French health officials said Friday they are investigating three suspected cases of a deadly new respiratory virus related to SARS, in people who had close contact in the hospital with France's only confirmed case.

Beatrice Degrugillers, a spokeswoman for the regional health agency in France's Nord-Pas-de-Calais region, said a nurse at the hospital where the man was hospitalized in late April has herself been under watch at the hospital in Douai since Thursday night.

A doctor and a former hospital roommate who had each been in contact with the first patient also remain hospitalized. Test results are expected later Friday.

If confirmed, the additional cases would heighten concerns about the virus' ability to spread easily between people. Health authorities have previously said the new coronavirus has spread in limited circumstances between people in very close contact, such as relatives taking care of family members.

In 2003, the spread of SARS in hospitals in Asia ultimately sparked a global outbreak. Officials consider any spread of a new virus in hospitals to be the first sign it is gaining the ability to infect humans easily.

On Wednesday authorities announced the 65-year-old Frenchman was France's first confirmed case of the novel coronavirus, which has killed 18 people since being identified last year in the Middle East.

The patient fell ill after returning from a nine-day vacation in Dubai in the United Arab Emirates as part of a package tour, the Health Ministry said.

The man, whose identity was not released, returned from Dubai on April 17. He was hospitalized with respiratory problems in the northern French city of Valenciennes on April 23, and transferred to a more advanced facility in Douai on April 29.

Paris' Pasteur Institute analyzed the man's virus and confirmed that it is a novel coronavirus.

Since September 2012, the World Health Organization has been informed of 30 confirmed cases of the virus, and 18 of the patients have died. Cases have emerged in Saudi Arabia, Jordan, the UAE, Qatar, Britain and Germany, and health officials say the virus has likely already spread from person to person in some circumstances.

Since the virus emerged last year, European authorities have put in place monitoring measures. In France, 20 people have already been examined for suspected cases of the virus, but the other 19 turned up negative, Health Minister Marisol Touraine said.

The patient who traveled to Dubai is the only positive case. His family members have been tested and are not infected.

By Julie Steenhuysen
Reuters

The U.S. Centers for Disease Control and Prevention (CDC) on Thursday warned state and local health officials about potential infections from a deadly virus previously unseen in humans that has now sickened 14 people and killed 8. 

Most of the infections have occurred in the Middle East, but a new analysis of three confirmed infections in Britain suggests the virus can pass from person to person rather than from animal to humans, the CDC said in its Weekly Morbidity and Mortality Report on Thursday.

The virus is a coronavirus, part of the same family of viruses as the common cold and the deadly outbreak of Severe Acute Respiratory Syndrome (SARS) that first emerged in Asia in 2003. The new virus is not the same as SARS, but like the SARS virus, it is similar to those found in bats.

So far, no cases have been reported in the United States.

According to the CDC's analysis, the infections in Britain started with a 60-year-old man who had recently traveled to Pakistan and Saudi Arabia and developed a respiratory illness on Jan. 24, 2013. Samples from the man showed he was infected with both the new virus and with H1N1, or swine flu.

This man subsequently passed the infection to two members of his household: a male with an underlying illness who became ill on Feb. 6 and subsequently died; and a healthy adult female in his household who developed a respiratory illness on Feb. 5, but who did not need to be hospitalized and has recovered.

The CDC said people who develop a severe acute lower respiratory illness within 10 days of returning from the Arabian Peninsula or neighboring countries should continue to be evaluated according to current guidelines.

The health agency said doctors should be watchful of patients who develop an unexplained respiratory infection within 10 days of traveling from the Arabian Peninsula or neighboring countries. The CDC has set up a special website with updates on the infections.

Symptoms of infection with this new virus include severe acute respiratory illness with fever, cough and shortness of breath. Neither the CDC nor the World Health Organization has issued travel restrictions related to the virus.

A baby born infected with the AIDS virus who got immediate treatment now has no detectable virus in her blood – not quite a cure, but so close to one that it has doctors talking about the possibility.

Her case, presented to a meeting of AIDS researchers that started Sunday, will prompt questions about how early babies should be treated – and further illustrates the possibility that immediate treatment with HIV drugs might stop infection in its tracks and could even have an impact on the AIDS pandemic.

“What we have identified is what we think is the first well-documented case of a functional cure in a neonatal child,” Dr. Deborah Persaud of the Johns Hopkins Children’s Center, the virologist who led the study, told NBC News.

