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Parasites: Tiny Bio-monitoring Tools in the Offing

There is an interaction among parasites, hosts, and the environment, and the latter is least understood
Dr Ummer Rashid Zargar
Srinagar | Posted : Feb 14 2018 1:29AM | Updated: Feb 13 2018 10:52PM
Parasites: Tiny Bio-monitoring Tools in the Offing
Representational Pic

The role of parasites in disease spread is well established, but their ecological relevance was wrongly kept under the carpet due to unknown reasons. However in recent decades (especially from 1990’s decade), importance of parasites in many ecological and biological phenomenon’s except their sole relevance as disease causing agents, is gaining momentum, thanks to tremendous efforts made by researchers. As ecologists and environmental managers are in search of new emerging and robust assessment tools, parasites provide unique features that are seldom possessed by conventional ecological sentinels. Although plagued with some issues, parasite in conjunction with other indicators could be an ideal and cost effective biomonitoring tool ready for the assessment of degraded environmental quality.

Parasitism –an intimate negative relationship between two different species-has been in recent times looked in different perspective. Up to early 1970’s, parasite was considered only an infectious agent having deleterious effects on their host. Parasitism was considered as ‘a life of large income without work’, which clearly suggest that parasites are fully adapted to take advantage of host resources. In other words, these tiny creatures were considered as idle fellows fancying their chances of survival at the cost of their host. With such narrative about parasite in the third quarter of 20th century, there was hardly any chance for them to be considered for new emerging studies, such as ecology, ecotoxicology and habitat management. Mostly, parasites were studied vis-à-vis disease in domesticated animals, wild animals and humans, and thus main focus was on epidemiology and eradication of disease. Even majority of published papers including fish parasites have been considered detrimental to the host. However, in early years of 1980s, ecologists were in search of emerging biomonitoring tools that might have more advanced features that would give better picture of environmental quality and parasites were the best choice before ecologist to test their suitability.


The interest in Environmental Parasitology started in 1980s with eminent parasitologists shifting their interest into various environmental aspects of parasites. With the creation of this platform, new comers in parasitology research took up various research problems dealing with association of parasites with altered environmental quality. Indeed, there was great surge in number of publications related to parasite-contaminant association in 1990’s and 2000 decade. With substantial breakthroughs in last two decades, environmental parasitologists have been able to bring parasites on the fore front so that their ecological roles are being accepted by non-parasitologists.

In recent past parasite ecologists advocate the usefulness of parasite organisms as warning sentinels or bio-indicator tools, nevertheless, some may raise question whether to use parasites as bio-monitoring tools or not. Those believing on modern probes will argue that when there are tools/equipment’s that are available for assessing pollution level at minute level, then why to use biological organisms for the same purpose. The reason for using biological organisms as bio-sentinels is that they display complex interactions with surrounding environment at different life stages. There is an interaction among pathogens/parasites, hosts, and the environment, and the latter is least understood. It is worth mentioning here that parasitic disease can also occur without the above interaction. However, stressful condition increases the chances of disease occurrence. Besides, disease occurrence this interaction will also provide us additional information regarding the environmental status of an ecosystem. 

Some ecologists suggest that there is need of holistic approach by integrating both modern as well as biological probes (including parasites) for investigating the pollution status of an ecosystem. So under these circumstances, there is urgent need to find new biological probes which are efficient, easily available and more importantly linked in ecological web in such a way that it gives accurate information about different aspects. Parasites in this sense are unique and can prove useful biological indicators as they show many versatile features which are absent in many organism.  Furthermore, the unsuitability of established biological indicators or sentinels under different ecological conditions and contamination types, makes parasites special in the sense that these can show even low contamination level in pristine conditions.

Parasites are most abundant creatures on earth as they are found in almost every ecosystem partly due to their high diversity and abundance.  Parasites, which were traditionally looked as infecting agents, are now seen in never aspects, whether it is their role in ecosystem, their role in the regulation of host abundance or as a pollution indication. Parasites of fish are useful biomarkers and appear to be more sensitive to environmental stressors than are the fish themselves. The possible reason could be that they are more numerous, have impact in ecosystem dynamics and show trophic relationships. Parasite responses to selected environmental stressors may be used to discriminate polluted and unpolluted sites. The use of parasites of fish as biomarkers has relevant application to fisheries management and coastal monitoring programs.

Based on past research and current progress, it can be safely said that parasites have emerged as an alternative for determination of environmental quality. However, there are various issues which hamper ecologists to suggest parasite impact assessment analysis. The lack of some parasite groups to respond to specific contaminants poses problem while selecting these sentinels. Similarly, some groups of parasites are less sensitive under multiple stress conditions and as such can give wrong information about the status of environment. Nevertheless, such issues are not found every parasite species. Selection of appropriate methodology and model is another hurdle which at times can give false results. As parasites are over dispersed, researchers need to select proper sample size for various environmental studies. It is also important that indicator potential of same parasite should be test in a series of battery of host species in order to reach to final conclusion.

Dr Ummer Rashid Zargar is SERB-DST Fellow, Department of Zoology, CUK, Sonwar Campus