Background: Lead exposure is associated with behavioral problems in children, but the ages when children are most susceptible to lead toxicity are unclear. Our objective was to evaluate the association of repeated blood lead concentrations with parent-reported behaviors and identify periods of heightened susceptibility.Methods: Between 2003-2006, we recruited pregnant women (n=389) living in homes built pre-1978 from Cincinnati, Ohio (HOME Study) and followed their children until age 8 years. We quantified lead in whole blood samples collected from children at ages 1, 2, 3, 4, 5, and 8 years. We assessed parent-reported child behavior using the Behavioral Assessment System for Children-2 (BASC-2) when children were ages 2, 3, 4, 5, and 8 years. Using linear regression with generalized estimating equations adjusted for covariates, we estimated associations of time-varying blood lead concentrations (ln-transformed, g/L) with behavioral profiles using the BASC-2 composite scales. We used multiple informant models to assess heterogeneity in these associations across exposure periods (n=241).Results: The median blood lead concentration peaked at 15 g/L around age 2 years (25th, 75th=10, 22 g/L) and gradually decreased to 6 g/L around age 8 years (25th, 75th=4, 9) g/L). Higher time-varying blood lead concentrations were associated with more externalizing problems (β:1.8-point; 95% CI= 0.3, 3.2). The association between blood lead levels and externalizing problems varied by exposure timing (lead x period interaction p-value=0.11), with heightened susceptibility around ages 3 (β:2.1-point; 95% CI= 0.6, 3.6) and 8 (β:3.5-point; 95% CI= 1.2, 5.7) years compared with other ages. Conclusion: Children with higher blood lead levels had more parent-reported hyperactive and aggressive behaviors. Future research could investigate if the periods of heightened susceptibility around ages 3 and 8 years are due to unique neurodevelopmental processes.

Four groups of six cats were kept in carpeted pens similarly infected with Ctenocephalides felis. One group was left untreated, but the other groups were treated every 28th day with either an insecticide (fenthion at 30 mg); or an inhibitor of insect development (lufenuron at 133 or 266 mg) or with both. A sudden upsurge in the numbers of fleas occurred on the control cats after 50 days. At this time, the three control strategies had reduced the counts by 91.3, 72.5 and 98.6 per cent, respectively. Thereafter, welfare considerations demanded the limitation of the flea burden on the control cats, but conditions were shown to be favourable for flea development throughout the study. The mean numbers of fleas on the treated groups after six months were 1.2, 11.0 and 0.4 respectively. After this, in addition to the fleas acquired in the pen, the cats were each infected weekly with five fleas to mimic roaming animals introducing extraneous fleas into the home. This produced no obvious effect on the counts and the mean values three months later were 0.5, 11.0 and 0.2, respectively. None of the strategies eradicated the flea population but they all reduced the numbers considerably and worked equally well whether or not small numbers of new fleas were introduced into the system. Significantly lower flea counts were maintained in the early and later stages of the study by the strategies including the insecticide.

Dictyocaulus viviparus were harvested from calves treated daily with albendazole at dose-rates sub-lethal to this parasite and from matched untreated calves. Male and female reproductive tracts from the worms were examined by light and transmission electron microscopy. A first description of the testis of this nematode is provided. Cell division in the germinal zone of both male and female worms was arrested by in vivo exposure to albendazole metabolites and the cytoplasmic threads connecting the germinal cells to the rachis disappeared. In male worms from treated calves, the rachis was absent from the growth zone and severe ultrastructural damage of spermatogonia, spermatocytes and spermatozoa was apparent. In female worms, the rachis remained intact in the growth zone, obvious abnormalities being confined to the germinal zone, where the cytoplasm of the oogonia was disrupted and few nuclei seen, and to the uteri and ovijector which contained only undifferentiated ova. The detrimental effects of albendazole metabolites on male and female worms were quickly reversed after withdrawal of medication.

ABSTRACTIn a series of three replicated and controlled trials, nine dogs artificially infected with Ctenocephalides felis were treated with a systemically active ‘spot‐on’ formulation of fenthion, six with a topical spray containing dichlorvos and fenitrothion and six with a surface active ‘spot‐on’ preparation containing permethrin, all at recommended dose rates. Good knockdown efficacy was apparent at eight hours with the dichlorvos/fenitrothion combination and at 24 hours with the other formulations. Efficacy values in excess of 95 per cent persisted for at least 22 days in the case of the systemic fenthion preparation and the permethrin product and eight days for the dichlorvos and fenitrothion combination. Twenty‐nine days after treatment there was still substantial protection in the fenthion‐ and permethrin‐treated animals, indicated by an 88 and a 77 per cent reduction in flea counts in the two groups, respectively.

ABSTRACTA controlled study was carried out in two replicated trials, each using three groups of domestic cats artificially infested with Ctenocephalides felis. In each trial three cats were treated with fenthion, three were treated with a dichlorvos/fenitrothion formulation, both at the recommended dose rate and the remainder acted as untreated controls. Good knockdown efficacy was evident 24 hours after both treatments. Efficacy values of 85 per cent or more were maintained for at least 15 days with fenthion and for less than eight days with dichlorvos/fenitrothion.

In a series of controlled trials involving 59 naturally infected greyhounds, fenbendazole at a dose rate of 50 mg/kg/day for three consecutive days reduced the overall numbers of third and fourth stage Toxocara canis by 94.0 per cent and third stage, fourth stage and immature adult stages of Toxascaris leonina by 92.4 per cent. In contrast, piperazine at 100 mg/kg had little or no useful effect against the larval stages of T canis and T leonina and variable efficacy against immature adult T leonina. Fenbendazole was also 100 per cent effective against immature Trichuris vulpis. In a separate controlled experiment, puppies in three litters exposed to reinfection with T canis were treated with fenbendazole at two weeks old and again only after their mean faecal egg counts exceeded 200 epg. Between one and three doses were required to suppress the output of eggs during the puppies' first 12 weeks of life.

ABSTRACTAn important factor in the life‐cycle of Toxocara canis is the dissemination of ova into the host's environment. This provides a reservoir for infection of the bitch with subsequent transmission of larvae to the fetus. Additionally, other warm‐blooded animals may acquire infection, thereby acting as paratenic hosts in subsidiary predator‐prey cycles. Embryonated ova are infective for man and may on occasion result in clinical disease.Information assessing the extent of such environmental contamination in the UK and denning the sources of the T. canis ova is reviewed. These data are of immediate practical importance as each contribution to the understanding of the epidemiology of toxocariasis facilitates the formulation of effective control measures.

ABSTRACTAn in vitro larval precipitate test using second-stage Toxocara canis larvae and an indirect fluorescent antibody (IFA) test employing cuticles of T. canis larvae as antigen were evaluated using antisera produced in pigs experimentally infected with T. canis, T. cati, Ascaris suum, Toxascaris leonina and Parascaris equorum. The former test was both specific and sensitive and is suggested as a reliable and simple method of detecting Toxocara antibodies in pigs. The latter test was considered unsuitable because of cross-reactions that occurred when sera from pigs infected with other ascarids were tested. An IFA test for Ascaris antibodies, employing cuticles of A. suum larvae as antigen, is described. The degree of specificity of this test suggests that it may be of value in the detection of antibodies to Ascaris in pigs under natural conditions.