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Mellor, P. S., & Hamblin, C. (2004). African horse sickness. Vet Res, 35(4), 445–466.
Abstract: African horse sickness virus (AHSV) causes a non-contagious, infectious insect-borne disease of equids and is endemic in many areas of sub-Saharan Africa and possibly Yemen in the Arabian Peninsula. However, periodically the virus makes excursions beyond its endemic areas and has at times extended as far as India and Pakistan in the east and Spain and Portugal in the west. The vectors are certain species of Culicoides biting midge the most important of which is the Afro-Asiatic species C. imicola. This paper describes the effects that AHSV has on its equid hosts, aspects of its epidemiology, and present and future prospects for control. The distribution of AHSV seems to be governed by a number of factors including the efficiency of control measures, the presence or absence of a long term vertebrate reservoir and, most importantly, the prevalence and seasonal incidence of the major vector which is controlled by climate. However, with the advent of climate-change the major vector, C. imicola, has now significantly extended its range northwards to include much of Portugal, Spain, Italy and Greece and has even been recorded from southern Switzerland. Furthermore, in many of these new locations the insect is present and active throughout the entire year. With the related bluetongue virus, which utilises the same vector species of Culicoides this has, since 1998, precipitated the worst outbreaks of bluetongue disease ever recorded with the virus extending further north in Europe than ever before and apparently becoming endemic in that continent. The prospects for similar changes in the epidemiology and distribution of AHSV are discussed.
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Mellor, P. S. (1993). African horse sickness: transmission and epidemiology. Vet Res, 24(2), 199–212.
Abstract: African horse sickness (AHS) virus causes a non-contagious, infectious, arthropod-borne disease of equines and occasionally of dogs. The virus is widely distributed across sub-Saharan African where it is transmitted between susceptible vertebrate hosts by the vectors. These are usually considered to be species of Culicoides biting midges but mosquitoes and/or ticks may also be involved to a greater or lesser extent. Periodically the virus makes excursions beyond its sub-Saharan enzootic zones but until recently does not appear to have been able to maintain itself outside these areas for more than 2-3 consecutive years at most. This is probably due to a number of factors including the apparent absence of a long term vertebrate reservoir, the prevalence and seasonal incidence of the vectors and the efficiency of control measures (vaccination and vector abatement). The recent AHS epizootics in Iberia and N Africa spanning as they do, 5 or more yr, seem to have established a new pattern in AHS virus persistence. This is probably linked to the continuous presence of adult C imicola in the area. Culicoides imicola is basically an Afro-Asiatic insect and prefers warm climates. Therefore its continuous adult presence in parts of Iberia and N Africa may be due to some recent moderations of the climate in these areas.
Keywords: Africa, Northern/epidemiology; African Horse Sickness/epidemiology/*transmission; African horse sickness virus/*physiology; Animals; Arachnid Vectors/microbiology; Ceratopogonidae/*microbiology; Culicidae/microbiology; Horses; Insect Vectors/*microbiology; Portugal/epidemiology; Spain/epidemiology; Ticks/microbiology
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Labruna, M. B., & Amaku, M. (2006). Rhythm of engorgement and detachment of Anocentor nitens females feeding on horses. Vet Parasitol, 137(3-4), 316–332.
