Abstract
The objective of this study was to identify potential mRNA expression changes in chicken livers associated with environmental exposure to dichloro-diphenyl-trichloroethane (DDT) and its metabolites (DDTs). In particular, we focused on genes relating to the immune system and metabolism. We analyzed liver samples from free-ranging chickens in KwaZulu-Natal, South Africa, for contamination by DDTs. This area predominantly uses DDT in its malaria control program, and homes are sprayed annually with the pesticide. Genes relating to the immune system and metabolism were selected as potential genetic biomarkers that could be linked to higher contamination with DDTs. RT-qPCR analysis on 39 samples showed strong correlations between DDTs contamination and mRNA expression for the following genes: AvBD1, AvBD2, AvBD6 and AvBD7 (down-regulated), and CYP17, ELOVL2 and SQLE (up-regulated). This study shows for the first time interesting and significant correlations between genetic material collected from environmentally-exposed chickens and mRNA expression of several genes involved in immunity and metabolism. These findings show the usefulness of analysis on field samples from a region with high levels of environmental contamination in detecting potential biomarkers of exposure. In particular, we observed clear effects from DDT contamination on mRNA expression of genes involved in immune suppression, endocrine-disrupting effects, and lipid dysregulation. These results are of interest in guiding future studies to further elucidate the pathways involved in and clinical importance of toxicity associated with DDT exposure from contaminated environments, to ascertain the health risk to livestock and any subsequent risks to food security for people.
Highlights
The KwaZulu-Natal Province of South Africa is currently considered an endemic area for malaria and the mainstay of malaria control is the use of DDT in indoor residual spraying (IRS) programs [1,2]
The objective of this study was to investigate mRNA expression changes associated with contamination by DDTs in free-ranging chickens from environmental exposure in an area where DDT is sprayed as part of a malaria control program
Concentrations of DDTs were comparable to those detected in chicken livers from Limpopo Province in another IRS-treated area of South Africa [52]
Summary
The KwaZulu-Natal Province of South Africa is currently considered an endemic area for malaria and the mainstay of malaria control is the use of DDT in indoor residual spraying (IRS) programs [1,2]. While exposure to DDTs is primarily via dermal contact and inhalation of aerosolized spray for workers administering DDT, ingestion is thought to be a more significant exposure route for other people and nontarget species such as livestock [5,6,7]. By the 1960s it became apparent that non-target species were susceptible to toxic effects, notably DDT affecting reproduction in birds of prey populations, publicized widely in Rachel Carson’s book “Silent Spring” [8]. Chickens show signs of DDT toxicity, but higher levels compared to other avian species are required before clinical signs are seen [17,18,19]. Clinical signs reported in chickens after DDT exposure include tremors, hyperexcitability, death, and various reproductive effects (reduced egg production and hatchability, reduced perinatal survival, decreased eggshell thickness) [20,21,22]. Despite the growing list of toxic effects of DDTs, our understanding of the mechanisms of action is still lacking
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