Page images
PDF
EPUB

HOSTS (Africa)

Bats

Almost any bat, whether it lives in large colonies or in small groups, may be parasitized by A. vespertilionis. All stages prob ably infest the same kinds of hosts.

Three species of chiropteran hosts are thus far known from the Sudan (records above). The Angolan larva is from Pipistrellus nanus. In Egypt, we find larvae chiefly on Otonycteris h. hemprichi, Rhinopoma hardwickei cystops and R. microphyllum, Taphozous p. perforatus and 1. nudiventris, Nycteris t. thebaica, Tadarida a. aegyptiaca and T. teniotis ruppelli. They are less numerous on Rhinolophus clivosus brachygnatus, R. mehelyi, Asellia t. triedens, Plecotus auritus christiei, Pipistrellus k. kuhli, and Rousettus a. aegyptiacus. Egyptian bats reviewed by Sanborn and Iloogstraal (1955).

Man

Nymphs and adults on several occasions have attacked us in caves and we easily induce it to bite ourselves in the laboratory (Hoogstraal 1952A, 1955B).

BIOLOGY

Life Cycle

In our laboratory, Mr. Sobhy Gaber successfully rears specimens of A. vespertilionis at 80°F. to 90°F. and 40% R.H. to 50% R.H, Egg batches consist of thirty to fifty eggs, one-fifth or one-sixth of which usually do not hatch. Larvae emerge from sixteen to twenty days after the eggs are laid and some will feed as quickly as four days afterwards. The duration of larval feed ing varies from fourteen to 31 days, but is usually seventeen to nineteen days. Five to ten days later larvae molt to nymphs, which are capable of feeding three or four days after this and after subsequent molts. Usually two feedings are indulged by nymphs, followed by a molt eight or nine days after the first meal and twelve to fourteen days after the second meal. Nymphs

become replete in from twenty to fifty minutes, usually in thirty to forty minutes. Males may emerge from the first nymphal molt, but usually nymphs, molt twice before becoming adults. Males and females may feed within seven days after molting. Duration of adult feeding is thirty or forty minutes. No female has ovi. posited within six months after the nymphal adult molt, even though she has been with a male continuously and both have had two to six blood meals. The first egg batch follows a blood meal by about a week. The first oviposition appears to trigger a physiological release mechanism for, in several instances, three months afterwards females have deposited a fertile egg batch with or without a meal. We are at present attempting to ascertain whether the long interval between molting and oviposition is peculiar to these laboratory observations or whether it is a usual feature in our local populations.

A. vespertilionis is more lethargic than A. boueti. Adults, if undisturbed while imbibing from a vein in the wing membrane of a bat, may remain attached for as long as five hours after engorgement is apparently completed. The feeding tick remains motionless with all legs down but, when fully distended without release of mouthparts from the host skin, it usually raises the fore legs to an antennalike position. During engorgement the beak is disengaged from the host skin only after considerable disturbance.

Large blood clots form at the site of the bite, both on the bat's body and in the wing membrane. This phenomenon, on bats, is in marked contrast to that observed by Lavoipierre and Riek (1955), using ticks from our collections, and laboratory rodents. The greater avidity with which these ticks attack bats probably accounts for the more conspicuous sequelae in these animals.

Larvae may be found anywhere on the body or wing membranes, but most commonly at the edge of the hairy parts, seldom on the head, feet, tail, or trailing edge of the wings.

Ecology

European and African populations of this tick, which thus far cannot be morphologically differentiated, withstand a wide

range of temperature and humidity conditions. Host flight habits account for the wide distribution of A. vespertilionis, but we are not aware that host migration is a factor in mixing populations from widely differing ecological situations.

