The World Health Organisation is tonight holding its pandemic alert at five, indicating that swine flu is spreading human-to-human in at least two countries in one WHO region.
The Ministry of Health has released the latest case figures on swine flu – 111 suspected cases (up from 104), 13 probable and 3 confirmed. The latest MoH update (14) on swine flu is here. Environmental Science and Research (ESR) has boosted its scientific capacity to handle testing of suspected swine flu cases.
The number of cases in isolation has increased from 111 to 121.
British scientists are continuing to answer questions on swine flu posed by journalists. The Science Media Centre in London collated the answers below.
If you have your own questions about any science-related aspect of swine flu, pandemics or vaccines, email the SMC (NZ) on smc@sciencemediacentre.co.nz and we’ll endeavour to get our experts to answer them.
Dr Mike Skinner, Senior Lecturer in Virology, Imperial College London:
What are the chances that this virus could in some way combine with H5N1 creating an easily-transmissible strain with a high mortality rate?
“Alan Hay made the point that this is probably no more likely than recombination of H5N1 with existing seasonal flu viruses creating such a strain, something that hasn’t happened in more than 5 years. Though this considerable validity, it really depends whether the virulence determinants of H5N1 reside on parts of its genome that can replace the swine flu equivalents without compromising the ready transmissibility of the swine flu.”
Can anyone comment on the idea that these potentially devastating zoonoses are the inevitable consequences of poor animal husbandry and unsanitary farming practises?
“No, not inevitably. Many factors may play a role. In many cases in the developing world it is due to extension of large scale farming into previously forested areas. Good examples would be Nipah virus and even SARS. In other cases, even in more developed countries, it can be due to the fact that the agent is relatively innocuous in the animal host, swine flu is a case in point and in the UK we have a potential issue in pigs with Hepatitis E.”
About viruses in general: I am assuming that a ‘successful’ virus is one which manages to transmit easily without seriously incapacitating or killing its host thus limiting its chances to spread and replicate. A strain which is easily transmitted and extremely virulent (like Ebola) presumably won’t get far because its carriers will die before they get a chance to pass it on. Is this the case? And if so how does it fit in with what we know about this and other pandemic-candidates?
“That’s generally true, the qualification is that this only applies if the host needs to be mobile to transmit the virus. If you’re a virus transmitted by mosquitoes, it doesn’t matter if you’re highly virulent, it might even increase the chance of the mosquito feeding successfully if the host is incapacitated (e.g. yellow fever). Another classic example is Rabbit haemorrhagic virus, which can be spread by blowfly feeding on the rotting carcass (advantage if host is dead).
“High virulence of variola major, without a vector, could be explained by the high environmental resistance of the desiccated virus spread as dust from encrusted lesions.
“Amongst bacteria, cholera is a good example, being spread through water via diarrhoea. That this doesn’t tend to apply to viruses is probably due to lower environmental resistance of the relevant viruses.”
Dr John McConnell, Editor of The Lancet Infectious Diseases:
Do we have any idea, even the vaguest ballpark idea, of the mortality rate for this virus yet?
“From published data on confirmed cases only, mortality rate in Mexico appears to be 4% and outside Mexico 1%. However, it’s far to early in the evolution of the epidemic for this figures to have any meaning.”
What are the chances that this virus could in some way combine with H5N1 creating an easily-transmissible strain with a high mortality rate?
“It might happen, but H5N1 has been around for at least 12 years in an environment where it could mix with other flu strains, and such a transmissible variety has not emerged. There is no more (nor less) likelihood now than there was before the emergence of Mexican swine H1N1 that a variant of H5N1 capable routine human to human transmission will emerge.”
Presumably it is fortunate that this pig strain arose on the other side of the world from where H5N1 arose?
“Of no consequence. It’s almost certain to get to the same places as H5N1 in the end, but see answer to above.”
Can anyone comment on the idea that these potentially devastating zoonoses are the inevitable consequences of poor animal husbandry and unsanitary farming practises?
“No good evidence one way or the other on this point. In Asia, from where most pandemics arise, pigs, birds, and people life together in what we in high-income countries would regard as unsanitary conditions, thus providing an ideal environment for the exchange of genetic material between the flu viruses to which the various creatures play host.
