AFTER FIFTY YEARS OF RESEARCH-of Dr S C Dutt

                                         DR MC AGRAWAL 

                FORMER Prof and Head, ICAR  EMERITUS SCIENTIST,
                                   Department of Parasitology

                             

                                          

         

I have read a couplet in recent past, which describes futility of life in following words

bina libas aaye the es  jahan mai, Bas ek kafan kee khatir etna  safar karna pada

(We entered in this world without clothes and traveled  a long journey only for a coffin)

This may be true for most of us who pass their life with no cause but certainly it is not true for persons like late Prof SC Dutt who devoted his whole life for scientific cause. The best testimony  of this is to check ,in present time, the relevance of his research work that was  carried out about fifty years back and his passing away in August,1980. There are two ways to assess, posthumously, the  scientific contributions of a scientist, - first, whether his research work is still cited in research papers and second if further research have supported or nullified his theories or observations; on both accounts he is a winner. I wish to extend the argument with some scientific achievements of Dr Dutt.

The nematode Filariids are known to utilize a mosquito or other blood sucking arthropod as its intermediate host. The filariids, belonging to the family Stephanofilariidae are prevalent in USA, Canada, and South East Asia including India and were first identified in 1933 as an agent for causing dermatitis- mainly in bovines. In India ,Hump-sore is a common skin disease of north-eastern cattle and its etiological agent ,Stephanofilaria assamensis , was identified and described ,first time, by Dr PG Pande  ,IVRI ,Izatnagar in 1936.Nevertheless , life cycle of any Stephanofilaria species remained obscured, though scientists were suspecting various blood sucking arthropods acting as intermediate host for this filariid. To the surprise of all, Dr SC Dutt discovered in 1963 its intermediate host being a Musca species- so far never suspected as an intermediate host for any filariid worm. Scientists were skeptical to this discovery and reluctant to accept the findings; as per general norms, the intermediate host for a filariid must be a blood sucker and Musca does not possess mouthparts enabling the fly to suck blood of the host –rather it is having lapping type mouth parts suitable to lap food material. Dr Dutt incriminated Musca conducens and put a satisfactory explanation for the fly acting as intermediate host. First the filariid is present not beneath the skin but in the skin and its microfilariae are not found in peripheral blood but remains in the skin. The fly has an enlarged chitinized mentum with a pre-stomal tooth and interdental armature (quite different from lapping type mouth parts of Musca domestica, the common house fly) with which it is able to scratch and tear the skin to feed on the serous blood mixed fluid which also contains microfilariae (infective stage for fly) thereby enabling the fly to play its vector role; blood is found an essential prerequisite for oviposition of these flies. This finding was confirmed subsequently by transmission experiments of other workers. Later, in 1970, Dr Dutt incriminated Musca planiceps as the vector for another species of the filariid i.e. Stephanofilaria zaheeri, the causative agent of ear-sore in buffaloes. Even after lapse of so many years of this unique discovery, no worker disputed the finding of M.conducens as intermediate host for S.assamensis or M.planiceps for S.zaheeri nor came out with the results showing any other insect as main intermediate host for the filariid.

The schistosomes or blood-flukes or Bilharzia have been the main field of research for Dr Dutt and he has made many new discoveries on this parasite. In the beginning of his career itself, he made an important discovery that contradicted the than existing hypothesis. As is well known, unlike to other trematodes, the schistosomes are unisexual where male and females are separate individuals, each developing from a single cercaria. While working on life cycle of the blood flukes, scientists found that the snails, the intermediate host where a single miracidium is developing into many cercariae, are regulating sex of the blood flukes by allowing development only of a particular miracidium. In 1930 and onwards, the scientists were working on life cycle of Schistosoma spindale and trying to develop the fluke in experimental animals. However, the animals developed only male S.spindale ; Fairley and associates used good number of guinea pigs  to develop S.spindale but neither its eggs nor females could be observed in any guinea pig prompting Fairley to hypothesize that there are some ‘host factors’ which are preventing development of female S.spindale. This led to  great interest in this discovery and may be visualized by the fact that the prestigious scientific magazine “Lancet” commanded this work in its editorial.

