« PreviousContinue »
pertinent host surveys may be included in the section entitled BIOLOGY, of which the host list should, of course, be considered an integral part. The common name of non_Sudanese hosts may be found in Allen's (1939) checklist of African mammals. After serious consideration of several suggestions that the scientific name of each kind of host be provided, it has been decided to do so only where the common name might frequently be confused, as for the "wild dogth or hunting dogra, Lycaon pictus.
All available references, including data on BIOLOGY of species discussed herein, have been summarized in more or less detail, de pending on the weight of their importance. It is hoped that this section will be especially useful in indicating further research problems.
DISEASE RELATIONS with which each species has been incriminated are usually merely listed by common name and etiologic agent. This section is intended only as a cross reference to subject chapters in the subsequent volume on disease relations. Unpublished results of work undertaken in the virology and bacteriology laboratories of NAMRU3 on Sudan ticks are also included in this section.
Miscellaneous REMARKS are included here. This section preceeds that on identification if most of the notes are taxonomic or else follows that on biology if mostly other subjects are involved.
Diagnostic criteria in addition to key characters are provided for IDENTIFICATION by the average reader. Where Sudan material or special studies modify previously accepted diagnostic features or are of other importance, greater detail is provided. Otherwise, no attempt has been made to present a full description of each species
since this falls in the province of more complete, overall taxonomic studies. For serious studies, specimens rather than written descrip tions are almost invariably required.
A word of explanation is due concerning the absence of species diagnosis for immature stages of ticks treated in this report. Often, when collections are made from hosts of smaller size, the only ticks on them are immature and the difficulty or impossibility of identifying them is most discouraging. Larvae and nymphs of about half the Sudan tick species have been described, but those of even fewer spe cies can be distinguished from all others with any degree of confi. dence. The inclusion of what we do know would be of little practical value, except to a very few most highly specialized students. Anyone favorably situated in this area with resources for rearing progeny from known, isolated female ticks can make valuable contribu tions in this respect. At the present time, Dr. Theiler and I are gathering data on this subject which will be published as soon as we have sufficient information to make a utilitarian report.
In morphological terminology, I have followed almost entirely the usage of Cooley (1946) and Cooley and Kohls (1944), except that I have substituted the word "segment" for "article" as used by these authors. Where Kohls has recently modified some designations, I have followed his lead. Cooley and Kohls' terms have not been extensive enough for adequate description of Rhipicephalus species, and I have been forced to add to them. Unfortunately, some termi. nology used by British, American, and other workers differs or con flicts. An International Committee needs be called to decide a standard set of morphological terms for the gross description of ticks. The problem is reasonably simple and could easily be settled. Consideration should also be given to standardizing insofar as possi. ble the morphological terms used for mites and ticks. Reference to terms appearing in this report is provided in various text figures.
FAMILY ARGAS I DAE
Argasid ticks (Family Argasidae) are called haim (d) in Sudani Arabic. They are leathery or "soft" ticks that secrete themselves in soil or in crevices, come out to feed for a short while, and then retreat to their hiding place. Two of the several argasid genera, Argas and Ornithodoros, are common in Africa. The term argasid should not be construed to refer to the genus Argas alone. The sole African representative of a third argasid genus, Otobius, an ear tick, has been introduced from America into South Africa, Madagascar, and parts of Central and East Africa, but is not known to occur in the Sudan. A variety of argasids occur through out most of the tropics and subtropics of the world. Fewer species live in temperate areas and very few inhabit arctic climes. Two spen cies presently are distributed widely as a result of human transportation of domestic fowls.
Argasid eggs, deposited at intervals in small batches and total ling only a few hundred, are laid in niches where females seek shelter. Chances that 'hatching larvae will find a favourable host nearby are reasonably good. Larvae of the two Ornithodoros species in the Sudan are nonmotile and do not feed; this feature of their life cycle is unique in the genus. Larvae of Argas feed on birds or bats, or less commonly on other animals, and remain on the host for several days to several weeks. Nymphs and adults of both genera feed for only a few minutes to a few hours at most, in marked contrast to the longer attachment time of most nymphal and adult ticks of the family Ixodidae. There are at least two and sometimes as many as six or more nymphal instars. Argasid adults take several blood meals, each of which is usually followed by a rest for digestion and, in the female, for oviposition. The genus Otobius, mentioned above, has more highly specialized feeding habits.
Argasid ticks are of considerable economic and medical importance in many parts of the world. However, at the present time they are apparently of less importance in the Sudan than in many other parts of Africa. As transportation facilities improve and urban areas become larger and more settled, it is to be expected that Ornithodoros moubata will become more widely established in human habi. tations of southern Sudan.
It should be noted that argasid ticks in general are xerophilic animals. Many students of their life cycle have failed to recognize this important fact. Although in localities of extremely low rela tive humidity argasids may seek a somewhat more humid microhabitat, these niches are seldom those with a significantly high relative bumidity. The few species extending into the humid tropics choose dry niches in dry habitats and do not thrive away from these retreats. Within this range, individual species have varying degrees of tolerance.
Examination of bird nests, caves, bat roosts, animal lairs, burrows, rodent nests, hyrax dens, and big game resting and rolling areas in the Sudan will undoubtedly reveal unrecorded or possibly even undescribed argasid species. Although of considerable medical importance and zoological interest, these ticks are not frequently collected because specialized efforts and techniques are necessary to obtain them. Sifting of soil or sand in animal burrows, caves, or dens is often most fruitful. Examination of rock interstices and searching under stones is also important in some situations. In vestigation of bird nests, especially those of larger birds, should yield mich interesting data. There is little doubt that at least one Argas parasite of birds, and Ornithodoros erraticus remain to be found in the Sudan, in addition to o. delanoel and some member of the 0. tholozani group.