THE COMPARATIVE SENSITIVITY OF SHEEP AND CHICKEN EMBRYOS TO BLUETONGUE VIRUS AND OBSERVATIONS ON VIRAEMIA IN EXPERIMENTALLY INFECTED SHEEP

The virus titre in sheep blood samples received from BT-suspected cases in the field was assayed in sheep and in chicken embryos. These infected blood samples represented 3 different BT virus types: 4, 10 and 16. Three identical experiments were performed, one with each of the 3 different virus types. Ten-fold dilutions of the infected blood samples were prepared and 1 ml of each blood dilution was inoculated IV into series of 10 to 12-month old susceptible sheep; at the same time 0.1 ml of each dilution was inoculated IV into series of 10 to 13-day-old chicken embryos. The virus titre was found to be similar when assayed in the two host systems. There was no correlation between the amount of virus inoculated and the severity of symptoms in the inoculated sheep. The virus content in daily blood samples collected from the experimental sheep was assayed by IV inoculation of CE. Virus was isolated from all the reacting sheep and was detected sometimes as early as 1 day PI and as late as 30 days PI. A high titre of log10 4.0 to 7.0 per 1 ml of blood was recorded during several consecutive days before and after the onset of clinical signs. There seemed to be an inverse ratio between the amount of virus inoculated and the number of days the virus persisted in the bloodstream. The neutralisation index in day 22 serum samples was 3.5 to 4.5. Virus was isolated from some of the reacting sheep on the day that these antibody levels were recorded. Since the comparative simultaneous titrations of BT virus in sheep and in CE yielded similar results, the IV inoculation of CE is advocated as the routine method to be employed for laboratory diagnosis of this disease.     

CLINICO-PATHOLOGICAL EFFECT OF BLUETONGUE VIRUS SEROTYPE 20 IN SHEEP

Fifty-four Merino crossbred sheep were inoculated with bluetongue virus serotype 20 (BTV-20) by the intravenous, subcutaneous and intradermal routes. BTV-20 was successfully transmitted by Culicoides (Avaritia) spp. No. 5 to two additional sheep. Clinical and pathological effects were studied. In the artificially infected sheep, clinical signs were observed after an incubation period of 6 to 10 days and consisted of pyrexia, oral and subcutaneous hyperaemia mild oedema of the ears, face and lips, and coronitis. The major internal pathological changes were petechial and ecchymotic haemorrhages in the tunica media of the pulmonary artery near its junction with the heart and mild haemorrhage and mild oedema in the intestines, coronet, lips, cheeks and ears. Viraemia was detected between day 2 and day 14 post inoculation. The two sheep infected by insect transmission were mildly affected and became viraemic between 16 and 19 days after transmission. No deaths occurred and under experimental conditions BTV-20 caused only mild disease in housed sheep. To date there has been no reported outbreak of natural bluetongue infection in Australia. Compared to other serotypes BTV-20 appears to be of low pathogenicity in sheep.     

TRANSMISSION OF A MUCOSAL DISEASE VIRUS INFECTION BETWEEN SHEEP

The transmission of mucosal disease virus (MDV) from infected ewes and their lambs to susceptible sheep was investigated. MDV was recovered from the amniotic fluid of an infected pregnant ewe and from the blood, nasal swabs and urine of hairy lambs. MDV infection was transmitted either at lambing, from infective foetal fluids or lambs, or later as a result of contact with a surviving with a hairy lamb and either aborted or gave birth to an infected hairy lamb. Adult sheep and 12-months-old sheep were less readily infected than were newborn lambs. Pregnant ewes were infected by contact with a hairy lamb and either aborted or gave birth to an infected hairy lamb. A method to minimise spread of the infection in the field is suggested.     