A functional cure, says Persaud, means the virus isn’t entirely gone, but it’s not doing any damage, either. Doctors think it was because they began therapy for the baby within 48 hours of being infected, she told a conference in Atlanta of HIV specialists.

The child, who lives in rural Mississippi, is now 2 1/2 and healthy. She was, like so many, born to a mother who didn’t know until right before she gave birth that she had the human immunodeficiency virus (HIV) that causes AIDS. Mom and baby both got a standard dose of HIV drugs right away – something that has been shown to prevent what’s known as mother-to-child transmission of the virus in newborns.

Johns Hopkins Medicine

Dr. Deborah Persaud of the Johns Hopkins Children's Center. She helped discover the case of a toddler who is close to being "cured" of HIV.

The baby was a little premature and so stayed in the hospital. Within 30 hours of birth she was re-tested and had clear evidence of HIV infection. Unusually, she then got a cocktail of three drugs at a dose normally reserved for more advanced cases.  It worked really well – pushing her virus down to what’s called undetectable levels. This is what doctors want with HIV, because if the virus can’t be found in the blood, then it can’t be spreading and damaging the immune system. HIV doesn’t kill directly – it kills patients by damaging their immune systems so bad they can’t fight off other infections.

The baby and her mom, who doctors aren't naming, got regular care and treatment by Dr. Hannah Gay at University of Mississippi Medical Center until she was 15 months old. Then, like so many children, she disappeared off the doctors’ radar screens. The mother brought her back briefly at 18 months but disappeared again but she missed at least eight months worth of drugs. When Gay caught up to her again, the baby was still well, despite having received no treatment. More remarkably, tests showed the virus had not come back.

“My first thought was, ‘oh my goodness. We have been treating an uninfected child,” Gay told NBC News. "But I checked the records which confirmed she was, in fact, infected.”

Dr. Katherine Luzuriaga of the University of Massachusetts Medical School, who also worked on the study, piled on with a battery of tests. Even a sensitive test called PCR, which can help find tiny bits of genetic material from a virus, couldn’t detect any evidence of HIV. This went far beyond the usual definition of "undetectable" in treating the AIDS virus - there really was no evidence the virus was there.

“What we did then was to get a group of collaborating laboratories together to apply ultra-sensitive testing  and say ‘can we detect any evidence of virus’,” Luzuriaga says. They did eventually find pieces of genetic material from the virus.

But Persaud has been unable to find any evidence of virus that can invade cells or replicate. “So the baby has remained off treatment. We are just watching and we will follow the baby and do additional testing.”

It’s not a true cure – what doctors call a “sterilizing” cure. There is still virus in the toddler’s body. But it’s not is a form that seems to be doing any damage. It doesn’t seem to be able to spread from one cell to another and it doesn’t seem to be damaging the child’s immune system.

About 34 million people globally are infected with HIV, the virus that causes AIDS; 25 million have died from it. While there’s no vaccine, cocktails of powerful antiviral drugs called antiretroviral therapy (ART) can keep the virus suppressed and keep patients healthy. No matter how long patients take ART, however, they are never cured. The virus lurks in the body and comes back if the drugs are stopped. Scientists want to flush out these so-called reservoirs and find a way to kill the virus for good.

“This has major implications for how we begin to think about treating children,” Persaud says. “Perhaps we can spare them a lifetime of treatment.”

But she adds, it’s one case.  “We need to figure out if this can be reproduced or replicated in other infants.”

Babies born to HIV-positive women are different from other HIV patients. Doctors know the precise moment that they are infected and can treat them right away. But usually they treat them with low doses of drugs for about six weeks and then wait to see if infection has really developed before they treat them again. If done right, this treatment around birth can prevent 95 percent of infections.

Up to now, only one person has been documented with a cure – the so-called Berlin patient, Timothy Brown, who was treated for leukemia with a bone marrow transplant that happened to come from a donor with a genetic mutation that makes immune cells resist HIV infection. The transplant replaced his own infected cells with healthy, AIDS-resistant cells. He is remains free of the virus more than five years later.

Dr. Dan Kuritzkes of Brigham and Women's Hospital and Harvard Medical School is treating two HIV other patients who, like Brown, got bone marrow transplants for leukemia or lymphoma. His team wants to see if they, too, can be cured. “They are doing fine,” he says – but continue taking HIV drugs to be safe.

