Thimerosal and autism – an overview, Part III

As promised, here’s part III of the thimerosal/autism controversy. Parts I and II are here and here, respectively.

Aren’t there studies that prove thimerosal causes autism in animals? No. There are studies that purport to do so, however, and we’ll be going over the most prominent ones to see why they don’t prove anything of the sort.

Mady Hornig’s mice: In 2004, a study was published by Hornig et al from Columbia University called “Neurotoxic effects of postnatal thimerosal are mouse strain dependent”. In it, different strains of newborn mice were injected with either thimerosal or placebo in doses approximating those in vaccines on a rather crowded dosing schedule (at mouse developmental stages equivalent to those of the human infant vaccine schedule). They found that a particular strain of autoimmune-susceptible mice, SJL/J, developed certain pathological behaviors and anatomical changes in their brains that correlated with administration of thimerosal – growth delay, reduced locomotion, exaggerated response to novelty, and densely packed, hyperchromic hippocampal neurons with altered glutamate receptors and transporters. They concluded these behaviors correlated to autism in humans.

The study didn’t mention this, but Dr. Hornig also released a video that showed the affected mice grooming each other to death and engaging in self-mutilation, a description of which made its way into a book sympathetic to the mercury militia, Evidence of harm by David Kirby:

“He has groomed through the skull, and eventually destroys his partner,” Hornig said.


There are a number of serious issues with this study, which (surprise, surprise!) was funded by, among others, Safeminds and the MIND Institute at UC Davis, CA:

*As Prometheus points out, the mice were given a dose of thimerosal equivalent to that which a boy in the 10th percentile of weight would be exposed to (as opposed to the average/median child at the 50th percentile, which would have been the natural dose to pick), and the spacing of the injections was only a few days apart,so that (unlike the situation in humans, where vaccines are given months apart) thimerosal from previous doses would not have had the opportunity to clear from the body. These two factors meant the mice were actually exposed to higher doses of mercury than most human babies would.

*There is no convincing evidence autism is an autoimmune disease.

*The behaviors displayed by the SJL/J mice are typical of the mouse strain – it apparently is a naturally aggressive one.

*Neither the diminished capabilities, nor the brain areas supposedly affected, correspond well to autistic human behavior.

*A study done in 2007 attempting to replicate the results of Hornig et al failed to do so.

Thomas Burbacher’s monkeys: A study done in 2005 on 41 infant Macaque monkeys, who were either given methylmercury orally or injected with vaccines to which thimerosal had been added by the researchers (by 2005, there were no more thimerosal-containing vaccines of the type given to infants in their first months to be found), at birth and once a week for the first 3 weeks of life. The study found that while thimerosal was cleared from the body in general, and the brain in particular, much faster than methyl mercury, the proportion (and absolute amount) of inorganic mercury (presumably derived from the Methyl mercury and thimerosal by a process called dealkylation) left in the brain was greater in the case of the thimerosal-exposed monkeys. The study’s conclusion, that the pharmacokinetics of Methyl and ethyl mercury are different enough so that one cannot be used to study the other, is correct. But the mercury militia (and apparently Burbacher himself, who is also funded by Safeminds) have seized upon the inorganic mercury left in the brain as some sort of “smoking gun”. However:

*The tight dosing schedule (4 shots, a week apart) causes the same potential overdose problems mentioned in Hornig et al, though this is not reflected in the monkeys’ blood levels.

*The thimerosal was added to thimerosal-free vaccines, and it was possible that some of it was already degraded into the form of inorganic mercury at the start of the experiment (Bartholomew Cubbins has a video about this study addressing this point; I confess to have found it very confusing before I went back to re-read the study in full, though).

*In real life, most infants are exposed to larger quantities of (environmentally-derived) methyl mercury than (vaccine-derived) ethyl mercury, and since methyl mercury sticks around in the body and brain in greater quantities and for much longer than thimerosal, over time you’d expect that most of the inorganic mercury found in the brain, say of a 1-year-old baby, would be derived from dealkylated methyl mercury, not dealkylated thimerosal. As the baby monkeys were sacrificed long before that and we don’t know what they were fed, this is not something that this study could test, but it’s of major clinical importance if one wants to claim that…

*Inorganic mercury in the minute quantities found in the brain actually cause autism, or any neurological dysfunction (something this study didn’t test for). There is no evidence for this as of today. The mercury militia engages in a good deal of backwards reasoning here.

Laura Hewitson’s monkeys: a series of 3 studies derived from one experiment with 16 Macaque monkeys, 13 of which were given the standard pre-1999 vaccine schedule given human infants, including MMR and thimerosal containing vaccines. The poster presentations of the studies at International Meeting for Autism Research last month (these have yet to be accepted to a journal or undergo peer-review) claim to have found differences in the injected monkeys’ behavior and gut inflammation after the MMR.

