Introduction to Parasitology

Suggested Textbook :

Markell and Voge’s Medical Parasitology. 9th ed. John DT & Petri WA. 2006.

Helminth 蠕蟲 (-ology) Nematoda 線蟲 Trematoda 吸蟲 Cestoda 絛蟲Protozoa 原蟲 (protozoology)Arthropoda 節肢動物 (Entomology 昆蟲學 )

Vector 媒介 : biological 生物性 , mechanical 機械性

Parasitic zoonoses 人畜共通寄生蟲病

Parasite 寄生蟲 : infection temporary 暫時性 , stationary 定留性

ecto-, endo- obligatory 專性 , facultative 兼性

pathogenic 致病性 , non-pathogenic 非致病性spurious 假性 , pseudo- 假的accidental 偶然

Host 宿主 : Final host (FH) (definitive host) 終宿主 Intermediate host (IH) 中間宿主 Paratenic host (transport host) 保幼宿主 Reservior host (RH) 保蟲宿主

Mode of infection : oral, skin penetration, congenital infection

Infective form 感染型

Effects of parasites on hosts :1. Compete for the nutrients2. Feed on host tissue3. Mechanical damage4. Toxic substance5. Others

-osis -asis

Prevention : 1. Treatment of patients and reservoir hosts2. Treatment of excreta of final hosts3. Control of vectors and intermediate hosts4. Prophylaxis against infections

Scientific nomenclature :

The “top ten” human parasites

Parasite No. infected ( 億 ) Deaths/year ( 萬 )

Ascaris 蛔蟲 13 2-6

Hookworms 鉤蟲 13 5-9

Trichuris 鞭蟲 9

Amebae 阿米巴 5 4-11

Malaria 瘧疾原蟲 4-4.9 250

Giardia 梨形鞭毛蟲 2

Schistosomes 血吸蟲 1.5 50-100

Filarias 絲蟲 1.46

Trypanosomes 錐蟲 0.25 6.5-10

Leishmania 利什曼原蟲 0.12 8

Outline of Nematoda ( 約 50 萬種 )

Morphology : generally elongated and cylindrical, tapering at both end

Differ greatly in size : (F > M) Strongyloides stercoralis 糞線蟲 2 mm Dracunculus medinensis 麥地那蟲 > 1 m

Body wall : cuticle 角皮層 hypodermis 皮下層 musculature 肌肉層

Digestive system : mouth buccal cavity esophagus intestine rectum anus

Reproductive system : male : single coiled tubule accessory copulatory apparatus : spicule 交尾刺

bursa 交尾囊 female : single or double tubules

Life cycle : Egg L1 L2 L3 L4 Adult

Oviparous 卵生 mature egg FH

Egg embryonated egg IH ( infective larva) FH hatched larva infective larva FH

IH ( infective larva) FH

Larviparous 幼生 (ovoviparous 卵胎生 ) Larva IH ( infective larva) FH

90% 於下肢

No immunity and cure

No reservior host

Transmission control

I. Ascaris lumbricoides 蛔蟲 The giant intestinal roundworm Ascariasis, ascariosis

Distribution : worldwide

Morphology : Male : 15–30 cm x 2–4 mm Female : 20–35 cm x 3–6 mm Egg : unfertilized, fertilized, embryonated, mature

Life cycle Prepatent period : 2 –3 months Life span : 1 – 2 years RH : pig (Ascaris suum ?) Infective form : mature egg (soil–transmitted) Mode of infection : contamination of food and water Habitat : small intestine

2-3 wks

Pathology and Symptomatology : Migrating larvae : fever, cough, hemmorrhage, eosinophilia, increased level of IgE pneumonitis (heavy infection) Adult worms : protein–energy malnutrition, vague abdominal discomfort, intestinal obstructions heterotopic (ectopic) 異所寄生

Pica 異嗜症

Loffler syndrome

Diagnosis : stool examination (20 萬 eggs/ 隻 /天 )

Treatment : Mebendazole (Vermox) Albendazole (Zentel) Pyrantel pamoate (combantrin) Levamisole (Tetramisole) Piperazine salts (Antepar) Surgical consideration

Prevention :Epidemiology :

II. Toxocara canis 犬蛔蟲 Toxocara cati 貓蛔蟲

toxocariasis

Distribution : cosmopolitan

Morphology : cervical alae 頸翼 T. canis male : 4–6 cm (max. 13) female : 6–10 cm (max. 20) T. cati male : < 6 cm female : < 12 cm Egg : pitted shell

T. cati 不經胎盤感染

L2

Encyst?

Infective form – mature egg (Soil–transmitted parasite)PH : man, mice, rat, rabbit, chicken, etc.

Pathology and Symptomatology : Granuloma in liver, lung, kidney, heart, striated muscle and eye

VLM (visceral larva migrans): asymptomatic or characterized by eosinophilia, hepatomegaly, pulmonary infiltration, hyperglobulinemia, fever and cough

OLM : eye lesion usually painless, unilateral and symptomless, may lead to total retinal detachment

(retinoblastoma ?)

