Savory - Arachnida 1977

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254 IV. DE ARACHNOLOGIA
leaves distinct, painful-feeling welts. Certain Dermanyssidae are also
proven transmitters of disease.
Some parasitic mites seem to be wholly innocuous and of no economic
significance. This appears to be true of the Halarachnidae. For example
the occurrence of Halarachne in the lungs and air passages of seals and
of Pneumonyssus in the lungs of Old World monkeys is only of interest
in showing how widely mites have sought for favourable environment.
The opposite is true of the Ixodidae, and to a lesser extent the
Argasidae. These large, hard or leathery-bodied ticks are not only
irritating, debilitating and sometimes lethal forms, but also have the
somewhat dubious honour of being the most versatile vectors of diseasecausing
viruses, rickettsiae, bacteria, spirochaetes and protozoa.
Ticks attack a great variety of host animals, with fish the only major
vertebrate exception, under a great variety of conditions; and seem to
vary from region to region not only in their ability to attack various
hosts, but also in the ability to transmit disease organisms. For these
reasons, tick specialists, research scientists and medical men admit that
much work remains to be done in the disciplines of tick taxonomy, tick
zoogeography, tick biology, tick physiology and disease organism
taxonomy and etiology. It seems, therefore, prudent that this presentation
be confined to the broad aspects of tick-caused maladies.
Irritation by ticks is, of course, more or less obvious. It varies from the
simple discomfort of individuals either climbing and walking over the
body or inserting their biting organs and sucking blood to the more complex
irritations caused by the hundreds or thousands of ticks in large,
debilitating infestations. Any or all of the ticks that attack man and
domesticated animals are capable of irritation.
Debilitation by ticks involves several factors, any of which, under
severe conditions, can result in the death of the attacked man or animal.
The first factor is the direct removal of blood, exsanguination, which
results in extreme host discomfort and lassitude and many cause
anaemia and death of the host. Second is the effect of tick toxins, tick
toxicosis, in hosts. Such may or may not be associated with and complicated
by blood removal. Several ticks attacking man have been
suspected or indicted in this respect; they are Argas reflexus in the
Near Ixodes ricinus in France and a species of Hyalomma in South
Africa. In animals, Ornithodorus lahorensis has caused toxicosis of sheep in
southern USSR, Ixodes ricinus a paralysis of foals in Azerbaijan, and
Hyalomma transiens "sweating sickness" in cows and goats in South
Africa. The third factor is tick paralysis, presumably caused by a neurotoxin.
This condition is known from several parts of the world and
may or may not be separable from tick toxicosis. Human tick paralyses
have been reported involving Dermacentor andersoni in Canada, Amblyom-
30. ECONOMIC ARACHNOLOGY 255
ma americanum in the southern United States and Otobius megnini, a
spinose ear tick, in South Africa. For animals, the incriminated ticks
and areas are Ixodes holocyclus in eastern Australia, species of
Ixodes and Rhipicephalus in South Africa, Dermacentor andersoni in
north-western United States and Dermacentor variabilis, Amblyomma
americanum and Rhipicephalus sanguine us in eastern and southern United
States.
As mentioned above, the most important and most complex tick
injuries involve the transmission of disease organisms. In the space
allotted here it is impossible to do more than mention and comment on
a few of the better known diseases and their known or suspected
vectors.
Among the tick-borne viruses, epidemics of Kyasanur Forest virus
have affected large numbers of people and monkeys in south-western
India. Haemaph)'salis spinigera is considered the important vector.
Colorado tick fever, transmitted by Dermacentor andersoni, is the most
prevalent human tick-borne virus disease in the western United States.
Rickettsiae and perhaps rickettsial-like organisms responsible for
spotted fever in the United States may be spread from rodents to human
beings by several kinds of ticks, but Dermacentor andersoni and other
of that genus are at present regarded as the primary vectors. Q
a world-wide rickettsial disease, has now been isolated from a
number of kinds of ticks, all of which could be vectors.
The bacterial etiological agent of Tularemia, FranciJella tularensis,
apparently has become adapted to several modes of transmission among
wildlife, to domestic animals and to man. Several genera of ticks.
Haemaphysalis, Dermacentor, Rhipicephalus and Ixodes, are capable of
harbouring the pathogen and transmitting the disease. Both ixodid and
argasid ticks of several genera have been shown to be vectors of the
disease known as Anaplasmosis, but the microbiological relationships
of the causal organism is still undecided. The coccus-like Anaplasma
bodies apparently are either protozoa, rickettsiae or bacteria.
Perhaps the most important human spirochaete disease is African
tick-fever or relapsing fever, known by African natives as Kimputu
and by Madagascan natives as Paraponjy. The causal spirochaetes,
apparently many varieties or species of Borrelia related to B. duttoni,
remain virulent for many years in argasid tick vectors of the genus
Ornithodorus including 0. moubata. Spirachaetasis of livestock can
also be transmitted by ixodid ticks of the genera Boophilus and
Rhipicephalus.
Red-water fever or Texas fever is by far the best known and most
important tick-borne protozoan disease of cattle, horses, sheep and dogs.
Since several causal organisms of the genera Piroplasma and Babesia