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A valuable account of building methods to eliminate tampan infestation has recently been published by Annecke and Quin (1952) and Annecke (1952). Reinforced concrete buildings, which replaced wattle and daub huts at a cost of L 13 per person, are said to have reduced deaths from relapsing fever on a large South African citrus plantation from forty to a single case annually. Additional benefits resulted from employees' social and economic betternent. These buildings were constructed by casting walls in a steel franed mold and raising precast concrete roof sections over them. Floors were made from a vermiculite and cement mixture. Acceptability to indigenous labor, ease of cleaning, and crackproof construction were important considerations. As the economic level of African labor rises, such prevention methods will become normal and expected, but today they are revolutionary.
The effect of domestic animals on o. moubata populations in houses appears to be moot. Under usual conditions it seems that domestic animals allowed to live in human habitations tend to allow an increase of ticks in these buildings. An exception is cited by Walton (1950A), who believes that in areas of hich humi. dity additional moisture provided by domestic animals in huts enouch to discourage the tampan. Rooms in which coats are kept in humid Kenya hills are free of ticks (Teesdale 1952).
Inasmuch as chickens often are said to be a favorite nymphal host, they probably should be excluded from buildings except pos sibly for periodic forays to feed on ticks near the surface of the ground. Knowles and Terry (1950) reported that chickens in Tancanyika are heavily infested with nymphal 0. moubata, but Phipps (1950) found no significant relation between the presence of ticks and fowls in the same area.
Gammexane (Hexachlorocyclohexane, BHC or benzene hexachloride) is generally considered to be the most promising chemical for controlling 0. moubata.
Ticks coming in contact with 0.5 per cent dust lose com ordination after five or six hours. During the first day they lose much of their body weight by excessive coxal fluid loss, defecation of milky fluid, and possibly by increased integumental
permeability. Their color darkens; they become more or less im mobile and usually die in a little over a week. Those that live fail to produce viable eggs. Application of 0.5 per cent gamme xane dust to floors and lower parts of walls sprinkled from perforated cigarette tins at the rate of three or four pounds of dust per hundred square feet is recommended, but frequent checks should be made where reinfestation is liable to occur (Jepson 1947).
Application of Jepson's findings on a township scale in Tanganyika was described in detail by Knowles and Terry (1950) using ing dust" (D220 compound one part, and diatomite four parts). These authors found that although total eradication is probably impossible, a townshipwide control program can almost eliminate relapsing fever in a fairly static population and is much cheaper than hospital treatment of the disease. Sampling methods and application methods were also stressed.
Factors to be considered in a control program and need for further research were discussed by Phipps (1950), who indicated the necessity of using tested diluents and making accurate surveys before and after treatment. The incidence of ticks and disease should also be checked before large scale programs are instituted for, in Phipps' opinion, not all places in which ticks abound are disease foci.
In Annecke and Quin's (1952) extensive chemical control program on a heavily infested South African citrus plantation, it was found that BHC applied as a spray to inner walls of huts in concentrations of 300 mg. gamma isomer (or upwards) per square foot (emulsion of 17% BHC with 4% gamma isomer) gave effective control. With lesser concentrations, tick populations increased rapidly after seven weeks. Surviving ticks from sprayed huts deposited considerably fewer eggs than normal females.
Nevertheless, the same authors report, reintroductions were so frequent that the authorities finally resolved to construct tickproof habitations. In spite of comparatively high initial cost in comparison with daub and wattle huts, this was found to be the only realistic approach to reducing deaths and man hours lost to relapsing fever.
Subsequently, Annecke (1952) reported that all huts treated with 600 mg. gamma isomer per square foot BHC remained free of 0. moubata for at least 27 months. When 300 mg. per square foot were used, huts remained free of ticks for twelve months.
The small amounts of BHC used in malaria control programs, 25 to thirty mg. gamma isomer per square foot BHC wettable powder, applied twice three months apart, has little effect on O. moubata, but Annecke (loc. cit.) believes the cumulative effect may reduce or destroy the tick.
The above remark immediately suggests the potentiality of tampan resistence to chemicals. So far as known, none has yet been demonstrated.
