1. DAC DIEM SINH HOC CUA SAN LA FASCIOLOPSIS BUSK
1.3. Vat chu trung gian cua F busk
Vat chu trung gian cua F. buski la cac loai oc nude ngot.
Oc nuPc ngot thuoc lop chan - bung, gom hai phan IPp: Probranchia (oc mang trudc) va Pulmonata (oc co phoi).
Co the oc tap trung thanh khoi, dupe bao boc boi lop vo da voi, kfch thuoc Ion nho khac nhau tuy theo timg loai. Nhirng oc song d nuPc ho hap bang mang. 6 can ho hap bang phoi. Mot phan co thd oc phan hoa thanh chan (la co quan van dong).
Trong nuoc, oc song d nhung do sau khac nhau, thdi gian hoat dong cua chung cung khac nhau. Ban dem, do cac loai thuc vat song trong nuoc hap thu oxy, thai khf cacbonic nen phan Ion cac loai oc tai, oc dia phai noi ldn mat nude de ho hap. Oc thudng bam vao cac vat noi trdn mat nuPc nhu la beo, cay co cho den 9, 10 gid sang hom sau moi chim xuong cac ting nude sau hon. Mot so loai oc tai, oc dia thuPng bam vao cac cay beo Nhat Ban, rau muong, rau lap, rong d cac ao, ho, song, suoi. Chung co the d noi am udt (khong ngap nude) trong mot thdi gian dai (Dang Ngoc Thanh va cs, 1980). Thuc an cua oc nude ngot la rong reu, beo, cac chat miin.
Theo Phan Trong Cung va cs (1991), oc nude ngot sinh san huu ti'nh, phan ldn la don tmh, mot so loai ludng ti'nh nhung khong tu thu tinh.
D6 Duong Thai va cs (1978) da t6ng hop ket qua phat hien ciia Barlow (1925). Tran Tam Dao (1956), Hua Bang Nhu (1964) ve oc ky chu trung gian cua san la ruot 1cm d
Trung Quoc gom cac loai: S. nitidella, G. chinensis, H. cantori, H. umbilicalis,
hemisphaerula....
Theo Phan Luc (1976), Nguydn Thi Le (1986), 6 Viet Nam, oc P. hemisphaerula, G.
sinensis va G. heudei la ky chu trung gian cua san la ruot lpn. Ty le nhidm Cercaria ciia
oc P. hemisphaerula b khu vuc trong rau xanh nuoi lpn co lidn quan tdi tinh hinh su
dung phan bon co u hay khong u va muc do bon phan d khu vuc do. Oc ky chu trung gian co kfch thuPc cang ldn thi ty le nhidm Cercaria cang cao. Trong tu nhien thudng tha'y oc P. hemisphaerula b cac ao co beo Nhat Ban, chung thuong tap trung d ke la beo, nha't la cac la beo dang thdi rua. O ruong muong cd muc nude nong, pH 6 - 7, oc thudng tap trung d cong, la rau dang thoi rua. 6 cac ruong muong dang trong thdi ky kho han, dat da nut ne, oc thudng tap trung d goc muong, ty le oc song la 90,3%. Trong ruong rau
✓ , L X
lap mat do oc thap hon. 0 ruong lua, ruong mdi cay, oc tap trung d goc lua hay treo minh trdn mat nude (Thai Tran Bai, 1977).
Gilman va cs (1982) da nghidn cuu ve oc - ky chu trung gian cua F. buski b
Bangladesh cho bie't, oc H. umbilicalis, S. trochoidues la ky chu trung gian cua san nay, ty le oc nhidm Cercaria la 1%.
Ono (1958) da dung nitrat canxi (Ca(NO-<)2) nong do 0,05 - 0,08%, sunfat ddng (CuS04) nong do 0,5; 1 va 2% dd diet oc.
Theo td chuc ve sinh quoc te (OMS) (1960) thi cac hoa chat tot nhat dung de diet oc phai la nhiing chat cd hoat lire chdng cac ky chu trung gian va ngan can sir sinh san cua chung, lieu dung phai thap hon 1/1.000.000, khdng doc cho ngudi va gia sue, khdng doc hoac ft doc cho sinh vat sdng d trong nude.