EFFECT OF FREEZING AND CHILLING ON THE VIABILITY AND INFECTIVITY OF THE METACERCARIAE OF HAPLORCHIS PUMILIO AND PROHEMISTOMUM VIVAX

Assiut University web-site: www.aun.edu.eg

EFFECT OF FREEZING AND CHILLING ON THE VIABILITY AND INFECTIVITY OF THE METACERCARIAE OF HAPLORCHIS PUMILIO AND PROHEMISTOMUM VIVAX

YOUSSEF, T.H.¹; HEFNAWY, Y.A.¹; KHALIFA, R.² and MAHMOUD, A.E.²

¹ Department of Food Hygiene, Faculty of Veterinary Medicine, Assiut University, Egypt

² Department of Parasitology, Faculty of Medicine, Assiut University, Egypt

Received: 31 December 2015;    Accepted: 30 January 2016

INTRODUCTION

Fishes are considered as one of the most valuable nutritive, tasty, palatable and easily digested protein for human. They can compensate the shortage in the animal protein where there is need to food as a result of rapid increase of world population particularly in developing countries and also due to the dramatic changes that occurred in animal and poultry production from emerging zoontic diseases such as bovine spongiform encephalopathy and avian influenza which affect the protein resources. However, fish may harbor many pathogens which constitute great problems either in cultured or wild fishes as they limit the fish production especially in subtopic countries like Egypt (Elamei, 2001).

Under natural conditions 50 – 90 % of freshwater fishes harbor at least one species of parasites (Sineszko, 1979). Parasitic diseases are considered to be serious problem rather than bacterial diseases in warm water fishes (Eissa et al., 1996).

Fresh water fishes are considered as one of the important sources of parasitic infection to man and fish eating mammals particularly after the increased pollution of rivers and lakes in Egypt (Mohamed, 1996). The public health importance of some internal parasitic diseases affecting Tilapia nilotica such as yellow grub which can be transmitted to human as a result of ingesting raw or improperly cooked fish and

Corresponding author: Dr. Youssef, T.H.

E-mail address: dr_toko@yahoo.com

Present address: Department of Food Hygiene, Faculty of Veterinary Medicine, Assiut University, Egypt

causing Halzoun like disease leading to laryngopharyngitis (Williams and Jones, 1976) while Prohemistomum vivax was rarely recorded to infect human and may cause death (Nasr, 1941).

MATERIALS AND METHODS

Fresh Tilapia nilotica and Clarias lazera fishes were examined for the presence of different metacercariae. Snips of muscles obtained from the head region (anterior part) of the fish, trunk region (middle part) and tail region (posterior part) were compressed between two slides and examined microscopically. Samples of the discovered metacercariae were fixed in 5% formalin, stained in acetic acid alum carmine and mounted in Canada balsm. Heavily infected fish were divided into three groups. The first group was used as positive control, the second group was exposed to chilling at temperature of (4 °C) and the third group was exposed to freezing at temperature   (-10 °C). The viability of the three groups was observed after interval 24, 48 and 72 hours microscopically. Then the time required for death of the encysted metacercariae was determined. Moreover, confirmation test was done by feeding parasites free laboratory albino rats on the three groups of encysted metacercariae and sacrification of rats from the 7^th day post infection to detect and count the adult flukes in their intestine (Wells and Randall, 1956, Syme, 1966).

Daily infection was done from the the three groups. In each experimental trial, confirmed viable 50 Haplorchis pumilio and 20 Prohemistomum vivax encysted metacercariae were given to each albino rat.

RESULTS

Table 1: Effect of chilling and freezing on the viability of encysted metacercariae in muscles of Tilapia nilotica.

+: viable encysted metacercariae

-: not viable encysted melacercariae

Table 2: Effect of chilling and freezing on the viability of encysted metacercariae in muscles of Clarias lazera.

+: viable encysted metacercariae

-: not viable encysted melacercariae

Table 3: Effect of freezing and chilling on the infectivity of metacercariae of Haplorchis pumilio and Prohemistomum vivax in Tilapia nilotica.

* The number of adults was within the same range throughout the three days of the experiment.

Freezing = -10 ^OC

Chilling = 4 ^OC

Table 4: Effect of freezing and chilling on the infectivity of metacercariae of Haplorchis pumilio and Prohemistomum vivax in Clarias lazera.

* The number of adults was within the same range throughout the three days of the experiment.

Freezing = -10 ^OC

Chilling = 4 ^OC

DISCUSSION

Effect of chilling of Tilapia nilotioca and Clarias lazera on viability and infectivity of encysted metacercariae:

1- Effect of chilling of Tilapia nilotioca:

Investigation of infested muscular tissues of T. nilotioca with encysted metacercariae at interval periods (0, 24, 48 and 72 hours) at chilling temp. (4°C) revealed that the encysted metacercariae were viable for 24 hours only and complete destruction occurred after 24 hours of chilling storage.

2- Effect of chilling of Clarias lazera:

Examintion of infested C. lazera at interval period of chilling (0, 24, 48 and 72 hours) at (4°C) revealed that the encysted metacercariae were viable for 48 hours and complete destruction occurred after 48 hours of chilling storage. The variation between the viability of encysted metacercariae infested the muscular tissues of T. nilotioca & C. lazera may be attributed to the variation in the host species.

3-Effect of freezing of Tilapia nilotioca & Clarias lazera on viability of encysted metacercaria:

Investigation of infested muscular tissues of T. nilotioca & C. lazera with encysted metacercariae at interval periods (0, 24, 48 and 72 hours) at of freezing temp. (-10°C) revealed that the encysted metacercariae were destroyed within 24 hours only. Experimental infection of laboratory rats with freezed and chilled 50 EMC of Haplorchis pumilio and 20 EMC of Prohemistomum vivax confirmed the data obtained for their viability.

CONCLUSIONS

Freezing of fishes for one to two days before consumption remains to be the best method for avoiding human transmission of fish borne parasites.

REFERENCES

Eissa, I.A.M.; Diab, A.S. and Badran, A.F. (1996): Studies on some internal parasitic diseases among wild and cultured Oreochromis niloticus fish. 7^th Sci. Cong., 17-19 Nov. 1996, Fac. Vet. Med., Assiut, Egypt.

Elamie, M.M.M.T. (2001): Studies on the diseases resulting from encysted metacercariae in some freshwater fishes. M.V.Sc. Thesis (Fish diseases and management), Fac. Vet. Med. Suez Canal Univ.

Mohamed, I.B. (1996): Pathological changes in some fish eating mammals as a result of consumption of fish infested with encysted metacercariae. PhD Thesis, (Pathology), Fac. Vet. Med., Cairo Univ.

Nasr, M. (1941): The occurance of Prohemistomum vivax infection in man, with redescription of the parasite. Lab. Med. Prog., 2: 135-149.

Sineszko, S.F. (1979): Effects of environmental stress on outbreak of infectiou diseases of fishes. J. Fish Biol., 6: 157-208.

Syme, J.D. (1966): Fish and fish inspection. 2nd Ed. 52-64. Univ. of Toronto.

Wells, H.H. and Randall, B.H. (1956): New hosts for trematodes of the genus Heterophyes in Egypt. J. Parasitol., 42: 287-292.

Williams, H.H. and Jones, A. (1976): Marine helminthes and human health. Commonu. Inst. Helminthol. Misc. Publ.3, 47.