美國猶他大學最新的調查發現，因為營養充足以及棲地關係而愈長愈大的糜鼠（deer mouse，或稱白足鼠）極有可能就是散佈致命漢他肺炎病毒元兇。
猶他大學科學家使用晶片大小的發報器以及五種顏色的螢光粉，紀錄糜鼠與糜鼠間接觸的頻率及時距。研究發現愈大愈老的糜鼠越有可能是漢他真兇。
研究期間，其他老鼠身上也植入無線發報器來追蹤老鼠間的接觸。這項實驗，首次驗證了單一野生物種個體間的疾病傳播，也出現了所謂的「20／80定律」。所謂「20／80定律」，指的是只要約20%的宿主族群即可擁有達80%的疾病傳染力。
猶他大學生物系教授帝爾倫（Denise Dearing）表示：「早先研究發現感染漢他病毒的老鼠普遍比未感染的要來的大。但他們卻沒有檢驗個體間的接觸，那些研究暗示這些（較肥）動物間有更頻繁的互動，這也是他們之所以被感染原因，眾人懷疑的謎底終於解開。」
以此作為博士研究的猶他大學博士生克雷（Christy Clay）表示，「20／80定律」在此之前還沒有應用在同種野生物交互感染的例子。
在人類性傳染疾病如愛滋、嚴重急性呼吸道症候群（SARS）也適用此定律，在這些例子中，也是一小群人就佔了疾病傳播的主因。至於麻疹、猴痘與牛痘也同樣適用。
克雷認為：「雖然這些肥大糜鼠極有可能傳播漢他病毒，但我們也不是鼓動消滅大鼠。野生生物食物鏈裡老鼠仍扮演重要角色。」但她同時建議，假使一個地方曾有又大又老的糜鼠出沒，正是一個畫定風險區的指標之一，好提醒人們特別當心。例如，清潔人員在在清掃老鼠排遺時，應避免吸入灰塵。
Deer mice that grow older and bigger due to better food, cover or nesting sites are the ones that are most likely to spread a deadly lung infection called hantavirus, according to new research from the University of Utah.
University of Utah scientists used microchip transmitters and five colors of fluorescent powder to document how often and how long deer mice came into contact with other deer mice. The study identified bigger, older mice as the culprits.
Radio transmitters were implanted in other mice to track their contacts during the study, which is the first to show that the so-called "20-80 rule" applies to a disease that is directly transmitted among members of a single species of wildlife.
The rule says that roughly 20 percent of a population accounts for about 80 percent of disease transmission.
Denise Dearing, a University of Utah professor of biology, says earlier research found that hantavirus-infected mice tend to be larger than uninfected mice. "But they didn't examine contacts between individuals," she says. Those studies "imply these [heavier] animals likely have more contacts, and that's why they are infected. Now we have shown what others suspected."
Christy Clay, who ran the study as part of her University of Utah Ph.D ,says the 20-80 rule never before has been seen in a disease transmitted by direct contact from a member of any wildlife species to another member of the same species
It has been seen in sexually transmitted diseases in humans, including AIDS, and in severe acute respiratory syndrome, or SARS, in which few people are responsible for transmitting the virus to others, she says. The rule also holds true for humans with measles, monkeypox and smallpox.
"We are not proposing you exterminate larger mice although they are most likely to spread hantavirus," Clay says, noting the wildlife food chain depends on mice.
But she suggests that if places where the animals are older and heavier could be identified, then a risk map could be drawn to show people which are the areas where they should take precautions such as avoiding inhaling dust when sweeping up mouse droppings.
