Number Of Lice Research Articles

A Count of Mallophaga on a Heavily Infested Hen

The literature contains many accounts of experiments on the control of Mallophaga infesting chickens, but little accurate information on the number of lice that may infest them. Because of difficulties in counting the lice on birds, many experimenters have expressed infestations in terms of degrees (Telford, 1947; Edgar et al., 1949; MacCreary and Catts, 1954). Among a smaller group who made counts, Creighton et al. (1947) considered any chicken as heavily infested that supported a population of over 75 lice. Moore and Schwardt (1954) recorded a mean average of 37 to 100 lice per bird. Fairchild and Dahm (1955), in a number of experiments, recorded averages of 83 to 256 lice per hen, with a maximum of 400 on one bird. This is a report on the number of lice counted on a 14-month-old hen that was placed in a deep freeze after it died from natural causes.Previous examinations …

The distribution of the eggs of Damalinia equi (Denny) and Haematopinus asini (L) on the Horse.

The eggs of Damalinia equi (Denny) and Haematopinus asini (L.) are attached to the hairs close to the skin with the end of attachment nearest to the skin. The oviposition behaviour of D. equi is similar to that of D. ovis (L.). The only observable differences are that the gonopods are not used at the time of egg laying and the fibre is grasped by the claspers. Temperatures between 32 and 38�C are required for the maximum number of lice in a population to oviposit. Skin temperature can determine the lateral distribution of the eggs in the natural environment. A fibre of suitable diameter is also necessary. D. equi cannot attach its eggs to the coarse hairs of the face, mane, tail, and legs whereas H. asini is able to do so. As the coarse hairs of the mane, tail, and legs are not shed with the fine hairs of the coat at the beginning of summer and winter the shedding of the coat effects a more severe reduction of the population of D. equi than of H. asini.

DDT resistance in Egyptian body lice.

Summary 1. The average mortality for adult Egyptian body lice from the vicinity of Cairo when exposed to DDT powder for 24 hours was 31 per cent for one tenth per cent DDT, 70 per cent for one per cent DDT, and 89 per cent for ten per cent DDT, giving an LD50 of 0.33 per cent. After four days of wear, sleeves which had been treated with 10 per cent DDT killed only 14 per cent of the lice exposed to them. 2. The results of a field test showed that 10 per cent DDT powder is still effective in reducing lousiness. The percentage of heavily infested people (harboring 10 lice or more) was reduced from 56 per cent before treatment to 9 per cent four weeks after treatment while the control group remained approximately the same. When 10 very heavily infested people were treated once each month for five months the number of lice was markedly reduced but about half remained relatively heavily infested. 3. Tests on cloth treated by dipping in acetone solutions of DDT showed that Egyptian body lice could be propagated on cloth which had been treated with a 1–5,000 dilution of DDT. After two generations these lice were established on cloth treated with a 1–2,000 dilution and maintained on it for four generations. The 1–10,000 dilution proved to be lethal to lice from four localities where it is unlikely that there had been previous contact with DDT.

Studies on populations of head-lice (Pediculus humanus capitis: Anoplura). II

1. The material which is discussed in the present paper consists of more than 2000 crops of hair collected from Sokoto, Nigeria; Nairobi and Kakamega, Kenya; Colombo, Ceylon; and Jerusalem, Palestine. The amount of material examined is considerable, but it must be admitted that it has not been found possible to obtain an unselected sample representative of any human community as a whole.2. The paper gives detailed information about the prevalence of head-lice in respect of the individual's race, sex, age, weight of crop of hair and the season of the year.3. The following general conclusions may be drawn:(a) The distribution of lice among a population of people is skew. Among infested persons the commonest count is always low (generally 1–10 lice), but occasional counts of many hundreds or a few thousands are recorded.(b) If the people are grouped by age, sex, etc. a positive correlation is generally found between the proportion of men in each group who are infested and the mean number of lice per infested person.(c) There is clear evidence from several places that season affects the frequency of infestation. In most but not all places the insect is most widely distributed in the colder, wetter part of the year. It is not known whether this is due to some effect of climate upon the insect itself or upon human habits and activity.(d) It will doubtless be found that the individual's race is an important factor in determining infestation, but little has yet been established on this subject.(e) Wherever material has been available from individuals of widely different age, it has been found that boys are more infested than youths, who in turn are more infested than grown men.(f) In some places females are more frequently infested than males, though it was established that there was no difference between the sexes at Kakamega.(g) The weight of the individual's crop of hair is in most places positively correlated with infestation.4. Many of the factors mentioned in 3 (d)–(g) are local and depend on racial customs. It is emphasized that further investigations would be most profitably carried out in the countries concerned by men well acquainted with the local people and their ways.5. There are probably a large number of individual differences due to sensitiveness, vanity, general health, etc.; these have hardly been studied at present but it is probable that collectively they are very important.

Studies on Populations of Headlice (Pediculus humanus capitis: Anoplura). I

Many biologists are at present interested in populations of animals, which are studied experimentally and also by more abstract mathematical methods, but it is frequently difficult to obtain facts about actual populations living under natural conditions unless they are studied by sampling, the accuracy of which cannot always be precisely defined. The method described in this paper tells us of the actual numbers of headlice in crops of hair on individual people. From it we may learn the proportion of people who are infested at different times or places, and the number of lice on different people: also the proportion of males, females and young in the louse population. The results with material from Woolwich and from Lagos are set out in this paper. Further work is now in progress on material received from several parts of the world: this material will be studied and the results published at a later date.

AN INTERESTING REACTION TO LOUSE BITES

Although the clothes louse is a known carrier of typhus and recurrent fevers and has recently been shown to be a carrier of trench fever, I am not aware of any published evidence that it may produce an illness due to a toxin or toxins introduced by its bite. Observations made while attempting to raise large numbers of lice for experimental purposes during the spring of 1918 appear to show that such an intoxication may result in persons bitten by large numbers of lice. The account given here is not presented as positive proof that such is the case, but rather to make available for other workers a record of our experiences. Experiments were begun on the louse problem in the spring of 1917, with lice collected from the clothing of men in a municipal lodging house. They were kept in an electric incubator, heated to from 28 to 30