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to AN INTRODUCTION TO THE STUDY OF VIRUSES 
The four chicks were confined in wire cages suspended 44 ft above 
the floor. Care was taken to prevent contact with contaminated 
material not air-borne. On the sixth day respiratory symptoms 
were observed in the chicks (Delay et al., 1948). There is probably 
little doubt that some of the insect viruses causing the polyhedral 
diseases are also air-borne in the sense that dried polyhedra are capable 
of being carried in the air for considerable distances. By this means 
the leaves of the food plant become contaminated and the polyhedra 
are ingested by the caterpillars. 
Arthropod Vectors 
The most important of the natural means of transmission of viruses 
is by agency of insects and, to a lesser degree, of other arthropods, but 
since the relationship between viruses and their arthropod vectors is 
an interesting and important one, it is dealt with at some length in 
the next chapter. For the moment it must suffice to give a list of the 
more important vectors and the viruses they transmit. Much of the 
information on the mite and tick vectors is taken from the British 
Museum (Natural History) pamphlet on Acari by S. Finnegan. 
TABLE | 
VIRUSES TRANSMITTED BY ARTHROPOD VECTORS 
Disease Vector Host and Possible 
Vertebrate Reservoir 
Tsutsugamushi disease Acarina Man, bandicoot, field 
(“scrub” or: o“‘rural’* Larvae of: mice 
typhus of Far East and Trombicula akamuski (Japan) 
“Hill” typhus of T. deliensis (Malaya) 
India) T. minor (New Guinea) 
Rocky Mountain Dermacentor andersoni Man, goats, hares, and 
spotted fever (Eastern D. variabilis small rodents 
and Western forms) 
Fiévre boutonneuse Dog tick Man, dog 
Rhipicephalus sanguineus 
South African tick Ticks Man, dog 
typhus Haemaphysalis leachi 
Sao Paulo rural typhus Tick Man, opossum 
Amblyomma cajennense 
“Q” fever Australia and Ticks Man, bandicoot 
U.S.A. Haemaphysalis humerosa 
Dermacentor andersoni 
D. occidentalis 
Amblyomma americanum 
Rhipicephalus sanguineus 
Louping ill Sheep tick Sheep 
Ixodes ricinus L. 
Rhipicephalus appendiculatus Neum. 
