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Ecological and demographic factors affecting elephant-parasites dynamics

Kasun Abeysinghe

What are parasites?
A parasite is an organism that spends a significant portion of its life in (internal or endoparasites) or on (external or ectoparasites) the living tissue of a host organism and which causes harm to the host without immediately killing it.

Why are parasites important?
Interaction between hosts and parasites is crucial for healthy functioning of ecosystems and parasites are important component of biodiversity. The importance of parasites can be looked at in two different angels:

  1. Agriculturist/Veterinary point of view
    Internal parasites most serious cause of production losses in farmed animals. The aim of control measures is to maintain their populations at levels that are compatible with economic production.
  2. Ecologist point of view
    Natural existing parasitism plays an important role in population maintenance and natural selection.

Which are the major internal parasites?
Helminthes and protozoa are the two main kinds of internal parasites. Helminths can be divided into three categories; nematodes (roundworms), cestodes (tapeworms) and trematodes (flukes). The importance of internal parasites is based on its disease-causing role such as prevalence, intensity of infection and pathogenicity.

Why are nematodes very important in understanding parasites-host dynamics?
Nematodes’ life cycle is very simple and they are easily detectable in fecal matter, hence are the most commonly assessed helminthes with regard to animal health.

Elephant host and parasites diseases
Parasitic disease results when the equilibrium between parasite and host is upset.

What are the reasons?
Confine elephants to restricted areas such as parks may favor the buildup of internal parasite infections through contaminated feeding grounds and nutritional stresses.

What are the techniques of assessing gastrointestinal parasites burden in host?

  1. McMaster – Quantitative
  2. Flotation – Qualitative
  3. Sedimentation – Qualitative

Can these methods be used to study free ranging elephants?
Compared to domestic animals, the fecal output of elephants is relatively high and it contains undigested fragments that are very large. Additional issues arise in the case of free ranging elephants due to logistics of collecting freshly deposited dung. Therefore there are a number of limitations in applying these methods to assess the fecal egg counts in elephants.

What are the limitations?
The McMaster, sedimentation and floatation methods for ‘fecal egg count’ estimation require samples to be collected within 1 hour of defecation, as rapid embryonic development occurs in parasite eggs in the defecated feces. Consequently these eggs will not float on to the surface of the salt solution used in the floatation method. Collection of samples within one hour of defecation in free ranging animals especially elephants is logistically difficult.

In the McMaster method for 4 g of sample, 56 ml of floatation solution has to be added. The volume of the floatation solution has to be increased in proportion to the weight of the sample. Therefore, to analyze a 12-20 g sample a large volume of floatation solution is required, making analysis tedious and cumbersome.

How to overcome these problems?
In our recent publication we describe a new method of quantifying nematode infections, based on faecal culture of nematode eggs and harvesting through Berman technique that is robust, easy to conduct and overcomes many of the problems with other techniques. Download pdf (590 KB)

On-going research topics

  • To assess patterns of gastro intestinal parasites load in wild Asian elephants in different localities in southern Sri Lanka.
  • To determine effects of demographic and habitat parameters on internal nematode burden in elephants.