Islam A F M F, Wong C W, Walkden-Brown S W, Colditz I G, Arzey K E, Groves P J
Animal Science, School of Rural Science and Agriculture, University of New England, Armidale, NSW 2351 Australia.
Avian Pathol. 2002 Oct;31(5):449-61. doi: 10.1080/0307945021000005824.
Much of the impact of Marek's disease in broiler chickens is considered to be due to immunosuppression induced by Marek's disease virus (MDV). The present study evaluates the effects of an Australian isolate of pathogenic MDV (strain MPF 57) and a non-pathogenic vaccinal strain of herpesvirus of turkeys (HVT) (strain FC 126) on the immune system of commercial broiler chickens for 35 days following challenge at days 0 or 3 of age. It also investigates the extent of protection provided by HVT vaccine against MDV-induced immunosuppression. Immune system variables, including relative lymphoid organ weight, blood lymphocyte phenotype (CD45+/CD3+, putatively T, and CD45+/LC+, putatively B) and antibody production following vaccination against infectious bronchitis (IB) at hatch, were used to assess the immune status of chickens. Immunosuppression was also assessed by susceptibility to secondary challenge with pathogenic Escherichia coli on day 29 post-MDV challenge. MDV infection reduced the weight of the thymus and bursa of Fabricius, the numbers of circulating T lymphocytes and B lymphocytes, and IB antibody titre. The timing of these effects varied. MDV infection greatly increased susceptibility to E. coli infection. HVT alone caused mild depletion of T and B lymphocytes but no effect on immune organ weight or IB titre. Vaccination with HVT provided good protection against most of the immunosuppressive effects of MDV but not against MDV-induced growth impairment and reduced responsiveness to IB vaccination, suggesting that recent Australian strains of MDV may be evolving in virulence to overcome the protective effects of HVT.
马立克氏病对肉鸡的许多影响被认为是由马立克氏病病毒（MDV）诱导的免疫抑制所致。本研究评估了一株澳大利亚致病性MDV分离株（MPF 57株）和一株火鸡疱疹病毒（HVT）非致病性疫苗株（FC 126株）在1日龄或3日龄攻毒后35天内对商品肉鸡免疫系统的影响。研究还调查了HVT疫苗对MDV诱导的免疫抑制的保护程度。免疫相关指标，包括相对淋巴器官重量、血液淋巴细胞表型（CD45+/CD3+，假定为T细胞，以及CD45+/LC+，假定为B细胞）和出雏时接种传染性支气管炎（IB）疫苗后的抗体产生情况，被用于评估鸡的免疫状态。还通过MDV攻毒后第29天对致病性大肠杆菌二次攻毒的易感性来评估免疫抑制情况。MDV感染降低了胸腺和法氏囊的重量、循环T淋巴细胞和B淋巴细胞的数量以及IB抗体滴度。这些影响出现的时间各不相同。MDV感染大大增加了对大肠杆菌感染的易感性。单独接种HVT导致T淋巴细胞和B淋巴细胞轻度减少，但对免疫器官重量或IB滴度没有影响。接种HVT可有效抵御MDV的大部分免疫抑制作用，但无法抵御MDV诱导的生长障碍以及对IB疫苗接种反应性的降低，这表明澳大利亚近期的MDV毒株可能在毒力方面发生了演变，从而克服了HVT的保护作用。
