Key aspects of 36 mosquito-borne arboviruses indigenous to Africa are summarized, including lesser or poorly-known viruses which, like Zika, may have the potential to escape current sylvatic cycling to achieve greater geographical distribution and medical importance. Major vectors are indicated as well as reservoir hosts, where known. A series of current and future risk factors is addressed. It is apparent that Africa has been the source of most of the major mosquito-borne viruses of medical importance that currently constitute serious global public health threats, but that there are several other viruses with potential for international challenge. The conclusion reached is that increased human population growth in decades ahead coupled with increased international travel and trade is likely to sustain and increase the threat of further geographical spread of current and new arboviral disease.

ObjectivesDichlorodiphenyltrichloroethane (DDT) was used worldwide until the 1970s, when concerns about its toxic effects, its environmental persistence, and its concentration in the food supply led to use restrictions and prohibitions. In 2001, more than 100 countries signed the Stockholm Convention on Persistent Organic Pollutants (POPs), committing to eliminate the use of 12 POPs of greatest concern. However, DDT use was allowed for disease vector control. In 2006, the World Health Organization and the U.S. Agency for International Development endorsed indoor DDT spraying to control malaria. To better inform current policy, we reviewed epidemiologic studies published from 2003 to 2008 that investigated the human health consequences of DDT and/or DDE (dichlorodiphenyldichloroethylene) exposure.Data sources and extractionWe conducted a PubMed search in October 2008 and retrieved 494 studies.Data synthesisUse restrictions have been successful in lowering human exposure to DDT, but blood concentrations of DDT and DDE are high in countries where DDT is currently being used or was more recently restricted. The recent literature shows a growing body of evidence that exposure to DDT and its breakdown product DDE may be associated with adverse health outcomes such as breast cancer, diabetes, decreased semen quality, spontaneous abortion, and impaired neurodevelopment in children.ConclusionsAlthough we provide evidence to suggest that DDT and DDE may pose a risk to human health, we also highlight the lack of knowledge about human exposure and health effects in communities where DDT is currently being sprayed for malaria control. We recommend research to address this gap and to develop safe and effective alternatives to DDT.

The pesticide DDT [1,1,1-trichloro-2,2-bis(chlorodiphenyl)ethane] is 1 of the 12 persistent organic pollutants (POPs) under negotiation at the Stockholm Convention to restrict or ban their production and use because of their toxicity, resistance to breakdown, bioaccumulation, and potential for being transported over long distances. DDT has estrogenic potential, and the main metabolite, p,p9-dichlorodiphenyl-dichloroethylene (p,p9-DDE), is a potent antiandrogen. In response to mounting evidence on the endocrine-disrupting influence of environmental chemicals on human health, this epidemiological study was initiated to test the hypothesis that nonoccupational exposure to DDT affects male reproductive parameters. In a cross-sectional study, healthy male subjects (n 5 311) between 18 and 40 years (23 6 5) of age were recruited from 3 communities in an endemic malaria area in which DDT is sprayed annually. A semen analysis according to World Health Organization (WHO) standards was performed. The Hamilton Thorne Computer Assisted Sperm Analysis (CASA) system was simultaneously used to determine additional sperm motility parameters. Blood plasma samples were assayed for p,p9-DDT and metabolites as a measure of exposure. The exposure levels were expressed as lipid-adjusted p,p9-DDT and p,p9-DDE values. The mean p,p9-DDT and p,p9-DDE concentrations were 90.23 mg/g (6102.4) and 215.47 mg/g (6210.6), respectively. The multivariate linear regression analyses indicated that mean CASA motility was lower with a higher p,p9-DDE concentration (b 5 20.02, P 5 .001) and the CASA parameter beat cross-frequency (BCF) was higher with a higher p,p9-DDT concentration (b 5 0.01, P 5 .000). There was also a statistically significant positive association between percent sperm with cytoplasmic droplets and p,p9-DDT concentration (b 5 0.0014, P 5 .014). The ejaculate volume (mean 1.9 6 1.33 mL) was lower than the normal range ($2.0 mL) according to WHO, and a significant decrease with increasing p,p9-DDE values was seen for both square roottransformed volume (b 5 20.0003; P 5 .024) and count (b 5 20.003; P 5 .04). Although there were no associations between either p,p9-DDT or p,p9-DDE concentrations and the rest of the seminal parameters, the incidence of teratozoospermia (99%; normal sperm ,15%) was high. Twenty-eight percent of the study group presented with oligozoospermia (,20 6 10 6 sperm/mL), which had a significant positive association with p,p9-DDE (odds ratio [OR] 5 1.001, P 5 .03). There was a significant positive association between participants with asthenozoospermia (32%) and p,p9-DDT (OR 1.003, P 5 .006) and p,p9-DDE (OR 1.001, P 5 .02). The results imply that nonoccupational exposure to DDT is associated with impaired seminal parameters in men. The high exposure levels of p,p9-DDT and p,p9-DDE are of concern because these levels could have far-reaching implications for reproductive and general health.

