Parasites and pollution: the effectiveness of tiny organisms in assessing the quality of aquatic ecosystems, with a focus on Africa

Abstract

The aquatic environment represents the final repository for many human-generated pollutants associated with anthropogenic activities. The quality of natural freshwater systems is easily disrupted by the introduction of pollutants from urban, industrial and agricultural processes. To assess the extent of chemical perturbation and associated environmental degradation, physico-chemical parameters have been monitored in conjunction with biota in numerous biological monitoring protocols. Most studies incorporating organisms into such approaches have focussed on fish and macroinvertebrates. More recently, interest in the ecology of parasites in relation to environmental monitoring has indicated that these organisms are sensitive towards the quality of the macroenvironment. Variable responses towards exposure to pollution have been identified at the population and component community level of a number of parasites. Furthermore, such responses have been found to differ with the type of pollutant and the lifestyle of the parasite. Generally, endoparasite infection levels have been shown to become elevated in relation to poorer water quality conditions, while ectoparasites are more sensitive, and exposure to contaminated environments resulted in a decline in ectoparasite infections. Furthermore, endoparasites have been found to be suitable accumulation indicators for monitoring levels of several trace elements and metals in the environment. The ability of these organisms to accumulate metals has further been observed to be of benefit to the host, resulting in decreased somatic metal levels in infected hosts. These trends have similarly been found for host-parasite models in African freshwater environments, but such analyses are comparatively sparse compared to other countries. Recently, studies on diplozoids from two freshwater systems have indicated that exposure to poorer water quality resulted in decreased infections. In the Vaal River, the poor water quality resulted in the extinction of the parasite from a site below the Vaal River Barrage. Laboratory exposures have further indicated that oncomiracidia of Paradiplozoon ichthyoxanthon are sensitive to exposure to dissolved aluminium. Overall, parasites from African freshwater and marine ecosystems have merit as effect and accumulation indicators; however, more research is required to detail the effects of exposure on sensitive biological processes within these organisms.

The potential use of Octolasmis spp. parasites in mud crabs Scylla spp. as a bioindicator for mercury pollution

“…Previous research has demonstrated that uptake of contaminants by aquatic animals can encourage increased parasitism (Tellez and Merchant 2015). There is evidence that parasites are significantly more common in poor water quality conditions (Gilbert and Avenant-Oldewage 2017). It is possible, that at the study site the presence of mercury in water and sediments, originating from upstream gold mining activities, could be a causal factor in the prevalence of the Octolasmis parasites.…”

Biomonitoring of Heavy Metal Pollution Using Acanthocephalans Parasite in Ecosystem: An Updated Overview

“…Moreover, Tellez and Merchant [86] investigate the exposure of both fish and alligators to parasites and heavy environmental pollution with heavy metals, using the monitoring programs as a useful tool to detect metal concentrations and exposure. Parasites, particularly intestinal trematodes, collectively accumulated higher levels of Se, Cu, As and Zn; they acted like sensitive bioindicators for heavy metals pollution [92]. In 2016, Bamidele and Kuton [93] used Parachanna obscura and Clarias gariepinus fish to evaluate the bioaccumulation of heavy metals in fish tissues and parasites (intestinal nematodes), as an indicator for heavy metals (Cu, Cr, Ni, Pb, and Fe) pollution in Lekki lagoon, Nigeria.…”

Impacts of trace metals on African common toad, Amietophrynus regularis (Reuss, 1833) and depuration effects of the toad's enteric parasite, Amplicaecum africanum (Taylor, 1924) sampled within Lagos metropolis, Nigeria

“…On the other hand, the concentration of the toxicant in the host may be reduced through accumulation by the parasites (Koprivnikar et al, 2007;Griggs and Belden, 2008). Intricate interactions between pollutants and parasites in the host have been reported (De Denato et al, 2017;Gilbert and Avenant-Oldewage, 2017), showing parasite's ability to reduce pollutants levels in infected hosts compared with uninfected conspecifics (Sures, 2007(Sures, , 2008Sures et al, 2017).…”