title: Trypanosoma cruzi-infected pregnant women without vector exposure have higher parasitemia levels: implications for congenital transmission risk.
abstract: BACKGROUND
  Congenital transmission is a major source of new Trypanosoma cruzi infections, and as vector and blood bank control continue to improve, the proportion due to congenital infection will grow. A major unanswered question is why reported transmission rates from T. cruzi-infected mothers vary so widely among study populations. Women with high parasite loads during pregnancy are more likely to transmit to their infants, but the factors that govern maternal parasite load are largely unknown. Better understanding of these factors could enable prioritization of screening programs to target women most at risk of transmission to their infants.
  
  
  RESULTS
  We screened pregnant women presenting for delivery in a large urban hospital in Bolivia and followed infants of infected women for congenital Chagas disease. Of 596 women screened, 128 (21.5%) had confirmed T. cruzi infection; transmission occurred from 15 (11.7%) infected women to their infants. Parasite loads were significantly higher among women who transmitted compared to those who did not. Congenital transmission occurred from 31.3% (9/29), 15.4% (4/26) and 0% (0/62) of women with high, moderate and low parasite load, respectively (χx2 for trend 18.2; p<0.0001). Twin births were associated with higher transmission risk and higher maternal parasite loads. Infected women without reported vector exposure had significantly higher parasite loads than those who had lived in an infested house (median 26.4 vs 0 parasites/mL; p<0.001) with an inverse relationship between years of living in an infested house and parasite load.
  
  
  CONCLUSIONS
  We hypothesize that sustained vector-borne parasite exposure and repeated superinfection by T. cruzi may act as an immune booster, allowing women to maintain effective control of the parasite despite the down-regulation of late pregnancy.
authors: Duke Global Health Institute, Duke University, Durham, NC, United States of America.
authors: Victoria R
authors: VR
authors: Rendell
authors: Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, United States of America.
authors: Robert H
authors: RH
authors: Gilman
authors: Laboratorio de Investigación en Enfermedades Infecciosas, Universidad Peruana Cayetano Heredia, Lima, Peru.
authors: Edward
authors: E
authors: Valencia
authors: Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, United States of America.
authors: Gerson
authors: G
authors: Galdos-Cardenas
authors: Laboratorio de Investigación en Enfermedades Infecciosas, Universidad Peruana Cayetano Heredia, Lima, Peru.
authors: Manuela
authors: M
authors: Verastegui
authors: Laboratorio de Investigación en Enfermedades Infecciosas, Universidad Peruana Cayetano Heredia, Lima, Peru.
authors: Leny
authors: L
authors: Sanchez
authors: Laboratorio de Investigación en Enfermedades Infecciosas, Universidad Peruana Cayetano Heredia, Lima, Peru.
authors: Janet
authors: J
authors: Acosta
authors: Laboratorio de Investigación en Enfermedades Infecciosas, Universidad Peruana Cayetano Heredia, Lima, Peru.
authors: Gerardo
authors: G
authors: Sanchez
authors: Universidad Catolica Boliviana, Santa Cruz, Plurinational State of Bolivia.
authors: Lisbeth
authors: L
authors: Ferrufino
authors: Hospital Universitario Japones, Santa Cruz, Plurinational State of Bolivia.
authors: Carlos
authors: C
authors: LaFuente
authors: Hospital Universitario Japones, Santa Cruz, Plurinational State of Bolivia.
authors: Maria del Carmen
authors: Mdel C
authors: Abastoflor
authors: Universidad Catolica Boliviana, Santa Cruz, Plurinational State of Bolivia.
authors: Rony
authors: R
authors: Colanzi
authors: Department of Epidemiology and Biostatistics, University of San Francisco School of Medicine, San Francisco, CA, United States of America.
authors: Caryn
authors: C
authors: Bern
mesh_terms: D000328:Adult; D014355:Chagas Disease / Q000097:blood / Q000469:parasitology / Q000635:transmission*; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D018445:Infectious Disease Transmission, Vertical; D059208:Parasite Load; D018512:Parasitemia / Q000097:blood / Q000635:transmission*; D011247:Pregnancy; D015597:Pregnancy Complications, Parasitic / Q000097:blood*; D014349:Trypanosoma cruzi; D055815:Young Adult