Biological Hazard in Food – Parasites 食物中的生物危害：寄生虫

广东疾控 · 公众号 · 养生 · 2017-03-22 21:35

正文

Parasites（寄生虫）

Bacteria appear as single cells and viruses appear as single particles, but this is not the case for parasites.

细菌以单细胞的形式存在，而病毒以单一粒子的形式存在，但寄生虫则不然。

Parasites

寄生虫

Parasites are organisms that can live on or in a host as well as to derive benefit from or at the expense of its host. They can be found on various kinds of food, such as meats, seafood and fresh produce, despite some of them may not be commonly known of harbouring parasites. Two main types of parasites found in food are protozoa and helminths (also known as worms).

寄生虫是居于宿主身上或体内以求本身得益或损害宿主利益的生物。虽然有些食物可能会较少人知道有寄生虫存在，但其实肉类、海产和生的农作物等不同种类的食物都可找到寄生虫。寄生虫主要分为原虫和蠕虫两大类。

Protozoa

原虫

Similar to bacteria, protozoa are single cell organisms and generally can be seen under light microscope. Yet, they are not able to multiply in food but in humans. Some protozoa produce cysts (closed sacs), which can resist destruction by gastric juice in stomach and help protozoa to transmit in food or environment. Infective dose is generally believed to be low and some protozoa may only require a few cysts to cause disease. Toxoplasma gondii and Giardia lamblia are common protozoa found in raw or undercooked meat and contaminated water respectively.

原虫与细菌相似，是单细胞生物，通常在光学显微镜下让人看见。虽然原虫不能在食物中生长，但却能够在人体内繁殖。部分原虫会产生包囊，让其免被胃部内的胃液杀死，令原虫能够在食物或环境中传播。一般相信只需很少数目便可引致原虫感染，部分原虫可能只需数个包囊便可令人患病。生或未经彻底煮熟的肉类中的弓形虫和受污染的水中的蓝氏贾第鞭毛虫都是常见的原虫。

Helminths

蠕虫

Helminths are larger organisms that compose of multiple cells and can vary a lot in size; some can grow up to more than six meters long. In their adult form, helminths cannot multiply in humans. Common helminths found in food are shown below:

蠕虫是较大的多细胞生物，不同种类的体型分别很大，部分可长逾六米。蠕虫的成虫不会在人体内繁殖。食物中常见的蠕虫见下表：

Eggs laid by helminths can be found in faeces, which can reinfest the host or release to the environment to infest other hosts. One of the roundworms, called pinworm, can lay eggs around anus, which cause intense itching. Children harbouring the worm may reinfest themselves by harbouring the eggs under their fingernails after scratching around the anus and subsequently transfer the eggs back to the mouth.

Illustration: Clonorchis sinensis: (left) adult and (right) egg (Photo: Dr. Samson S.Y. Wong, Department of Microbiology, University of Hong Kong)

插图 : 中华肝吸虫 :( 左 ) 成虫及 ( 右 ) 虫卵 ( 照片来源 : 香港大学微生物学系黄世贤医生 )

蠕虫虫卵可存在于粪便中。这些附有虫卵的粪便令蠕虫可再寄生于该名宿主，又或排放往环境中再寄生于其他宿主。属于蛔虫之一的蛲虫，会在肛门附近产卵，令人奇痒无比。体内有蛲虫的儿童在搔抓肛门四周后，便会把虫卵藏在指甲缝内，之后可能会因吃下虫卵而再受感染。

Life Cycle of Parasites

寄生虫的生命周期

Some parasites are free-living, while some require to parasitise other organisms in whole or some part of their life cycle. There may be more than one host in the life cycle of the parasite. Sometimes humans help the spread of parasites by being a definitive host which a parasite reaches sexual maturity and reproduces.

The life cycles are quite different depending on the types of parasites. Some protozoa are transmitted through faecal-oral route via infested food handlers or fresh produce nourished with faecal contaminated water. Some parasites, like flukes and tapeworms, have complex life cycles in which some unrelated hosts may be involved at different stages. For example, the flukes mentioned above need to go through some developmental stages in the snail before reaching the food vehicles that are consumed by humans.

有些寄生虫可独立生活，但有些则须在整个或部分生命周期中寄生在其他生物内。寄生虫在生命周期内可能会有超过一个宿主。有时人类也会成为寄生虫的最终宿主（即寄生虫在该宿主体内处于性成熟期并能生殖后代），协助传播寄生虫。

寄生虫的生命周期各有不同，视乎种类而定。有些原虫会由受感染的食物处理人员或用受粪便污染的水作灌溉的生吃农作物经口粪途径传播。至于吸虫和蛔虫等寄生虫，则有较复杂的生命周期，在不同的阶段可能会寄生在毫无关系的宿主内。举例来说，上文提及的吸虫便需在螺内经过不同的发展阶段，然后才沾染在人们食用的食物传播媒介。

（来源：香港食物安全中心）

（感谢世界卫生组织新发传染病监测研究与培训合作中心陈伟师博士提供专业指导）

统筹：lily

美编：雷未明

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