But a third patient he was treating suffered a relapse of lymphoma and died. “It sort of underscores what these patients have been through,” he said. No one thinks a bone marrow transplant represents a real-life treatment for anyone with HIV, because it’s so hard on the body.

Kuritzkes said AIDS experts have wondered whether very early treatment of newborns could be in fact treating their infection rather than preventing it.

“It’s exciting because there are undoubtedly other children in this situation,” he said. His team is taking part in several studies looking at whether it is possible to eradicate the reservoirs of virus in adults that should have results within a year.

There are also patients called “elite controllers” who seem to stay well and suppress the virus without the need for drugs.

Luzuriaga says this toddler is not an elite controller. “You can detect HIV DNA in their cells. And you can culture virus from them,” she said. “We just think that this baby has much tighter control, much tighter control. This baby hasn’t rebounded off therapy.”

“Our next step is to find out if this is a highly unusual response to very early antiretroviral therapy or something we can actually replicate in other high-risk newborns,” says Persaud.

It might be that quick treatment stopped the virus from hiding out in the baby’s body, and allowed the drugs to do their work and stop the spread of the virus.

Ami Schmitz contributed to this story.

Talk about this story on the NBC News Health Facebook page.

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A cottonmouth, also known as a water moccasin. A new study shows cottonmouths and other vipers can harbor easterm equine encephalitus virus

Snakes may provide a winter hiding place for a virus that’s causing an unusually severe outbreak in the U.S. northeast this year, and this could be good news for control efforts, researchers said on Monday.

They found eastern equine encephalitis virus (EEE for short) in cottonmouths and copperhead snakes and said it’s likely the reptiles incubate the virus while they hibernate over the winter. When they come out in spring, mosquitos feast on the snakes and then pass it to birds.

The study, published in the American Journal of Tropical Medicine and Hygiene, explains why EEE keeps coming back in northern states where mosquitos hunker down for the winter and where many birds take off for warmer climes. “There must be a way that the virus manages to overwinter. We think it’s the snakes, because they do overwinter in these sites,” said Dr. Thomas Unnasch of the University of South Florida, who led the study.

Eastern equine encephalitis is rare but highly deadly – it kills about a third of victims who develop the worst symptoms -- and there’s no cure for it. Survivors often have permanent brain damage. It infects people, horses and birds along the Atlantic and Gulf coasts, Michigan and Ohio. Usually there are only about six human cases a year according to the Centers for Disease Control and Prevention, but seven people in Massaschusetts have been affected this year alone. While there is a vaccine for horses, there is not one for people, and two have died this year from EEE.

It’s a year-round threat in Florida but further north it doesn’t start affecting horses or people until late summer. Unnasch and colleagues have been trying to figure out why for years.

“You know how they used to say follow the money? We followed the mosquito,” Unnasch told NBC News. Female mosquitoes spread the virus as they look for blood meals to nourish their eggs.

In the summer, it’s clear, the virus infects birds. They don’t get sick and their bodies get rid of the virus after a few days, but because there are so many birds the mosquitoes keep it circulating. “You have a pretty good, high concentration of mosquitoes then that have this infection,” Unnasch says.

“Now all the birds decamp for the winter. They migrate. You have these ladies running around, these mosquitoes, and they can’t find their favorite hosts, the birds and so they feed on whatever they can find.” That's when humans and horses are at risk.

Scientists couldn’t figure out what other animals were harboring the virus, so they tested the blood in infected mosquitoes. It turned out that mosquitoes infected with EEE had often just feasted on snake blood. How? “Right around their eyes,” Unnasch said. The membrane that covers a snake’s eyes is soft and mosquitoes can feed there.

Tests on cottonmouths in the Tuskeegee National Forest in Alabama confirmed a fairly high percentage were infected with EEE, as well as at least one copperhead. It doesn’t make the snakes sick and they seem to stay actively infected for months on end, Unnasch said.

So when it gets cold up north and the migrating birds leave, the snakes are still infected with EEE and they hibernate. In the spring, newly hatched mosquitoes feed on the snakes and get infected. “They act as the Typhoid Mary of the virus,” Unnasch said.

Copperheads are related to rattlesnakes and there are plenty of both in the north, Unnasch noted.

This is actually good news for control efforts, Unnasch says. “What usually happens is we pretty don’t worry about this too much until it jumps out and starts infecting humans and horses,” he said. That’s usually late in the summer, when the mosquitoes get desperate enough to bite people and horses.

