10,000 Yosemite tourists could face deadly virus

[Orphia Nay]

Around 10,000 visitors to California's Yosemite National Park could have been exposed to a deadly virus that kills one in three victims and cannot be cured.

Officials say six cases of the rare hantavirus pulmonary syndrome (HPS) have been confirmed so far.
...
People are infected with the rare lung disease by breathing in dust contaminated by rodent droppings.

It is thought that the outbreak at Yosemite was caused by mice nesting in the insulation of the Signature Tent Cabins in the Curry village section of the park....

The National Park Service (NPS) has written to around 2,900 people who booked stays in the Boystown area tent lodgings between June 10 and August 24, alerting them to keep an eye out for symptoms of HPS.

http://www.abc.net.au/news/2012-09-01/yosemite-tourists-could-face-deadly-virus/4237950

 

[Skeptic Ginger]

There will be an incredibly small number of them who actually get infected by the sin nombre (hanta) virus in the end. So far there are 2 deaths and only a handful of infections.

 

[Orphia Nay]

I do hope it's only a few, although it's still tragic for those few.

 

[Skeptic Ginger]

I do hope it's only a few, although it's still tragic for those few.

It will only be a few, but you're right, no less tragic for those unlucky ones.

 

[casebro]

But is there an antibody test?

We always hear about these extreme death rate, but that is of hospitalized victims. How many of the rest of us have been exposed, got the disease in a mild case, and go on about our business? I suspect that like other viruses, some are susceptible, some not at all, and the feeble get sicker and the most feeble die. I don't expect the population to be decimated soon. I do expect the budget of the CDC to grow.

And there is nothing new about Hanta. IRC the MASH tv show did an episode on it in the 70s, said show took place in Korea in the 50s.

And hanta has been around the American southwest for long enough now that if it was going to kill 1/3 of people, the Anmerican south west would BE a ghost town, instead of just having some ghost towns.

Alarmism.

 

[Skeptic Ginger]

But is there an antibody test?

We always hear about these extreme death rate, but that is of hospitalized victims. How many of the rest of us have been exposed, got the disease in a mild case, and go on about our business? I suspect that like other viruses, some are susceptible, some not at all, and the feeble get sicker and the most feeble die. I don't expect the population to be decimated soon. I do expect the budget of the CDC to grow.

And there is nothing new about Hanta. IRC the MASH tv show did an episode on it in the 70s, said show took place in Korea in the 50s.

And hanta has been around the American southwest for long enough now that if it was going to kill 1/3 of people, the Anmerican south west would BE a ghost town, instead of just having some ghost towns.

Alarmism.

It's only alarmish because the public health needs to get the message out and the news media hypes it up to sell news.

As for the epidemiology, inapparent infections or not, the case rate is very low with occasional small clusters usually tied to heavy deer mice years. So it doesn't necessarily matter if the reason for low case rates is no infection or inapparent infections.

However, there are some prevalence studies. And there is an antibody test:

the earliest case of a serologically confirmed SNV infection was in a person who developed an HPS-compatible illness in July 1959 and was found to have IgG antibodies in September 1994. The earliest case of HPS to be confirmed by IHC with direct visualization of hantaviral antigens in postmortem tissue involved a patient who died in 1978....

...Among U.S. mammalogists and rodent workers with varying degrees of rodent exposure, the seroprevalence of SNV antibodies was 1.14%. In contrast, a recent HPS seroprevalence study focused on selected occupational groups with frequent contact with rodents and their excreta (e.g., farm workers, laborers, professionals, home repairers, service industry and park service workers, heating and plumbing contractors, utility workers, and technicians) found no evidence of SNV infection.

So it does have a low prevalence and a high case fatality rate.

 

[Soapy Sam]

Sounds like the Park Service are being super cautious, which is understandable.
The press less so. Also understandable.
Fingers crossed...

