似蚓蛔線蟲俗稱蛔蟲，為寄生人體的腸道線蟲中體形最大者，其成蟲寄生于人的小腸，引起蛔蟲病（Ascariasis)。
犬弓首線蟲（Tosocaracanis)，簡(jiǎn)稱犬蛔蟲，是犬類常見的寄生蟲，但其幼蟲能在人體內(nèi)移行，引起內(nèi)臟幼蟲移行癥（Visceral larva migrans，VLM)。
一、形態(tài)
1. 成蟲
長(zhǎng)圓柱形，形似蚯蚓，活時(shí)成粉紅色或微紅色，死后為白色；體表有細(xì)橫紋和兩條明顯的側(cè)索；雌蟲長(zhǎng)約20-35cm，尾端鈍圓，雄蟲15-31cm，尾斷向腹面卷曲。
2. 受精蛔蟲卵
Freshly passed Ascaris eggs from faeces.
The eggs may appear from light to dark brown in color. Interference contrast. ×400. Enlarged by 5.4.
Ascaris eggs showing cleavage.
This process normally occurs in the soil and leads to the formation of the larva. Interference contrast. ×400. Enlarged by 5.4
Fertilised eggs of Ascaris dissected from the uterus.
As these eggs have not been exposed to intestinal contents no faecal debris is seen and the outer mammillated layer is completely intact. Interference contrast. ×400. Enlarged by 5.4.
大小約為45-75×35-50μm，寬橢圓形，（因與膽汁接觸而)呈棕黃色，表面有一層波浪狀的蛋白質(zhì)膜，內(nèi)含一大而圓的卵細(xì)胞，卵細(xì)胞與卵殼間有星月形空隙。
3. 未受精蛔蟲卵
|
| |
|
|
 |
|
left: Fertilised eggs of Ascaris dissected from the uterus. As these eggs have not been exposed to intestinal contents no faecal debris is seen and the outer mammillated layer is completely intact. Interference contrast. ×400. Enlarged by 5.4. right: Unfertilised eggs of Ascaris dissected from the uterus. Note the difference in shape and the disorganized contents interference contrast. ×400. Enlarged by 5.4. | |
長(zhǎng)橢圓形，大小約為88-94×39-44μm，卵殼內(nèi)含許多大小不等的折光性顆粒。
注意：若蛔蟲卵的蛋白質(zhì)膜脫落，卵殼則成無色透明，應(yīng)注意與其他線蟲卵的鑒別。
