Estimation of fecundic life span of Wuchereria bancrofti from longitudinal study of human infection in an endemic area of Pondicherry (south India).

The fecundic life span of adult female W. bancrofti was estimated by longitudinal study of microfilaraemia in a cohort of population (7,525) in Pondicherry. The estimation was based on a deterministic model, using the rate of loss in infection. The life span of the parasite was 10.2 yr without chemotherapy, while it was reduced to 5.3 yr following diethyl-carbamazine therapy. The analysis of mean microfilarial counts in microfilaraemic persons without chemotherapy indicates that the rate of production of microfilaria by the adult female is stable at least for a period of five years.

A mathematical analysis of various factors involved in transmission of bancroftian filariasis in Pondicherry.

The variation of clumping factor in microfilaraemia among different age groups was observed in Pondicherry for 1981 and 1986. The clumping factor was minimum in the age group 0-5 yr and it was maximum in 16-20 yr group in 1981 and 21-25 yr in 1986. The variation in clumping factor resembled the changes in microfilaria (mf) rate. Multiple linear regression analysis showed that the multiple correlation between mf rate and the other parameters i.e., median microfilarial density (MFD50), clumping factor in human population, and, infection rate and infectivity rate in vector population was highly significant. The relationship between filariometric indices in human host and vector population may provide the basis on which a mathematical model on transmission of filariasis could be developed.

Parasitological aspects of malaria persistence in Koraput district Orissa, India.

A sample survey in 37 villages covering 10,733 people in 1986-87 in the Koraput district, Orissa showed that the malaria prevalence is of a much higher order than that reported by the National Malaria Eradication Programme (annual parasite incidence between 14.3 and 26.8 during 1981-86). Out of 833 positives detected 714 had Plasmodium falciparum, 86 had P. vivax, 12 had P. malariae and 21 had mixed infections. There were 650 asymptomatic parasite carriers and 127 gametocyte carriers. The infant parasite rate was 15.82 per cent and average enlarged spleen (AES) in 2 to 9 yr old children was 1.98. In a year round fever survey in 22 villages, 5520 blood smears were collected and 1364 were found positive for malaria, with 77.3 per cent P. falciparum. In a mass blood survey conducted in a labour camp at an irrigation project, 610 people were examined, and 181 were positive. Nearly 40 per cent of migrants and 22 per cent of locals were positive, P. falciparum being dominant.

Impact of 50 years of vector control on the prevalence of Brugia malayi in Shertallai area of Kerala state.

This article examines the long term effects of vector control on the prevalence of B. malayi infection and disease, by comparing the results of 3 earlier studies (1934, 1955, 1976) in one area of south India with a recent (1986) survey. The data indicate that disease and infection prevalence have declined continuously over the last 50 years. Infection has declined (from 21 to 2%) more markedly than disease (from 24 to 10%). Age-specific data indicate that this difference is due to the irreversibility of the clinical signs and the long term survival of diseased cohorts. The results indicate that the prevalence of clinical brugian filariasis can be reduced using vector control and that such control programmes cannot be evaluated in short term or by using crude morbidity statistics.

A simple deterministic model for host-parasite relationship in Wuchereria bancrofti infection & its relevance to parasite regulation in human host.

A deterministic immigration-death model, which reflects the population dynamics of W. bancrofti in human host has been applied to study the relationship between vector and human infections. Application of the model showed that the rate of acquisition and loss of human infection were approximately equal (L = 0.130 and M = 0.129). The relationship of infective resting density (IRD) in vector population with maximum intensity (Imax) of infections and microfilaria prevalence (MFP) in human population were examined by using the least squares polynomial regressions. The fifth order polynomial regressions were found to be adequate to describe the observed pattern (Imax vs IRD: R2 = 0.8464, P = 0.0015; MFP vs IRD: R2 = 0.7246, P = 0.019). The observed relationships indicated that at an infective resting density of 0.26 per man hour or above, the density-dependent factors start regulating the human infections, which showed a declining trend, following this level.

Malaria in Koraput district of Orissa.

Incidence and prevalence of malaria was studied in the predominantly tribal district of Koraput, Orissa state. In the mass blood surveys in 61 malarious villages, a total of 12,122 persons were examined and 1,604 (13%) were found positive for malaria. Infant parasite rate was 23% and young children 2-4 years old were the worst affected (parasite rate 27.2%). P. falciparum, P. vivax, and P. malariae accounted for 80, 10 and 3% respectively of all infections. A sample of 2,554 children below 10 years of age were examined for splenomegaly. The spleen rate in 2-9 year old children was 22% and the average enlarged spleen (AES) was 2.06. There was no association between size of the spleen and species of parasite. Fever survey was done for a year in 22 villages and 5,511 blood samples were collected of which 24.8% were positive for malaria parasite. The annual parasite incidence (API) was 32.4 per 1000 infants and 89.5 per 1000 population. Children, 2-4 years old recorded the highest incidence (457/1000). The age pattern of prevalence and incidence indicate high level of acquired immunity in the population. Prevalence and incidence varied among different tribal communities. Prevalence of infection and splenomegaly was higher among children of Bonda, Kondh and Poroja tribes. The role of genetic factors in malaria is discussed.

Detection of Plasmodium ovale in Koraput district, Orissa state.

We report for the first time the detection of P. ovale infection in three patients in two hilly villages of Koraput district, Orissa state, India. The identification of the parasite was confirmed by the Imperial Colleage of Science and Technology, London.