculated with either the parental strain or passage 135 (T953 P135) of EHV-1 strain T953. The animals were observed for fourteen days, euthanized and their tissues analyzed for the presence of EHV-1. At the conclusion of the fourteen day observation period, all of the mice infected with T953 P135 survived and regained their pre-inoculation body condition. Furthermore, there were significant differences in virus titer and viral DNA concentrations between T953 P135 and the parental strain, further confirming the attenuated phenotype of the virus. Taken together, data from this study clearly demonstrates that sequential cell culture passage of the neuropathogenic T953 strain of EHV-1 results in attenuation for young adult BALB/C mice.

Este trabalho teve por objetivo avaliar as alterações respiratórias e neurológicas resultantes da infecção por via intranasal das diferentes estirpes nacionais do herpesvírus equino tipo 1 (EHV-1) em hamsters comparando sua susceptibilidade com estudos sobre infecção do EHV-1 em camundongos e equinos. Para isso, hamsters sírios machos, três semanas de idade, foram infectados por via intranasal com as estirpes do EHV-1 obtidas a partir de fetos abortados e potro neonato infectados (A4/72, A9/92, A3/97 e Iso/72). Os animais foram pesados e examinados diariamente em busca de sinais clínicos e neurológicos. Conforme os sintomas neurológicos apareceram, grupos de cinco hamsters foram eutanasiados por overdose de isoflurano na primeira etapa do projeto, e, de cetamina/xilazina por via intraperitoneal na segunda etapa. Na necropsia, sistema nervoso central (SNC), pulmão, fígado, baço e timo foram coletados para isolamento viral em cultura de células E-dermal e para análise histopatológica. Na segunda etapa do projeto, a lavagem broncoalveolar (LBA) com 3 ml de PBS por hamsters foi realizada para determinar a resposta inflamatória pulmonar através da contagem total e diferencial de leucócitos. Similar aos experimentos com camundongos, hamsters desafiados com as estirpes virais A4/72 e A9/92 apresentaram manifestações clínicas severas no terceiro dia pós-inoculação (dpi), tais como perda de peso aguda, dispnéia, desidratação, decúbito e morte. Observou-se também sinais neurológicos como hiperexcitabilidade, paralisia, espasmos, perda de propriocepção, andar em círculos e convulsões. Ao contrário dos camundongos, que não desenvolveram a doença; hamsters inoculados com as estirpes virais A3/97 e Iso/72 manifestaram sintomas respiratórios e neurológicos agudos entre quarto e quinto dpi, sendo as alterações respiratórias as mais evidentes, principalmente hemoptise e conjuntivite. O isolamento do vírus a partir do SNC foi positivo em todos os animais infectados; no entanto, todas as amostras de pulmões foram positivas apenas nos grupos infectado pelas estirpes virais A9/92 e A4/72. Todas as estirpes do EHV-1 foram isoladas a partir do baço, no entanto, a partir do timo foram isoladas apenas as estirpes A9/92 e A4/72, e, de fígado somente a estirpe viral Iso/72 não foi isolada. No LBA, a contagem total de leucócitos não demonstrou diferenças de valores significativas entre os grupos experimentais, sendo apenas evidente a presença de eritrócitos, macrófagos e neutrófilos na maioria dos esfregaços dos hamsters infectados. Porém, na contagem diferencial de leucócitos observou-se um aumento significativo de neutrófilo com consequente diminuição significativa de macrófagos nos hamsters infectados pelas estirpes virais A3/97, Iso/72 e A4/72 quando comparados ao grupo controle. Os hamsters infectados pela estirpe viral A9/92 mantiveram valores próximos aos do grupo controle. Ao avaliar microscopicamente o SNC, fígado e pulmão dos hamsters infectados foi observado infiltrado inflamatório, necrose e manguito perivascular em SNC; leucocitose e necrose no parênquima hepático com discreta pericolangite e proliferação de ducto biliar; e em pulmão observou inflamação, necrose, edema e hemorragia em bronquíolos e alvéolos. Concluindo, os resultados apontaram o hamster como a espécie mais susceptível à infecção pelo EHV-1 servindo como um modelo experimental complementar para estudos de doenças respiratória e neurológica provocadas por este agente em equinos / This study aimed to evaluate the respiratory and neurological disorders resulting from intranasal infection with different national strains of equine herpesvirus type 1 (EHV-1) in hamsters comparing their susceptibility to studies about EHV-1 infection in mice and horses. Therefore, male Syrian hamsters, three weeks of age, were infected via intransal with EHV-1 strains obtained from aborted fetuses and neonatal foal infected (A4/72, A9/92, A3/97 and Iso/72). The animals were weighed and examined daily for clinical search and neurological signs. As neurological symptoms appeared five hamsters groups were euthanized by isoflurane overdose in the first stage of the project, and ketamine/xylazine via intraperitoneal in the second stage. At necropsy, central nervous system (CNS), lung, liver, spleen and thymus were collected for virus isolation in E-dermal cell culture and histopathological analysis. In the second stage