 

[Skeptic Ginger]

01 Sep 2012 Hantavirus update 2012 - Americas (27): USA (CA)

The entry repeats the Reuter's report and the following is the moderator's comment:

[As mentioned in yesterday's ProMED-mail post [archive no. 20120831.1275463], the hantavirus in this month's [August 2012] reports from California is doubtless Sin Nombre virus, which is endemic there. Its rodent host is the deer mouse, _Peromyscus maniculatus_. It is unusual to have these 6 cases occur in a single, very limited focal area, Curry Village, within the space of 2 months. This suggests that the deer mouse population is abundant in Curry Village, and perhaps supporting active virus transmission and shedding there at this time. It is prudent for Park Service personnel to have warned Curry Village campers of the risk of exposure to Sin Nombre virus, so that they can seek medical attention promptly should symptoms appear.

An image of _Peromyscus maniculatus_, the rodent host of Sin Nombre virus, can be accessed at http://www.ask.com/wiki/Peromyscus_maniculatus.

A HealthMap/ProMED-mail interactive map showing the location of Yosemite National Park can be seen at http://healthmap.org/r/3bLD. - Mod.TY]]

With 6 cases being a big cluster, it gives one an idea just how low the total risk actually is.

 

[Skeptic Ginger]

Sounds like the Park Service are being super cautious, which is understandable.
The press less so. Also understandable.
Fingers crossed...

I suspect it is just as much the result of the health department telling them what to do.

 

[casebro]

It's only alarmish because the public health needs to get the message out and the news media hypes it up to sell news.

As for the epidemiology, inapparent infections or not, the case rate is very low with occasional small clusters usually tied to heavy deer mice years. So it doesn't necessarily matter if the reason for low case rates is no infection or inapparent infections.

However, there are some prevalence studies. And there is an antibody test:....

So it does have a low prevalence and a high case fatality rate.

But if 1 1/4% have the antibodies, how many had an identified case? THAT would give the actual fatality rate. Mayb I'll go look at the link. I suspect it will be 'high', but not near 50%, eta to follow.

eta: Not enough numbers given to tell an actual fatality rate. No sample size, no 'recognized cases' within that sample size to even state whether the death rate is higher or lower than the common cold. But with about 30 fatalities per year in 34 states, LOTS of people get exposed without 50% dying.

Hey, it's an outdoors sport thing. I bet more outdoorsmen die by lightning strike or bee sting. And the above study was done on 'rodent workers'. Occupational exposure, anybody?

 

[Skeptic Ginger]

But if 1 1/4% have the antibodies, how many had an identified case? THAT would give the actual fatality rate. Mayb I'll go look at the link. I suspect it will be 'high', but not near 50%, eta to follow.

You might might be able to tweak the info playing with the math. It's not really necessary with these low numbers. Remember that 1.25% is the rate of a very highly exposed group and the denominator is not 1.25% of the population. You'd need to use the number of people in the specific population tested to know how many people that 1.25% represented. It could be 3 people.

The fatality rate comes from comparing survivors with symptomatic cases to fatalities. The low antibody rate tells us very few asymptomatic cases occur.

 

[casebro]

But even fewer symptomatic cases?

But if they tested a group of 10,000, in which six known cases had occured, with three deaths, that would be three deaths in 114 cases. Less than 3% fatal. NOT a "high fatality" disease. Or maybe it is, by today's standards ?

Leading off topic towards statistics, what number of data cases could come out with 1.14%? It has to be a whole number, no half-IGGs. The results could NOT have been 1.14 in 100. 114 per 10,000, umm maybe. 57 per 5,000? ummm 11:1,000 ? nope. Got it, 4 sero-positives out of 350, that is 1.1428%. Now the question is, is a study of 350 statistically significant? BUT, again,how many reported cases in the 350? 6? or ZERO ?

So, we haven't been given enough info to know how high the fatality rate is, only that there is low transmission and rarer fatalities.

 

[Skeptic Ginger]

But even fewer symptomatic cases?

But if they tested a group of 10,000, in which six known cases had occured, with three deaths, that would be three deaths in 114 cases. Less than 3% fatal. NOT a "high fatality" disease. Or maybe it is, by today's standards ?

Leading off topic towards statistics, what number of data cases could come out with 1.14%? It has to be a whole number, no half-IGGs. The results could NOT have been 1.14 in 100. 114 per 10,000, umm maybe. 57 per 5,000? ummm 11:1,000 ? nope. Got it, 4 sero-positives out of 350, that is 1.1428%. Now the question is, is a study of 350 statistically significant? BUT, again,how many reported cases in the 350? 6? or ZERO ?

