28 STUDIES ON NASAL SCHISTOSOMIASIS [Vol. XXIV, Part I,
more or less selective habit of grazing; they generally avoid swampy pasture and
thereby minimise the chances of picking up infection. The goats are more akin to
buffaloes and have preference for grass growing over the margin of swamps, pools,
etc.
All ages and sex, exposed to infection, contract the disease; and upon the inten-
sity of infection depend the clinical manifestations, increasing as the host advances
in age due to continued re-infection, as it has been found by some workers that the
final host appears to be unable to develop any specific resistance to fasciola, which,
once acquired, it continues to carry. The longevity of F. hepatica has been worked
out to be many years and the same may apply to other species of the genus.
Distribution
Investigations indicated that the high incidence groups are geographically
scattered along the water-pockets in the beds of the notoriously vagrant Kosi and
its numerous capricious channels and tributaries. This suggests that the bionomics
of the molluscan intermediary will prove to be of great epidemiological significance.
Snails collected from the area and later identified here revealed that Limnaea auri-
cularia race rufescens have the widest distribution throughout the region. Unlike
Limnaea luteola, this snail species was found to favour somewhat deeper water.
Experimental evidence obtained by some workers [Bhalerao, 1933 and Srivastava,
1944] in this direction has indicated that this snail is the vector of what they believed
to be Fasciola gigantica in India. Srivastava was, however, able to infect experi-
mentally some Limnaea luteola as well with the miracidia of this fluke. This snail
was also found in the area, although in much lesser number. Indoplanorbis exustus
were also quite common there. These have been shown to act as intermediaries for
various paramphistomes, which are abundant there, particularly Paramphistomum
explanatum.
Prevalent species
There is no recorded evidence of any attempt made to find out the prevalent
species of Fasciola in this locality or elsewhere in Bihar, although the infection seems
so widely distributed there. Both the species F. hepatica and F. gigantica have been
reported from India [Bhalerao, 1935], the former chiefly from the cold Himalayan
regions while the latter are mostly from warmer areas having wider distribution
throughout the country. There, however, still exists some controversy over the
occurrence of both the species in the area under survey. In the present work an
attempt was made to settle the matter.
Living adult flukes were collected from buffaloes and goats in Purnea and
Supaul respectively. In the live state the body of these worms is greyish in colour
and is extremely contractile. They were fixed in 10 per cent hot formalin, some
between two glass slides to keep them flat, and were then preserved in 10 per cent
formalin. These were later stained and mounted for specific diagnosis. They
were found to be quite distinct from either F. hepatica or F. gigantica. This
has been described as a new form and named Fasciola indica Varma, 1953. Not a
single specimen of true F. hepatica Linne [1746 and 1758] or of F. gigantica Cobbold
[1855] was found in this collection and it is quite probable that the new species