Abstract: The present study evaluated the engorgement and drop-off rhythms of Anocentor nitens females feeding on horses. Drop-off rhythm was evaluated at 6h-intervals (06:00, 12:00, 18:00, and 00:00 h) on horses held in stalls or in a pasture. A new method of marking feeding female ticks (the bowknot technique) was developed to evaluate ticks on horses in pasture that attached to different parts of the horse's body. This technique was highly successful, indicating no significant interference on tick engorgement rate or final tick weight, length and reproductive capability. Horses held in the pasture during the summer produced only 28.2% of the tick detachment during the daylight period from 06:00 to 18:00 h. In contrast, 53.4% of the ticks detached during this same 12 h-period during the winter. This difference was probably related to the longer scotoperiod during the winter. Different drop-off rhythms were observed for females attached to different anatomical parts of the horse's body. For example, ticks attached to the ears, perineum, and tail showed similar drop-off patterns, but were different from ticks attached to mane, rump and other body parts. The idiosoma length of the feeding female ticks was individually measured every 6 h until the engorged female detached naturally. The engorgement rate (increase in millimeters of the body length per hour) was evaluated during the last 96 h of parasitism. The highest engorgement rates were observed during the last 24 h of parasitism (approximately 0.16 mm/h), which were four-fold higher than the engorgement rates of the previous 3 days ( approximately 0.04 mm/h), demonstrating that these lower and higher values corresponded to the slow and rapid feeding phases reported elsewhere. Based on these data, the 6 mm idiosoma length was estimated as the minimal length that would correspond to the time point (i.e. 24 h before detachment) during which ticks would undergo the rapid feeding phase and detach as fully engorged females. When this 6 mm length was tested to estimate the number of engorged females detaching from horses in a period of 24 h, the estimated accuracy varied from 58.5 to 97.7% (mean: 73.3%).
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Boucher, J. M., Hanosset, R., Augot, D., Bart, J. M., Morand, M., Piarroux, R., et al. (2005). Detection of Echinococcus multilocularis in wild boars in France using PCR techniques against larval form. Vet Parasitol, 129(3-4), 259–266.
Abstract: Recently, new data have been collected on the distribution and ecology of Echinococcus multilocularis in European countries. Different ungulates species such as pig, goat, sheep, cattle and horse are known to host incomplete development of larval E. multilocularis. We report a case of E. multilocularis portage in two wild boars from a high endemic area in France (Department of Jura). Histological examination was performed and the DNA was isolated from hepatic lesions then amplified by using three PCR methods in two distinct institutes. Molecular characterisation of PCR products revealed 99% nucleotide sequence homology with the specific sequence of the U1 sn RNA gene of E. multilocularis, 99 and 99.9% nucleotide sequence homology with the specific sequence of the cytochrome oxydase gene of Echinococcus genus and 99.9% nucleotide sequence homology with a genomic DNA sequence of Echinococcus genus for the first and the second wild boar, respectively.
Keywords: Animals; Base Sequence; DNA, Helminth/chemistry/genetics; Echinococcosis/parasitology/pathology/*veterinary; Echinococcus multilocularis/*isolation & purification; Electron Transport Complex IV/chemistry/genetics; France; Histocytochemistry/veterinary; Liver/parasitology/pathology; Male; Molecular Sequence Data; Polymerase Chain Reaction/veterinary; Sequence Alignment; Sus scrofa/*parasitology; Swine Diseases/*parasitology/pathology
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Forbes, A. B. (1993). A review of regional and temporal use of avermectins in cattle and horses worldwide. Vet Parasitol, 48(1-4), 19–28.
Abstract: Ivermectin and abamectin are two members of the group of parasiticides known as the avermectins; ivermectin was first registered as an injectable treatment for cattle in 1981. Since then, abamectin has been registered for cattle and ivermectin for horses. The relative popularity of the avermectins amongst farmers and veterinarians can be attributed to their spectrum of activity, convenience, wide margin of safety and the improved health and performance of stock following their use. Patterns of use in grazing animals apply equally to the avermectins as to other antiparasitics, particularly anthelmintics; these are based on a knowledge of epidemiology integrated with practical management considerations. For cattle, programs are commonly aimed at control of abomasal nematodes of the genera Ostertagia and Haemonchus. Use of avermectins is largely strategic in cattle, treatments being favored at the end of the period of transmission of these parasites; this frequently coincides with housing, entry into a feedlot or movement to another pasture. Simultaneous control of important ectoparasites at this time is an added benefit. Prophylactic use of avermectins at pasture is primarily targeted at the young first season grazing animal. In horses, a bimonthly treatment schedule during the period of risk has proved effective in helping prevent adverse effects of the main target parasites, including large and small strongyles and stomach bots. These patterns of use can be applied to the evaluation of the potential for avermectin residues in feces to have impact on pasture ecology. The evidence presented suggests that any effects are temporally and spatially limited. After more than a decade of practical use, there is no indication that avermectins have had a significant impact on pasture ecology and the environment.