THE SEROLOGICAL RESPONSE OF CHICKENS TO AUSTRALIAN LENTOGENIC STRAINS OF NEWCASTLE DISEASE VIRUS

SUMMARY: Australian lentogenic Newcastle disease viruses were evaluated as uninactivated vaccines in Australian chickens, the response being evaluated by the production of haemagglutination-inhibition (HI) antibodies. Two viruses, V4 and PM9, induced high levels of antibody and were readily transmissible between chickens by contact exposure. Three other viruses were poorly immunogenic and poorly transmissible. Chickens vaccinated intramuscularly with the V4 strain produced higher HI antibody titres than chickens vaccinated by the orotracheal, intranasal and intraocular routes. HI antibody titres in chickens vaccinated with the V4 strain reached peak levels 3 to 5 weeks after vaccination and waned considerably during the next 2 to 4 weeks. However, low levels of HI antibody persisted for at least 36 weeks after vaccination. Intramuscular vaccination with the V4 strain of one-day-old chicks lacking maternal antibody to Newcastle disease virus resulted in 42–70% mortality and the survivors developed very high titres of HI antibody. Similar chickens inoculated orotracheally showed signs of depression and developed high titres of HI antibody, but there were no mortalities. Chickens 1-, 2-, 3- and 4-weeks-old and lacking maternally derived HI antibody to Newcastle disease virus suffered no adverse reaction to intramuscular or orotracheal vaccination. The antibody response of the 1-week-old chickens was considerably poorer than that of the older chickens. Following orotracheal vaccination with the V4 strain, chickens with low levels of maternally derived antibody responded with low levels of HI antibody. On the other hand, in the progeny of hens hyperimmunised with the V4 strain the production of active antibody following orotracheal vaccination was delayed until the level of passive antibody had declined considerably. There was no response to intramuscular vaccination in congenitally hyperimmune chickens. The minimum HI antibody inducing dose of V4 vaccine, when measured 3 weeks after vaccination of 6-weeks-old chickens, was 10^5.6 50% egg infectious doses.     

TRANSMISSION OF FUSIFORMIS NODOSUS INFECTION FROM CATTLE TO SHEEP

Three of twelve experimental sheep developed benign foot-rot after grazing for three months with a steer infected with Fusiformis nodosus. F. nodosus was isolated from the steer, and it had a similar protcolytic index to strains isolated from benign foot-rot in sheep. Histological changes in the interdigital skin of the infected steer and sheep were similar. In both species F. nodosus, F. necrophorus and spirochaetes had invaded the epidermis. Chronic inflammation and hyperkeratosis were associated with this invasion. The relevance of these findings to ovine foot-rot eradication campaigns on properties where sheep graze with cattle is discussed.     

THE OVIPOSITIONAL RESPONSE OF THE AUSTRALIAN SHEEP BLOWFLY, LUCILIA CUPRINA, TO FLEECE-ROT ODOURS

SUMMARY The ovipositional response of Lucilia cuprina flies to odours emanating from fleece-rot lesions of greasy wool in which Pseudomonas aeruginosa bacteria proliferated, was studied. Fractionation of the fleece-rot odours was carried out by bubbling the volatile components through hydrochloric acid and sodium hydroxide solutions to remove basic odours and acidic odours respectively. It was found that the acidic/neutral odours of fleecerot wool, when perfused into wet, greasy wool, stimulated L. cuprina to oviposit. On the other hand, the basic/neutral odours of fleece-rot wool were virtually unattractive to the gravid fly. Similarly, the acidic/neutral odours emanating from fleece-rot lesions of clean wool from which the non-fibre components, wax, suint and epithelial debris, had been removed by scouring, were found to be unattractive to the gravid fly in choice tests.     

蓝舌病病毒内蒙古分离株的特性研究

蓝舌病病毒内蒙古株是继云南株、四川株之后,从隐性感染的山羊血液中分离获得的目前在中国唯一一株接近于蓝舌病毒血清17型的毒株.将他与云南毒株和美国17型毒株进行比较,发现其血清学反应群特异性完全相同;中和试验表明与云南毒株之间无交叉保护反应,与美国17型毒株有交叉保护反应,但中和不彻底;电镜下其形态与云南、美国毒株完全一致;核酸电泳分析,具有4组10基因片段,带型为3:3:3:1,第7、8、9片段不融合,与云南、美国毒株基本一致,但1、2、3组中迁移率有差异;人工接种绵羊、山羊、鸡胚,其病理变化和临床反应与云南、美国毒株比较有较大差异.