Mf Density Research Articles

Antifilarial Effect of Solamargine Isolated from Solatium khasianum

AbstractAn active principle isolated from the ripe berries of Solarium khasianum is a steroidal alkaloid glycoside, solamargine, which killed in vitro 100% adults and microfilariae (mf) of Setaria cervi at a 4 mg/ml concentration in 60 and 88 min, respectively. The drug, when administered orally at 100 mg/ kg to rats, in which S. cervi adults were implanted intraperitoneally, reduced the blood mf count by more than 30% after the first phase of treatment for 10 days. The mf count showed an increase of 72% after the second phase of treatment. Following the third and the fourth phases of treatments, the mf density was reduced by more than 90%. One hundred percent reduction of mf count was obtained 15 days after the fourth and final phase of treatment which was of 5 days duration. At the evaluated dose (100 mg/kg × 4 phases), solamargine killed 100% of adult worms without incident toxicity.

Side reactions following ivermectin therapy in high density bancroftian microfilaraemics

Side reactions following ivermectin treatment were evaluated in sixty males with high density bancroftian microfilaremia (GM 1388/ml). Following a single oral dose of ivermectin of different strengths (20, 50, 100 or 200 μg/kg), microfilariae clearance and side reactions were monitored in a double blind fashion. Microfilaria levels fell rapidly after ivermectin administration in all dosage groups and 98% of pretreatment microfilariae was cleared after 12 h of treatment. The rate of microfilaria (mf) clearance was slower with 20 μg/kg than with the highest dose (200 μg/kg) administered. Forty-six patients (77%) became amicrofilaraemic within 2 weeks of treatment. Side reactions were noted in 97% of cases. The most common reactions were fever, headache, weakness, myalgia and cough which appeared by 12 h and subsided by 72 h following treatment. The frequency and intensity of side reactions were related to pretreatment mf densities and were independent of the dose administered. Unusual side reactions were noted in a few patients with high density microfilaraemia. These included intense cough, shortness of breath, blood tinged mucoid expectoration associated with patchy pneumonitis of the lung. Itchy rashes, lymphatic nodules and raised alkaline phosphatase level were also observed in some patients. These side reactions were transient, self limiting and were not serious enough to warrant any treatment. These exaggerated unusual reactions were possibly due to allergic response of the susceptible host to rapid killing of large number of microfilarae.

Factors affecting transmission of Wuchereria bancrofti by anopheline mosquitoes. 4. Facilitation, limitation, proportionality and their epidemiological significance

Quantitative understanding of the transmission dynamics of lymphatic filarial parasites is essential for the rational planning of control strategies. One of the most important determinants of transmission dynamics is the relationship between parasite yield, the success rate of ingested microfilariae (mf) becoming infective larvae in a mosquito vector, and mf density in the source of the human blood meal. Three types of relationship haye been recognized in human filaria/mosquito couples—limitation, facilitation and proportionality; facilitation has hitherto been observed only in the couple Wuchereria bancrofti/Anopheles gambiae in Burkina Faso, in experimental studies on a high density mf carrier. The present paper demonstrates facilitation in W. bancrofti/An. gambiae and W. bancrofti/An. arabiensis in lower mf density carriers in The Gambia and Tanzania, and in W. bancrofti/An. funestus in Tanzania. Facilitation was not found in An. melas in The Gambia nor in An. merus in Tanzania. Analysis of published data shows limitation at low level mf densities in W. bancrofti/Culex quinquefasciatus in Sri Lanka, and in the same couple in India. Limitation also occurs in Brugia malayi/Aedes togoi in experimental cats; proportionality occurs in B. malayi/Mansonia bonneae in Malaysia. The epidemiological significance of these host/parasite relationships is discussed, and supporting evidence for its validity is presented from the published results of large-scale control programmes.

