When I first stepped to Parasitology world, which if I remember correctly was in my 3rd yr vet school, I was asked to find the parasite which was present in the belly of the cattle examining a cup of ”poop”. This was my first step in parasite identification. Examining the egg structure I could easily say that this animal is having Paramphistomum, a tiny fluke in its belly (http://en.wikipedia.org/wiki/Paramphistomum). This was my first ever parasitology diagnosis and I was hailed for my success. As time passed by and I understood more Parasitology, I started to play with more poops and was gradually promoted to blood and tissue samples to find parasites. Now it was a challenge for me to identify the parasites as there were so many parasites which looked pretty identical for me yet different in theory. Now I could feel, no-one can master in parasite identification unless you are a real expert and you have played enough with each and every species which I thought was not possible in this planet. It was then, when I really realized the importance of molecular method of identification for the first time. Now being graduate student specializing in Parasitology I can by no ways convince myself in taking morphological basis as the ultimate guide to the identification of the parasite species, nevertheless, I still believe in this method to be useful for some particular species and widely valuable in narrowing down the search spectrum of parasite of concern.
Morphology has been considered the valuable tool in both identification and taxonomy or the parasite over the years. The general external morphology of a parasite provides the most immediate and evident source of comparative features. The study of internal structures in more detail with the advent of ultra-sophisticated microscopy techniques has aided in differentiation to much more depth. Identification on the basis of physical structure and form is relatively inexpensive and studies can be carried out in the field. It is cost effective and demands relatively simpler tools. This method can be useful at least in least developed and developing countries where the modern PCR based assays are impractical. Looking at practical grounds in the developing countries like Nepal, where I am from, I could easily treat the animals based on egg morphology at least because I could tell that the animal has Trematodes and we have one drug “Oxycolozanide” effective to kill all Trematodes (http://www.ncbi.nlm.nih.gov/pubmed/3447575) .I cannot imagine using expensive molecular methods to identify the organism and only treat the animal and there’s no point in doing that. So, morphological identification is still a valuable asset in the field diagnosis of parasitic infestation.
When it comes to narrowing down the organism to species, subspecies and even strain level, it is now clear that morphological basis is unreliable if used as the sole distinguishing criterion. Especially for the research purpose we don’t want to take a chance and relying upon just based upon observations. Despite the increasing use of electron microscopy, the range of morphological features is limited in many organisms, and morphologically indistinguishable sibling species are common among parasites. Furthermore, there are examples where no morphological differences are detectable between parasite isolates with remarkably distinct epidemiologically relevant characters. Morphology may also be host influenced (Schantz et al., 1976; Constantine et al., 1993). In the case of Echinococcus granulosus, morphological characteristics induced during development in a particular species of intermediate host are recognizable in the definitive host in the form of rostellar hook differences. With the advent of sensitive, reliable and time saving molecular methods of identification the job of parasitologists have become easier and this has really contributed in the field of Parasitology. With the help of these approaches, the more detailed and in-depth studies describing inherent properties of the parasite is feasible now-a-days which has a immense contribution in the fields of medicine and research.
Taking an example from the morphology class, Mani explained different morphological features which could be a basis of identification to group the parasite in a certain taxonomical group. Despite having practical difficulties and some sort of confusions, this method is going to be valuable in the process in a long run. It’s amazing, however, to know how nature has created such subtle yet significant differences in these tiny creatures and are so consistent enough to help ” so called” scientist like me to differentiate them.
The follow up papers were the excellent examples to justify the point. Although molecular method is valuable in grouping these parasites in a specific taxonomic group, there are yet some practical confusions which demand the more precise and conclusive approaches to sort out the things and determine with confidence to the species level.
For me these methods are equally valuable. In my research case, I use the morphological feature called “dorsal spine”, the magical tiny little spine at the base of the tail in the larvae of protostrongylid, as a first basis of identification of my parasite of concern. By this I could exclude several other parasite larvae which are present in the sample, which makes my job much easier. But then, I cannot remain without using the PCR based method and sequencing the larvae for the final identification and distinguish the dorsal spine larvae to the species level. So, both the methods should be used in conjunction whenever necessary and one cannot exclude the importance of either of the methods for the benefit of this wonderful world of parasites and scientific community as a whole.
Posted by Pratap Kafle