ISOLATION OF VIBRIO PARAHAEMOLYTICUS FROM MUSCA DOMESTICA VICINA AND CHRYSOMYIA MEGACEPHALA IN CALCUTTA

Sporadic non-seasonal cases of gastroenteritis due to Vibrio parahaemolyticus infection occur in Calcutta throughout the year, involving poor socioeconomic group of non-vegetarian and strict vegetarian habits. In an attempt to search the reservoir of this infection, isolates of few fresh non-marine animals were examined and V parahaemolyticus was demonstrated in the following fishes: Caridina rajadhari (chingri), Amblybharingondon mola (mourolla), Bardus tieto (punti), Glossogobbius guiris (bete) and Apoeryptes laneeolatus (goole). Out of 100 samples of pond water ,around the slum areas in Calcutta, positive isolation of V parahaemolyticus biotype I was detected in 35. However, attempts to isolate V parahaemolyticus biotypes from 50 normal human stools, 258 faecal samples of crow and 250 stools of dog yielded no positive result (Chatterjee, 1974). V. parahaemolytieus was also isolated in about 30% marine sample, i.e., Hooghly river water and marine shrimps in Calcutta (Chatterjee et al., 1973). In the city of Calcutta house flies and other related flies abound. Do tlfey play any role as the reservoir of this bacterium ? An attempt was. made to isolate JI' parahaemolyticus biotype I from the whole body washings and viscera of the rues collected from fish stalls and sweet shops of Calcutta.


INTRODUCTION
Sporadic non-seasonal cases of gastroenteritis due to Vibrio parahaemolyticus infection occur in Calcutta throughout the year, involving poor socioeconomic group of non-vegetarian and strict vegetarian habits. In an attempt to search the reservoir of this infection, isolates of few fresh non-marine animals were examined and V parahaemolyticus was demonstrated in the following fishes: Caridina rajadhari (chingri), Amblybharingondon mola (mourolla), Bardus tieto (punti), Glossogobbius guiris (bete) and Apoeryptes laneeolatus (goole). Out of 100 samples of pond water ,around the slum areas in Calcutta, positive isolation of V parahaemolyticus biotype I was detected in 35. However, attempts to isolate V parahaemolyticus biotypes from 50 normal human stools, 258 faecal samples of crow and 250 stools of dog yielded no positive result (Chatterjee, 1974). V. parahaemolytieus was also isolated in about 30% marine sample, i.e., Hooghly river water and marine shrimps in Calcutta (Chatterjee et al., 1973).
In the city of Calcutta house flies and other related flies abound. Do tlfey play any role as the reservoir of this bacterium ? An attempt was. made to isolate JI' parahaemolyticus biotype I from the whole body washings and viscera of the rues collected from fish stalls and sweet shops of Calcutta.

MATERIALS AND METHODS
Samples of flies were collected once in a week in sterile test tubes, separately from fish markets and sweet shops situated in the heart of Calcutta city. Different fish and sweet shops in the same locality were selected each time.

Records of the Zoological Survey of India
As soon as the collection was brought to the laboratory, the tubes containing the flies were kept in ice for 20 minutes so as to anaesthetize them for dissection. Five flies each from fish and s,veet shop were selected at random for dissection.
Prior to dissection, each fly was dropped in a labelled sterile test tube having 10 lml. of alkaline peptone water containing 3 % NaCl (P 9.2), with the help lof a sterile forceps. Each tube was then shaken thoroughly, so as to wash the fly externally and kept as such for 10 minutes. Internal viscera of each fly was then dissected on a sterile slide using sterile forceps and needles. Internal organs so dissected were then drained into another labelled tube (label corresponding to its washing) containing 10m!. of peptone solution.
The washings of individual flies and internal viscera so collected were then bacteriologically investigated for isolation of V. parahaemolyticus biotype I according to the method of Chatterjee (1974).   External washings of 11 C. megacephala caught from both kinds of shops did not yield any positive result.
Out of 9 viscera of C. megacephala studied, V parahaemolyticus was isolated from 2 specimens (22.22 %), obtained from fish stalls.
It was observed that the flies of both species were attracted to fish and sweetmeat, but the number of M. d. vicina was much greater than that of C. megacephala in both types of shops. Potentially pathogenic V. parahaemolyticus biotype I was present in both the species of flies.
From the whole-body washings of the flies the rate of isolation was comparatively low and isolation was only positive in M.d. vicina.
Examination of the viscera of those flies revealed interesting results.
The rate of isolation of V parahaemolyticus from the viscera (22.22 %) was higher than that of the washings (5.61 %) in both the species of fties. However from the viscera of C. megaeephala caught from sweet shops no V. parahaemolyticus was isolated uptil now.
The results indicate that the organisms get suitable environment in the viscera of the flies to survive.
This study reveals that house flies and other related flies play a role as reservoir of V. parahaemolyticus in Calcutta. No other reference has been quoted in the literature to the occurrence of V. parahaemolyticus in flies.
The rate of infection of the viscera of both species of Dies is alarming, indicating a thorough study of the (epidemiology of parahaemolyticus gastroenteritis in Calcutta through the year.