A placebo-controlled double-blind trial for the treatment of Bancroftian filariasis with ivermectin or diethylcarbamazine

Therapeutic efficacy and clinical side-effects of ivermectin (single dose of 100 μg/kg) and diethylcarbamazine (DEC) (3 mg/kg for one day, then 6 mg/kg daily for 12 d) were evaluated for microfilaricidal effect in Bancroftian filariasis. Seventy-one microfilaraemic consenting adult male patients (⩾100 microfilariae (mf)/ml) were randomly assigned to receive ivermectin, DEC or placebo and kept in hospital for 15 d. Those receiving placebo were treated with ivermectin on day 9. Ivermectin (19 ‘double-blinded’ and 22 ‘unblinded’ patients) caused an abrupt reduction in mf count to 1 · 5% of the pre-treatment level 12 h after drug administration and to 0 · 06% on day 14, with recrudescence to 1 · 8% after one month and to 9·2% after 3 months. DEC (30 patients) caused a gradual drop in mf count to 1 · 1% of the pre-treatment level on day 14, which increased to 2 · 4% after one and 3 months. The total scores of side-effects were 77 (1%), 305 (2·1%) and 311·5 (3·0%) for placebo, ivermectin and DEC respectively; the differences between DEC or ivermectin and placebo were statistically significant. Ivermectin produced lower side-reaction scores than DEC and the differences were highly significant at the 95% confidence level. Side-effects were mainly headache and body aches in the ivermectin patients, which appeared as early as 4 h after drug administration, resolved within 36 to 48 hours, and were significantly related to mf densities. Side-effects in DEC patients were mainly testicular and epididymal pain and swelling, unrelated to mf densities, which began at day 2 and continued to day 7. Single dose ivermectin was more effective in reducing microfilaraemia in Bancroftian filariasis than a 13 d course of DEC for a period of about 2 months after treatment, and side effects were of shorter duration.

A quantitative approach to the relationship between Wuchereria bancrofti microfilaria counts by venous blood filtration and finger-prick blood films

Counts of nocturnally periodic Wuchereria bancrofti microfilariae (mf) in 20 mm 3 finger-prick blood films were compared with membrane counts after filtration of 1 ml of venous blood for their efficacy in determining the prevalence of Bancroftian filariasis. The technique used for spreading and staining the blood films was critically important to the sensitivity of this screening procedure. There was good agreement between the 2 methods. Four statistical approaches were used to measure the correlation between the 2 sampling methods: 2 linear regression methods using untransformed and transformed data, and 2 nonparametric rank correlation methods. Based on the statistical analyses, this study strongly supports the general observation that finger-prick blood samples tend to contain more mf than equivalent volumes of venous blood, at mf densities high enough to be detectable by the finger-prick technique. It also demonstrates that finger-prick samples provide good estimates of mf densities and prevalence of infection except in areas of very low mf densities, where the membrane filtration method would provide a more accurate estimate of prevalence. Regression analyses using untransformed and transformed data, and the rank correlation tests, demonstrated a strong statistically significant correlation ( P < 0·001) between venous and finger-prick mf counts.

Age Specific Patterns of Change in the Dynamics of Wuchereria bancrofti Infection in Papua New Guinea

Results of a longitudinal study of the age-specific dynamics of Wuchereria bancrofti infection in a community of East Sepik Province, Papua New Guinea (PNG) are described. Microfilarial (mf) density and serum levels of W. bancrofti phosphorylcholine-containing antigen (PC-Ag) in individuals were used as indirect measures of adult worm burden. These parasitological data were collected from 126 subjects greater than 4 years of age at two time points, 12 months apart, prior to the administration of the antifilarial drug diethylcambamazine (DEC). No significant changes in levels of mf density were observed for the study population between these two time points. However, significant changes in the levels of circulating PC-Ag were noted in subjects less than or equal to 20 years of age, but not in subjects greater than 20 years of age, between these two time points. The apparent shorter half life of circulating PC-Ag compared to that of mf makes antigenemia a more sensitive measure of the dynamics of adult worm populations. These data are discussed in terms of a basic mathematical model describing the dynamics of adult worm populations in relation to their life expectancy and attrition of larvae during establishment. Consideration of these data in the context of this simple immigration/death model suggests that the differences observed in patterns of change in intensity of infection between subjects less than or equal to 20 years old and those greater than 20 years old may be consistent with the acquisition of resistance to superinfection with increasing age.