Keywords: Animals; Anthelmintics/therapeutic use; Arthropods; Cattle; Cattle Diseases/drug therapy/*prevention & control; Ectoparasitic Infestations/drug therapy/prevention & control/veterinary; Horse Diseases/drug therapy/*prevention & control; Horses; Insecticides; Ivermectin/*analogs & derivatives/*therapeutic use; Nematode Infections/drug therapy/prevention & control/veterinary; Parasitic Diseases/drug therapy/prevention & control; *Parasitic Diseases, Animal
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Hutchinson, G. W., Abba, S. A., & Mfitilodze, M. W. (1989). Seasonal translation of equine strongyle infective larvae to herbage in tropical Australia. Vet Parasitol, 33(3-4), 251–263.
Abstract: Longevity in faeces, migration to and survival on herbage of mixed strongyle infective larvae (approximately 70% cyathostomes: 30% large strongyles) from experimentally deposited horse faeces was studied in the dry tropical region of North Queensland for up to 2 years. Larvae were recovered from faeces deposited during hot dry weather for a maximum of 12 weeks, up to 32 weeks in cool conditions, but less than 8 weeks in hot wet summer. Translation to herbage was mainly limited to the hot wet season (December-March), except when unseasonal winter rainfall of 40-50 mm per month in July and August allowed some additional migration. Survival on pasture was estimated at 2-4 weeks in the summer wet season and 8-12 weeks in the autumn-winter dry season (April-August). Hot dry spring weather (pre-wet season) was the most unfavourable for larval development, migration and survival. Peak counts of up to 60,000 larvae kg-1 dry herbage were recorded. The seasonal nature of pasture contamination allowed the development of rational anthelmintic control programs based on larval ecology.
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Hurn, S. D., & Turner, A. G. (2006). Ophthalmic examination findings of Thoroughbred racehorses in Australia. Vet Ophthalmol, 9(2), 95–100.
Abstract: OBJECTIVE: To record the prevalence and document the types of eye disease in population of Thoroughbred racehorses in Victoria, Australia. DESIGN: Prospective study. ANIMALS: Two hundred four Thoroughbred racehorses. PROCEDURE: All horses and both eyes were examined at four metropolitan and two country racing stable complexes. Ophthalmic exam was performed following dark adaptation with a transilluminator, biomicroscope, and direct ophthalmoscope. Intraocular pressures were measured when indicated. Both pupils were dilated with tropicamide when indicated. RESULTS: One hundred eighty-two (89.2%) flat-racing and 22 (10.8%) jump-racing (hurdle or steeple) horses were examined. Age range: 2-9 years (mean 3.7 years, median 3); 97 (47.5%) male-neuter, 74 (36. 3%) female, 33 (16.2%) male. Potential vision-threatening eye disease was present in 15 (7.4%) different horses: complete lenticular cataracts 3, posterior lens luxation and cataract 1, large peripapillary 'butterfly' inactive lesions 3, large peripapillary 'butterfly' active lesions 2, peripapillary focal inactive 'bullet hole' chorioretinal lesions (> 20) 5, optic nerve atrophy 1. Non-vision threatening eye disease was present in 117 (57.4%) different horses, involving one or more ocular structures: lower eyelid scars 3; periocular fibropapillomatous disease 1; third eyelid squamous cell carcinoma 1; corneal scars 6; corneal band opacity 2; anterior iris synechia 1; developmental cataracts 36 (17.2%); peripapillary focal inactive 'bullet hole' chorioretinal lesions (< 20) 103 (50.0%); linear peripapillary hyperpigmentation bands 16 (7.9%). Unusual variations of normal ocular anatomy and colobomata was recorded in 11 (5.4%) different horses: granular iridica hypoplasia 3, granular iridica hyperplasia 2, multilobular granular iridica cyst 1, microcornea 1, hyaloid remnant 1, rotated optic nerve head 1, coloboma of the lens 1, atypical coloboma of the retina 1. CONCLUSIONS: This survey demonstrates that the prevalence of vision-threatening eye disease in racing horses may be greater than previously perceived, and highlights the importance of ocular examination within any routine physical examination of horses.