A control program in Fort Jameson township of Northern Rhode sia has recently been reported by Holmes (1953). Heavy spraying with a five percent BHC solution resulted in general diminution of the tick population but did not result in its elimination. It was found that the most economical form for achieving a hundred percent kill was five percent BHC powder mixed with 95% (by weight) sawdust diluent, or with chaff left from pounding corn. To obtain a sackful of this mixture, a container holding 64 pounds of forty percent BHC cattle dip wettable powder was mixed with fifty pounds of sawdust. This mixture was then laid as a four inch wide bar. rier, thick enough to insure that ticks must come in contact with it when passing, at the base of all inside walls of the house. The barrier was maintained for three weeks and frequently inspected, especially where it passed door openings, to insure that it was not scattered. This time period should reach all nymphs hatching from eggs laid before the chemical is applied (more or less ex ceptionally a somewhat longer hatching period may be involved, but for practical purposes this time is probably usually effective HH). Elimination of tampans was obtained by this method, but reinfestation occurred within a year to a year and a half. Fleas, Congo floor maggots, and bed bugs were also killed. In the fol lowing year, the number of cases of relapsing fever from treated houses was considerably reduced. The cost of this program was so low that other authorities commenced similar control programs.
A control program using 0.5 percent gammexane powder (0.034) was undertaken in houses in humid Kenya hills (Teesdale 1952). Reapplications had to be made every month or two to control nymphs that had hatched from eggs, the latter being resistant to the chemical. Killing effects diminished in treated huts fifty days after application. The low cost of gammexane was said to allow its purchase and use by Africans.
Although most recent workers favor BHC dusts over spray so lutions, Anderson (1947) reported good control in Somaliland coffee houses with a three percent solution of gammexane in diesoline, *666 sprayla (crude benzene hexachloride, 12% gamma isomer) at a dosage of 1,250 mgm. per square foot of soil was recommended by Hocking (1946), who found DDT at the same dosage less effective. On the basis of experiments in two localities in Kenya, Heisch and Furlong (1954) recommend a spray of gammexane wettable powder P.520 rather than gammexane insect powder for tampan control.
Investigators have reported that DDT is of less effective ness than gammexane in controlling tampans. Among these, Jepson (1947) found that five percent DDT dust is slower and less effective than gammexane, although after about three weeks a mor. tality of fifty percent to eighty percent obtained. Holmes (1953) also indicated that gammexane provides a more complete and rapid kill than DDT. Annecke and Quin (1952) considered that various types of DDT applications lacked sufficient residual effect to be considered useful.
The inefficacy of many chemicals for killing 0. moubata and the usefulness of gammexane and of E605F (diethyl nitrophenylmono_thio-phosphate) for this purpose were reported by Enigk (1948). Belgian tests with three preparations of the gamma isomer have been reported by Pierquin (1950). Sprays of iCyclotox' contain ing a large proportion of the gamma isomer killed about half the ticks in eight to ten days when applied in Belgian Congo huts. In the laboratory, where the ticks could be kept in closer contact with the chemical, all died after varying lengths of time with different concentrations and preparations (Himpe and Pierquin 1951). The authors conclude that spraying a volatile substance on soil is of less value than mixing it with soil.
The possibility of controlling 0. moubata by feeding hosts on certain chemicals was explored by De Meillon (1946). Fifty mgm. of pure gamma isomer of gammexane were mixed with agar and water and fed to rabbits four or five times. The ticks fed only briefly and showed either incoordination or death afterwards. The domesticated tampan's predilection for human blood obviously limits the application of this interesting approach,
0. moubata is also susceptible to arsenic compounds in the blood of animals. Injections of neoersphenamine have been used in rabbits for this purpose (De Meillon, Thorp, and Hardy 1948). The failure of 2:3 dimercaptopropanal (British anti-lowisite) to alter the toxicity of neoarsphenamine was described by Thorp, De Meillon, and Hardy (1948).
In testing insect and tick mortality when exposed to dry insecticidal film, Busvine and Barnes (1948) found that o. moubata nymphs are resistant to DDT but susceptible to gammexane and pyrethrins. Busvine and Nash (1953) also determined that films of oil solutions are better than dry films for testing insecticides because they give a sharper dose/kill relation.
The value of certain derivatives of phenol and naphthalene as soilfumigants in hut floors has been suggested (Robinson 1944A).
Derris powder failed to affect nymphal 0. moubata in Russian laboratory tests (Mironov, Nabokov, and Kachalova 1946). Pyrethrum sprays and dusts are highly toxic (Robinson 1942C,D,1943B, 1944B) but field tests have not been undertaken, probably due to high cost of pyrethrum and effectiveness of cheaper BHC.
Sulfur dioxide or cyanide fumigation has little effect on 0. moubata, and sprays of kerosene and formalin are not success Ful (Hopkins and Chorley 1940). A spray consisting of 30 cc. turpentine, 50 cc. twenty-five percent alcohol, 5 cc. kerosene and a little white soap was suggested by these authors, though it is expensive and troublesome to prepare. Their best recommendation was a coarse, roughly filtered spray consisting of 1 pounds of paradichlorobenzene in one gallon of kerosene applied under high pressure at the rate of twelve to fourteen gallons per two thousand square feet of surface (also reported by Hargreaves 1936).