Factors influencing malaria endemicity in Yunnan Province, PR China (analysis of spatial pattern by GIS). Geographical Information System.

This study is an initial attempt to apply disease mapping through Geographical Information System (GIS) with multiple regression analysis to determine the nature and extent of factors influencing malaria transmission in Yunnan Province, PR China, particularly in border areas. Secondary county-based data covering the period 1990 to 1996 were collected and analyzed. The malaria situation in Yunnan Province as a whole is influenced mainly by the combined effects of the physical environment, the presence of efficient vector species, and mobile population along international borders with Myanmar, Lao PDR and Vietnam.

Profile of Morong, Bataan, an area of low malaria endemicity in the Philippines.

A malaria study area in the Philippines is described. It consists of the municipality of Morong, Bataan on the Island of Luzon. In January 1992, the population was 19454 in 106 villages located on a narrow coastal plain, or in valleys of streams running from the mountainous interior. This is an area of low level but persistent seasonal transmission of malaria with approximately one thousand cases reported each year, mainly from February to July. In spite of the low level of malaria, it is apparently quite stable. The study site has been used to investigate parameters leading to stable malaria. Hypotheses tested were that there was substantial under reporting of cases; that there was strain specific immunity stabilising the incidence of malaria and that malaria transmission in this area is highly localised in small regions with a high enough malaria prevalence to account for the year to year stability. The study plan included cross sectional surveys of parasite prevalence and seropositivity, longitudinal surveys, passive case detection, entomological surveys, anthropological surveys to assess knowledge of malaria and documentation of the health-seeking behaviour of the population.

Vector abundance and behaviour in an area of low malaria endemicity in Bataan, the Philippines.

The vectorial importance of known and potential vectors in Morong, Bataan, Philippines was assessed based on human and animal baited collections of adult mosquitoes and on larval collections. Anopheles flavirostris, the principal vector in the Philippines, was the most abundant among human landing catches, followed by An. maculatus sensu lato (s.l.). Both showed similar seasonal abundance with a peak during the early drier part of the year, which coincided with the peak in malaria cases. Both An. flavirostris and An. maculatus s.l. fed throughout the night with the broad peak of capture from 00:00 to 04:00 and from 22:00 to 00:00, respectively. The two species had similar parous rates (0.76 and 0.72, respectively) giving an average life span equivalent to four feeding cycles. Neither vector was abundant with average human landing rates on collectors of 0.6 and 0.4 mosquitoes per person per night, respectively over the study period. An. maculatus s.l. showed a stronger preference for outdoor feeding compared to An. flavirostris. An. maculatus s.l. was markedly zoophilic with a biting rate on water buffalo 50 times the human landing rate. An. flavirostris was less zoophilic with a corresponding ratio of 7.5. It was concluded that in this area, An. flavirostris is the principal vector. The combination of localised transmission, late night biting pattern and localised breeding sites of An. flavirostris suggest that the use of bed nets and environmental management are relevant control measures that can be implemented through community participation.

Field epidemiological studies on malaria in a low endemic area in the Philippines.

Field epidemiological studies were conducted to examine factors affecting endemicity in an area with a low prevalence of malaria. Two annual cross sectional surveys were done to estimate parasite prevalence rates at two periods in time, to determine the distribution of the parasitemic population and to describe the serological status of the population. A longitudinal study of a sample of infected people was used to measure reinfection rates and antibody dynamics. A 2 year passive case detection was done to estimate the number and distribution of people with symptomatic infections. Malaria was found in all age groups, with marked clustering of cases. Active and passive case detection and serological surveys all gave a similar pattern of malaria distribution: generally low prevalence with small foci of relatively high endemicity. The infection frequencies were generally similar in all age groups, measured by both active and passive case detection. There was a high frequency of P. falciparum gametocytemic infections in the asymptomatic cases found through active case detection. Twenty to 39 year old males had the highest frequency of infection by active case detection, and 10-19 year old males by passive case detection. These two groups were also more likely to be gametocyte positive than their female counterparts, suggesting that in this community, this portion of the population acts as the main reservoir of infection.

Stability of malaria in a community in Bataan, the Philippines: prospects for control.