Bioassays are well established in the pharmaceutical industry and single compound analysis, but there is still uncertainty about their usefulness in environmental monitoring. We compared the responses of five bioassays designed to measure estrogenic activity (the yeast estrogen screen, ER-CALUX, MELN, T47D-KBluc, and E-SCREEN assays) and chemical analysis on extracts from four different water sources (groundwater, raw sewage, treated sewage, and river water). All five bioassays displayed similar trends and there was good agreement with analytical chemistry results. The data from the ER-CALUX and E-SCREEN bioassays were robust and predictable, and well-correlated with predictions from chemical analysis. The T47D-KBluc appeared likewise promising, but with a more limited sample size it was less compelling. The YES assay was less sensitive than the other assays by an order of magnitude, which resulted in a larger number of nondetects. The MELN assay was less predictable, although the possibility that this was due to laboratory-specific difficulties cannot be discounted. With standardized bioassay data analysis and consistency of operating protocols, bioanalytical tools are a promising advance in the development of a tiered approach to environmental water quality monitoring.

ABSTRACT:In response to mounting concerns about the endocrine-disrupting influence of environmental chemicals on human health, this epidemiological study was initiated to test the hypothesis that nonoccupational exposure to the estrogenic pesticide 1,1,1-trichloro-2,2-bis(chlorodiphenyl)ethane (DDT) affects male reproductive parameters. One hundred and sixteen men aged 27 years (SD ϭ 8.2) living in malaria endemic-areas in Chiapas (Mexico), where DDT was sprayed until 2000, participated in a cross-sectional study. Semen analyses were conducted according to World Health Organization methods and a quality control program was followed. DDT exposure was defined as the level of blood plasma p,pЈ-dichlorodiphenyl dichloroethylene (DDE), the major metabolite of DDT. The p,pЈ-DDE concentration adjusted for total lipids was 100 times higher than that reported for nonexposed populations at 45 plus or minus 32 g/g (mean Ϯ SD). Crude regression analysis showed that several sperm motion parameters, including the percentage of motile sperm, decreased with higher p,pЈ-DDE concentrations (␤ ϭ Ϫ8.38; P ϭ .05 for squared motility), and the percentage of sperm with morphological tail defects increased with higher plasma p,pЈ-DDE concentration (␤ ϭ 0.003; P ϭ .017). Insufficient sperm chromatin condensation was observed in 46.6% of participants, and the most severe category of incomplete DNA condensation was also positively correlated with p,pЈ-DDE concentration (r ϭ .223; P ϭ .044). Therefore, nonoccupational exposure to DDT, as assessed by plasma p,pЈ-DDE concentrations, is associated with poorer semen parameters in men, indicating adverse effects on testicular function and/or the regulation of reproductive hormones. Previously, a causal role of environmental toxicants in human male infertility has been lacking because observed effects have been the result of unusually high exposures, either occupationally or as a result of industrial accidents, resulting in unprecedented controversy (reviewed by Cheek & McLachlan, Environmental hormones and the male reproductive system. J Androl. 1998;19:5). This is the first epidemiological study demonstrating effects after nonoccupational exposures to DDT. Based on these findings, the effect of DDT on male reproductive health should not be ignored.