Public health officials may be waiting until too late to try to control the outbreaks, Unnasch said. “They’ll go out spray like crazy and try to control the mosquitoes.” But it’s expensive then.

But if the virus is only beginning to escape in spring, it might be cheaper and easier to go to the swampy areas where the snakes are hibernating, and spray for the relatively few mosquitoes that are around then. “You might be able to interrupt the viral amplification cycle,” Unnasch said, “You might be able to do ounce of prevention, which is better than a pound of cure.”

Is there a lesson here for West nile virus, another mosquito-borne infection that's causing an unusual amount of trouble this year? CDC reports 3,545 cases of West Nile virus disease in people, including 147 deaths. Unfortunately not, says Unnasch -- West Nile is not related to EEE and while it passes from birds to mosquitoes to people, it has a different cycle of infection.

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State health officials reported a seventh human case of EEE in Massachusetts.

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CDC says jump in West Nile cases is slowing

Frederick A. Murphy / CDC handout via EPA file

A new virus that appears similar to rabies, but has the symptoms and lethality of Ebola, shown here, has been dubbed the Bas-Congo virus. It killed two teenagers in the Congo in 2009.

A virus that killed two teenagers in Congo in 2009 is a completely new type, related to rabies but causing the bleeding and rapid death that makes Ebola infection so terrifying, scientists reported on Thursday. They’re searching for the source of the virus, which may be transmitted by insects or bats.

The new virus is being named Bas-Congo virus, for the area where it was found.  Researchers are finding more and more of these new viruses, in part because new tests make it possible, but also in the hope of better understanding them so they can prevent pandemics of deadly disease.

The virus infected a 15-year-old boy and a 13-year-old girl in the same village in Congo in 2009. They didn’t stand a chance, says Joseph Fair of Metabiota, a company that investigates pathogens. Fair is in the Democratic Republic of Congo now, under contract to the U.S. Agency for International Development (USAID) to help battle an ongoing Ebola outbreak.

“They expired within three days,” Fair said in a telephone interview. “It was a very rapid killer.”

A few days later a male nurse who cared for the two teenagers developed the same symptoms and survived. Samples from the lucky nurse have been tested and it turned out a completely new virus had infected him, Fair and other researchers report in the Public Library of Science journal PLoS pathogens.

The genetic sequences went to Dr. Charles Chiu, of the University of California, San Francisco.

“We were astounded that this patient had sequences in his blood from a completely unknown and unidentified virus,” Chiu said. They weren’t expecting that.

“Congo is very much known for having Ebola and Marburg outbreaks. Yet about 20 percent of the time we have hemorrhagic fever outbreaks that are completely negative, which means unknown causes and they are not Ebola.”

The sequencing puts this new virus on its own branch of the bad virus family tree -- somewhat related to Ebola and the virus that causes Lassa fever, another horrific killer, and most closely related to the rhabdoviruses. This family usually only infects animals with one notable exception -- rabies.

But rabies is not known to cause hemorrhaging. It’s plenty horrible on its own, of course, killing virtually all patients if they aren’t vaccinated soon after infection. 

A nurse who took care of the first infected nurse had antibodies to the new virus. It doesn’t look like the teenagers infected one another, says Fair, but they probably infected the first nurse, who probably infected the second. Tests of other villagers have found no more evidence of the virus, however, which is good news.

“Although the source of the virus remains unclear, study findings suggest that Bas-Congo virus may be spread by human-to-human contact and is an emerging pathogen associated with acute hemorrhagic fever in Africa,” the researchers wrote.

Africa is loaded with nasty viruses. Lassa fever virus comes from a family known as arenaviruses and causes 500,000 cases of hemorrhagic fever a year. Crimean-Congo hemorrhagic fever and Rift Valley Fever viruses are in another family called bunyaviruses; Ebola and Marburg viruses are filoviruses that kill anywhere between 30 percent and 90 percent of victims. They’re also helping wipe out great apes such as gorillas in Central Africa. This adds a new one to the list.

It worries Chiu because its closest relative is spread by biting flies in Australia. “We think that is potentially a valuable clue. This virus may have come from an insect vector,” Chiu says. “What is scary about this virus is if it does happen to be spread by insects, it has the potential to be something like West Nile."

