6/27/2010

Monkeys and Mice: A Literature Review the Anti-Vaccine Folks Should Embrace But Won't

ResearchBlogging.org


Aschner and Ceccatelli (2010) review the relevant data for thimerosal as a cause of autism. They conclude there is "no reliable data indicating that administration of vaccines containing thimerosal is a primary cause of
autism. However, one cannot rule out the possibility that the individual gene profile and/or gene–environment
interactions may play a role in modulating the response to acquired risk by modifying the individual susceptibility."

Aschner and Ceccatelli first discuss all the possible exposures to mercury that occur in the environment. There's a lot of potential exposures to mercury, with fish being the primary exposure to methylmercury.

Of interest is this paragraph:

"The incidents in Japan and Iraq revealed the particularly devastating neurotoxic effects of MeHg on the developing nervous system. Lately, also exposure to much lower level of MeHg from dietary sources was shown to have unfavorable neurodevelopmental effects as reported by prospective studies of populations in the Faroe Islands and New Zealand (Kjellstrom et al. 1989; Grandjean et al. 1997). Recent studies point to the critical role that maternal diet can play in the onset of MeHg developmental neurotoxicity (Davidson et al. 2008)." (Aschner and Ceccatelli)

It makes almost no sense on a practical level for parents to be raging against thimerosal while ignoring the reality that their children's exposure to methylmercury is far more pervasive.

Aschner and Ceccatelli note that thimerosal was removed from vaccines under the assumption that toxicity would be similar to methylmercury exposure,  but that since that removal, "it has been shown that the kinetics of tissues disposition and metabolism differ from those for MeHg." They continue: "While the scientific literature supports the concept that MeHg is a potent developmental neurotoxin, the assertion that thimerosal leads to developmental disorders in children is hypothetical and unsubstantiated, resting on indirect and incomplete information, primarily from analogies with MeHg."

As a purely precautionary action, reducing thimerosal exposure made practical sense while conducting studies to look at the potential for neurotoxicity. Unfortunately, we know that those who latched onto thimerosal as a potential cause of autism, have used this cautionary act as proof that the government and pharma knew it was a problem. It's evident from careful and exhaustive reading of parents who buy into the vaccine causation theory that facts and evidence aren't necessary for this belief system to maintain itself  more fervently over time and as each potential theory is shot down.

Safety studies on thimerosal have now been conducted. So have studies looking at autism rates as thimerosal was removed from vaccines.  Aschner and Ceccatelli  conclude from these studies: "Simply stated, MeHg is not a suitable reference for evaluating ethylmercury toxicity. Key observations to substantiate this statement include the following: (1) mercury clears from the body much faster after the administration of ethylmercury than after the administration of MeHg; (2) the brain-to-blood mercury concentration ratio established for MeHg will overestimate mercury in the brain after exposure to ethylmercury; and (3) because ethylmercury decomposes much faster than MeHg, the risk of brain damage is less for ethylmercury than for MeHg."

Aschner and Ceccatelli even spend a fair amount of time reviewing Burbacher's study on monkeys that the anti-vaccine folks love to trot out. Hornig's mice study is also reviewed. If the anti-vaccine folks were about scientific evidence, then they'd have to embrace the conclusions that Aschner and Ceccatelli come to, but anyone who's spent time reading those who embrace autism as vaccine injury knows once they're aware of Aschner and Ceccatelli's literature review, they'll be quick to reject it, especially since the conclusion of the literature review on thimerosal and autism is: "Methodologically sound and rigorous epidemiological
studies have largely failed in finding a significant correlation between thimerosal-containing vaccines and autism. However, efforts to reduce the exposure of infants, children, and pregnant women to any form of mercury from various sources should continue."

Aschner, M., & Ceccatelli, S. (2009). Are Neuropathological Conditions Relevant to Ethylmercury Exposure? Neurotoxicity Research, 18 (1), 59-68 DOI: 10.1007/s12640-009-9113-2

1 comment:

Roger Kulp said...

I know it's unrelated,but this antivaccine/mercury garbage would never have gotten off the ground, if more doctors had done a better job,of working up,and diagnosing these children in the first place. Most of the bloggers who do a really good job of ripping holes in the antivax movement, rarely address the reason that parents embrace all this antivax garbage in the first place.I think that a lot of it has to do with the fact too any parents have been told this or that medical,developmental (Like motor development,or not being toilet trained.)or behavioral problem is "just a part of autism",when it really isn't. They have seen doctors who are simply not bright enough,concerned enough,too lazy,or too busy,to look for genetic syndromes like the one that caused my "autism".If the child has both autism,and other medical issues,they probably have mutations on more than one cromosome,as I do.

I am convinced that many so called "rare" genetic syndromes are really not that rare after all.Doctors simply have not bothered to look for them,and a lot of the children who have these undiagnosed syndromes,are auistic, and have either intellectual disability,or a lot of "comorbid" medical issues.Anybody who is really interested in stopping all this this crap about vaccines,and mercury,ought to make it a priority to make sure these children get proper diagnoses in the first place.