1 78 Arthropods as Essential Hosts of Pathogenic Organisms 



Several other cestode parasites of domestic animals are believed 

 to develop their intermediate stage in certain arthropods. Among 

 these may be mentioned : 



Choanot&nia infundibulformis,oi chickens, developing in the house- 

 fly (Grassi and Rovelli) ; 



Davainea cesticillus, of chickens, in some lepidopter or coleopter 

 (Grassi and Rovelli) ; 



Hymenolepis anatina, H. gracilis, H. sinuosa, H. coronula and 

 Fimbriaria fasciolaris, all occurring in ducks, have been reported as 

 developing in small aquatic crustaceans. In these cases, cysticer- 

 coids have been found which, on account of superficial characters, 

 have been regarded as belonging to the several species, but direct 

 experimental evidence is scant. 



ARTHROPODS AS INTERMEDIATE HOSTS OF NEMATODE WORMS 



Filariasis and Mosquitoes A number of species of Nematode 

 worms belonging to the genus Filaria, infest man and other verte- 

 brates and in the larval condition are to be found in the blood. 

 Such infestation is known as filariasis. The sexually mature worms 

 are to be found in the blood, the lymphatics, the mesentery and sub- 

 cutaneous connective tissue. In the cases best studied it has been 

 found that the larval forms are taken up by mosquitoes and undergo 

 a transformation before they can attain maturity in man. 



The larvae circulating in the blood are conveniently designated 

 as microfilariae. In this stage they are harmless and only one species, 

 Filaria bancrofti, appears to be of any great pathological significance 

 at any stage. 



Filaria bancrofti in its adult state, lives in the lymphatics of man. 

 Though often causing no injury it has been clearly established that 

 they and their eggs may cause various disorders due to stoppage 

 of the lymphatic trunks (fig. 119). Manson lists among other effects, 

 abscess, varicose groin glands, lymph scrotum, chyluria, and ele- 

 phantiasis. 



The geographical distribution of this parasite is usually given as 

 coextensive with that of elephantiasis, but it is by no means certain 

 that it is the only cause of this disease and so actual findings of the 

 parasites are necessary. Manson reports that it is "an indigenous 

 parasite in almost every country throughout the tropical and sub- 

 tropical world, as far north as Spain in Europe and Charlestown in 