The significance of low density microfilaraemia in the transmission of Wuchereria bancrofti by Culex (Culex) quinquefasciatus Say in Sri Lanka

Laboratory-bred Culex quinquefasciatus were fed on carriers with low and moderate densities of microfilariae (mf) of Wuchereria bancrofti. In the first series of experiments, mosquitoes were dissected 12 d after feeding. The percentage of infected mosquitoes and the numbers of larvae per infected mosquito were directly proportional to the mf density at the time of feeding. There was an overall high infection rate and a wide distribution of larvae per individual mosquito at all levels, except for the 4 lowest counts. Of the 4 carriers with counts of 5 mf/ml and less, 3 were capable of infecting Cx quinquefasciatus, giving infection rates of 1·0%, 7·4% and 12·0% respectively. In the second series, some mosquitoes were dissected immediately after feeding and the remainder 12 d later. There was a good correlation between the number of mf ingested and the number of infective larvae per mosquito. The high infection rates in Cx quinquefasciatus when fed on low-density microfilaraemiac arriers, and the varying number of larvae in individual mosquitoes, suggest that low-density carriers could be a source of infection. Field studies were also carried out in 3 different areas with mf rates of 7·24%, 0·72% and 0·16%, respectively. In the 2 areas with low mf rates, infection rates in mosquitoes were 1·32% and 1·08% respectively. Cx quinquefasciatus fed on a carrier with a residual microfilaraemia of 19 mf/ml following treatment with diethylcarbamazine had an infection rate of 13·8%. These studies suggest that the examination of recently fed houseresting populations of Cx quinquefasciatus could be a sensitive method for measuring the prevalence of mf in the human population.

Frequency distribution of lymphatic filariasis microfilariae in human populations: population processes and statistical estimation

This paper uses simple mathematical models and statistical estimation techniques to analyse the frequency distribution of microfilariae (mf) in blood samples from human populations which are endemic for lymphatic filariasis. The theoretical analysis examines the relationship between microfilarial burdens and the prevalence of adult (macrofilarial) worms in the human host population. The main finding is that a large proportion of observed mf-negatives may be 'true' zeros, arising from the absence of macrofilarial infections or unmated adult worms, rather than being attributable to the blood sampling process. The corresponding mf distribution should then follow a Poisson mixture, arising from the sampling of mf positives, with an additional proportion of 'true' mf-zeros. This hypothesis is supported by analysis of observed Wuchereria bancrofti mf distributions from Southern India, Japan and Fiji, in which zero-truncated Poisson mixtures fit mf-positive counts more effectively than distributions including the observed zeros. The fits of two Poisson mixtures, the negative binomial and the Sichel distribution, are compared. The Sichel provides a slightly better empirical description of the mf density distribution; reasons for this improvement, and a discussion of the relative merits of the two distributions, are presented. The impact on observed mf distributions of increasing blood sampling volume and extraction efficiency are illustrated via a simple model, and directions for future work are identified.

Effect of two successive annual treatments with single doses of ivermectin on microfilaraemia due to Wuchereria bancrofti var. pacifica

Between 1986 and 1988 a single-blind, dose-ranging study was carried out in French Polynesia to determine the efficacy and tolerability of single 50, 100, 150 and 200 μg/kg doses of ivermectin in Wuchereria bancrofti carriers. Forty male microfilariae (mf) carriers between 18 and 50 years of age, in whom mf density was ⩾20 mf/ml, were treated twice at a one-year interval. Twelve months after the second treatment, in carriers who were given a dose ⩾100 ng/kg, mean mf density was 4–7% of the initial pretreatment mf density. Therefore, several successive annual treatments with single doses ⩾100 μg/kg of ivermectin should result in reducing mf densities to a very low level. Nevertheless, at 9 months after the second treatment, residual parasitaemia ranged from 1 to 2182 mf/ml (median 85) in 30 patients. Finally, in patients with pretreatment mf counts ⩽150 mf/ml, mean mf density was 2·8 and 8·9 mf/ml, respectively, during the 2 six-month periods following treatment, while in patients with pretreatment mf densities >150 mf/ml (median 1500) it was 92·3 and 334·1 mf/ ml during the same periods. These results suggest that, when implementing filariasis control programmes, the best strategy might be administration of several treatments with a single dose of ivermectin every 6 months to the entire population, at least in French Polynesia. Afterwards, when mf densities had been reduced to a relatively low level (100–150 mf/ ml), annual treatments could be considered.

