Dr. Donald Thea

GLG News by Dr. Donald Thea, Professor of International Health

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PCR detetction of Salmonella food contamination not yet ready for prime time.

May 22, 2007

Analysis of:New Test May Allow For Rapid Detection Of Salmonella In Meat | www.medicalnewstoday.com

PCR is an invaluable tool in the research setting but has only limited usefulness in a clinical context and, in my opinion, even more limited application for broad-based surveillance applications such as this. While PCR done well under laboratory conditions with samples spiked with known quantities of salmonella are able to be done with exquisite sensitivity (picking up all instances of salmonella) and specificity (not falsely picking salmonella when it isn't there), but getting these levels of test performance in an abbatoir or meat-packing facility will be challanging. PCR is notoriously susceptible to cross contamination and is very demanding of proper laboratory technique. Its ability to detect minutely small quantities (e.g. one bacteria or virus) of a pathogen make it prone to false positives. There are also many species of non-pathgenic Salmonella that might be detected (depending on the configuration of the primers used in the PCR) which may also result in false positives. 

Limited human-H5N1 to-human transmission documented

August 2, 2006

Analysis of:Bird Flu Passed From Son to Father, W.H.O. Says | www.nytimes.com

This is the best and most well-documented case of human-to-human (H2H) transmission that has yet occurred.

Genetic testing (we are told but data not yet released) indicates that a 'minor' mutation has occurred but it isn't considered to be one that confers more efficient H2H transmission.

H2H transmission as was documented between the father and son here, has likely occurred before but the issue of concern is the high infection rate within one family cluster (see previous post).

The dreaded start of Human to Human Pandemic Flu transmission? - Well not probably

August 2, 2006

Analysis of:Bird Flu Passed From Son to Father, W.H.O. Says | www.nytimes.com

In a closed meeting in Indonesia on Friday June 23 WHO and other experts have pronounced that the epidemiologic investigation of a family cluster of 7 cases (6 fatal) that occured at the end of May in Indonesia probably resulted in one true 3-way transmission event (person A to person B to person C).

If so, this will be the best documented individual event thus recorded. From an AP report the evidence supporting this finding is that a 'very small' mutation has occured, which was found in the last two infected individuals in the transmission chain (father and son). It is also reported that the mutations were enough to identify the concordance of the viral strains infecting these two individuals but not extensive enough to promote facilitated person-to-person spread of the virus.

Fortunate, if true because this specific strain was highly lethal (6 of 7 deaths) in this particular family. In the absence of any plausible explanation for this high lethality in this cluster, it has been suggested that this particular family has a naturally occuring genetic susceptibility to H5N1 avian influenza. No evidence has been provided to support this theory, however.

H5N1 Human Influenza: more and more like 1918 Spanish influenza

June 15, 2006

Analysis of:Differential Expression of Chemokines and Their Receptors in Adult and Neonatal Macrophages Infected with Human or Avian Influenza Viruses. | www.journals.uchicago.edu

This paper presents in vitro data which shows that monocyte-derived macrophages - the cells which largely flood the lungs during disease - elaborate much higher levels of chemokines to infection with H5N1 than to human influenza strains. These high levels are consistent with the 'cytokine storm' picture of rapidly progressive immune dysfunction characterized by human infection with H5N1.

Moreover, adult macrophages appear to be able to produce far higher levels of the chemokines: CCL2, CCL3, CCL5 and CXCL10. This is strong invitro support for the age-specific severity referred to above and that profound immune dysregulation is the major clinical event in severe H5N1 infection.

Good progress with H5N1 pandemic influenza DNA vaccine

June 8, 2006

Analysis of:Vical Avian Flu Vaccine Data Meets NIH Grant Funding Requirement | ir.vical.com

This news release reports that Vical has received accelerated access to $2.6 million in seed funding to develop a human DNA vaccine against H5N1 avian influenza after reviewing the preliminary, preclinical data recently reported (see: http://ir.vical.com/ireye/ir_site.zhtml?ticker=vicl&script=415&layout=-6&item_id=850402). The prior news release reported that, with the use of a Vical proprietary adjuvant (Vaxfectin™), there was both good immune response to a three component DNA vaccine and, more importantly, 100% protection in mice and ferrets against a lethal viral challenge with a wild type H5N1 strain.

Are we ready? Family cluster of Avian Influenza investigated.

June 5, 2006

Analysis of:Pandemic Flu Dry run is cause for concern | www.nature.com

This report of the field investigation of the recent family cluster outbreak in Indonesia provides relevant and interesting details. Worringly, the response was slow and somewhat ineffectual with incomplete containment of several infected family individuals.

Effective and complete surveillance of surrounding communities, especially in population dense areas would be necessary to contain the spread of an easily transmissible strain of avian influenza, but this experience indicates that it will be difficult.

Of particular note in this story is the claim that there were much higher viral loads in the throats and nose of some patients - something that has not been documented previously and would be expected in a human-to-human easily tranmissible strain.

No mutations have been reported but, as typical, the WHO is not releasing the genotypic information to the scientific community.

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