Paragonimus westermani 卫氏并殖吸虫 (lung fluke,肺吸虫)

Introduction The reproductive organs of paragonimus stand side by side Adult worms usually live in the lungs of man and carnivores causing paragonimiasis，so they are also called lung flukes It is essentially a zoonosis, reservoir hosts including dogs, cats and tigers In china, there are two species of lung flukes of medical importance: Paragonimus westermani, Pagumogonimus skrjabini

It is the main kind of lung flukes infecting man Introduction Paragonimus westermani was first found in a Bengal tiger’s lung in India in 1877 It is the main kind of lung flukes infecting man In China, P. westermani prevalent in 23 provinces, city and autonomic region except Xinjiang, Xizang, Qinghai, Gansu, Ningxia, Inner Mongolia and Shandong

Introduction Infection occurs in Asia (especially in China, Korea, India, Japan, Laos, Philippines, Sri Lanka, Thailand, Viet-Nam), Central-West Africa, South America (Ecuador, Perù, Venezuela)

Morphology Adult worm Elliptic, dorsally convex while ventrally flattened as half of a peanut Reddish-brown in color About 7.5-124-61-3 mm (length:width=2:1) The ventral sucker is located in the central position of the body Two testes, the ovary and the uterus are situated side by side – characteristic configuration

Oral sucker ventral sucker ceca ovary uterus Vitelline follicles Testes

Oral sucker spines Excretory pouch ventral sucker

Egg Size about 10055µm Thick and asymmetric shell Morphology Size about 10055µm Thick and asymmetric shell A distinct operculum An ovum surrounded by more than 10 yolk cells operculum ovum yolk cell shell

Morphology

Life cycle

Life cycle Infective stage: metacercaria Infective route: oral consumption (eating raw fresh water crabs and crayfish with metacercariae) Development in definitive hosts including pre-adult migration Site of inhabitation: lungs

Two intermediate hosts 1st int. host is melania snail Life cycle Two intermediate hosts 1st int. host is melania snail 2nd int. hosts are crab and crayfish Ectopic parasitism caused by worm wandering – cerebral, abdominal, etc Eggs discharged with sputum or feces Reservoir hosts: carnivores such as tiger, wolf, fox, dog, leopard, cat, etc

1st int. host cercaria

Life cycle 2nd int. host Crab (Eriocheir sinensis) Crayfish

Pathogenesis Stages take responsibility -- adult and pre-adult worms (migration and lodging) Pathology including cell infiltration  granuloma formation  encapsulation (lung: duct to bronchiole) abscess stage cystic stage scar formation

Dog infected with Paragonimus westermani shows multiple worm nodules. Pathogenesis Dog infected with Paragonimus westermani shows multiple worm nodules.

Pathogenesis Dog infected with Paragonimus westermani shows worm nodules and an opening from which an adult worm escaped.

Pathogenesis A computerized tomography shows multiple calcified density in the right frontal and temporal areas of chronic cerebral paragonimiasis patient.

Clinical features Paragonimiasis may be classified into 4 types Pulmonary type: the symptoms resemble pulmonary tuberculosis with low fever, loss of appetite, night sweating, chest pain, loss of weight and rusty sputum Abdominal type: abdominal pain，diarrhea or dysentery with blood and mucus Subcutaneous type: the wandering and painless subcutaneous nodules Brain type: epilepsy, hemiplegia, aphasia

Diagnosis History of eating raw crustaceans (crabs or crayfish) Etiological diagnosis – finding eggs in sputum and feces Sputum examination: Direct sputum smear Alkali digestive method (10%NaOH) Stool examination: Direct fecal smear Alkali digestion Water sedimentation method  Biopsy for Subcutaneous type  CT for brain type  Immunological tests for reference

Treatment and Prevention praziquantel Prevention: Treat patients and carriers Avoid eating raw fresh water crabs and crayfish Avoid sputum and stool getting into water Control of reservoir hosts

Pagumogonimus skrjabini A unique species only endemic in China, about 15 provinces reported cases Pathology mainly caused by the wandering pre-adult worm Subcutaneous type is the most common clinical features Diagnosis through skin biopsy Praziquantel is the choice for treatment