Friday, 24 January 2014

Bacterial infections and behaviour

I'm more than a little interested in bacteria on this blog. Indeed, quite a lot of chatter here has been dedicated to the various bacteria residing in our deepest, darkest recesses specifically with conditions like autism in mind. I'm also pretty interested in how other bacteria might also have the potential to do so much more than just affect a physical response. Take the issue of PANDAS (or PANS) as one example or even the notion of psychological development being linked to bacteria (in mice at least). Indeed, this piece in the New Scientist was a particularly interesting read for me (although I prefer the term psychobacteriomics...).
Garden of Earthly Delights @ Wikipedia 

Today's post deals with a triad of papers which are united in their suggestion that infection caused by bacteria may indeed have some important repercussions for conditions such as autism, schizophrenia and psychotic illness. So without further ado...

First we have the paper by Ousseny Zerbo and colleagues* who reported that although no overall "association between diagnoses of any maternal infection during pregnancy and ASD [autism spectrum disorder] was observed" in their cohort, women diagnosed with a bacterial infection during a hospital admission were "at increased risk of delivering a child with ASD". You can read more details about this study in the accompanying press release (see here) or media (see here). I should point out that this authorship group have some research form in the area of infection and autism as per my 'you give me fever' post.

Then we have the paper by Nielsen and colleagues** who, based on quite a large study group, reported that "individuals who have had a hospital contact with infection are more likely to develop schizophrenia". Further that: " Bacterial infection was the type of infection that was associated with the highest risk of schizophrenia (RR = 1.63; 95% CI: 1.47-1.82)".

Finally, the paper by Blomström and colleagues*** completes the triad and their suggestion of "a small but statistically significant association between hospital admissions for infections, in general, throughout childhood (0-13 years) and a later diagnosis of nonaffective psychosis" which "seemed to be driven by bacterial infection".

As you might already have noticed these are studies of association and correlation and so can't necessarily show causality (i.e. that bacterial infection caused autism or schizophrenia or psychotic illness). Indeed, given the complexity and heterogeneity present in these conditions, including quite a lot of chatter about spectrums, it would be foolhardy to pin it down to just one factor as being causative. I should also point out that the relative risk of bacterial infection being linked to autism, schizophrenia or psychosis were also quite low in these studies despite the connections being made.

That being said, the suggestion of a link between behaviour and a history of direct or indirect contact with bacterial pathogens is not something new. I've gone on (and on) about the concept of maternal immune activation and autism for example (see here and here) and the interesting data being generated in this area of investigation culminating with things like MAR autism and the recent leaky mice guts study. That alongside the fact that use of LPS (lipopolysaccharides) is a tool of choice when it comes to modelling bacterial infection on mouse models of autism or schizophrenia (see here). When it comes to specific agents harbouring bacteria, that's also been the topic of some discussion too (see here).

There is more to do in this area in terms of issues like tracking down exactly what types of bacteria might show more involvement in any relationship and the mechanism of effect (Inflammation? A link to those jumping genes?). Indeed, whether certain types of bacterial infection might be more commonly associated with parts of the autism or schizophrenia spectrums as per what we found on two occasions (here**** and here*****) when it came to the parent-reported frequency of impetigo in some cases on the autism spectrum. Just one example of where research might start looking.

Likewise, questions remain about the early treatment of bacterial infections and whether these might modify the risk of future development of the conditions being associated by these studies. Bear in mind however, that the use of antimicrobials (antibiotics) as the treatment of choice have also received some research attention both positive and not-so-positive (see here and here) when it comes to autism and schizophrenia.

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* Zerbo O. et al. Maternal Infection During Pregnancy and Autism Spectrum Disorders. J Autism Dev Disord. 2013 Dec 24.

** Nielsen PR. et al. Hospital Contacts With Infection and Risk of Schizophrenia: A Population-Based Cohort Study With Linkage of Danish National Registers. Schizophr Bull. 2013 Dec 30.

*** Blomström A. et al. Hospital Admission With Infection During Childhood and Risk for Psychotic Illness--A Population-based Cohort Study. Schizophr Bull. 2013 Dec 23.

**** Whiteley P. Developmental, behavioural and somatic factors in pervasive developmental disorders: preliminary analysis. Child Care Health Dev. 2004 Jan;30(1):5-11.

***** Whiteley P. et al. Trends in Developmental, Behavioral and Somatic Factors by Diagnostic Sub-group in Pervasive Developmental Disorders: A Follow-up Analysis. Autism Insights 2009:1 3-17

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ResearchBlogging.org Zerbo O, Qian Y, Yoshida C, Grether JK, Van de Water J, & Croen LA (2013). Maternal Infection During Pregnancy and Autism Spectrum Disorders. Journal of autism and developmental disorders PMID: 24366406