Ecology

All stages congregate on walls, in crevices, or between boards of poultry houses. Around Cairo we find literally tens of thousands under loose bark, in crevices, and on the trunks of trees in citypark heron rookeries. Trees in which chickens roost are frequently reported as hiding places for A. persicus. Other habitats have been discussed under HOSTS above.

The ability of eggs, larvae, nymphs and adults to withstand a wide range of temperature and humidity conditions has been studied by Bodenheimer (1934). Fifty-nine observations of nymphs and adults in temperature gradients ranging from 2°C. to 47.7°C. failed to exhibit a significant response to changing temperature stimuli. While the vital optimum of the egg stage is 20°C. and 80% relative humid ity, the tolerance to fluctuating climatic factors is remarkably great. Even at 20% relative humidity, mortality is only slightly greater than at optimum conditions of environmental moisture. The thermal constant for the egg stage is 316 day-degrees. At temperatures of from 33°C. to 18°C., eggs hatch in from 10.5 days to 33.3 days (from highest to lowest temperature). Temperatures of 15°C. and below inhibit egg hatching. At high temperature (33°C.), a relative humidity of at least 60% is necessary for hatching. At moderate temperature (18°C. to 27°C.), there is little difference in numbers of larvae hatching from eggs maintained at various percentages of relative humidity ranging from twenty to a hundred.

The ability of A. persicus to withstand desiccation and high temperatures has been studied by Lees (1947) in his excellent re search on transpiration and epicuticle structure in ticks.

In Argentina, the optimum temperature for egg hatching is said to be between 22°C. and 38°C. with relative humidity from 90% to 100%. Mortality increased from 4.85% under the above conditions to 22.45% at 37°C. and 80% to 95% relative humidity. Roveda (1940)7

It appears, from these observations as well as from the com paratively great adaptability of this species as demonstrated by its wide geographical range, that Argas persicus is less restricted by higher humidity factors than are many other argasids.

In cold climates such as Saratov, Russia, development occurs only at temperatures over 20°c. Exposure to high humidity (presumably at cold temperatures) kills the ticks (Olenev 1926,1928A).

The presence or absence of A. persicus in coastal areas fre quently is referred to in literature. Lounsbury (1903B) stated that A. persicus is everywhere common in South Africa, including coastal towns and areas. Howard (1908) reported that in South Africa this tick is common except near the coast and that the same distributional pattern had been reported from Australia. Records from a number of other localities indicate that the fowl tick does indeed inhabit coastal areas. For instance, Theodor (1932) reports this species especially common along the Mediterranean coast and in Jordan Sea areas of Palestine. In Egypt, we find it commonly in coastal villages and cities. We have also found cast nymphal skins at Djibouti, the seaport of French Somaliland. It occurs at Port Sudan on the Red Sea coast of Sudan (Sudan Government Collection record) and at Hodeida on the opposite coast in Yemen (Hoogstraal, ms.). In Reunion, Gillard (1949) reported the fowl tick particularly common on the coast, and in Madagascar it occurs chiefly in coastal areas (Bück 1935,1948A,C).

Concerning altitudinal range, A. persicus is frequently reported as common in lowlands and rare or absent in highlands. In mountains of the Sinai Peninsula of Egypt we find numerous speci mens at elevations up to 6000 feet.

Lewis (1939A) stated that in Kenya A. persicus is present only in European areas. This is certainly not true for the Sudan, where chicken flocks of many remote, indigenous tribes have been known to be infested for half a century. More recently, Wiley (1953) indi cated that the fowl tick is increasing its range in Kenya.

An apparent negative geotropism displayed by unfed larvae reared from adults collected from trees serving as a heron rookery has been observed by Dr. H. S. Hurlbut at NAMRU-3, Cairo. At the same time, larvae from adults collected from chicken houses ap peared to show a positive geotropism. The F1 larvae of adults from heron rookeries were inclined to prefer herons rather than chickens as hosts and the reverse appeared true for larvae from adults from chicken houses. Informal as these observations are, they suggest an interesting research problem.

DISEASE RELATIONS

MAN: Reported sequelae of the fowl argas' bite range from itching to death. Actually, there are no trustworthy accounts of severe illness resulting from a fowl argas bite. Anthrax (Bacillus anthracis), however, has been transmitted to man by the bite of this tick in the laboratory on one known occasion. Speci mens have been experimentally infected with plague (Pasteurella pestis) and with yellow fever virus. A. persicus has been reported in textbooks and discussion papers to transmit human relapsing fever (Borrelia spp.) but there does not appear to be a shred of conclusive evidence to support this claim. Experimental studies to date negate this possibility. The little work done on A. persicus in relation to typhus has gone only far enough to show that the etiologic agent (Rickettsia prowazekii) survives in the tick for ten days. The fowl tick is susceptible to parenteral infection with West Nile virus but does not transmit the virus.

