Tropical Diseases/Chapter 43
CHAPTER XLIII
III. PARASITES OF THE LUNGS
ENDEMIC HÆMOPTYSIS
PARAGONIMUS WESTERMANI (Kerbert, 1878)
Synonyms.—Distoma westermani: D. ringeri; D.pulmonis; D. pulmonale; D. cerebrale; Mesogonimus westermani; M. pulmonalis; M. ringeri.
History.— This disease and the characteristic ova appearing in the sputum of the subjects were described by Baelz and the author in 1880. Ringer, in 1881, was the first to find the mature parasite which was afterwards described by Cobbold under the name Distomum ringeri; subsequently it was recognized to be identical with the previously described Paragonimus westermani of the tiger. The main features of its life-history and pathological bearings have been worked out recently by Japanese observers.
Geographical distribution.— Endemic hæmoptysis occurs in China, Japan, Korea, Formosa, and the Philippines. In many of the endemic districts a notable percentage of the population is affected. Thus, Kakami states that in certain Korean villages 32 per cent, of the men, 48 per cent, of the dogs, and 1 to 2 per cent, of the pigs are infected with the parasite causing this peculiar form of hæmoptysis. It is not improbable that, as knowledge extends, the disease will be found to exist in other countries. The cause, Paragonimus westermani, has been found in the United States in the cat, in the dog, and in the domesticated hog; ere long, therefore, we may hear of endemic hæmoptysis in man in America. The Chinese and Japanese are nowadays to be found in almost every land, and doubtless they carry with them their peculiar parasites— Opisthorchis sinensis, Fascio lopsis buski, Schistosomum japonicum, and also P. westermani. The establishment of these exotic species will depend, among other things, on their finding appropriate intermediary hosts.
Symptoms.— The subjects of endemic hæmoptysis have a chronic cough, which is usually most urgent in the morning on rising. The fits of coughing eventuate in the expulsion of a peculiar rusty-brown, pneumonic-like sputum. This sputum can be produced at will almost at any time, and often in considerable quantity. In addition to the chronic cough and the tenacious rusty expectoration referred to, the patient is liable to irregular attacks of hæmoptysis. Though usually induced by violent exertion, occasionally such attacks come on without apparent cause. The hæmoptysis may be trifling; on the other hand, it may be so profuse as to threaten life— at all events, to cause intense anæmia.
The sputum.— On placing a minute portion of the viscid, pneumonic-like sputum under the microscope, its peculiar colour is found to be due partly to red blood-corpuscles, partly to a crowd of dark- brown, thick-shelled, operculated ova (Fig. 161). These ova vary a good deal in size and shape; they are all distinctly oval, have a yellow, smooth, double-outlined shell, and measure from 80 to 100 μ. in length by 40 to 60 μ in breadth. If the sputum be shaken up in water, and the water be renewed from time to time, in the course of a month or six weeks— longer or shorter according to temperature a ciliated miracidium is developed in each ovum. When the ovum is mature, on placing it on a slide and exercising slight pressure on the cover-glass the operculum will be forced back, and the miracidium will immediately emerge and begin to swim about and gyrate in the water.
Pathological anatomy.— On making a section of the lungs in this disease, a larger or smaller number of what are known as " burrows " are discovered scattered about this organ, particularly towards the periphery. These burrows consist of areas, somewhat larger than a filbert, of infiltrated lung tissue in which can be seen a number of tunnels filled with the same material that constitutes the characteristic sputum, and also containing one, two, or more small trematodes. The septa between the tunnels may break down and a considerable cavity be thus produced; and as this occurs in connection with one of the bronchi, with which the tunnels always communicate, it may give rise to the appearance of
Fig. 161.—Ova of Paragonimus westermani in sputum.
a dilated bronchus. One burrow may communicate with another.
When first discovered it was supposed that P. westermani was confined to the lungs. We now know that it may affect the liver, peritoneum, testes, intestine, skin, muscle, and brain. In the brain it forms a sort of tunnelled tumour similar to those in the lungs, and by the pressure or irritation proceeding from this tumour may give rise to a peculiar and ultimately fatal form of Jacksonian epilepsy.
