FILARIID.E 



249 



Pathogenesis. — The disturbances caused l)y the presence of the 

 mature filarial are principally mechanical. Dependinjj: upon their 

 number, they more or less interfere with the circulation, in some cases 

 forming- a thrombus which may give rise to emboli in the branches of 

 the pulmonaiy artery. In such cases necrotic 

 areas in the lungs with abscess formation may 

 result. 



The larvae, probably- by their toxic protlucts. 

 bring about anaemia with a leucocytosis which, 

 depending upon the number of the parasites 

 present, may be more or less pronounced. As 

 a result of the invasion of the heart, local mani- 

 festations of endocarditis are to be looked foi-. 

 The heart's action is variouslv disturbed, lead- 

 ing to dropsical conditions accompanied l)y 

 cough and dyspnoea. Nephritis and convul- 

 sions may develop as a later complication. If 

 the condition terminates in death, it is usually- 

 from paralysis of the heart or a general weakness 

 followed by complete paralysis. 



Diagnosis. — The parasites ma}- be present 

 without causing observable manifestations, 

 while, on the other hand, no line of clinical 

 symptoms can with certainty be attril)uted to 

 such invasion. A more precise diagnosis can 

 usually be made by microscopic examination of 

 the blood for demonstration of the jiresence of 

 the larvae. Under low magnification, a drop of 

 infected blood placed between a slide and a 

 coverslip will reveal fine worm-like larvae in 

 snake-like movements between the corpuscles. 

 It is claimed by most investigators that they 

 appear in greatest numbers in the peripheral 

 circulation during the night, and, therefore, that 

 amination is best drawn during these hours. 



Infection. — The manner of natural infection with this parasite has 

 not yet been satisfactorily determined. Manson concluded from his 

 investigations that the larvae of Filaria bancrofti (F. sanguinis hominis) — 

 a blood parasite of man resembling the species under consideration — 

 pass into the digestive tract of a mosquito (Culex) when it sucks the 

 blood of an affected person. Later the mosquito, after depositing its eggs 

 upon the water, dies, the body disintegrates, and the lai-val filariae are lib- 

 erated, man becoming infected by drinking the water thus contaminated. 

 It has been held that Dirofilaria immitis has a similar development. 



Fig. 129. — Dirofilaria im- 

 mitis; male at loft, female at 

 right, — natural size (after 

 Railli.'t). 



blood for such ex- 