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Ben-Shlomo, G., Plummer, C., Barrie, K., & Brooks, D. (2012). Characterization of the normal dark adaptation curve of the horse. Veterinary Ophthalmology, 15(1), 42–45.
Abstract: Objective The goal of this work is to study the dark adaptation curve of the normal horse electroretinogram (ERG). Procedures The electroretinographic responses were recorded from six healthy female ponies using a contact lens electrode and a mini-Ganzfeld electroretinographic unit. The horses were sedated intravenously with detomidine, an auriculopalpebral nerve block was then performed, and the pupil was fully dilated. The ERG was recorded in response to a low intensity light stimulus (30 mcd.s/m2) that was given at times (T) T = 5, 10, 15, 20, 25, 30, 40, 50, and 60 min of dark adaptation. Off-line analysis of the ERG was then performed. Results Mean b-wave amplitude of the full-field ERG increased continuously from 5 to 25 min of dark adaptation. The b-wave amplitude peaked at T = 25, however, there was no statistical significance between T = 20 and T = 25. The b-wave amplitude then remained elevated with no significant changes until the end of the study at T = 60 (P > 0.49). The b-wave implicit time increased continuously between T = 5 and T = 20, then gradually decreased until T = 60. No distinct a-wave was observed during the testing time. Conclusions Evaluation of horse rod function or combined rod/cone function by means of full-field ERG should be performed after a minimum 20 min of dark adaptation.
Keywords: adaptation; curve; dark; electroretinography; equine; scotopic
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Muscatello, G., Gilkerson, J. R., & Browning, G. F. (2007). Comparison of two selective media for the recovery, isolation, enumeration and differentiation of Rhodococcus equi. Vet Microbiol, 119(2-4), 324–329.
Abstract: The use of selective media to facilitate the isolation of Rhodococcus equi from environmental and clinical samples has aided studies of the ecology of R. equi and the epidemiology of disease caused by R. equi. Here, we compared the efficacy of two selective media (NANAT and modified CAZ-NB) for the recovery of six defined strains of R. equi and for the isolation and enumeration of both avirulent and virulent R. equi from 60 paired soil samples from horse farms using colony blotting and DNA hybridisation. No difference was found between the two media in the recoverability of defined strains of R. equi or the proportion of soil cultures positive for R. equi or virulent R. equi. NANAT medium was significantly less inhibitory of bacterial growth from soil culture compared to mCAZ-NB (P = 0.001), but there was no difference between the media in the number of R. equi colonies recovered. Soil cultured on mCAZ-NB medium yielded a significantly greater number of virulent R. equi colonies than NANAT (P = 0.03). The proportion of R. equi that were virulent in soil cultures on mCAZ-NB (32%) was more than three times that seen in cultures on NANAT (9%). Thus modified CAZ-NB appeared to be a better selective media for studies where the optimal recovery of virulent R. equi is required, such as in studies of the gastrointestinal carriage of virulent R. equi and of subclinically infected foals.
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Hughes, K. L., & Sulaiman, I. (1987). The ecology of Rhodococcus equi and physicochemical influences on growth. Vet Microbiol, 14(3), 241–250.
Abstract: Growth of Rhodococcus equi was studied in vitro. Optimal growth occurred under aerobic conditions between pH 7.0 and 8.5, at 30 degrees C. R. equi survived better in a neutral soil (pH 7.3) than it did in two acid soils (pH less than 5.5). It grew substantially better in soils enriched with faeces than in soils alone. Simple organic acids in horse dung, especially acetate and propionate, appear to be important in supporting growth of R. equi in the environment. The ecology of R. equi can be best explained by an environmental cycle allowing its proliferation in dung, influenced by management, grazing behaviour and prevailing climatic conditions. Preventive measures should be aimed at reducing or avoiding focal areas of faecal contamination in the environment.
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