So, we haven't been given enough info to know how high the fatality rate is, only that there is low transmission and rarer fatalities.

I'm unclear how you are getting the 114 cases. You don't know that all 10,000 people were exposed. Those were not the people whose serologies were tested.

Repeating what I quoted:

Among U.S. mammalogists and rodent workers with varying degrees of rodent exposure, the seroprevalence of SNV antibodies was 1.14%. In contrast, a recent HPS seroprevalence study focused on selected occupational groups with frequent contact with rodents and their excreta (e.g., farm workers, laborers, professionals, home repairers, service industry and park service workers, heating and plumbing contractors, utility workers, and technicians) found no evidence of SNV infection.

Tourists in at risk cabins would be closer to the zero seroprevalence groups.

As an example, I worked with people studying hantavirus prevalence in the native deer mice. [warning, the following is gross]

They put mice in a blender and liquify them, then run the tests. That would be a whole other level of exposure than contact with nests in a tent house.

 

[Estellea]

Too bad the media didn't include what future visitors could do to reduce their exposure potential. Milder winters coupled with drought conditions are perfect conditions for increased hantavirus prevalence among rodent populations as well as increased transmission to humans.

Este

 

[Estellea]

As an example, I worked with people studying hantavirus prevalence in the native deer mice. [warning, the following is gross]

They put mice in a blender and liquify them, then run the tests. That would be a whole other level of exposure than contact with nests in a tent house.

That is not what the protocol is for collecting samples for testing and particularly gross and unethical if the animals were alive.

Este

ETA: I'm not shooting the messenger (I apologise if it read that way). I just don't want to let anyone get the impression that this is an acceptable proceedure.

 

[casebro]

I'm unclear how you are getting the 114 cases. You don't know that all 10,000 people were exposed. Those were not the people whose serologies were tested.

With the lack of sufficient data to back up your quote of "a high fatality rate", I was just trying to guess at the number of subjects studied to get the 1.14% of positive serology tests. 114 positives out of 10,000 subject would do that. Better yet, 4 positives out of 350 samples fit, at 1.1428%. They did state in your link that the subjects were 'rodent handlers', I take that to mean high risk subjects. And the results I presume mean that 1.14% got the infection with out needing hospitalization. They got over it, and now have + serologies. Hey, if they studied those who already had confirmed illnesses, they would have said so instead of "rodent handlers".

But you haven't backed up your claim of "high fatality rate" with anything, since you have no data on total number of illnesses, only number of hospitalized patients. The 1.14% of positive serologies proves that more people get it without needing hospitalization, therefor "highly fatal" is in doubt. To ME. How about anybody else weighing in?

 

[casebro]

Hmm, re-reading the OP subject line, 10,000 tourists exposed.

Lets keep an eye on this, and see how many confirmed cases happen. THAT will give us some data to discuss, eh?

This endemic incident has 6 so far, but I would need to read more to find fatality numbers. Were the 6 among the tourists, or among the staff?

 

[Estellea]

Casebro, estimating case fatality rates of any pathogen is imperfect. We use the number of reported cases as the denominator and deaths as the numerator. There are always going to be a number of unreported cases either due to misdiagnosis or mild clinical course. That's why it's an estimate. Sin nombre and closely related hantaviruses have an estimated 36% case fatality rate.

Este

 

[Estellea]

Hmm, re-reading the OP subject line, 10,000 tourists exposed.

Lets keep an eye on this, and see how many confirmed cases happen. THAT will give us some data to discuss, eh?

This endemic incident has 6 so far, but I would need to read more to find fatality numbers. Were the 6 among the tourists, or among the staff?

Could have been exposed, not definitively exposed.

Este

 

[Skeptic Ginger]

That is not what the protocol is for collecting samples for testing and particularly gross and unethical if the animals were alive.

Este

ETA: I'm not shooting the messenger (I apologise if it read that way). I just don't want to let anyone get the impression that this is an acceptable proceedure.

Of course they killed the mice first. All I can say is that's what the researchers I worked with did. I provided policy advice, TB tests and vaccinations for the company doing the research. I was not one of the researchers. And they did a lot of other research.