West Nile showed up in the United States for the first time in 1999, having never been seen here before. It causes regular outbreaks in Africa and parts of Europe, however, and some experts think a mosquito or an infected person carried it on a flight to New York. It’s killed 147 people in an especially bad U.S. outbreak this year, although more than 90 percent of people infected with West Nile never even know it.

New viruses often cause disease -- there was severe acute respiratory syndrome or SARS, which killed 800 people and infected 8,000 in 2003 before it was stopped. Scientists are now watching a similar virus that has emerged in the Middle east.

Chiu says there is not enough information to know how deadly the new Bas-Congo virus is.

“It  has probably been lurking out there in remote areas and causing sporadic cases of hemorrhagic fever and no one had the resources to discover it,” Chiu said. “This is probably the tip of the iceberg. I believe there are many, many more of these emerging viruses that have yet to be discovered,” he added.

“This points to the importance of being vigilant, especially these remote areas of Africa and Asia. This is the area that I believe the next generation of emerging viruses will come from.”

Fair agrees, and says his team will be looking. They’ll also be checking to see if bats or insects can spread it. “It is a frightening prospect. That is why the next step in this process is to look for the vector,” Fair said.

That’s not so easy. Fair’s team and hundreds of other scientists have been looking for the reservoir -- the animal or insect source --of Ebola. That would be a bat or other creature that can carry it without getting sick itself. So far they have had no luck, although fruit bats are a major suspect.

And for the new Bas-Congo virus, the trail is now three years old. “Everything we do will be as a forensic investigation,” Fair said. “We really have to go look for a needle in a sack of needles.”

And in the meantime, there’s an outbreak of Ebola to cope with. Fair says a coordinated effort is going on, although this isn’t the worst outbreak he has seen. It’s killing about 30 percent to 40 percent of patients -- not nearly as bad as some strains, which killed up to 90 percent of victims.

“If you had to get Ebola, this is the strain to get,” he said.

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Global health officials are closely monitoring a new respiratory virus related to SARS that is believed to have killed at least one person in Saudi Arabia and left a Qatari citizen in critical condition in London.

The germ is a coronavirus, from a family of viruses that cause the common cold as well as SARS, the severe acute respiratory syndrome that killed about 800 people, mostly in Asia, in a 2003 epidemic.

In the latest case, British officials alerted the World Health Organization on Saturday of the new virus in a man who transferred from Qatar for treatment in London. He had recently traveled to Saudi Arabia and is now being treated in an intensive care unit after suffering kidney failure.

WHO said virus samples from the patient are almost identical to those from a 60-year-old Saudi national who died earlier this year. The agency isn't currently recommending travel restrictions and said the source of infection remains unknown. Still, the situation has raised concerns ahead of next month's annual Hajj pilgrimage, which brings millions of people to Saudi Arabia from around the world.

Health officials don't know yet whether the virus could spread as rapidly as SARS did or if it might kill as many people. SARS, which first jumped to humans from civet cats in China, hit more than 30 countries worldwide after spreading from Hong Kong.

"It's still (in the) very early days," said Gregory Hartl, a WHO spokesman. "At the moment, we have two sporadic cases and there are still a lot of holes to be filled in."

He added it was unclear how the virus spreads. Coronaviruses are typically spread in the air but Hartl said scientists were considering the possibility that the patients were infected directly by animals. He said there was no evidence yet of any human-to-human transmission.

"All possible avenues of infection are being explored right now," he said.

No other countries have so far reported any similar cases to WHO, he said, and so far there is no connection between the cases except for a history of travel in Saudi Arabia.

Hartl said the first patient may have had an underlying condition but it probably didn't make him more susceptible to catching the virus.

Other experts said it was unclear how dangerous the virus is.

"We don't know if this is going to turn into another SARS or if it will disappear into nothing," said Michael Osterholm, a flu expert at the University of Minnesota. He said it was crucial to determine the ratio of severe to mild cases.

Osterholm said it was worrying that at least one person with the disease had died. "You don't die from the common cold," he said. "This gives us reason to think it might be more like SARS." SARS killed about 10 percent of the people it infected.

Britain's Health Protection Agency and WHO said in statements that the 49-year-old Qatari became ill on Sept. 3, having previously traveled to Saudi Arabia. He was transferred from Qatar to Britain on Sept. 11 and is being treated in an intensive care unit at a London hospital for problems including kidney failure. Respiratory viruses aren't usually known to cause serious kidney problems.

