The Eco-Epidemiology of Pacific Coast Tick Fever in California

Rickettsia philipii (type strain “Rickettsia 364D”), the etiologic agent of Pacific Coast tick fever (PCTF), is transmitted to people by the Pacific Coast tick, Dermacentor occidentalis. Following the first confirmed human case of PCTF in 2008, 13 additional human cases have been reported in California, more than half of which were pediatric cases. The most common features of PCTF are the presence of at least one necrotic lesion known as an eschar (100%), fever (85%), and headache (79%); four case-patients required hospitalization and four had multiple eschars. Findings presented here implicate the nymphal or larval stages of D. occidentalis as the primary vectors of R. philipii to people. Peak transmission risk from ticks to people occurs in late summer. Rickettsia philipii DNA was detected in D. occidentalis ticks from 15 of 37 California counties. Similarly, non-pathogenic Rickettsia rhipicephali DNA was detected in D. occidentalis in 29 of 38 counties with an average prevalence of 12.0% in adult ticks. In total, 5,601 ticks tested from 2009 through 2015 yielded an overall R. philipii infection prevalence of 2.1% in adults, 0.9% in nymphs and a minimum infection prevalence of 0.4% in larval pools. Although most human cases of PCTF have been reported from northern California, acarological surveillance suggests that R. philipii may occur throughout the distribution range of D. occidentalis

Parasitism in Children Aged Three Years and Under: Relationship between Infection and Growth in Rural Coastal Kenya

<div><p>Background</p><p>Parasitic infections, which are among the most common infections worldwide, disproportionately affect children; however, little is known about the impact of parasitic disease on growth in very early childhood. Our objective was to document the prevalence of parasitic infections and examine their association with growth during the first three years of life among children in coastal Kenya.</p><p>Methodology/Principal Findings</p><p>Children enrolled in a maternal-child cohort were tested for soil transmitted helminths (STHs: <i>Ascaris</i>, <i>Trichuris</i>, hookworm, <i>Strongyloides</i>), protozoa (malaria, <i>Entamoeba histolytica</i> and <i>Giardia lamblia</i>), filaria, and <i>Schistosoma</i> infection every six months from birth until age three years. Anthropometrics were measured at each visit. We used generalized estimating equation (GEE) models to examine the relationship between parasitic infections experienced in the first three years of life and growth outcomes (weight, length and head circumference). Of 545 children, STHs were the most common infection with 106 infections (19%) by age three years. Malaria followed in period prevalence with 68 infections (12%) by three years of age. Filaria and <i>Schistosoma</i> infection occurred in 26 (4.8%) and 16 (2.9%) children, respectively. Seven percent were infected with multiple parasites by three years of age. Each infection type (when all STHs were combined) was documented by six months of age. Decreases in growth of weight, length and head circumference during the first 36 months of life were associated with hookworm, <i>Ascaris</i>, <i>E</i>. <i>histolytica</i>, malaria and <i>Schistosoma</i> infection. In a subset analysis of 180 children who followed up at every visit through 24 months, infection with any parasite was associated with decelerations in weight, length and head circumference growth velocity. Multiple infections were associated with greater impairment of linear growth.</p><p>Conclusions/Significance</p><p>Our results demonstrate an under-recognized burden of parasitism in the first three years of childhood in rural Kenya. Parasitic infection and polyparasitism were common, and were associated with a range of significant growth impairment in terms of weight, length and/or head circumference.</p></div

Results of longitudinal models describing the association between infant parasitic infection and growth parameters.

<p>Shown are the multiply-adjusted impacts of infection on weight, length and head circumference Z-scores at follow up age milestones.^{<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0003721#t002fn002" target="_blank">*</a>}</p><p>*Longitudinal Models: Controlled for age, sex, birth weight, birth length, birth head circumference, and maternal education.</p><p>^aN of 545 cohort represents all of the children followed over the first 36 months of life.</p><p>^bN of 180 is a subset of the 545 cohort representing the children following up at every visit in the first 24 months of life.</p><p>^cns: not statistically significant.</p><p>^dTukey adjusted p-value with the effect size (+/-) and arrow indicating direction of effect.</p><p>Results of longitudinal models describing the association between infant parasitic infection and growth parameters.</p

Impact of multiple parasitic infections on growth.

<p>WHO-standardized weight, length and head circumference growth charts for two male infants experiencing multiple parasitic infections in the first 24 months of life.</p

Cumulative incidence of parasitic infections.

<p>Shown are rates of any parasitic infection (solid lines with circles) or of >1 (multiple) parasitic infections (dashed lines with squares) by the age of each study visit during the first 36 months of life for the total study cohort (N = 545), and for the first 24 months of life for the full follow-up cohort (N = 180). The number of children infected at each time point is indicated near the marker.</p

Prevalence of infection at regular study follow-up visits from 6–36 months of age.

<p>Bars represent the percent of children infected at each visit. Lines represent cumulative incidence of infection over time.</p

Maternal and infant characteristics.

<p>*KSh: Kenyan Shillings</p><p>^<b>€</b>cm: centimeters</p><p>^¥g: grams</p><p>Maternal and infant characteristics.</p

Average length, weight and head circumference Z-scores.

<p>Data summarized for all children (N = 545) at each follow up time point.</p