- Giai doan thur ba tir 35 ngay 63 hoac 70 ngay sau khi nhiem 6 giai doan nay, ca'u true va churc nang ciia cac tuyen bi mit di din dan.
2. DICH Tfc HOC BENH TIEN MAO TRUNG 1 Ph&n bd cua benh
2.1. Ph&n bd cua benh
Benh tien mao triing phan bd rat rong, tir phfa tay sang phfa ddng ban c£u. Phia tdy ban cau thuoc chau My, phfa ddng ban cau trai dai tir chau Phi cho den Philippine. Theo
Euzeby (1984), benh pho bien d trau, bo, ngira cac nude nhiet ddi 6 chau Phi, chau A va Nam My.
6 chau Phi, benh trai dai tir tay sang dong, phfa bac qua vung sa mac Sahara, doc theo bo bien Atlantique Dia trung hai.
t 1
Benh tien mao trung xay ra voi ten goi "benh Surra" 0 A rap Saudi, Yemen, Sultanate, A Rap thong nhat, Tho Nhl Ky, Israel, Syrie, Afganistan, Pakistan.
O chau A, benh xua't hien d Trung A (thuoc Lien Xo cu), An Do, Malaysia, ban dao Dong Duong, Trung Quoc, Indonexia, Philippine.
6 chau Au, benh xua't hien d Bungaria (nay da duoc thanh toan), hien chi con 6 vung Volga va Nam Capcase (Lien Xo cu).
6 chau My, benh xuat hien d Trung My, Nam My, dac biet ph6 bie'n d Brazil, Mexico, Venezuela, Colombia.
Chau Uc cung da duoc xac dinh la co benh tien mao trung (Reid, 2002).
Losos G. T. (1972) cho rang, benh tien mao trung pho bien nha't d chau A va chau Phi, tir An Do den Srilanca, Trung Quoc, Indonexia, Thai Lan, Lao, Camphuchia, Iran, Philippine.
6 Viet Nam, benh tien mao trung tha'y 6 hau het cac vung sinh thai khac nhau: mien nui, trung du, ddng bang, ven bien. Theo Pham Sy Lang (1982), benh tien mao trung co d tat ca cac tinh mien Bac (Bac Kan, Lang Son, Tuyen Quang, Thai Nguyen, Ninh Binh, Ha Tay). Trau, bo nhidm benh vdi ty le cao va thay doi giua cac vung khac nhau (trau, bo d dong bang nhidm tidn mao trung cao hon vung trung du va mien nui, dac biet d trau, bo co nguon goc tir mien nui chuyen xuong viing dong bang).
2.2. Vat chu va vat moi gidi truyen benh tien mao trung
Trong tu nhidn, tidn mao triing ky sinh d hau het cac loai thu nuoi va thu hoang, thay nhieu hon 6 trau, bo, ngua, trau bo rimg, huou, nai, ho, bao, su tir, cho, meo, lac da, voi, tho, chuot cong, chuot lang, chuot bach..., nhung khong ky sinh d nguoi.
Ld Ngoc My va cs (1994) da dieu tra tinh hinh nhidm tidn mao triing d trau bo Viet Nam. Ket qua cho tha'y, trau bo nhidm tidn mao triing voi ty le cao (21,27%), trong do trau bo nuoi d cac tinh mien nui phfa Bac nhidm T. evansi cao hon d dong bang. Theo Ld Due Quyet va cs (1995), Pham Chien (1999), trau d mot so tinh midn Nam va Tay Nguyen nhidm tidn mao triing la 22,12%; bo la 6,6 - 10,3%. Phan Luc va Nguydn Van Tho (1995) cho bie't, ty le nhidm tien mao triing ciia bo d mot sd dia phuang midn Bac la 5,9%. Theo Ha Viet Luang (1998), ty le bo nhidm tidn mao triing d cac tinh mien Trung la 8,99%.
Sir lay truyen tien mao triing tir trau, bo dm sang trau, bo khoe la nhd cac loai ruoi hut mau (thuoc ho phu Stomoxydinae) va cac loai mong hut mau (thuoc ho Tabanidae).
do lai hut mau gia sue khoe, trong khi hut mau se truy&i tien mao trung tir v6i hut vko mau con vat khoe. Sir lay truyen nay mang tinh chit co hoc. Nhu vay, ru6i va mdng hut mau la nhiing vat moi gidi truydn bdnh tidn mao trung quan trong.
Ruoi trau Stomoxys sp. Mdng Tabanus rubidus
Hinh 117. Con triing moi gidi truyen benh tien mao triing
Theo Phan Dich Lan (1974, 1994, 2004), ph£n ldn cac loai mong tap trung 6 khu vuc mien nui va trung du. Trong 53 loai mong thi co tdi 44 loai phan bo 6 viing rimg nui co dd cao dudi 1.000 met so vdi mat nude bien, cang len cao sd' loai cang l't d in (dd cao trdn 1.000 met chi cd 26 loai). 6 vung trung du (rimg thua, do cao khdng qua 500 met so vdi mat nude bien cd 27 loai; viing doi troc chi cd 9 - 11 loai; viing rimg nui ven bi£n phat hien chi co 8 loai.