Orac does a far better job at analyzing the bad science behind these studies than I ever would, so go over there and take a look. The fact that 1) Hewitson and her husband are parents to an autistic child and are (or were) litigants in the Autism Omnibus hearings, 2) the husband has long been a contributor the the autism/vaccines theory, and 3) that Andrew Wakefield is a co-author to these studies has nothing to do with it, I’m sure. 😉

But didn’t Bernadine Healy, the former director of the NIH, just say the autism/vaccine question is still open?

She did, though it comes down to her being a good deal more impressed by the research than most of the scientific community. As well as holding a rather naive belief that “I think the public’s smarter than that. The public values vaccines.”. Has she really not seen what happened in the wake of Wakfield’s study in Britain? You can see the CBS interview with her here. Kev at LeftBrainRightBrain has a good post regarding Healy’s credentials and history as well.

But if the thimerosal/autism link is such hooey, why are thousands of parents having their day in court about the issue? Doesn’t that prove there’s something to it? No. Parents who feel their child was harmed by vaccines can file a claim with the VICP (Vaccine Injury Compensation Program), which was set up in 1988 as a no-fault method to compensate children genuinely injured by vaccines by the Department of Health and Human Services. If a specific known reaction occurs within a certain time frame from receipt of the vaccine, compensation is automatic – see table of reactions; if the reaction, however, is an unrecognized one or outside of the time frame stated, it’s considered “off-table” and the family needs to prove that there really is a connection between the administration of the vaccine and the ensuing complication – legal proof, incidentally, not far more rigorous scientific proof. As autism is not such a recognized complication and the connection between the vaccines and the child’s diagnosis of autism may be months or years apart, any claim brought to the VICP would fall under the latter type.

As the autism/vaccines theory became popular among parents of autistic children, there was demand for a court proceeding which would address the multitude of claims these parents brought to the VICP and compensate them accordingly, and to allow experts on both sides of the equasion to hash out in court whether the theory that vaccines (either thimerosal, MMR, or a combination) cause autism is in any way convincing. The trials are prsided over by specially-trained judges called Special Masters, who can also scientifically evaluate the evidence presented, though the cases will still be decided by legal, not necessarily scientific, standards of proof. You can read more about this at the Health Resources and Services Administration’s website.

The proceedings started in June 2007 with test cases (such as Michelle Cedillo, mentioned in Part I); at this time, experts are just wrapping up their testimony regarding the general theory of the thiemrosal/autism causation theory. Kev has been following, transcribing, and commenting on parts of the current session. Autism Diva (who has, regretabbly, stopped blogging) has lots of the dope from last year’s proceedings.

But didn’t the courts already concede that there was a link between autism and vaccines when they ordered the HHS to compensate Hannah Poling? No, and incidentally this isn’t really connected to thimerosal, but it’s current so I’m addressing it. Hannah Poling is a very special case – she apparently has a mitochondrial disorder, meaning that the mitochondria in her cells (responsible for rengenerating ATP, the body’s main energy ‘coin’) are defective. Any oxidative stress, such as a fever, could cause mental and general deterioration in such a child, and it was alleged that a febrile reaction following her vaccines caused her to develop autistic symptoms. Again, the standard of proof is the legal one; nobody can say for sure that there is an obvious cause-and-effect here. here’s a good, comprehensive review of the Poling case.

Where can I find more reliable information on the subject? The most current information, ironically, is usually found on the blogs and not at the ‘mainstream’ sites. Kev, Autism Diva (no longer updated), Kristina Chew, PhD, Autism News Beat and of course Orac write on the subject as a matter of course. Many of these are either on the atustic spectrum or parents of autistic children, hence their interest in the subject.

Kathleen Seidel’s Neurodiversity (weblog and site) is one I’d mentioned before regarding the MMR/vaccine contorversy, and it deserves a special metion here as well; Seidel has, simply put, done the work of a whole team of researchers in putting together the most comprehensive collection of original research and source materials regarding thimerosal as well.

And of course, there are the usual suspects: the FDA, CDC, WHO…I trust you to able to find those on your own 😉 .

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4 Responses

  1. Nice summary.

    Too many times, people don’t look at these studies. People say, “thimerosal and animals” and people say “look it proves autism”.

    The recent Hewiston monkey study is a prime example. Did they make autistic monkeys? Nope.

    I will expand on your comment about the Berman study–the one that failed to reproduce the Hornig study. They tried hard. As I recall, they went so far as to have a group of mice with 10x the dose of thimerosal as the Hornig mice. Still no autism and, more importantly, not even the strange behaviors that Hornig saw.

    Oh, yeah, it was done by MIND too.

  2. Yet another fabulous post, Esther. Keep up the good work!


  3. This is a very clear, accessible series. Thank you. I’d already done enough reading to feel comfortable vaccinating my children, but this gave me a lot more information than anything I’ve read before.

  4. Thank you. 🙂 . Lisa, that’s exactly what I was trying to achieve – an accessible resource for laypeople.

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