The Joint Committee of the World Health Organization and the Food and Agricultural Organization (1959) defined the zoonoses as "those diseases and infections naturally transmitted between vertebrate animals and man". This is not a zoological term, but a medical term which was introduced by Virchow to categorise diseases like bovine tuberculosis which man acquires from animals. Unfortunately many zoologists and veterinarians have failed to recognise the restricted use of the term and it is not uncommon, especially in the United States, to find that purely animal diseases are classified as zoonoses. This misuse of the term has resulted in a good deal of confusion, but in spite of this the existence of the name "zoonoses" has served a useful purpose in focussing attention on the zoological aspects of infectious diseases. Medical epidemiologists are no longer content to confine their attention to interhuman transmission ; in every situation, no matter whether the disease is caused by a virus, a bacterium, a fungus, a protozoan, a helminth, or an arthropod, the question has to be asked, "Is this a zoonosis?" As a result, more and more diseases which were thought to be confined to man are being added to the list of zoonoses and several syndromes classified as being of "unknown aetiology" are now believed to be due to abortive infections with organisms from animals.In dealing with the zoonoses it is essential to discover the direction of transmission ; it is of little value to know that a particular organism is found in both man and animals. What we are really concerned about is the relative significance of man and animals as maintenance hosts of the particular infections. As far as the filarial parasites are concerned, we are only beginning to realise that they represent one of the most interesting and almost unexplored groups of the zoonoses. The present paper can do no more than summarise existing information and suggest lines for further study.