Nhung loai mong pho bidn d ta't ca cac vung la: Tabanus rubidus, T. striatus, Chrysops dispar, Chrysozoma assamensis.
Nhung loai mong chi gap d vung nui la: Tabanus flavistriatus, T. fumifer, Chrysops vander.
Mien Bac nude ta cd 4 loai ruoi hut mau, 2 loai pho bie'n d tat ca cac viing la
Stomoxys calcitrans va Liperosis exigua\ 2 loai chi thay d nhirng vung sinh canh dac
biet: loai Bdellolarynx sanguinolentus (chi xuat hien d vung cd do cao dudi 1.000 met), loai Stomoxys indica (chi tha'y d vung nui Cam Thuy - Thanh Hoa).
Phan Dich Lan (1994, 2004) cho bie't, kiem tra d nhieu dia diem thay hai loai mong
T. rubidus va T. striatus mang tidn mao triing vdi ty le 15,2% va 14,0%; ruoi hut mau
Stomoxys calcitrans mang tidn mao triing vdi ty le 12,5%. 6 nhung viing dang co benh
tidn mao trung, kidm tra ruoi va mong hut mau dd dang tim thay tidn mao trimg.
Sau khi theo mau vao voi hut ruoi va mong, tien mao triing vin sdng den gid thu 53, thdi gian hoat dong manh nhat la tir gid thu nhat den gid thur 34, trung binh la 24 gid. Su
hoat dong cua tien mao trung yeu dzin tir gid thu 35 den 42. Tir 46 - 53 gia thi tien mao trung ngimg hoat dong.
Hinh thai tien mao trung khi d trong voi ru6i, mong bien doi theo thai gian: tir 1 - 34 gid co hinh thai, kich thudc binh thudng; 35 - 45 gid: tien mao trung co hinh dang thay doi, tang kfch thudc chidu rong va thd dan; 46 - 53 gid: tien mao trung truang to, du6i thang, mat kha nang di ddng va ngimg han hoat dong.
Thuc nghiem da chung minh kha nang gay benh cua tien mao trung sau khi xam nhap vao mdng Tabanus rubidus nhu sau: Thdi gian tir gid thur 1 den thu 5, tien mao trung co kha nang gay benh va lam chd't chuot bach tuong tu nhu khi truydn thang mau co tidn mao triing cho chuot; tir gid thur 6 den thur 7 chi con 30% sd chuot thf nghiem phat benh, thdi gian gay benh keo dai va thdi gian chet cua chuot cung dai. Dieu nay co thd giai thfch la, do doc luc ciia tidn mao triing giam dan va sd luong tidn mao triing con hoat lire gay benh cung giam dan sau khi chung xam nhap vao mdng Tabanus rubidus.
2.3. Tuoi vat chii, miia mac benh
Trau, bo va cac loai gia sue khac d moi lura tuoi deu nhidm tidn mao triing va deu phat benh, co the dan de'n tir vong hoac suy nhugc, thie'u mau, giam sure de khang, giam kha nang sinh de va sue san xua't.
Phan Dich Lan (1994, 2004) da tong hgp ket qua dieu tra 3.172 trau d cac tinh dong bang: trau dirdi 3 nam tuoi nhidm thap nha't (3,2 - 6,1%), trau 3 - 5 tuoi nhidm cao hon (10,6 - 12,7%). trau 6 - 8 tuoi nhidm cao nhat (12,9 - 14,8%), trau trdn 9 nam tuoi ty le nhidm giam thap han trau 3 - 8 nam tuoi.
Theo Phan Van Chinh (2006), ty le nhidm tidn mao triing cao nha't d 4 - 8 nam tu6i (trau: 12,71%; bo: 5,77%), thap nhat la trau, bd dudi 3 nam tuoi (6,92% va 2,31%).
Miia lay lan benh thudng xay ra trong cac thang ndng am, mua nhieu (tir thang 4
den thang 9). Thdi gian nay dieu kien sinh thai thuan lgi cho cac loai ruoi, mong phat trien, hoat dong manh, hut mau sue vat va truyen tidn mao triing. Theo Luckins (1988), sir xua't hien lugng lan ruoi, mong trong mua mua nong am luon co lidn quan den tinh hinh dich td benh tidn mao triing d trau, bd, dd, lac da. Tir cudi miia thu, miia dong va dau miia xuan, trau bd nhidm tidn mao triing phai sdng trong dieu kien thdi tiet lanh, thieu thuc an nen sue dd khang giam, benh thudng phat ra vao thdi gian va trau bo bi do nga hang loat.
Tien mao triing co sire de khang yeu, dd chet khi tiep xuc vdi nirdc cat, con va thudc sat triing.