MICRO-PARASITES 243 



mouth and intestinal tract, is due to infection with the genera Monilia 

 and Oidium. Perhaps the best known fungus parasitising birds is 

 Aspergillus fumigatus (see tail-piece Chapter i, p. lo), which is localised in 

 the respiratory tract. The spores of this plant are widely distributed in 

 nature and the birds inhale them with dust or pick them up with 

 mouldy food or water. They form colonies in the lungs and air passages 

 and some birds are highly susceptible to the bacteria-like toxins they 

 produce. Several allied species are known and sometimes multiple in- 

 fections occur when Penicillium and Mucor moulds are found in associa- 

 tion with Aspergillus. We have frequently observed mycosis in wild 

 wood-pigeons from all parts of Britain and Dane records A. fumigatus 

 in the air sacs of the manx shearwater. 



As we have seen in the preceding chapters, fungi are also most useful 

 to birds since they are hyper-parasites of many species of arthropods 

 and helminths which parasitise avian hosts. One of the best known 

 genera is Empusa (Entomophthoraceae) of which various species cause 

 a fatal disease in mosquitoes (including the house-gnat) and other 

 Diptera such as blow-flies, house-flies, and midges, and also in mites. 

 Large numbers attack roundworms at all stages of their development. 

 Some extremely interesting fungi, such as the genera Dactylaria and 

 Dactyella (Hyphomycetales), capture certain parasitic nematodes alive 

 during their free-living stages. They are snared by means of loop- 

 shaped portions of the mycelium, each of which operates on the Hues of a 

 sphygmomanometer. Contact with the prey causes the loops to swell 

 suddenly and constrict round the worm which is held fast and ulti- 

 mately consumed. 



There is a curious and obscure group of parasites, the Sarcosporidia, 

 members of which are located in the striated muscles of mammals and 

 birds. At one time they were classified as Protozoa but are now con- 

 sidered to be fungi. Surface feeding ducks are the most heavily infected 

 group, but they have been recorded from 28 species of birds from 

 eight different orders. The larger forms of the parasite can be seen as 

 httle white streaks in the striated muscles which give the fibres a 

 "wormy" appearance. When removed from the tissues each resembles a 

 minute colourless spindle. The body is divided into chambers, which, 

 in fully developed specimens, are filled with sickle-shaped spores. The 

 life-cycle of Sarcocystis is not properly understood, although there is 

 some evidence that infection can occur after ingesting urine and faeces 

 from animals with the disease. On the Continent avian sarcosporidiosis 



FFC— R 



