Maternal antenatal mood and child development: an exploratory study of treatment effects on child outcomes up to 5 years.

Effective treatment of maternal antenatal depression may ameliorate adverse neurodevelopmental outcomes in offspring. We performed two follow-up rounds of children at age 2 and age 5 whose mothers had received either specialized cognitive-behavioural therapy or routine care for depression while pregnant. Of the original cohort of 54 women, renewed consent was given by 28 women for 2-year follow-up and by 24 women for 5-year follow-up. Child assessments at the 2-year follow-up included the Parenting Stress Index (PSI), Bayley Scales of Infant Development (BSID-III) and the Child Behaviour Checklist (CBCL). The 5-year follow-up included the Wechsler Preschool and Primary Scales of Intelligence (WPPSI-III) and again the CBCL. Treatment during pregnancy showed significant benefits for children's development at age 2, but not at age 5. At 2 years, intervention effects were found with lower scores on the PSI Total score, Parent Domain and Child domain (d=1.44, 1.47, 0.96 respectively). A non-significant trend favoured the intervention group on most subscales of the CBCL and the BSID-III (most notably motor development: d =0.52). In contrast, at 5-year follow-up, no intervention effects were found. Also, irrespective of treatment allocation, higher depression or anxiety during pregnancy was associated with higher CBCL and lower WPPSI-III scores at 5 years. This is one of the first controlled studies to evaluate the long-term effect of antenatal depression treatment on infant neurodevelopmental outcomes, showing some benefit. Nevertheless, caution should be taken interpreting the results because of a small sample size, and larger studies are warranted.

Host immune status affects maturation time in two nematode species--but not as predicted by a simple life-history model.

In theory, the age at which maturation occurs in parasitic nematodes is inversely related to pre-maturational mortality rate, and cross-species data on mammalian nematodes are consistent with this prediction. Immunity is a major source of parasite mortality and parasites stand to gain sizeable fitness benefits through short-term adjustments of maturation time in response to variation in immune-mediated mortality. The effects of thymus-dependent immune responses on maturation in the nematode parasites Strongyloides ratti and Nippostrongylus brasiliensis were investigated using congenitally thymus-deficient (nude) rats. As compared with worms in normal rats, reproductive maturity of parasites (presence of eggs in utero) in nude rats occurred later in S. ratti but earlier in N. brasiliensis. Immune-mediated differences in maturation time were not associated with differences in worm length. Thymus-dependent immunity had no effect on prematurational mortality. Results are discussed in relation to theoretical expectations and possible explanations for the observed patterns in parasite maturation.

The evolutionary ecology of host-specificity: experimental studies with Strongyloides ratti.

Factors constraining the evolution of host-specificity were investigated using a gastrointestinal parasitic nematode, Strongyloides ratti. S. ratti is a natural parasite of rats which can also reproduce, with decreased success, in laboratory mice. Observed host-specificity arose from lower establishment, reduced per capita fecundity and more rapid expulsion of parasites from mice relative to rats. Variation in the efficacy of thymus-dependent immunity between host species (rats and mice) was insufficient to explain the majority of the observed differences in parasite establishment and reproductive success. The role of natural selection in determining host-specificity was addressed using experimental selection followed by reciprocal fitness assays in both host species. Experimental selection failed to modify the host-specificity of S. ratti to any measurable degree, suggesting either a lack of genetic variation for this trait or the involvement of as yet unidentified factors underlying the differences in S. ratti fitness in rats and mice respectively. These results are discussed in relation to competing theoretical models of ecological specialization, host immunology and previous attempts to experimentally alter the host-specificity of parasitic nematodes.

The control of morph development in the parasitic nematode Strongyloides ratti.

The parasitic nematode Strongyloides ratti has a complex life cycle. The progeny of the parasitic females can develop into three distinct morphs, namely directly developing infective third-stage larvae (iL3s), free-living adult males and free-living adult females. We have analysed of the effect of host immune status (an intra-host factor), environmental temperature (an extra-host factor) and their interaction on the proportion of larvae that develop into these three morphs. The results are consistent with the developmental decision of larvae being controlled by at least two discrete developmental switches. One is a sex-determination event that is affected by host immune status and the other is a switch between alternative female morphs that is affected by both host immune status and environmental temperature. These findings clarify the basis of the life cycle of S. ratti and demonstrate how such complex life cycles can result from a combination of simple developmental switches.

Influence of rat strain on larval production by the parasitic nematode Strongyloides ratti.

The course of infection with Strongyloides ratti in a range of rat strains was assessed by monitoring the production of larvae. To our knowledge, this is the first such study of S. ratti using its natural host Rattus norvegicus. Host strain influenced the pattern of larval production. The results were qualitatively the same for 2 S. ratti lines of North American and Japanese origin.