Factors affecting transmission of Wuchereria bancrofti by anopheline mosquitoes. 3. Uptake and damage to ingested microfilariae by Anopheles gambiae, An. arabiensis, An. merus and An. funestus in East Africa

Laboratory observations were made on the uptake of microfilariae (mf) of Wuchereria bancrofti by Anopheles gambiae, An. arabiensis, An. merus and An. funestus. Over host mf densities ranging from 450/ml to 1735 mf/ml neither the percentage of mosquitoes ingesting mf nor the mean number of mf per mosquito was correlated to host mf density. All mosquito species damaged mf during ingestion but the proportion harmed was independent of host mf density. The mean proportion damaged was 0–67 in An. Gambiae, 0'51 in An. Merus, 0'47 in An. Arabiensis and 0'26 in An. Funestus. A comparison of the mean number of undamaged mf ingested and the number of larvae in the thoracic muscles revealed that not all undamaged mf were able to reach the thoracic muscles.

Microfilaria density distribution in the human population and its infectivity index for the mosquito population.

A new method of computing the infectivity index of microfilariae (mf) for the mosquito population is proposed using the estimated mf density distribution in the human population. the observed density distribution is considered a compound of the Poisson and the gamma distributions. The former distribution describes the probability of a specimen containing a specified number of mf and the latter describes the density distribution of mf in the host population. The mf infectivity index is the probability that a blood meal will include at least 1 mf, conditional on the population-density distribution of mf as specified by the gamma distribution. Actual data indicate that this population-density-based infectivity index can be considerably different from the conventional index based on the survey-density distribution. The level of the carrier rate of mf in a survey is greatly influenced, apart from the sample variation, by the average volume of blood taken from each person. The rate computed on the estimated population-density distribution of mf is convertible to any base amount of blood.

Factors affecting transmission of Wuchereria bancrofti by anopheline mosquitoes. 1. Uptake of microfilariae

Ingestion of Wuchereria bancrofti microfilariae (mf) from humans by 639 Anopheles gambiae, 557 An. arabiensis, 117 An. melas and 9 An. funestus was investigated. The mf densities in blood fell into 3 groups; 0–32mf/ml, 107–122 mf/ml and 421–1140 mf/ml. In An. gambiae and An. arabiensis percentage of mosquitoes ingesting mf was strongly associated with mf density in host blood; in An. melas the association was much weaker. Mean number of mf ingested per mosquito was also strongly correlated to mf density in An. gambiae and An. arabiensis but not in An. melas. At low mf densities both An. gambiae and An. arabiensis concentrated mf, with concentration decreasing as density increased. From regression analysis, observed and expected uptake of mf would be equal at 622·9 mf/ml in An. gambiae and 391·6 mf/ml in An. arabiensis.

Factors affecting transmission of Wuchereria bancrofti by anopheline mosquitoes. 2. Damage to ingested microfilariae by mosquito foregut armatures and development of filarial larvae in mosquitoes

Microfilariae (mf) of Wuchereria bancrofti from the midgut of 639 Anopheles gambiae, 557 An. arabiensis, 117 An. melas and 9 An. funestus were examined immediately after the mosquitoes had fed on carriers with different densities of mf. The percentages of mf damaged during ingestion were 57·1–60·0 in An. gambiae, 33·3–50·6 in An. arabiensis and 38·7–55·7 in An. melas. In each species the percentage of mf damaged was independent of mf density in the human host. A further 3657 An. gambiae, 2875 An. arabiensis, 347 An. melas and 32 An. funestus were examined 7 d or more after feeding on mf carriers. In An. gambiae and An. arabiensis, mean numbers of larvae per mosquito were strongly correlated to mf blood density, with similar regression slopes to those obtained from the regression of mf blood density on mean uptake of mf/mosquito. The ratio of mean numbers of larvae per mosquito to mean numbers of intact mf ingested per mosquito increased as the density of mf in the human host increased in An. gambiae and An. arabiensis, but decreased in An. melas as host mf density increased.

Stage-specific protective immunity to microfilariae of Litomosoides carinii in Mastomys natalensis.

Experiments were performed to know whether immunity to microfilariae (mf) is effective to the protection against infection with infective larvae (L3) of Litomosoides carinii in Mastomys natalensis. Animals were immunized subcutaneously with 5×105 live mf at two week intervals for six times. Mf in peripheral blood were detected on the following day of subcutaneous inoculation, and mf density increased gradually during five weeks. The mf density in the blood began to decline from five weeks and four of 8 animals became amicrofilaremic after six weeks. Immunofluorescence revealed that these immunized individuals developed antibodies not only against mf but also against both L3 and adult worms. Beginning at 11 weeks after initiation of immunization, animals received the challenge infection with L3, and the protective effect induced by mf immunization was examined by the worm recovery three and 14 weeks after challenge infection. There was no suppressive effect of immunization with live mf to the challenge infection as determined by recoveries of developing and adult worms. These results indicated that protective immunity induced by mf immunization was stage-specific and not effective against L3 to adult stage worms of L. carinii in M. natalensis.

