Dunn John R, Witter Richard L, Silva Robert F, Lee Lucy F, Finlay James, Marker Bryan A, Kaneene John B, Fulton Richard M, Fitzgerald Scott D
USDA, Agricultural Research Service, Avian Disease and Oncology Laboratory, East Lansing, MI 48823, USA.
Avian Dis. 2010 Sep;54(3):1038-49. doi: 10.1637/9348-033010-Reg.1.
Marek's disease virus (MDV) is ubiquitous within commercial poultry flocks because current vaccines do not prevent MDV infection or transmission. In order for newly-evolved MDV strains to become established within a flock, it seems inevitable that any new strain would need to infect and replicate in chickens previously infected with resident MDV strains. This phenomenon is difficult to detect and there is no clear evidence that it is even possible. Four experiments were performed to demonstrate superinfection and evaluate the effect of time between challenges on the effect of superinfection with the use of two pairs of fully virulent MDV strains that could be discriminated by novel technology: 1) JM/102W and rMd5//38CVI, and 2) rMd5 and rMd5//38CVI. Feather follicle epithelium (FFE), spleen, and tumor samples were collected at single or multiple time points from the same bird to determine the frequency and distribution of each virus present following superinfection, with the use of pyrosequencing and immunohistochemistry. Superinfection was observed in 82 of 149 (55%) FFE samples following short-interval challenge (24 hr) compared to only 6 of 121 (5%) samples following long-interval challenge (13 days), indicating a strong influence of challenge interval. In cases where the first inoculated virus was weak or delayed, the second inoculated virus was detected in 42 of 95 (44%) birds. In tumors from dually challenged birds, the second virus was again present much more often following short-interval challenge (68%) compared to long-interval challenge (11%). Virus mixtures in tumors were less common compared to those in FFE samples. Vaccination with turkey herpesvirus had no significant effect on the virus frequency for either virus pair or challenge time interval, suggesting these conclusions may be applicable to vaccinated chickens in the field. These studies demonstrated superinfection for the first time with two fully virulent MDV strains and suggest that short-interval challenge exposure and/or weak initial exposures may be important factors leading to superinfection--a prerequisite for the establishment of a second virus strain in the population. This model system should be useful to elucidate this important phenomenon further.
马立克氏病病毒（MDV）在商业家禽群中普遍存在，因为目前的疫苗无法预防MDV感染或传播。为了使新进化的MDV毒株在鸡群中立足，任何新毒株似乎都不可避免地需要在先前感染了常驻MDV毒株的鸡体内感染并复制。这种现象很难检测到，而且甚至没有明确证据表明它是可能的。进行了四项实验来证明超感染，并评估两次攻毒之间的时间间隔对超感染效果的影响，使用了两对可通过新技术区分的完全毒力的MDV毒株：1）JM/102W和rMd5//38CVI，以及2）rMd5和rMd5//38CVI。在同一鸡只的单个或多个时间点采集羽毛滤泡上皮（FFE）、脾脏和肿瘤样本，通过焦磷酸测序和免疫组织化学来确定超感染后每种病毒的频率和分布。短间隔攻毒（24小时）后，149个FFE样本中有82个（55%）观察到超感染，而长间隔攻毒（13天）后，121个样本中只有6个（5%）观察到超感染，表示攻毒间隔有很大影响。在首次接种的病毒较弱或延迟的情况下，95只鸡中有42只（44%）检测到第二次接种的病毒。在双重攻毒鸡的肿瘤中，与长间隔攻毒（11%）相比，短间隔攻毒后第二次病毒出现的频率再次高得多（68%）。与FFE样本相比，肿瘤中的病毒混合物不太常见。用火鸡疱疹病毒接种疫苗对任何一对病毒或攻毒时间间隔的病毒频率均无显著影响，表明这些结论可能适用于田间接种疫苗的鸡。这些研究首次证明了两种完全毒力的MDV毒株的超感染，并表明短间隔攻毒暴露和/或初始暴露较弱可能是导致超感染的重要因素——这是在鸡群中建立第二种病毒毒株的先决条件。这个模型系统应该有助于进一步阐明这一重要现象。
