238 FLEAS, FLUKES AND CUCKOOS 



The spirochaetes are classified by some zoologists as Protozoa and 

 by others as bacteria. The electron microscope has shown recently that 

 at least some spirochaetes possess long filamentous processes. Therefore 

 the chief feature which was supposed to distinguish them from bacteria 

 — motility without flagella — seems to have been disposed of. Spiro- 

 chaetes are active colourless thread-like organisms which can move with 

 equal ease either backwards or forwards. There is a central filament or 

 axis around which the body is wound like a spiral staircase round the 

 newel. The number of spirals varies but is constant for each species. 

 Spirochaetes reproduce by transverse fission and there is apparently no 

 sexual process. The best known and most notorious genus is Treponema 

 which includes the causative agents of syphilis, yaws and relapsing fever. 

 One species, T. anserinum, parasitises birds and is the cause of relapsing 

 fever in geese and other farmyard fowl on the Continent. It has not 

 been recorded from wild birds in Britain, but it is known to infect species 

 such as the little owl, snipe, sparrow and crow which are on the British 

 list. Syphilis is spread from one individual to another by contact of 

 infected surfaces, but relapsing fever of both man and birds is spread by 

 blood-sucking arthropods. The chief carriers of avian spirochaetes — 

 of which there may be several distinct species — are ticks of the genus 

 Argas, but red mites [Dermanyssus gallinae) can also act as vectors. 

 The spirochaetes are taken up during a blood meal and in the case 

 of the tick invade the various tissues of the body including the salivary 

 glands. They also enter the eggs, perhaps as many as thirty to one 

 Ggg^ and the disease is thus inherited by succeeding generations of 

 ticks. 



Not unnaturally the bacteria which infect birds have been studied 

 chiefly in poultry. When a particular disease is recognised in chickens 

 and ducks, particularly if it is the cause of financial losses, it is worked on 

 fairly intensively and as a result it is often subsequently tracked down in 

 wild birds. This has been the case with so-called fowl cholera* {Past- 



*It is worth drawing attention to the perverse popular names given to the diseases 

 of pouhry, which might well have been designed especially to confuse the ordinary 

 parasitologist. Thus the term " fowl cholera" is applied to a disease allied to the 

 plague or pest, and not even distantly related to cholera of man. Therefore the 

 true cholera which attacks birds has to be called a "vibrio infection." The term 

 "fowl pest" is reserved for a disease caused by a virus, which has nothing whatsoever 

 in common with Pasteurella pestis, the causative agent of plague in man. The well 

 known and relatively innocuous disease of children known as chicken pox, has on 

 the other hand, nothing to do with chickens, nor does it attack birds, and it is not 

 a true pox. 



