题目内容
A team of international researchers has found new evidence that an endangered subspecies of chimpanzee is the source of the virus that causes acquired immune deficiency syndrome (AIDS) in humans. Experts said the finding could lead to new treatments for AIDS and contribute to the development of a vaccine against the disease.
The research team said the chimp -- a subspecies known as Pan troglodytes native to west central Africa -- carries a simian immunodeficiency virus (SIV) that is closely related to three strains of human immunodeficiency virus (HIV), the virus that causes AIDS. One of these strains, HIV-1, has caused the vast majority of the estimated 30 million HIV infections around the world.
The researchers are uncertain when the chimp virus, called SIVcpz (for simian immunodeficiency virus chimpanzee), first infected humans, although the oldest documented case of HIV has been linked to a Bantu man who died in Central Africa in 1959. But they said the virus, which does not appear to harm the chimps, was most likely transmitted to humans when hunters were exposed to chimp blood while killing and butchering the animals for food. Once transmitted to humans, the researchers believe the virus mutated into HIV-1.
Team leader Beatrice Hahn, an AIDS researcher at the University of Alabama in Birmingham, said the chimps have probably carried the virus for hundreds of thousands of years. Since humans have probably hunted the animals since prehistoric times, Hahn said the virus may have jumped to humans on many occasions, but was not transmitted widely among humans until the 20th century. Increased hunting of the chimpanzees, along with human migration to African cities and changing sexual mores, could help explain the recent epidemic, Hahn said.
Scientists had long suspected that a nonhuman primate was the source of HIV-1. Earlier studies suggested that the sooty mangabey monkey, a native of West Africa, was the likely source of HIV- 2 -- a rarer form. of the AIDS virus that is transmitted less easily than HIV-1. However, only a few samples of SIV strains exist, making it difficult for researchers to confidently connect the strains to HIV-1.
As part of their effort to discover the source of HIV-1, the research team studied the four known samples of SIVcpz. They learned that three of the four samples came from Chimps belonging to the subspecies P.t. troglodytes. The remaining sample came from another subspecies, Pan troglodytes schweinfurthii, which inhabits East Africa.
The team then compared the SIVcpz strains to each other and found that all three of the viruses from P.t. troglodytes were closely related, while the virus from P.t. sehweinfurthii was genetically different. Next they compared the SIVcpz strains to the main subgroups of Hiv-1, known as M, N, and O. Their comparisons showed that the P.t. troglodytes viruses strongly resembled all three HIV-1 subgroups.
Additional evidence that HIV-1 could be linked to P. t. troglodytes came when the researchers examined the chimps' natural habitat. The researchers quickly discovered that the chimps live primarily in the West African nations of Cameroon, the Central African Republic, Gabon, Equatorial Guinea, and the Republic of the Congo, the geographic region where HIV-1 was first identified.
Upon closer study, the researchers learned that the chimps were being killed in growing numbers for the so-called bushmeat trade, a trend assisted by the construction of new logging roads in once remote forests. The researchers said that continued hunting of the animals meant that many people are still likely to be exposed to SIVcpz, increasing the risk of additional cross-species transmissions.
Many AIDS researchers welcomed the team's finding, but said the new work had not proved the connection definitively. Most of the doubts centered on the difficulty
查看答案
搜索结果不匹配？点我反馈
更多问题
Since chimpanzees are genetically very similar to humans,
Which of the following statements is CORRECT？
In Hardy's novel, Tess of the D'Urbervilles, it was _____ that led to the heroine's tragic
For much of the world, the death of Richard Nixon was the end of a complex public life. But researchers who study bereavement wondered if it didn't also signify the end of a private grief. Had the former president merely run his allotted fourscore and one, or had he fallen victim to a pattern that seems to afflict longtime married couples: one spouse quickly following the other to the grave？
Pat, Nixon's wife of 53 years, died last June after a long illness. No one knows for sure whether her death contributed to his. After all, he was elderly and had a history of serious heart disease. Researchers have long observed that the death of a spouse, particularly a wife, is sometimes followed by the untimely death of the grieving survivor. Historian Will Durant died 13 days after his wife and collaborator, Ariel; Buckminster Fuller and his wife died just 36 hours apart. Is this more than coincidence？ "Part of the story, I suspect, is that we men are so used to ladies feeding us and taking care of us," says Knud Helsing, an epidemiologist at the Johns Hopkins School of Public Health, "that when we lose a wife we go to pieces. We don't know how to take care of ourselves." In one of several studies Helsing has conducted on bereavement, he found that widowed men had higher mortality rates than married men in every age group. But, he found that widowers who remarried 'enjoyed the same lower mortality rate as men who'd never been widowed.
Women's health and resilience may also suffer after the loss of a spouse. In a 1987 study of widows, researchers from the University of California, Los Angeles, and UC, San Diego, found that they had a dramatic decline in levels of important immune-system cells that fight off disease. Earlier studies showed reduced immunity in widowers.
For both men and women, the stress of losing a spouse can have a profound effect. "All sorts of potentially harmful medical problems can be worsened," says Gerald Davison, professor of psychology at the University of Southern California. People with high blood pressure, for example, may see it rise. In Nixon's case, Davison speculates, "the stroke, although not caused directly by the stress, was probably hastened by it." Depression can affect the surviving spouse's will to live; suicide is elevated in the bereaved, along with accidents not involving cars.
Involvement in life helps prolong it. Mortality, says Duke University psychiatrist Daniel Blazer, is higher in older people without a good social-support-system, who don't feel they're part of a group or a family, that they "fit in" somewhere. And that's a more common problem for men, who tend not to have as many close friendships as women. The sudden absence of routines can also be a health hazard, says Blazer. "A person who loses a spouse shows deterioration in normal habits like sleeping and eating," he says. "They don't have that other person to orient them, like when do you go to bed, when do you wake up, when do you eat, when do you take your medication, when do you go out to take a walk？ Your pattern is no longer locked into someone else's pattern, so it deteriorates."
While earlier studies suggested that the first six months to a year -- or even the first week- were times of higher mortality for the bereaved, some newer studies find no special vulnerability in this initial period. Most men and women, of course, do not die as a result of the loss of a spouse. And there are ways to improve the odds. A strong sense of separate identity and lack of over-dependency during the marriage are helpful. Adult sons and daughters, siblings and friends need to pay special attention to a newly widowed parent. They can make sure that he or she is socializing, getting proper nutrition and medical care, expressing emotion and, above all, feeling needed and appreciated.
According to researchers, Richard Nixon's death was
微信支付 
支付宝支付