The continuing spread of a deadly disease that affects the UK's native oak trees is causing concern among tree professionals and conservation groups.

不断蔓延的致死病毒已经使英国本土橡树大面积受到感染，这种病毒已引起专业人士以及环境保护组织的深切关注。

Acute Oak Decline can kill an infected tree in just a few years

Acute Oak Decline (AOD), caused by a bacterial¹ infection, can kill an infected tree in just a few years.

Some tree experts are comparing AOD to Dutch elm disease（荷兰榆树病） , which killed millions of trees throughout the UK during the 1970-80s.

They said extra funds for more research into the disease were urgently needed.

Although AOD has been confirmed in 55 cases, the number of trees displaying symptoms was steadily² increasing, delegates at the Royal Forestry³ Society's (RFS) annual conference were told.

The disease affects the UK's two native species of oak - sessile（无柄的，固着的） and pedunculate（有梗的） . To date, there have been no confirmed cases in other species of oaks found in Britain, such as Turkey and red oaks.

'Extensive bleeding'

Information from Forest Research, the scientific department of the UK Forestry Commission, says the new disease affects oaks more than 50 years old.

Symptoms are "extensive stem bleeding" in which dark fluid seeps⁴（渗出，漏） from small cracks（裂缝，裂纹） in the bark and runs down the tree trunk.

In early stages of the disease, the health of a tree's canopy⁵ does not appear to be affected⁶, but it may become thinner as the tree succumbs⁷ to（屈服于） AOD.

On its website, Forest Research says: "The incidence of AOD in Britain is unquantified at this stage, but estimates put the figure at a few thousand affected trees.

"The condition appears to be most prevalent in the Midlands and investigations⁸ to determine the extent of the disorder⁹ are under way."

A spokesman told BBC News: "Forest Research pathologists（病理学家） have isolated¹⁰ a previously¹¹ unidentified bacterium¹² they believe is highly likely to be playing a key role in the Acute Oak Decline observed in Leicestershire and elsewhere.

"However, the full cause of the condition is thought likely to be complex, involving a number of factors besides the bacterium. A research report is currently awaiting peer review."