Diagnosis : Biopsy Serologic tests

Treatment : Mebendazole Albendazole + Corticosteroids (anti–inflammatory) Surgery (OLM)

Epidemiology : children, owners of dogs or cats (seroprevalence : 5% in USA, France)Prevention :

III. Anisakine Nematodes 海獸胃線蟲 Herring worm, codworm

Anisakis spp. : A. simplex, A. typica, A. physeterisPseudoterranova (=Teranova, Phocanema) spp.Contracaecum spp.etc.

Distribution : cosmopolitan

Morphology : Anisakis sp. : male 3–9 cm female 6–10 cm infective larva 2–3.5 cm x 0.3–0.6 mm

Life cycle : IH : small marine crustaceans PH : marine fishes and squids FH : marine mammals Habitat : FH – stomach Man – stomach, intestine, throat

Pathology and Symptomatology Transient anisakiasis : throat irritation nausea, gastric distress within a few hours after ingestion of fish

Eosinophilia Pain, ulcer and granuloma of stomach and small intestine; bloody stool; severe appendicitis; usually mistaken for carcinoma

Diagnosis : Identification of specimens removed by gastric

endoscopy or surgery

Treatment

Pluck out the worms by using a gastroscope

Surgical operation

Prevention

據台大獸醫系費昌勇教授報告，他們對自 1994 年 1月到 1997 年6月這段期間在台灣擱淺的十七種鯨豚 205 隻作樣本採集，發現其中就有 29.27% 的鯨豚感染有海獸胃線蟲的成蟲；而太平洋岸的海魚中有 80% 以上的魚帶有海獸胃線蟲幼蟲。

IV. Gnathostoma spp. 棘口線蟲 Gnathostoma spinigerum , gnathostomiasis

Distribution : Far East

Morphology : headbulb 頭球 , hooklets, cuticular spines Male : 11–25 mm Female : 25–54 mm

G.I.

Life Cycle : 1st IH : copecopds 水蚤 (Cyclops spp.) 2nd IH and PH : crustaceans (experimentlly), freshwater fish, amphibians, reptiles, birds and mammals (except felines and canines) RH : felines and canines

Mode of infection

Pathology and Symptomatology : CLM : rash, stabbing pain, pruritis VLM Neurological g. : eosinophilic myeloencephalitis Ocular gnathostomiasis : palpebral edema ( 長江浮腫 ) , exophthalmos, subconjunctival hemorrhage, blindness

Diagnosis : history Identification of the removed worms

Treatment : Albendazole, surgery

Prevention

V. Enterobious vermicularis 蟯蟲 pinworm (spindle–shaped)

Distribution : worldwide 溫帶多於熱帶 , 都市多於鄉村

Morphology : cephalic alae, esophageal bulb Male : 2–5 mm Female : 8–13 mm Egg : asymmetrical shape

Life Cycle : Infective form : emberyonated egg

(6–7 hrs after oviposition) Prepatent period : 15–43 days (3–4 weeks is more common) Life span : 4–8 weeks Habitat : cecum

Mode of infection *Family infection, retroinfection

幼蟲不會移行

Pathology and Symptomatology : Asymptomatic or Peranal, perineal or vulval pruritis Appendicitis Heterotopic parasitism : peritonitis

Diagnosis : Anal swab (Graham’s Scotch tape swab technique)

Treatment : Mebendazole Albendazole Pyrantel pamoate Pyrvinium pamoate Piperazine salts

Prevention :

VI. Angiostrongylus cantonensis 廣東血線蟲Rat lung worm, angiostrongyliasis

Distribution : Southeast Asia and pacific islands 日、中、台、泰、越、馬來西亞、夏威夷、大溪地等

Morphology : Male : 16–19 mm (small bursa) Female : 21–25 mm Barber’s pole pattern – white uterine and black intestine Egg : hatch in the lung of rat

Life cycle : IH : land snail – 非洲大蝸牛、扁蝸 freshwater snail – 圓田螺、福壽螺、元寶螺 slug 蛞蝓 PH : 渦蟲、蛙、蛇、蝦、蝲蛄、螃蟹等 RH : rat, bandicoots Accidental host

Mode of infection ? Habitat ?

I.H.

F.H.

Pathology and Symptomatology : Asymptomatic or Eosinophilic meningitis Eosinophilic meningoencephalitis

Fever, vomiting, nausea, severe headache, stiff neck, sensory impairment, death Eye invasion – visual impairment, ocular pain

Diagnosis : Young adults in CSF Blood and CSF : eosinophilia, pleocytosis CT, ELISA

Treatment : Anthelmintic treatment is not recommended Supportive treatment, corticosteroid Removal of CSF Immunotherapy ?

Prevention :