In Qatar, Mohammed bin Hamid Al Thani of the Public Health Department said the patient was in Saudi Arabia for Ramadan during the summer and became ill after returning to Qatar. Doctors could not immediately identify the virus and decided he should be treated in London.

A public health official, Abdullakef al-Khal, said there is no indication that the patient's family or others were infected.

"There is no special alert for now," he said. "We are being vigilant."

David Heymann, chairman of the Health Protection Agency, said the new virus didn't appear that similar to SARS.

"It isn't as lethal as SARS and we don't know too much about its transmissibility yet," he said. "If people are getting infected, they aren't getting serious disease."

Heymann said none of the health workers involved in treating the Qatari patient had become ill.

Saudi officials said they were concerned that the upcoming Hajj pilgrimage next month could provide more opportunities for the virus to spread. They advised pilgrims to keep their hands clean and wear masks in crowded places.

Several disease outbreaks have occurred during The Hajj including the flu, meningitis and polio.

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An Ebola outbreak in Democratic Republic of Congo risks spreading to major towns if not brought under control soon, the World Health Organization said on Thursday.

The death toll has more than doubled since last week to 31, including five health workers. There is no treatment for Ebola, which is highly contagious and can cause internal bleeding. Depending on the strain, it kills between 50 percent and 90 percent of victims.

"The epidemic is not under control. On the contrary the situation is very, very serious," Eugene Kabambi, a WHO spokesman in Congo's capital Kinshasa, told Reuters by telephone.

"If nothing is done now, the disease will reach other places, and even major towns will be threatened," he said.

The disease has so far struck in the towns of Isiro and Viadana in Orientale province in the north east.

In August, 16 people in neighboring Uganda died from Ebola infections, although health experts said the two epidemics are not connected. They have blamed the Congolese outbreak on villagers eating contaminated meat in the forests that cover the region. 

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By Ronnie Cohen
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U.S. health officials have sent warnings to 39 other countries that their citizens who stayed in Yosemite National Park tent cabins this summer may have been exposed to a deadly mouse-borne hantavirus, a park service epidemiologist said on Tuesday.

Of the 10,000 people thought to be at risk of contracting hantavirus pulmonary syndrome from their stays in Yosemite between June and August, some 2,500 live outside the United States, Dr. David Wong told Reuters in an interview.

Wong said U.S. Department of Health and Human Services officials notified 39 countries over the weekend, most of them in the European Union, that their residents may have been exposed to the deadly virus.

The lung disease has so far killed two men and sickened four other people, all U.S. citizens, prompting the U.S. Centers for Disease Control and Prevention to issue a health alert.

Officials are concerned that more Yosemite visitors could develop the lung disease in the next month or so. Most of the victims identified so far were believed to have been infected while staying in one of 91 "Signature" tent-style cabins in the park's popular Curry Village camping area.

There is no cure for the disease, but early detection through blood tests greatly increases survival rates.

"I want people to know about this so they take it seriously," Wong said. "We're doing our due diligence to share the information."

Last week, park officials shut down the insulated "Signature" tent cabins after finding deer mice, which carry the disease and can burrow through holes the size of pencil erasers, infesting the double walls.

Officials are continuing to investigate additional possible cases of the disease, which has killed 64 Californians and about 590 Americans since it was identified in 1993, Wong said.

Early symptoms include headache, fever, muscle aches, shortness of breath and coughing. The virus may incubate for up to six weeks after exposure and can lead to severe breathing difficulties and death.

Experts say hantavirus, which kills 36 percent of those it infects, has never been known to be transmitted between humans.

Four of those known to be infected at Yosemite this summer slept in the insulated tent cabins. One slept elsewhere in Curry Village, located in a valley beneath the iconic Half Dome rock formation, and the sixth case remains under investigation.

One man from northern California and another from Pennsylvania died, while three victims have recovered and a fourth remains hospitalized, the state Department of Public Health said.

Nearly 4 million people visit Yosemite each year, attracted to the park's dramatic scenery and hiking trails. Roughly 70 percent of those visitors congregate in Yosemite Valley, where Curry Village is located.

Hantavirus is carried in viral particles inhaled from rodent feces and urine. People also can be infected by eating contaminated food, touching contaminated surfaces or being bitten by infected rodents.

Hantavirus previously infected two Yosemite visitors, one in 2000 and another in 2010, but at higher elevations.