“Keeping vast numbers of pigs in industrial farming conditions does of course provide many hosts in which the flu virus can reproduce, and the more flu virus there is the more chance there will be of genetic mutation. On the other hand, pigs kept in industrial farming conditions will probably receive better veterinary care than those kept in a Chinese backyard, and pigs bred indoors are less likely to come into contact with birds carrying flu viruses.”
About viruses in general: I am assuming that a ‘successful’ virus is one which manages to transmit easily without seriously incapacitating or killing its host thus limiting its chances to spread and replicate. A strain which is easily transmitted and extremely virulent (like Ebola) presumably won’t get far because its carriers will die before they get a chance to pass it on. Is this the case? And if so how does it fit in with what we know about this and other pandemic-candidates?
“Quite a philosophical question. Of course, a virus isn’t capable of caring about success or failure. The virus also doesn’t care whether it’s host lives or dies, just as long as the host lives long enough to continue the chain of transmission. In this sense, it could be argued that Ebolavirus isn’t successful because transmission requires direct contact with body fluids and the host tends to be too disabled to spread the virus far and wide.
“If Ebola virus could think it might regard human beings as a bit of a dead end reproduction wise, whereas it’s probably quite “happy” ticking over in its natural reservoir host, which are probably bats. Perhaps a measure of “success” of a virus (or any other infectious organism) is something called the “basic reproduction number” (R0), which is defined as the mean number of secondary cases a typical single infected case will cause in a population with no immunity to the disease in the absence of interventions to control the infection. By this measure, the measles virus, with an R0 of 12-18, is more “successful” than the influenza virus (R0 = 2-3).”
Does anyone know how many countries have pandemic preparedness plans and what the global stocks of antivirals look like in different countries? I’ve asked Roche and WHO and nobody seems to be able to tell me these rather basic facts.
“The man to ask about pandemic preparedness plans is Richard Coker at the London School of Hygiene and Tropical Medicine. The Roche representative I’ve seen talk at conferences on Tamiflu stockpiles is David Reddy. Stockpiles of Relenza (zanamivir), produced by GSK, need also to be considered.”
Dr Diana Bell, Centre for Ecology, Evolution and Conservation, School of Biological Sciences, University of East Anglia:
What are the chances that this virus could in some way combine with H5N1 creating an easily-transmissible strain with a high mortality rate?
“That’s a good question (we do research on H5N1 impacts) and we mustn’t take our eyes off the H5N1 ball. The latter is still causing outbreaks and deaths in African and Asian countries less equipped medically to deal with both viruses. It’s just not front page news anymore. It also raises another question about H1N1. Can it cause infection and mortality in a wider range of species like H5N1.”
Presumably it is fortunate that this pig strain arose on the other side of the world from where H5N1 arose?
“Yes for those countries where H5N1 has become endemic and have fewer medical facilities namely Asian and African countries. On the other hand, countries like Vietnam with experience of dealing with outbreaks of both SARS and H5N1 have been swift to implement surveillance at airports for instance.”
Can anyone comment on the idea that these potentially devastating zoonoses are the inevitable consequences of poor animal husbandry and unsanitary farming practises?
“H5N1 probably arose from the highly artificial environment created by intensive farming (which allows for the potential of highly pathogenic viruses) of poultry and SARS has been attributed to mixing of species in an extensive wildlife trade network. We have to learn the lesson that intensive farming carries risks.”
Hannah Rhind, Public Relations Executive, Product Communications, Roche Products Limited:
Does anyone know how many countries have pandemic preparedness plans and what the global stocks of antivirals look like in different countries? I’ve asked Roche and WHO and nobody seems to be able to tell me these rather basic facts.
“In response to your final question, to date, Roche has fulfilled Government pandemic orders amounting to 220 million treatment courses of Tamiflu. 5 million packs were also donated to the WHO in 2006, 2 million treatment courses of which are for WHO regional stockpiling and 3 million treatment courses of which constitute a “Rapid Response” stockpile.
“Unfortunately I can’t provide specific information on the amounts stockpiled by various countries, but I can tell you that the UK is one of the world-leading countries in terms of pandemic preparedness.”