of the project, bronchoalveolar lavage (BAL) with 3 ml of PBS per hamsters was performed to determine the pulmonary inflammatory response through the total and differential leukocyte count. Similar to the experiments with mice, hamsters challenged with viral strains A4/72 and A9/92 had severe clinical manifestations in the third day post-inoculation (dpi), such as acute weight loss, dyspnea, dehydration, recumbency, and death. It was also observed neurological signs such as hyperexcitability, paralysis, spasms, loss of proprioception, circling and convulsions. Unlike mice, which did not develop disease; hamsters inoculated with viral strains A3/97 and Iso/72 showed acute respiratory and neurological symptoms between fourth and fifth dpi, and the most evident respiratory distress was hemoptysis and conjunctivitis. The virus isolation from CNS was positive in all infected animals; however, all lung samples were positive only in groups infected by A9/92 and A4/72 viral strains. All EHV-1 strains were recovered from spleen, however, only A9/92 and A4/72 viral strains were recovered from thymus, but only Iso/72 viral strain was not recovered from liver. BAL total leukocyte count showed no significant differences in values between the experimental groups but the presence of erythrocytes, macrophages and neutrophils were evident in most smears of infected hamsters. However, in the leukocyte differential count it was observed a significant increase in neutrophils with consequent significant reduction of macrophages in hamsters infected by viral strains A3/97, Iso/72 and A9/92 when compared with the control group. Hamsters infected with the A9/92 viral strain maintained values similar to the control group. When evaluating microscopically the CNS, liver and lungs of infected hamsters it was observed inflammatory infiltrate, necrosis and perivascular cuff in CNS; leukocytosis and necrosis in the liver parenchyma with discrete pericholangitis and bile duct proliferation; and inflammation, necrosis, edema and hemorrhage in the bronchioles and alveoli. Concluding, the results showed the hamster as the most susceptible species to EHV-1 infection serving as a complementary experimental model for studies of respiratory and neurological diseases caused by this agent in horses

Este trabalho teve por objetivo avaliar as alterações respiratórias e neurológicas resultantes da infecção por via intranasal das diferentes estirpes nacionais do herpesvírus equino tipo 1 (EHV-1) em hamsters comparando sua susceptibilidade com estudos sobre infecção do EHV-1 em camundongos e equinos. Para isso, hamsters sírios machos, três semanas de idade, foram infectados por via intranasal com as estirpes do EHV-1 obtidas a partir de fetos abortados e potro neonato infectados (A4/72, A9/92, A3/97 e Iso/72). Os animais foram pesados e examinados diariamente em busca de sinais clínicos e neurológicos. Conforme os sintomas neurológicos apareceram, grupos de cinco hamsters foram eutanasiados por overdose de isoflurano na primeira etapa do projeto, e, de cetamina/xilazina por via intraperitoneal na segunda etapa. Na necropsia, sistema nervoso central (SNC), pulmão, fígado, baço e timo foram coletados para isolamento viral em cultura de células E-dermal e para análise histopatológica. Na segunda etapa do projeto, a lavagem broncoalveolar (LBA) com 3 ml de PBS por hamsters foi realizada para determinar a resposta inflamatória pulmonar através da contagem total e diferencial de leucócitos. Similar aos experimentos com camundongos, hamsters desafiados com as estirpes virais A4/72 e A9/92 apresentaram manifestações clínicas severas no terceiro dia pós-inoculação (dpi), tais como perda de peso aguda, dispnéia, desidratação, decúbito e morte. Observou-se também sinais neurológicos como hiperexcitabilidade, paralisia, espasmos, perda de propriocepção, andar em círculos e convulsões. Ao contrário dos camundongos, que não desenvolveram a doença; hamsters inoculados com as estirpes virais A3/97 e Iso/72 manifestaram sintomas respiratórios e neurológicos agudos entre quarto e quinto dpi, sendo as alterações respiratórias as mais evidentes, principalmente hemoptise e conjuntivite. O isolamento do vírus a partir do SNC foi positivo em todos os animais infectados; no entanto, todas as amostras de pulmões foram positivas apenas nos grupos infectado pelas estirpes virais A9/92 e A4/72. Todas as estirpes do EHV-1 foram isoladas a partir do baço, no entanto, a partir do timo foram isoladas apenas as estirpes A9/92 e A4/72, e, de fígado somente a estirpe viral Iso/72 não foi isolada. No LBA, a contagem total de leucócitos não demonstrou diferenças de valores significativas entre os grupos experimentais, sendo apenas evidente a presença de eritrócitos, macrófagos e neutrófilos na maioria dos esfregaços dos hamsters infectados. Porém, na contagem diferencial de leucócitos observou-se um aumento significativo de neutrófilo com consequente diminuição significativa de macrófagos nos hamsters infectados pelas estirpes virais A3/97, Iso/72 e A4/72 quando comparados ao grupo controle. Os hamsters infectados pela estirpe viral A9/92 mantiveram