The parasite (Fig. 162).—The parasite itself is reddish brown in colour, thick and fleshy, and oval in form. So thick is it that its transverse section is almost round. It measures 8 to 16 mm. in length by 4 to 8 mm. in breadth, and is covered with broad scale-like spines. The anterior extremity is bluntly rounded and without cephalic cone; the oral sucker (Fig. 162, m) (0·88-1·12 by 0·80-0·83 mm.) terminal or sub-terminal; ventral sucker (Fig. 162, ac) (0·88-1·2 by 0·86-1·44 mm.) slightly larger than the oral sucker and situated somewhat anteriorly to the middle of the body. The pharynx is elongate, but the oesophagus is very short, so that the bifurcation of the intestine is considerably anterior
Fig. 162.—Paragonimus westermani. (Partly after Looss.)
a, Magnified; b, natural size. (See text.)
to the ventral sucker. The intestinal cæca (Fig. 162, i) run somewhat zigzag to the caudal end of the body. The genital pore opens close to the posterior margin of the ventral sucker. The testes (Fig. 162, t,t) are tubular, ramified, and situated on each side of the middle line, one slightly posterior to the other. The ovary (Fig. 162, o) is branched and is placed somewhat posteriorly to the ventral sucker, and either to the right or left of the middle line. The shell gland is lobate; the uterus (Fig. 162, ut) short and usually massed; the vitellaria (Fig.162, vg) are marginal and greatly developed.
For many years the mode in which this parasite entered man was unknown. Analogy suggested that the ova expectorated by the host were washed into water—rivers, ponds, wells, etc.— that the miracidium, on being hatched out, entered some undetected mollusc; but further than this conjecture could not venture until Nakagawa, Kakami, Myairi, Yoshida, and other Japanese investigators showed that on escape from the egg the miracidium enters a fresh- water snail probably Melania libertina or M. obliquegranulosa—wherein it undergoes the usual developmental changes of sporocyst and redia, eventuating in the formation of cercariae. The cercarite in due time escape into the water, and, finding their way into certain species of fresh-water crabs—Potamon obtusipes, Eriocheir japonica, Potamon dehaanii—encyst themselves in the liver, muscles, etc., and especially in the gills of the crustaceans, and undergo developmental changes. Their further progress is not exactly known, but in dogs or cats fed on infected crabs the cercariae, on reaching the ileum of these vertebrates, escape from their cysts in from twenty-four to forty-two hours, penetrate the gut wall and pass into the peritoneal cavity, and a few of them, traversing the diaphragm, enter the lungs; a few pass into the liver, muscles, and other organs and tissues, and, after about ninety days, having attained sexual maturity, produce eggs. It is still doubtful as to how the encysted cercaria escapes from the crab, and as to how it obtains, in nature, access to man. However it may be in Japan, where raw fish is often eaten, neither the Koreans nor the Formosans eat uncooked crabs, and yet P. westermani is very common in certain districts of Korea and Formosa. Possibly encystment in the crab is not a biological necessity for the parasite; it may be that the cercarias, which can penetrate the cuticle or organs of the crab, can also penetrate those of man, and that man is infected with P. westermani in the same way as he is infected with the three species of schistosomes—S. haematobium, S. mansoni, and S. japonicum.
Diagnosis.—Diagnosis of endemic haemoptysis is at once established by the discovery of the characteristic ova in the almost equally characteristic sputum. Rales and other physical signs of lung consolidation are not usually discoverable. If the intestine or liver is implicated, ova may appear in the stools.
In the case of one-sided convulsions, or in hemiplegic affections occurring in a native of or in a visitor from the countries in which this trematode is endemic, the sputum should be examined on the chance of discovering evidence of the parasite. Should ova be found, there is a strong presumption that the cerebral trouble arises from trematode tumour in the brain. Treatment.— Hitherto no means of expelling this parasite from the lungs has been discovered. In the case of cerebral distomatosis it might be possible by an operation to remove the parasite and associated tumour, and thus afford a chance of recovery in what has hitherto proved a fatal condition.
Prophylaxis in this, as in so many animal parasitic diseases, principally lies in the direction of securing a pure water-supply for drinking and bathing purposes, and avoiding all uncooked articles of diet which might be supposed to contain the young parasites. The sputum should be destroyed.
NOTE.— Musgrave (Philippine Journal of Science, March, 1907) has shown that paragonomiasis is not uncommon in the Philippines. He met with 17 cases in one year. He gives a detailed account of the pathological anatomy of this helminthiasis, bringing out especially the important fact that in a proportion of instances the infection is of a general character, the peculiar bluish cyst-like burrows of the parasite occurring in many organs and tissues. The infiltration of the tissues by the eggs produces, especially in serous membranes, little brownish-red patches, sometimes quite visible to the naked eye. The intestinal submucosa is a common seat of infiltration, and here the presence of the ova may give rise to inflammatory reaction, ending, perhaps, in ulceration and in the appearance of ova in the stools.
In reading Musgrave's paper I was particularly struck by the statement that in one of his cases he found no fewer than 100 mature parasites congregated in a psoas abscess. It is usually believed that the flukes enter their vertebrate hosts as cercariæ, and that they at once proceed to their permanent habitat and to sexual maturity. If this be the case with P. westermani, it is difficult to understand how, without any special anatomical lead, so large a number as 100 cercarite contrived to arrive at exactly the same spot.