Tissue and Blood Residing Nematodes Filarial worm Trichina worm
Common Characteristics • Biohelminth • Need intermediate host • Location (residing site) • Tissue and blood • Ovoviviparous (larviparous) • adult female deposit larvae
Filaria • 2 types of filaria • Lymphatic filaria • Tissue filaria • Subcutaneous tissue (O.volvulus, L.loa) • Peritoneal cavity (M.perstans) • All species are transmitted by insect vectors • 8 species could infect human being
Most Important Species • Tissue filaria • Onchocerca volvulus: river blindness • Loa loa: subcutaneous swelling • Lymphatic filaria • W. Bancrofti • B. Malayi
Wuchereria bancrofti班氏吴策线虫Brugia malayi马来布鲁线虫
Morphology • Adult • Grossly a white silk, thread-like • W.b > B.m
Microfilaria (Mf) • Appear in host peripheral circulation during night • Structure • Cephalic space • Somatic nuclei • Caudal nuclei • Sheath, etc.
Microfilariae measure 270 by 8 m, have a sheath and a tail with terminal constriction, elongated nuclei and absence of nuclei in the cephalic space. They have nocturnal periodicity. (Wet mount preparation).
Brugia malayi: the tail is tapered and present a constriction. The last two nuclei are divided by the constriction.
Brugia malayi:the cephalic space is longer than broad (in W.bancrofti is as long as broad).
Main Points of Life Cycle • Location (adult): lymphatic system • W.b: superficial and deepere.g. lower limbs, groin, scrotum, etc. • B.m: superficiale.g. mainly in lower limbs • Infective stage: filariform larva • Infection route: mosquito inoculation • Discharge stage: microfilaria
Intermediate host & vector: mosquito • W.b: Culex (Anopheles) • B.m: Anopheles (Aedes) • Infection threshold • 15-100Mf/20mm • Mf show nocturnal periodicity
Nocturnal periodicity • Mfs appear in the peripheral blood in high density during the night, but hide in the pulmonary capillaries during the daytime while the host is awaken. • W.b: 10 Pm ~ 2 Am • B.m: 8 Pm ~ 4 Am
Pathogenesis • Main pathogenic factor • Adult • Acute stage • Lymphangitis, Lymphadenitis • B.m: lower limbs • W.b: limbs & uro-gential (epididymitis, orchitis)
Chronic stage • Elephantiasis could be seen in both filarial infection • W.b: chyluria, hydrocele
Lymphatic filariasis: elephantiasis is the last consequence of the swelling of limbs and scrotum.
Lymphatic filariasis: elephantiasis of scrotum. Genital manifestations are frequent in W.bancrofti infections while they are rare during B.malayi infections.
elephantiasis Hydrocele testis
Epidemiology • Distribution: • Tropic region, coexist with mosquito • W.b: global • B.m: Asia • China • 15 provinces, mixed • Shandong,Tai wan,Hainan only W.b
Lymphatic filariasis have a wide geographic distribution. W.bancrofti and B.malayi infect some 128 million people, and about 43 million have symptoms. B.malayi infection is endemic in Asia(China, Corea, India, Indonesia, Malaysia, Philippines, Sri Lanka). W.bancrofti has a larger distribution : Asia (China, India, Indonesia, Japan, Malaysia, Philippines, South-East Asia, Sri Lanka, Tropical Africa, Central and South America, Pacific Islands.
Endemic links • Source of infection • Patient • Mosquito • W.b: Culex (Anopheles) • B.m: Anopheles (Aedes) • Susceptible population: human • Natural & social factors
Laboratory Diagnosis • Etiological examination • Stained thick blood smear: first choice of methods • Blood drop microscopy: used in the field • Hetrazan induced method • Lymph node biopsy
Principle of Control • Mass treatment: Hetrazan • Hetrazan-salt: 0.3%, 6 months • Elephantiasis-baking bandage • Mosquito biting control
Biological characteristics • Zoonosis • Ovoviviparous • Adult & larva live in the same host individual • Adult: small intestine • Larva: striated muscle
Main Points of Life Cycle • Infective stage: capsulated larva • Infection route: eating raw or improperly cooked pork or its products • No extra-hostal developing, but must change host to finish the life cycle exists many reservoir host • Human acts as I.H and D.H
Pathogenesis • Main pathogenic factor: larva • Invasion stage (intestinal phase): minor digestive disturbance • Migration stage (muscular phase): fever; eosinophilia; circumorbital edema; myositis; Muscular tenderness • Encystment stage: recovery
Epidemiologiy • Cosmopolitan, esp. in Europe and North-America • China, esp. in Yunnan province: due to raw pork consumption
Diagnosis • Based on the basis of clinical symptoms and history • Etiological diagnosis • Biopsy of skeletal muscle • Immunological diagnosis
Control methods • Hygienic education • Properly cooking pork • Low temperature storage of pork(all larvae are killed at -15ºC for 24hs) • Scientific raising pigs: heat treatment of garbage used as pig food