# 2988
Not everyone who catches a virus develops symptoms. In fact, the percentage of people sickened can be surprisingly small.
A good example is West Nile Virus.
Roughly 80% of the people infected develop no symptoms. They are `sub clinical’ cases. Only about 1 in 150 develop severe symptoms. Roughly 20% experience mild symptoms .
It is the same with influenza.
During the 1918 Spanish Flu, as terrible as that was, only about 30% of the population fell ill. The majority apparently were immune, or experienced sub clinical infections.
Thus far, we’ve seen scant evidence that the H5N1 virus produces sub clinical symptoms in people. But the problem is, very few seroprevalence (blood antibody) studies have been done.
Over the past few months we’ve seen a decided change in the demographics of bird flu cases coming out of Egypt; a shift to toddlers from adults, and a less severe form of the virus.
This has some scientists asking if a sub-clinical `silent’ infection might be being passed among people in Egypt?
While there is currently no scientific evidence to support the idea, scientists believe we should be looking for antibodies (indicating previous exposure to the virus) among people exposed to infected chickens.
People who show antibodies, but who did not fall ill, would prove that they had a sub clinical infection.
This is, quite frankly, a badly needed study. A lack of seroprevalence studies has been an ongoing disappointment for many of us who follow the avian flu story.
Reuters has the story this morning. Follow the link to read it in its entirety.
INTERVIEW-Concerns arise over symptomless Egypt bird flu cases
Wed Apr 8, 2009 7:13am EDT* WHO concerned about possible bird flu human carriers * U.N. body to test if cases exist * Worries about mutation of the pathogenic virus
By Cynthia JohnstonCAIRO, April 8 (Reuters) - The World Health Organisation is concerned some Egyptians may carry the highly pathogenic bird flu virus without showing symptoms, which could give it more of a chance to mutate to a strain that spreads easily among humans.
Whether such cases exist still has to be put to the test and will be the focus of a planned Egyptian government study backed by the global health body, said John Jabbour, a Cairo-based emerging diseases specialist at WHO.
"This is a concern only, now. It is a question to be asked," Jabbour told Reuters. He said a change in the pattern of human bird flu infections this year in Egypt had raised concerns about the existence of so-called sub clinical cases.
The most populous Arab country, which has been hit harder by bird flu than any other country outside of Asia, has seen a surge in infections this year.
While the H5N1 virus only rarely infects people, experts fear it could mutate into a form that humans could easily pass to one another, sparking a pandemic that could kill millions.
The emergence of symptomless human carriers of the virus would be a worrisome development because it could allow the virus, undetected and untreated, more time to mutate inside the human body, Jabbour said.
We also learn from this article something which has been suspected for several days, that cases #61 and #62 who fell ill within days of each other, were cousins.
We’ve previously heard that they were next door neighbors, which has led to speculation that H-2-H (human-to-human) transmission may have been involved.
The burden of proof required to establish H-2-H transmission is pretty high, and it can therefore be difficult to prove. Proximity and a gap in onset dates isn’t enough to `prove’ H-2-H, even if it does raise suspicions.
According to this article, authorities believe both boys were infected from a common source – infected birds.
He added that two toddlers from the northern province of Beheira infected within days of one another in March were cousins. But he said the boys were believed to have contracted the virus from the same sick birds, not from each other.
Even if this case involved the H-2-H transmission of the virus (unproven), we’ve seen that before, and so it would not signify anything particularly new.
So far, there are no signs of sustained, efficient transmission of the virus here, and that is really the concern.