In late fifties, Dr SC Dutt meticulously planned his experiment to check this hypothesis by infecting 24 guinea pigs with different number of S.spindale cercariae (8,000 to 50,000/animal) and sacrificing the animals between 33-153 days post exposure. He provided conclusive evidence of developing females with production of eggs and pseudo-tubercles in the guinea pigs thereby negating the existing hypothesis.  His observations were correct was further proved when in 1990, Dr Anjana Mishra, in her Ph. D. research program  infected albino mouse, albino rats, rabbits and guinea pigs with different doses of S.spindale cercariae and killed them at different time intervals. Interestingly, in these comparative studies, guinea pig emerged as most suitable host for development of S.spindale with highest percentage of fluke development and presence of hundred percent viable eggs, at a time. Therefore, claim of Dr Dutt that guinea pig is developing both sexes has further been strengthened by later research work.

I will like to attract attention on another important problem in late 1960. The etiological agent for nasal granuloma was discovered by Dr Rao MAN in 1933 being a new schistosome species i.e. S.nasale. Though the blood fluke exists  both in cattle and buffalo, it is causing lesions only in cattle while buffalo is maintaining the parasite without any lesions. This led to the possibility of existing two strains or subspecies – one in cattle causing lesions and other in buffaloes without any lesions. Therefore, Dr Dutt decided to solve this problem and conducted cross-transmission experiments in 1968 where cattle were infected with S.nasale of buffalo origin and vice versa. By his experiments, Dr Dutt proved non-existence of two sub-species or strains and its only host species which is responsible for this difference. Subsequent workers confirmed experimentally this finding paving the way to investigate host factors responsible for these differences. The present knowledge also supports the hypothesis of Dr Dutt but with a difference i.e. there appears different geographical strains of S.nasale which is behaving differently – there is one strain in Tamilnadu for which sheep and goats are also susceptible, another strain in Maharashtra where goat is resistant, yet another strain in Jabalpur for which local cattle (but not cross bred cattle) are resistant. All these speculations have been made on epidemiological grounds and biological and biochemical confirmations are still awaited.

There are many other land mark contributions of Dr SC Dutt to the biological sciences and it’s difficult to narrate all of them,here. However, I may mention few of them briefly. Till late fifties, very little was known about Schistosoma indicum though the blood fluke was in lime light because of its resemblance  with Schistosoma haematobium which was found existing in Gimvi village of Ratnagiri district by Gadgil and Shah in 1952. Dr Dutt thoroughly investigated the parasite in association with Dr HD Srivastava including its morphology, life cycle, host susceptibilities that culminated in to publication of an ICAR technical bulletin (34) on Schistosoma indicum. Dr Dutt discovered a new blood fluke (Orientobilharzia dattai) where male was containing many testes ; first the parasite was put ,by them, in the genus Ornithobilharzia but subsequently they created a new genus Orientobilharzia making O.dattai, its type species. The argument put forward was that while Ornithobilharzia contains both avian and mammalian blood flukes, Orientobilharzia possesses exclusively mammalian schistosomes. It may be clarified that the name dattai in the new blood fluke species does not represent Dr SC Dutt  but it was christened in the name of Dr SCA Datta who was the then Director of IVRI, Izatnagar. Interestingly, this new species, unlike to its sister species Orientobilharzia bomfordi ( created by Dr RE Montgomery in 1906 in honor of Dr Bomford but its existence is disputed) , is accepted as a  valid species and occurring in many parts of India. Ironically, there is no further discovery of new schistosome species in India since O.dattai in 1955 and  Dr Dutt’s work remained last taxonomic work for Indian schistosomes though there is dire need of solving many taxonomic problems related to Indian schistosomes.   Another land mark contribution of Dr SC Dutt is about determining intermediate hosts for schistosome species. Prior to his studies, both Indoplanorbis exustus and Lymnaea luteola were incriminated intermediate hosts for S.nasale, S.spindale and S.indicum . By his analytical work , he proved that it is only I.exustus which is intermediate host for all these three Schistosomes exhibiting most restricted host specificity at intermediate level which is in contrast to their final host range. The claim of Dr Dutt still holds true and has been accepted by all scientific fraternity without any exception .

Certainly, this is not a small achievement that even after fifty years there is no one who disputed his findings- further research only supported his observations. A serious thought in this direction should to be given to analyze the reasons responsible for such high quality of research work from late Dr Dutt as it will be  important for our young or emerging scientists . I have witnessed his research persuasions (1970-1974) in the department of Parasitology as his post graduate as well as a Senior Research Assistant  and I have seen this eminent scientist sitting on a steel stool making microscopic studies for hours together which is difficult to follow by most of us. Secondly, he had no hurry to publish his observations , rather he continued to verify his observations by different angles and submitted his research papers only after being satisfied with his observations.