FOWLS: The fowl argas is frequently so numerous that birds are killed by exsanguination. Spirochetosis Borrelia anserina (= B. gallinarum)7 of chickens, ducks, geese, turkeys and canaries is a serious disease transmitted by A. persicus nearly everywhere that it is found, but not everywhere. Fowl piroplasmosis (Aegypt ianella pullorum) is also transmitted by the fowl argas, which also has been suggested to be a vector of Grahamella gallinarum. ▲ condition called fowl paralysis by some students and tick paralysis by others, due possibly to a toxin from the tick, sometimes occurs after bites. Chicken cholera or fowl plague (Pasteurella avicida). may cause the death of birds that eat infected ticks. Virus in duced fowl tumors are not transmitted by bites of the fowl argas. See next paragraph.

WILD BIRDS: Populations of this tick from Egyptian rookeries of the buff-backed heron or cattle egret have been found infected with Salmonella typhimurium, but others from chicken yards were negative for Salmonella spp.

CATTLE: Successful experimental transmission of anaplasmosis (Anaplasma marginale) by A. persicus has been reported.

MISCELLANEOUS: It has been claimed that West African speci mens have been found infected with Q fever (Coxiella burnetii). In Egypt, the fowl argas is infected with one or more viruses distinct from West Nile but otherwise unidentified.

REMARKS

An excellent and detailed study of the internal and external morphology of A. persicus has been presented by Robinson and David son (1913A,B,1914), and by Patton and Cragg (1913). An earlier work is that of Heller (1858). Rohr (1909) reported on life cycle and biological studies in Brazil, and included a few photomicrographs of internal organs. Regeneration of broken appendages has been reported by Hindle and Cunliffe (1914) and by Nuttall (1920B), Sensory perceptions have been studied by Hindle and Merriman (1912). The coxal cymatium of A. persicus has been discussed by Schulze (1936A), who also (1941) described and illustrated the haller's organ. Micks (1951) gives an account of a convenient rearing technique and life cycle observations and Sapre (1943) described his method for laboratory rearing. Immunity of chickens to bites of the fowl argas has been studied by Trager (1940). Anticoagulin in the salivary glands and gut has been reported by Nuttall and Strickland (1909) and by Cornwall and Patton (1914). The salivary glands have been described and illustrated by Heller (1858) and Elmassian (1910).

Larvae of clothes moths, Tineola biselliella, have been ob served attacking living larvae of A. persicus in laboratory colonies (Volimer 1931).

According to Zuelzer (1921), A. persicus and A. reflexus mate and produce fertile offspring. We have been unable to duplicate these results in our Cairo laboratories.

Observations on the bacteriostatic factors in blood-engorged ticks, including A. persicus (Anigstein, Whitney, and Micks 1950A, B), prompted further studies showing that bacterial growth inhibition in vitro is comparable with the phenomenon induced by antibiotics (Whitney, Anigstein, and Micks 1950) and that a blood hydrolysate called sanguinin is responsible (Micks, Whitney, and Anigstein 1951). This subject is reviewed under 0. moubata (page 178).

Symbiots of A. persicus have been described in some detail by Cowdry (19250,1926A,1927) and by Jaschke (1933).

The subgenus Argas is tentatively defined as follows:

"Parasites chiefly of fowls. Morphological characters entirely of genus Argas. Sutural line (i.e. lateral groove) encircling body. With a flattened body flange morphologically differentiated dorsal ly and ventrally by a row of quadrate cells or by fine striations or wrinkles; body shape elongate. Integument finely wrinkled; discs conspicuous, radially distributed; lacking ventral "paired organ". Hood lacking; mouthparts posterior of anterior body margin by a distance about equalling their own length. Legs moderate; tarsal humps lacking".

A. reflexus was designated as the type species of the genus Argas by Latreille (1802) and is so considered by Cooley and Kohls (1944) and by Pospelova Shtrom (1946) Nuttall et al (1908) preferred to use A. persicus 7. A. reflexus would, therefore, also be the type species of the subgenus Argas.

The size of each stage and of each sex, engorged and unengorged, has been reported by Hooker, Bishopp, and Wood (1912) and by Campana Rouget (1954).

IDENTIFICATION

A. persicus is easily recognized by characters listed above for the subgenus Argas, with the restriction that its dorsal and ventral periphery is marked by a row of quadrate "cells (fine striations in A. reflexus).

The male is seldom over 5.0 mm. long and has a semicircular genital aperture. The female measures from 4.0 mm. to 11.0 mm. long and has a narrow, transverse genital aperture.

Nymphs are similar to adults except that they lack a genital aperture although advanced instars may have a shallow depression in its place.

Larvae are nicely illustrated in various editions of Brumpt's

Precis.