Nakagawa has found that the miracidia infest certain fresh water molluscs and become cercariae in this first intermediate host. From this host the cercariae go to certain fresh water crabs and encyst in this second intermediate host, either in the liver or in the gills. In Japan one of these crab hosts, Potamon dehaanii, is eaten both raw and cooked.
Fig. 114.—Paragonimus westermanni; photograph from a sexually immature specimen. (From Tyson.)
Experimental feeding of puppies on infected crabs brought about infection with the lung fluke. It is thought that the fluke, after leaving the cyst, goes through the intestine to the abdominal cavity. Thence it perforates the diaphragm and enters the pleural cavity, finally penetrating the lung to become encysted there. The lung is the favorite site but wandering flukes may invade other tissues and organs even invading the central nervous system.
Besides man, dogs, cats and especially hogs may be infected.
Symptomatology, Diagnosis and Treatment
The case is usually considered as one of chronic bronchitis on account of the occurrence of cough and morning expectoration of a gelatinous sputum which is usually brownish. It is popularly known as endemic haemoptysis for the reason that after violent exertion, or at times without manifest reason, attacks of haemoptysis of varying degrees of severity come on. The signs on percussion are usually insignificant while those on auscultation at the time of haemoptysis are often marked. The symptoms often disappear for months to again reappear.
Fig. 115.—Anatomy of trematoda (flukes) of man. O S, oesophageal sucker. Ph, pharynx. Oes, oesophagus. O P, genital pore. V S, ventral suckers or acetabulum. Ut, uterus. Int, intestines. Ov, ovary. Sh G, shell gland. T, testicles. T G, yolk glands or vitellaria. Exc, excretory pore.
The course of the disease is very chronic, often lasting many years. As a rule the patient is fairly well nourished although recurring attacks of haemoptysis may bring on a rather marked anaemia. Jacksonian epilepsy has been reported as occurring in paragonomiasis, the ova being found in cysts of the brain. There is some question as to whether some of the reports as to paragonomiasis may not have been connected with infections with Japanese schistosomiasis.