A quantitative analysis of the diagnostic value of diethylcarbamazine provocation in endemic Wuchereria bancrofti infection

The efficiency (Δ) of the day-time provocative effect of diethylcarbamazine (DEC) on the circulation of microfilariae (mf) of nocturnally periodic Wuchereria bancrofti compared with the night mf count was evaluated in terms of sensitivity and specificity. In one test, the mean mf count for finger-blood samples from the same person on 3 successive nights was compared with the day-time post-DEC count; another test compared the mf count in one night-time finger-blood sample with the following day-time post-DEC count. Both tests were efficient (Δ = 0·74 and 0·77, S.E. = 0·07 and 0·07, respectively). Night and day-time post-DEC mf counts were significantly correlated ( r = 0·81, P < 0 sd001, and r = 0·79, P < 0·001 for the 2 tests respectively), but mf densities tended to be relatively lower after DEC provocation than in the corresponding night-blood samples. In both tests the regression coefficients differed significantly from zero ( P < 0·001). The simple 24h test was almost as efficient as the 3-nights test and based on its regression relationship, a table is presented predicting the expected night mf counts from the observed day-time post-DEC counts. The provocative dose of DEC, 2 mg/kg body weight, evoked no side-reaction in either microfilaraemic or uninfected persons.

DOUBLE-BLIND STUDY OF IVERMECTIN AND DIETHYLCARBAMAZINE IN AFRICAN ONCHOCERCIASIS PATIENTS WITH OCULAR INVOLVEMENT

In a randomised double-blind study, ivermectin was compared with diethylcarbamazine (DEC) and placebo in the treatment of onchocerciasis in 30 male patients from Mali with moderate to heavy Onchocerca volvulus infections and ocular involvement. 10 patients received a single oral dose of ivermectin, 12 mg, 10 received DEC daily for eight days (total dose 1·3 g), and 10 received matching placebo. Patients were examined periodically for twelve months. Punctate keratitis disappeared in 6 of 7 ivermectin patients but increased in DEC patients. Numbers of O volvulus microfilariae (mf) in the anterior chamber decreased slowly and eventually disappeared in most ivermectin patients during the six months following treatment; anterior chamber mf disappeared more rapidly in some patients after DEC, but reappeared within six months of stopping treatment. Both ivermectin and DEC caused a prompt decrease in mean skin mf density; density then increased in both groups over the twelve month observation period, reaching 9% of pretreatment values in ivermectin patients and 45% in the DEC group. Analysis of adult O volvulus from nodules excised at three and twelve months post treatment showed no effect of either drug on viability; however, there was evidence of degeneration of intra-uterine developing mf in the ivermectin group. Side-effects were less frequent and less severe in ivernectin patients than in DEC patients. Ivermectin as a single oral dose appears to be a more effective microfilaricidal drug than DEC in onchocerciasis.

Parasitological, serological, and clinical studies of Wuchereria bancrofti in Limbe, Haiti.

A survey for Wuchereria bancrofti in Limbe, Haiti (est. pop. = 10,500) revealed that 17% (231/1,450) had a patent infection. Nearly half of those surveyed harbored fewer than 10 microfilariae (mf) per 20 mm3 of finger-prick blood; the median mf density for females and males was 12.4 and 9.5, respectively. Parasitemias occurred as early as age 4. Antibody titers greater than or equal to 1:20 against adult D. viteae antigen were observed in 38% of microfilaremic individuals and in 29% of amicrofilaremic individuals. Peak antibody responsiveness (40%) was observed between 5 and 9 years of age. In all age groups there was no correlation between mf density and antibody titer. Among the mf carriers, 5.6% had no clinical symptoms. Lymphangitis was a common feature with 14.3% having lymphedema, 8.2% with edema of the lower extremities, and 1.3% reporting episodes of chyluria. Genital involvement among women was rare, but in males 5.4% had genital swelling and 4.5% had hydroceles. Culex pipiens quinquefasciatus (Say) was observed to support the complete development of W. bancrofti in Limbe.

