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West Nile virus remains viable for at least three months in 2. savi , and transmission of the virus to mice by the bite of pare er ..infected ticks has been demonstrated. Similarly,
specimens experimentally infected with Sindbis virus transmit the organism when biting.
Spirochetosis of chickens Borrelia anserina) is not trans. nitted by this tampan.
See remrks under 2. moubata, pages 189 and 190.
All tick genera, save those in the family Argasidae and Nuttalliella, in the family Nuttalliellidae*, fall into the f§EIIy_Ix3dIdae and are referred to as ‘hard ticks“ or mixodids". The use of the term ixodid is not confined to the genus Ixodes. In Sudani Arabic, hard ticks are called "'gurad"' ( -!;’e-7".
All ixodid genera that normally inhabit Africa also occur in the Sudan with the exception of Rhi icentor**. This genus is represented bw'§. ladi er (Neumann, - bicornis Nuttall and Warburton, 19 in neighboring Belgian Congo (guaert 1931,) and further south in Africa. R. nuttalli Cooper and Robinson, 1908, occurs on various animals in Szutfi Africa and in Southest Africa.
*The family Nuttalliellidae (Schulze 1935) contains only a si le, exceedingly rare species, Nuttalliella ua Bedford, 1931(2), described from Little N~ es rica. This family appears to be a F"missing link". A scutal outline is present but not structurally differentiated from the leathery, papillated inte. gument. Though the mouthparts are anterior as in Ixodidae, the palpal segments are movable as in Argasidae, but an inner groove on the second segment is suggestive of the reduction in Ixodidae, in which the terminal segment is essentially merely a small appendage of the penultimate segment. The biology of this strange species is unknown.
**Rhipicepha1us (Pter odes) fulvus Neumann, 1913, a remarkable aberrant parasite of Néfihaes rice, is frequently treated as a monotypic genus and sometime as a subgenus of Rhi ice halus. See Neumann (1913) for description of male and CoIas.BeIcour (1932) for description of female, nymph, larva, hosts, biology, and disease relations.
In addition to African genera discussed herein, several others have been described from other continents, chiefly by Schulze. Many of these genera, however, meet with little general acceptance among contemporary specialists. A useful smnmary, including Schulze's and others‘ genera, may be fouxrl in Baker a.nd Wharton (1952). In general, however, "textbook genera“, as used by Neunnnn and by Nuttall and Warburton, usually suffice and are of considerable practical and scientific value. They should be little tampered with if at all. Special groups of ticks may be readily categorized at the subgeneric level to provide a useful sounding board for their acceptance by specialists.
Ixodid ticks occur throughout the world wherever terrestrial vertebrates are fourfl. They attack most land mammals and some mrine forms. Some ixodids parasitize birds and reptiles, some feed on amphibians. Adults of few if any ixodids regard man as a host of predilection but many attack him in the absence of other available hosts. Larvae a.nd nymphs are much more common and se_ rious pests of man than adults.
Morphologically, these ticks differ from argasids by the presence in all stages of a dorsal scutum. Ixodid xmuthparts are always anterior and visible from above; the body is oval. Larvae have six legs; nymphs have eight legs a.nd a female type scutum but lack both porose areas on the basis capituli and the genital aperture of the female. The female scutum covers only the anterior portion of the dorsmn, the male scutum extends to the posterior margin of the body. Eyes may be present or ah. sent. Nymphs and adults have a spiracular plate situated lateral.ly, posterior of each hind leg. Palpi, clearly segmented and movable in argasids, are limited in ixodids to segments 2 and 3 a.nd to a more or less well developed segment 1; segment 4 is inserted ventrally into a pit of segment 3.
Biologically, the majority of ixodids display comparative uniformity within rather narrow limits. Exceptions are notorious but few. The number of species is small, somewhere around five hundred. Ixodids are highly adapted to parasitic life but one is prone to wonder how they have succeeded in the battle for survival. Their aimless wandering habit and dropping from hosts and their indiscriminate ovipositicn proves fatal to many indi.
viduals, even though they survive long periods without food. Their extended life cycle subjects them to many adversities depending on season and the peregrinations of their hosts. The requirement of two or more kinds of hosts, often with divergent habits, limits their distribution to certain faunal areas. The comparativelylarge size of females makes them subject to injury and tempting food for predatory arthropods and vertebrates. Certain pathogenic organisms, fungi, and hymenopterous parasites kill them. Ticks have little protection against an enemy except their ease of con
cealment. They are particularly susceptible to attack duing the lethargic premolting and the weak postmolting period.
On the other hand, many biological features enable ticks to survive especially well. They lay numerous eggs and withstand a comparatively wide temperature and humidity range with greater ease than many other arthropods. They survive for months or years without food and often gain considerable protection from the concealed places in which they feed on the host. They frequently are offered a wide choice of appropriate hosts. Should they annoy the host, the animal is usually powerless to rid itself of the parasite. Ticks' slow metabolic rate has certain advantages and the leathery, usually inconspicuous, integuent offers some protection from living enemies, water, and chemicals. Parthenogenesis, pos
sibly a common occurrence though not well studied, may aid sur_ vival.
The genus Ixodes, as a biological unit, shows much divergence from the usual patterns of ixodids. The biology of this genus must be considered independently but in relation to other genera. Review summaries frequently leave the student with the impression
that the unique biological characters of Ixodes ticks are also characteristic of other ixodid genera.
The degree of host specificity in ixodid ticks varies from genus to genus or within certain subgroups of various genera.
Generalizations on this point should be very carefully qualified.
Eggs are laid only once; promiscuously; at one time and place; and are always numerous, sometimes numbering over 10,000. Eggs
hatch in from two weeks to several months, depending mostly on climatic factors.
larvae are active and sometimes are easily visible as hun.
dreds or thousands of them rest on grass awaiting a host. Larvae often parasitize small mamals, birds, and reptiles, sometimes in their nests or dens. Only a few kins choose largeranimals for hosts. Thickness of the host skin is possibly an important factor in restricting larvae to smaller animals. Larvae seldom feed within a week after hatching.
After some days of feeding, larvae olt to nymphs on the same host (two_host type of life cycle), or drop from the host mdwmtmehmrmhtowwm(wmamfitwedlfle cycle) on the ground. Exceptions are the single_host boophilid ticks (and a few others) that molt an remain on a single host during their lifetime. Nymphs that have molted on the ground seek a new host, sometimes the same type they fed on as larvae but, more commonly, animals similar to hosts peferred by adults. After several days of feeding, nymphs drop to the ground; he. come quiescent for a time, then molt to adults. There is only a single instar in the nymphal stage (see footnote, page l4l). Some species may undergo one or another of these variations in life cycle, depeding on climatic, seasonal, or nutritional fac_ tors, most of which are still poorly evaluated.
There is evidence that in certain three-host species (in which larvae characteristically feed on small mammals) larvae that feed on a somewhat larger animal, such as a hare, my remain on the host, molt to nymphs, and continue feeding. They drop from the larval.nymphal host only before molting to the adult stage.
Nymphs and females become tremendously engorged and new cuticle is developed duing the rather slow feeding process in order to accommodate the huge volume of blood ingested. Males become only slightly distended if at all, apparently, as in argasid ticks, by stretching the integument although they may remain in a feeding position for months, even after the slaugh_ tered host's skin has been removed.
As reservoirs of a great variety of pathogenic organisms,
ixodids are pre_eminently important, whether they act as vectors or not. As vectors, they transmit a greater variety of organisms