European and South African populations exist under temperate climatic conditions with pronounced seasonal changes and with moderate to heavy rainfall. Those of Egypt and of northern Sudan normally tolerate the most extreme arid niches in which any arthro pod is known to survive. Their engorged larvae, however, are found usually among moist dung or in dung between crevices of bats' retreats. Just where females commonly oviposit in nature and where unengorged larvae rest before seeking a host has not yet been satisfactorily determined

Throughout Europe and Africa interstices in the walls of bat_ infested caves and buildings are the most common habitats of A. vespertilionis. They may also be found in tree holes and in other situations frequented by certain bats. In Cairo a specimen, recalling Robert Burns' wee louse, has been taken from a worshipper during church service by an observant but distracted friend sit ting behind. In Iraq, Patton (1920) reported the same or a closely related species in Bedouin tents in which bats presumably rested by day.

Egyptian specimens hide alone or clustered in large or small groups usually well concealed between shale or in crevices of walls. Some individuals are observed wandering openly on the walls. Unconcealed individuals are noted much more frequently in those caves or niches that only erratically harbor a few bats than in large caves where many bats usually roost. Possibly our entry into caves infrequently visited by any animals induces these ticks to investigate the possibility of a meal.

Small numbers of the round batsargas frequently are found in niches in the most unexpected cliffsides where a few old pellets of dung indicate that hermit bats such as Otonycteris h. hemprichi occasionally spend the day. These ticks lead a most uncertain existence and often wait months on end for a host, as revealed by their compressed bodies and by the age and scarcity of hosts' dung in these places.

In Egypt, A. vespertilionis occurs with the more common A. boueti and with the less common A. confusus and A. transgariepinus. A. vespertilionis and the other two species are rare, however, in the comparatively humid situations in Cairo favored by the fruit bat parasite, Ornithodoros salahi.

DISEASE RELATIONS

MAN: Mild itching resulting from a bite may persist for several weeks.

BATS: Large blood clots form at the site of the bite, both on the host's body and on the wing membrane.

It has been stated that this tick is a vector of a spiro_ chete of bats but reports of conclusive supporting evidence have thus far not been located.

In the Cairo area blood of a few of these ticks has been found to contain a most interesting organism resembling, accord ing to Dr. P. C. C. Garnham (correspondence): "the sporozoites of a Haemo proteid; they are not unlike the sporozoites of Leuco cytozoon

described from the abdominal cavity of Similium flies. Unfortunately, it has thus far been impossible to undertake further study of this phenomenon.

Egyptian specimens examined in NAMRU.3 laboratories have been negative for spirochetes, viruses, rickettsiae, and Shigella organisms.

FEMARKS

The taxonomy and biology of bat-infesting Argas ticks is presently being studied and the first report, on A. boueti and A. confusus has been presented (Hoogstraal 1955B). The second Section will deal with the confounded status of Argas (Carios) vespertilionis. Some workers have considered Carios as a full genus, indiscriminately including in it features of a variety of species based on vague and ambiguous remarks in the literature.

The presence of the ventral paired organ related the subgenus Carios to the subgenus Chiropterargas and separates Carios from the subgenus Argas and from other subgenera. The presence of a lateral suture and of peripherally differentiated integument, and the absence of an appendagelike hood clearly separates the subgenus Carios from the subgenus Chiropterargas.

The name vespertilionis was assigned by Latreille in 1802, not in 1796 as stated by most authors. The reference to this name as of 1796 (Hoogstraal 1955B) derives from an editorial change.

Schulze (1943B) noted that the immature stages of species of this group ("A. pipistrellae") have especially highly devel oped terminal branching of midgut diverticula but little basal branching.

DENTIFICATION

Males and females are alike except that males average some what smaller in size and their genital aperture is semicircular in outline, rather than narrowly ovoid, and is not bounded by thickened rugose lips as in females.

In both sexes and in nymphs, a definite lateral suture en circles the body, a dorsal and ventral row of rectangular "cells marks the body periphery, no appendagelike hood is present over the mouthparts, but ventral paired organs are present just posterior of the anus.

The body outline is generally circular or subcircular, but may be somewhat longer or wider in some specimens. Few individuals reach six millimeters in length or breadth. The integument is smooth, marked by a fine network of small, irregular cells among which regular, subparallel rows of larger discs radiate.

Legs arise from the anterior half of the body and are shorter than the body; coxae are contiguous; and tarsi are tapered and lack dorsal humps.

« PreviousContinue »