Efficacy Of Mass Treatment For Control Of Human Filariasis.

This study was carried out for three years from 1968 to 1970. Three coastal villages and four remote islets of Che Ju Island were surveyed and 90% of all inhabitants were blood smeared. These study areas were grouped into five according to its characteristic for evaluation of mass treatment with diethylcarbamazine citrate (Hetrazan U.S.P.) and insecticide spray in control of human filariasis. To set baseline up for control group, placebo was administered. Followings are the results obtained: 1. 81.1% of all mf positives accepted and completed the mass chemotherapy; main reason for refusal was side reactions told by neighboring villagers who experienced them. 2. 6 mg of hetrazan/kg B.W. X12 doses given every day turned mf postives to mf negative in 92.1%. The patients who had high mf density remained mf positive in 16.5% whereas only 2.1% for low mf density. 3. 73.8% of mf positives after the treatment showed marked decrease in mf density. Most of them to less than 15n mg/20 mm(3) of blood that can not infect mosquito effectively. 4. Mosquito infection rates were also dropped markedly in areas where mf positive were mass treated. 5. Side reaction induced by diethylcarbamazine was frequent(64%-90%) and various. The most frequent symptom was headache and fever. 6. DDT spray did not influence human mf rate and mosquito infection rate.

Ecology of filariasis on Che Ju Island.

Study of filariasis to determine important factors involved in its ecology was carried out on Che Ju Island for three consecutive years from 1968 to 1970 in seven villages, three coastal villages and four islets remote from the main island. One village which was located in mountainous area far from the coast was surveyed to serve as control area. About 90% of population inhabiting the study area had at least one blood smear during the three-year period; about one third had three blood smears, and a little over one third had two, and the rest only one examination. Animal and mosquito surveys were carried out at the same period. Followings are the results obtained: 1. All human cases but several had microfilariae identical to the description of B. malayi. The several cases who had morphologically different microfilariae from that of B. malayi need further study for definite conclusion. 2. Five persons randomly sampled from Mf positives and bled every two hours demonstrated nocturnal periodicity between 9 p.m. and 3 a.m. 3. Human is considered to be only reservoir host for human filariasis in the area since animal survey and experimental exposure to the infective larvae of human filaria species showed failure to infect animals. 4. Microfilaria rate, microfilaria density, prevalence of elephantiasis varied by area and age with correlation, which indicated cumulative process of the parasite by repeated exposure and development of host immunity to certain extent. 5. Clinical manifestation of filariasis (symptom complex and elephantiasis ) taken from history and inspection was low in its prevalence with range of 0.9% 11.8% of total population. Only 5.2% of 517 Mf positives had the clinical manifestation. 24.8% of 109 persons with clinical manifestation had microfilaria; 42.9% with symptom complex only, 23.1% with both symptoms and elephantiasis, and none with elephantiasis only were microfilaria positive. 6. Ae. togoi was the only species infected with the filaria. Mosquito infection rate by area showed positive correlation to the Mf rate and density of human population; where the Mf rate and density were high, the mosquito infection rate also high.

Relation of age, sex, and microfilaria density to treatment of sub-periodic filariasis with diethylcarbamazine.

Summary A study group of 175 mf carriers of varying ages and mf densities, were treated for 5 or 6 days at 6 mg/kg and again after 6 mo. with a total dose of DEC between 60 and 72 mg per kg of body weight and examined regularly for microfilariae by two 20 cmm samples of blood at 1 week, 6 months, and 2 and 3 years after the beginning of therapy. The frequency of adverse reactions to the first administration of DEC varied directly with the pretreatment mf density of the carriers and with the age group receiving treatment: carriers with initially low counts and in the younger age groups, 0 to 19 years, experienced significantly fewer reactions to DEC than those with higher counts or in the older age groups, suggesting that, whatever the nature of these reactions, they appear to be related to the intensity of the infection and to the length of exposure to mf products. No correlation could be found between age groups or sex distributions and the percentage of carriers who remained positive 1 week after therapy or several months or years later. A significant positive correlation, however, was consistently found between pretreatment mf density and percentage of carriers found positive at various intervals after treatment, in that the highest positive rates after treatment were found among the carriers with highest initial counts, indicating that the dosage of DEC may have to be gauged to the pretreatment mf density of the individual person or to the population at risk, in order to insure optimal therapeutic results.