valores próximos aos do grupo controle. Ao avaliar microscopicamente o SNC, fígado e pulmão dos hamsters infectados foi observado infiltrado inflamatório, necrose e manguito perivascular em SNC; leucocitose e necrose no parênquima hepático com discreta pericolangite e proliferação de ducto biliar; e em pulmão observou inflamação, necrose, edema e hemorragia em bronquíolos e alvéolos. Concluindo, os resultados apontaram o hamster como a espécie mais susceptível à infecção pelo EHV-1 servindo como um modelo experimental complementar para estudos de doenças respiratória e neurológica provocadas por este agente em equinos / This study aimed to evaluate the respiratory and neurological disorders resulting from intranasal infection with different national strains of equine herpesvirus type 1 (EHV-1) in hamsters comparing their susceptibility to studies about EHV-1 infection in mice and horses. Therefore, male Syrian hamsters, three weeks of age, were infected via intransal with EHV-1 strains obtained from aborted fetuses and neonatal foal infected (A4/72, A9/92, A3/97 and Iso/72). The animals were weighed and examined daily for clinical search and neurological signs. As neurological symptoms appeared five hamsters groups were euthanized by isoflurane overdose in the first stage of the project, and ketamine/xylazine via intraperitoneal in the second stage. At necropsy, central nervous system (CNS), lung, liver, spleen and thymus were collected for virus isolation in E-dermal cell culture and histopathological analysis. In the second stage of the project, bronchoalveolar lavage (BAL) with 3 ml of PBS per hamsters was performed to determine the pulmonary inflammatory response through the total and differential leukocyte count. Similar to the experiments with mice, hamsters challenged with viral strains A4/72 and A9/92 had severe clinical manifestations in the third day post-inoculation (dpi), such as acute weight loss, dyspnea, dehydration, recumbency, and death. It was also observed neurological signs such as hyperexcitability, paralysis, spasms, loss of proprioception, circling and convulsions. Unlike mice, which did not develop disease; hamsters inoculated with viral strains A3/97 and Iso/72 showed acute respiratory and neurological symptoms between fourth and fifth dpi, and the most evident respiratory distress was hemoptysis and conjunctivitis. The virus isolation from CNS was positive in all infected animals; however, all lung samples were positive only in groups infected by A9/92 and A4/72 viral strains. All EHV-1 strains were recovered from spleen, however, only A9/92 and A4/72 viral strains were recovered from thymus, but only Iso/72 viral strain was not recovered from liver. BAL total leukocyte count showed no significant differences in values between the experimental groups but the presence of erythrocytes, macrophages and neutrophils were evident in most smears of infected hamsters. However, in the leukocyte differential count it was observed a significant increase in neutrophils with consequent significant reduction of macrophages in hamsters infected by viral strains A3/97, Iso/72 and A9/92 when compared with the control group. Hamsters infected with the A9/92 viral strain maintained values similar to the control group. When evaluating microscopically the CNS, liver and lungs of infected hamsters it was observed inflammatory infiltrate, necrosis and perivascular cuff in CNS; leukocytosis and necrosis in the liver parenchyma with discrete pericholangitis and bile duct proliferation; and inflammation, necrosis, edema and hemorrhage in the bronchioles and alveoli. Concluding, the results showed the hamster as the most susceptible species to EHV-1 infection serving as a complementary experimental model for studies of respiratory and neurological diseases caused by this agent in horses

Equine herpesvirus type-1(EHV-1) is a complex virus known for inducing various forms of disease in horses. In recent years, the number of cases of neurological disease caused by this virus has increased. While there are a number of possible sources for this recent surge, this project set out to determine if a genotypic shift in the latent population of the virus in favor of the neuropathogenic form of EHV-1 is the basis for the recent increase in frequency of EHV-1 neurologic disease. To ascertain if such a shift has in fact occurred, 450 EHV-1 isolates were obtained from fetal tissues resulting from single, sporadic cases of abortion in Thoroughbred broodmares in central Kentucky. Furthermore, the isolates utilized were from different decades (1951-2006) to determine if the genotypic shift was time-related. The isolates were propagated in cell culture, purified and the viral DNA isolated. Real-time allelic discrimination PCR analysis was performed on the DNA samples to identify the genotype of EHV-1. Statistical analysis of the PCR data indicates that the latent mutant population does appear to be increasing. Therefore, the recent increase in the number of outbreaks of EHV-1 neurological disease will most likely continue unless measures are devised to curtail further spread of the pathogen.