As well as carrying out epidemiological studies, some researchers have tried to ascertain whether there is any evidence of abnormal persistence of measles virus in children with autism, in particular those with bowel disease. This is a very difficult area of research, requiring obsessive attention to detail, particularly in avoiding cross‐contamination with measles virus, rigorous testing and selection of controls. Early studies had suggested the presence of measles virus antigen in the bowel wall of patients with Crohn's disease.12,13
However, subsequent studies,14,15
including one from the original research group,16
have cast doubt on these findings. A number of groups aligned with the original protagonists of a link have suggested that measles virus can be found in the peripheral blood,17
and cerebrospinal fluid (CSF)19
of a high proportion of children with autism and bowel problems. Independent researchers have not been able to study the presence of measles virus in the bowel and CSF of such children as, in the absence of any therapeutic benefit to the children, most practitioners have considered it unethical to obtain bowel biopsies or CSF. They have attempted to replicate the findings on peripheral blood but have been unable to do so. Afzal et al
using similar methodology to Uhlmann et al
sought measles antigen in peripheral leucocytes of children with autism and known to have received MMR vaccine. They were unable to isolate it, in spite of finding it in known positive samples, such as brain tissue from subacute sclerosing panencephalitis (SSPE). Another independent study examined peripheral white cells and found that it was easy to obtain false positive results using the methodology of Uhlmann et al.
However, when carefully modified, positive results were only obtained from known positive samples and not from children with autism.21
This does not explain why some groups obtained positive results in children with autism and not in “control” children, but does emphasise the importance of correct technique. In a further study (Baird et al
. Measles vaccination and antibody response in autism spectrum disorders, unpublished), using highly sensitive techniques, evidence of measles viral genome was found in the blood of 1/98 children with autism spectrum disorders (ASD), 2/70 children with learning disorders without ASD and 0/90 controls. These positive findings could not be reproduced. Even if measles virus were found to persist in children with autism, it is worth remembering the cautionary words of Morris and Aldulaimi,22
who in commenting on the paper by Uhlmann et al
, pointed out that the presence of measles virus does not imply causation. Indeed in this case it may be that rather than the measles virus “causing” the bowel problems, the colitis or the developmental disorder “causes” the persistence of the measles virus. This could be a reflection of the inability of patients with a developmental disorder or enterocolitis to clear the virus: the enterocolitis may cause failure of viral clearance. They concluded “…in no way can the data presented here be used to support the generalisation that MMR causes all autism and/or inflammatory diseases of the bowel”.