Emerging diseases and immunity

[Cedars]

Originally Posted by mynah

It depends on how you define "species jump". Some would say a species jump had taken place once a disease had been transmitted from the host species to another species for the first time: In this article, for instance rabies due to Australian bat lyssavirus is listed among diseases that had undergone a species jump, even though only two human cases (both transmitted through bat bites) have been recorded. One should also keep in mind the stringent measures some countries took to limit the spread of avian flu: Vietnam, for instance, culled its entire farmed bird population and started anew with imported hatchlings.

Fair enough. Some would say such things. I dont consider the avian flu a true jump yet, as it is not spreading as canine distemper did through the seal populations (and apparently the lion populations of Africa), nor is it like the parvo virus jump from cats to dogs in the late 70s or early 80s. A true jump (imo) requires the disease to be transmittable on a comparable level with the original host infection rate. The avian bird flu H5N1 tears through bird populations with a high percentage of them becoming ill and then dying. This also makes the efforts of Vietnam importing new populations of chickens pretty pointless, in that wild birds are the main carriers of H5N1. Unless of course they are importing birds who are carrying some type of immunity to this strain, as some wild asian mallards seem to have.

As far as rabies (and I am not sure its a good example), well theres all kinds of strains out there which have become specialized for one type of host (canine rabies) but is transmittable to a whole host of animals, man included. Is it really a new jump or an old genetic code that rears its head during mutations, hence the bat transmission being something that should be expected, rather than declared a new specie jump? Does anyone know where these particular bats obtained their original infection from? Would be kinda ironic if it was from some domestic animal, say a dog brought over on one of the prison transports to australia so many years ago.

Originally Posted by mynah

The WHO defined three stages and six phases in the development of a flu pandemic: By their definition, avian flu had reached stage two (pandemic warning period) and was entering phase 4 ("Minor outbreaks of limited distribution from human to human occur, although such outbreaks are highly localised. This appears to indicate a viral strain that is not yet well equipped to infect humans.") when the tide was turned.

What tide was turned? Theres like 65,000 flu related deaths in the USA a year and not one of them related to H5N1. We have what? Less than 400 H5N1 (or is it 800?) deaths worldwide with the potential for a handful of them being person to person transmissions. Does the potential exist for H5N1 making a transition into something like the spanish flu? Sure. But it also has the potential of making that 'true jump' without being more than a typical flu season with all its new strains and variations of the same old, same old.

If I remember right, they have already seen mutation in the ebola virus which allows more of its hosts to survive. Its really not in a virus best interest to kill its host, well not kill them fast anyways. I suppose this is part of the evolutionary reason why viri and bacteria can mutate so fast. Whoops, I didnt mean to burn down the house Honest!

[mynah]

This also makes the efforts of Vietnam importing new populations of chickens pretty pointless, in that wild birds are the main carriers of H5N1. Unless of course they are importing birds who are carrying some type of immunity to this strain, as some wild asian mallards seem to have.

I'm not sure just what measures Vietnam took apart from the cull. (There were no chickens or ducks when I visited the country at the end of 2005, but according to Hanoi newspaper reports at the time, chicken would soon be available again.) The campaign did seem to have positive effects: After 61 cases were recorded in Vietnam in 2005, there were none at all in 2006. Since then, however, there have been a few cases. It would seem to me that Vietnam has a special problem in that many rural people, especially women, spend much of their working day in open water.

As far as rabies (and I am not sure its a good example), well theres all kinds of strains out there which have become specialized for one type of host (canine rabies) but is transmittable to a whole host of animals, man included. Is it really a new jump or an old genetic code that rears its head during mutations, hence the bat transmission being something that should be expected, rather than declared a new specie jump? Does anyone know where these particular bats obtained their original infection from? Would be kinda ironic if it was from some domestic animal, say a dog brought over on one of the prison transports to australia so many years ago.

I mentioned rabies specifically because it is one of the conditions that are problematic as far as the definition of a species jump is concerned. (Its unique and aggressive mode of transmission is responsible for its widespread presence in many mammals, rather than its transmissibility.) Australian bat lyssavirus (which is present in most states, but not outside Australia) is not a typical rabies virus, and appears to be quite different from the canine rabies virus - but that is a very interesting question! The original host of rabies viruses has never been found, but is most likely to be an African bat. There are several rabies strains that do not spread all that readily between species: If a rabid dog bites another dog and a human, for instance, the dog is far more likely than the human to get rabies.

What tide was turned? Theres like 65,000 flu related deaths in the USA a year and not one of them related to H5N1. We have what? Less than 400 H5N1 (or is it 800?) deaths worldwide with the potential for a handful of them being person to person transmissions. Does the potential exist for H5N1 making a transition into something like the spanish flu? Sure. But it also has the potential of making that 'true jump' without being more than a typical flu season with all its new strains and variations of the same old, same old.