West Nile virus is now in 48 states, has made nearly 1,600 people ill and killed 66 of them, federal health officials said on Wednesday. But don’t expect Hurricane Isaac, which is now dumping tons of rain on Louisiana, to make matters any worse, they said.

The case count keeps 2012 on track to be the worst year for West Nile since the virus first came to the United States in 1999, the Centers for Disease Control and Prevention said. And some of the sickest people will never fully recover, the CDC says.

“As of August 28, 2012, 48 states have reported West Nile virus infections in people, birds, or mosquitoes. A total of 1,590 cases of West Nile virus disease in people, including 66 deaths, have been reported to CDC,” the agency says.

“Over 70 percent of the cases have been reported from six states (Texas, South Dakota, Mississippi, Oklahoma, Louisiana, and Michigan) and over 45 percent of all cases have been reported from Texas.”

Health officials are not sure why West Nile is so bad this year or why Texas has been so hard-hit. The very hot summer may have been a factor, but viruses like West Nile have complicated and hard-to-follow life cycles, they said.

West Nile is spread by infected mosquitoes, which breed in water. But CDC officials said they doubted Hurricane Isaac would worsen the epidemic, because mosquitoes like stale, standing water, which is likely to be washed away by a hurricane.

The CDC’s Dr. Lyle Petersen, an expert on mosquito-transmitted disease, says the virus has to pass from mosquitoes to birds and back to mosquitoes to take hold in an area, and big storms mess up that cycle of transmission. “The end result is that hurricanes and floods do not have a major impact,” Petersen told reporters in a conference call.

“Heavy rainfall can certainly eliminate breeding sites rather create them,” he added. But in the weeks after a storm, pools of water can form and make new sites for the insects, he added. After Hurricane Katrina struck the Gulf coast in 2005, a few more cases of West Nile were reported but that was more likely because so many people were outside, repairing homes and cleaning up debris, he said.

“We continue to preach the message of making sure you are raining your yards,” said Texas state health commissioner Dr. David Lakey.

Heat could be a factor, also, if it incompletely dries up pools of standing water. “There has been a lot of speculation about the heat wave this year and could this partially have caused this effect, and the answer is yes,” Petersen said. But, he added, other heat waves have not led to outbreaks.  

 Officials in the Dallas area have been spraying pesticides to kill mosquitoes and Lakey and Peterson both said that should start cutting reported cases of West Nile there. It takes a few weeks for cases to be reported, so they said the number of reported cases will probably rise before it starts to fall.

More than half the cases reported so far this year have been of neuroinvasive disease – meaning the brain and spinal cord are affected. Peterson said it’s unlikely there’s an unusually high proportion of severe cases compared to years past. He notes that 80 percent of people infected with West Nile never even feel particularly sick, and it’s the serious cases that are more likely to get noticed and counted.

But people with neurological symptoms can be in serious trouble. There are three types – meningitis, which is inflammation of the spinal cord; encephalitis, which is when the brain is infected and inflamed; and acute flaccid paralysis, caused when both the brain and spinal cord are damaged. About one in 150 people infected with West Nile develop severe illness, according to the National Institutes of Health.

Patients with meningitis must be hospitalized but usually recover, Petersen said. About 10 percent of patients with encephalitis die, and those who survive may have subtle neurological effects long term. Patients who develop paralysis are in the worst trouble – a third recover, a third have some weakness long term and a third never recover, Petersen said. Some patients have had paralyzed limbs for years now.

Lakey says people of all ages have been affected, but the older people are, the more likely they are to be seriously ill. People with damaged immune systems, such as cancer patients, are at higher risk.

By the time patients with neurological symptoms get to the hospital, the virus has already invaded the nervous system, Petersen says. There’s no drug to treat West Nile virus anyway, and this effect makes it hard to develop one, because it’s hard to make a drug that can penetrate the central nervous system.

And because West Nile is so spread out and sporadic, it’s hard to even try to develop a drug or vaccine to fight it, Petersen said. Drug companies need lots of guaranteed cases of a disease to test whether a new vaccine or drug actually works.

“We are dealing with a low-incidence disease most years, (with) cases that are widely dispersed,” Petersen said. “The thought of trying to produce a phase 3 clinical trial to show efficacy is fairly daunting."

Related links:

Is spraying for West Nile safe?

Cluster of hantavirus cases worries officials

Five things you need to know about West Nile virus