I was referring to avian flu specifically, but perhaps it is too early to speak of the tide turning: Around 1975 the WHO thought it had malaria licked. There has been a decline in the number of cases of avian flu, but vigilance should be maintained. Worryingly, recent cases appear to have an increased mortality rate - although it could be that at the height of the outbreak more people with milder symptoms reported to doctors, or that doctors were more likely to have patients with flu symptoms tested.

If I remember right, they have already seen mutation in the ebola virus which allows more of its hosts to survive. Its really not in a virus best interest to kill its host, well not kill them fast anyways. I suppose this is part of the evolutionary reason why viri and bacteria can mutate so fast. Whoops, I didnt mean to burn down the house Honest!

Probably the most important reason why emerging diseases seem to decrease in virulence - and certainly a more plausible explanation than that people acquire immunity en masse to a particularly virulent strain.

[Cedars]

Originally Posted by mynah

I mentioned rabies specifically because it is one of the conditions that are problematic as far as the definition of a species jump is concerned. (Its unique and aggressive mode of transmission is responsible for its widespread presence in many mammals, rather than its transmissibility.) Australian bat lyssavirus (which is present in most states, but not outside Australia) is not a typical rabies virus, and appears to be quite different from the canine rabies virus - but that is a very interesting question! The original host of rabies viruses has never been found, but is most likely to be an African bat. There are several rabies strains that do not spread all that readily between species: If a rabid dog bites another dog and a human, for instance, the dog is far more likely than the human to get rabies.

Australian bat lyssavirus - Wikipedia, the free encyclopedia
Thought a link to ABLV might be useful.

There are many variables regarding infection rates of rabies, I would like to see a link verifying a dog is more likely to get rabies than a human all things being equal. There are variables in how infected the source dog is, how deep the bite wound, how many bites, etc (such as related bleeding, viral access to central nervous system, etc) which do impact the rate of infection for all mammals as I understand it. There can be some very long incubation rates before rabies symptoms appear, but again, the body is not recognizing this virus as an invader, allowing it to continue to reproduce before it finally finds a way into the central nervous system.

Originally Posted by mynah

I was referring to avian flu specifically, but perhaps it is too early to speak of the tide turning: Around 1975 the WHO thought it had malaria licked. There has been a decline in the number of cases of avian flu, but vigilance should be maintained. Worryingly, recent cases appear to have an increased mortality rate - although it could be that at the height of the outbreak more people with milder symptoms reported to doctors, or that doctors were more likely to have patients with flu symptoms tested.

Define vigilance. We had people mass consuming anti-virals to the point of causing shortages, price hikes and worse yet drug resistant flu strains all due to the increased awareness of a handful of cases of infections.

We diverted millions of dollars of research funding to investigate. How much time was lost on these other issues? How many other proven infection control programs lost funding (such as malaria) as funds were re-allocated to chase this particular OMG! the Experts Say We Gotta Do Something Now headline news bulletin flashed across the screen. We wont ever know.

And after all of this, we still dont have a mutated H5N1, and if I remember correctly, if it does mutate to a deadly epidemic/pandemic type infection, it will still take 6 months before the first vaccinations are available to the people on the short list (you know, politicians, their families, etc) and the medical people, emergency responders, etc.

6 of 1, half dozen of another. I really dont worry too much about what if a new disease pops up in the congo, in viet-nam, in china....

[mynah]

Originally Posted by Cedars

There are many variables regarding infection rates of rabies, I would like to see a link verifying a dog is more likely to get rabies than a human all things being equal. There are variables in how infected the source dog is, how deep the bite wound, how many bites, etc (such as related bleeding, viral access to central nervous system, etc) which do impact the rate of infection for all mammals as I understand it. There can be some very long incubation rates before rabies symptoms appear, but again, the body is not recognizing this virus as an invader, allowing it to continue to reproduce before it finally finds a way into the central nervous system.

You'll find most of what you want to know - well, perhaps more than you'd like to know - about rabies in this online book.

Two interesting facts about immunity to rabies:

Whereas early and appropriate treatment after exposure almost always always prevent rabies from developing in humans, such treatment is ineffective in dogs. (This is not to be confused with vaccination in animals, which is generally effective.)

It would seem that the human immune system does react to rabies exposure, and sometimes overcomes the virus. A fur trapper who had killed thousands of foxes in a rabies endemic area, for example, was found to have antibodies against the virus in his blood, even though he had never been vaccinated against rabies or received treatment after being bitten.

Define vigilance. We had people mass consuming anti-virals to the point of causing shortages, price hikes and worse yet drug resistant flu strains all due to the increased awareness of a handful of cases of infections.

If a severe strain of a virus that previously did not infect people it all begins to do so, one should take notice. If it begins to get spread directly from person to person, it is an indication that the outbreak may be progressing to phase 5 (Phase 5: More generalised outbreaks are seen, but transmission between humans is still limited. Indications are that the virus is still not readily transmissible between humans, but that it is becoming so. The risk of a pandemic is now significant.) Phase 6 is the pandemic itself. Though the incidence of H5N1 avian flu has decreased, it has not gone away - and the disease caused by it remains severe.

6 of 1, half dozen of another. I really dont worry too much about what if a new disease pops up in the congo, in viet-nam, in china....

As AIDS did? Remember, in these days of global travel, a new disease may just be a plane flight away... Here in South Africa, we are bearing the consequences of a government ignoring a new killer disease because acknowledging it happened to be politically inconvenient. As a consequence, average life expectancy is now down to 42 years.

[Cedars]

Originally Posted by mynah

You'll find most of what you want to know - well, perhaps more than you'd like to know - about rabies in this online book.

Two interesting facts about immunity to rabies:

Whereas early and appropriate treatment after exposure almost always always prevent rabies from developing in humans, such treatment is ineffective in dogs. (This is not to be confused with vaccination in animals, which is generally effective.)

I will read the book later today if time permits.

I would like to say that because a treatment used on people does not work on dogs does not bear relation to whether or not a human is at equal risk for developing rabies without treatment. We develop treatments for canine diseases which do not work on similar humans diseases also. Lots of promising clinical trials on people have failed when they were successful on dogs (and other lab animals).

Originally Posted by mynah

It would seem that the human immune system does react to rabies exposure, and sometimes overcomes the virus. A fur trapper who had killed thousands of foxes in a rabies endemic area, for example, was found to have antibodies against the virus in his blood, even though he had never been vaccinated against rabies or received treatment after being bitten.

Yes, and when spanish flu raged around the world not everyone exposed developed the disease. That is a immune system genetic difference that is apparent in most (if not all) diseases which rage through a population, whether human or animal.

Originally Posted by mynah

If a severe strain of a virus that previously did not infect people it all begins to do so, one should take notice. If it begins to get spread directly from person to person, it is an indication that the outbreak may be progressing to phase 5 (Phase 5: More generalised outbreaks are seen, but transmission between humans is still limited. Indications are that the virus is still not readily transmissible between humans, but that it is becoming so. The risk of a pandemic is now significant.) Phase 6 is the pandemic itself. Though the incidence of H5N1 avian flu has decreased, it has not gone away - and the disease caused by it remains severe.

Except that H5N1 human exposures typically do not cause the disease in humans. As I have said, the risk of developing this particular disease is primarily due to the handling of infected animals, rather than simple exposure such as with a typical human flu. I have participated in the butcher of animals and the cleaning of their pens. It was very important that I not do certain things, such as being very careful while making cuts to not cut myself, exactly so I did not expose myself to a disease that animal may harbor which would not normally affect a human unless you did something to expose yourself.

Originally Posted by mynah

As AIDS did? Remember, in these days of global travel, a new disease may just be a plane flight away... Here in South Africa, we are bearing the consequences of a government ignoring a new killer disease because acknowledging it happened to be politically inconvenient. As a consequence, average life expectancy is now down to 42 years.

AIDs discussion should probably have its own thread. As far as just a plane flight away, while true, we do have the example of SARs which never turned into the global pandemic, yet still exists out there in the real world. If I remember right, less than 9,000 deaths since its beginning.

Gotta go birding now.

[mynah]

I'd like to return to the subject of killer flu later (haven't had time for detailed postings recently!), but a classical situation concerning emerging diseases has arisen uncomfortably close to where I live.

On 12 September a woman aged 36 was airlifted, accompanied by a paramedic, from Zambia to a private hospital in Johannesburg, South Africa. She had fallen ill three days previously. In spite of treatment, she died two days later of symptoms suggesting viral haemorrhagic fever. However, tests for all known HFs came back negative.

On 27 September the paramedic (36) was admitted with similar symptoms. He died on 1 October. A nurse (34) who had treated the first patient sought medical treatment early in October and died in hospital 3 October. Another woman who had worked in the same ward has also died, but a link has not been confirmed.

The WHO is now investigating the outbreaK.

Since then, 121 people have been quarantined. Experts consider Crimean Congo fever the most likely culprit, although a number of findings are not consistent with such a conclusion, including:

* CCF, a tick-borne disease with a mortality of some 30 percent, is rarely transmitted from human to human, and secondary cases are rarely fatal.
* Most people who succumb to HFs only do so in the second week, whereas these patients died within five days or fewer.
Tests for CCF and all other known HFs have proven negative.
* The 100 percent mortality rate so far - in spite of good quality hospital care - is another obvious cause for concern.

[mynah]

Latest news in is that two more people have been admitted to hospital. No indication has been given of their condition.

[mynah]

Don't worry, they keep on telling us...



Janusz Paweska, head of the special pathology unit at the South African National Institute for Communicable Diseases, at work in Johannesburg.

[mynah]

This could be the next big one...

Coming soon to an airport near you?

[mynah]

Latest news:

Breaking news: WHO on high alert

This is beginning to look even more like the big one. It has many characteristics not seen in the SARS and avian flu outbreaks in Asia, and has many of the hallmarks of a pandemic: High mortality rate especially among young adults, novel genetic composition, is spread from person to person, and is spreading from town to town... In addition, Americans may take notice of the fact that it has already crossed their borders...