Malaria in Morong, Bataan, The Philippines, a municipality with relatively low level, but stable malaria is associated with small foci of relatively high endemicity. Although there is little association between age and symptomatic malaria, there is a reservoir of asymptomatic cases which are present throughout the year. Risk analysis suggests that the greatest risk factor in acquiring malaria depends on place of residence and not on occupation, including those associated with forest activities such as charcoal making. Foci of infection and the timing of symptomatic cases is closely correlated with breeding sites and abundance of adult Anopheles flavirostris. In spite of this close association, widely held views in the community that malaria is not related to mosquito transmission are likely to make better malaria control based on vector control difficult to sustain. Observation of treatment practices in the community and estimates of the number of apparently asymptomatic carriers from active case detection illustrate the importance of delayed treatment in providing a continuing reservoir of infection. These results highlight the need for improved early case detection and treatment.

A symposium on containment of mefloquine-resistant falciparum malaria in Southeast Asia with special reference to border malaria.

Important questions related to the factors responsible for and contributing to the origin and spread of multi-drug resistant falciparum malaria at the Thai-Cambodian and Thai-Myanmar border areas are discussed, including the current geographical distribution of multi-drug resistance and the prevention and control of this phenomenon. Specific recommendations are made on epidemiological surveillance, drug deployment, vector control, and the problem of migration which plays a major role in the dissemination of resistant parasite populations. The recent advent of mefloquine resistance of P. falciparum in Thailand may serve as fair warning in the absence of stern measures for preventing the occurrence of resistance to the next and currently last line of antimalaria drugs, especially those with a long half-life, in areas with intensive, uncontrolled malaria transmission, such as tropical Africa.

Symptomatic identification of malaria in the home and in the primary health care clinic.

In endemic areas in the absence of microscopy, the WHO case definition of malaria is the presence or a history of fever without other obvious cause. Yet there is little empirical evidence on the accuracy, predictability and reliability of clinical signs and symptoms for diagnosing malaria within different endemic settings. Studying patients in endemic communities in the Philippines, we found that fever alone did not discriminate well for malaria. In contrast, a sequential occurrence of fever, chills and/or sweating, or a combination of all three symptoms was a good general predictor of the disease. However, the place of diagnosis and observation (home or clinic), age, and season affected the positive predictive values obtained. Specificities and positive predictive values were greatest (over 80%) for those at most risk--children under 9 years of age in highly endemic communities--and were most reliable when the diagnosis was made at home. Predictive values were also greatest during the season when childhood acute lower respiratory infections in the study area increase. The good predictability of clinical signs and symptoms for high-risk groups suggests that simple protocols can be developed for the management of malaria in endemic areas of the Philippines.

PIP: Over the past 30 years, the mountainous area of Kalinga Apayao Province on Luzon Island in the Philippines was extensively deforested due to slash and burn farming. The malaria risk is reduced, but malaria is still endemic. During 1990-1992, morbidity surveys identified 614 malaria cases. Researchers wanted to determine the accuracy, predictability, and reliability of clinical signs and symptoms for diagnosing malaria. Most individuals (89%) claimed to have had fever, yet just 35.4% had a body temperature greater than 37.6 degrees Celsius. Only 51.8% of fever cases had parasitemia, indicating that the World Health Organization's recommended case definition of malaria (i.e., presence or history of fever) did not adequately identify malaria. Further, prior to this study, about 50% of the area's children were usually infected, but just 11.3% of children younger than 6 in this study had fever. A good general predictor of malaria included a sequential occurrence of fever, chills and/or sweating, or a combination of all 3 symptoms. The positive predictive values were: at-home observation and diagnosis (74-76% vs. 69-72% at the rural health clinic), age younger than 9 years (80-84% vs. 65-69% for = or 10 year olds), and presentation during November-January (94-100% vs. 74% for February-October). November-January was the season when the prevalence of acute lower respiratory infections was highest. These results demonstrate that health workers can develop simple algorithms with good predictability of clinical signs and symptoms for high-risk groups to manage malaria in endemic areas of the Philippines.

Halofantrine in the treatment of acute uncomplicated falciparum malaria in the Philippines.

In an open clinical trial, thirty patients 14 to 44 years old and with acute uncomplicated falciparum malaria were given halofantrine hydrochloride 500 mg (2 tablets) 6-hourly for 3 doses, a total dose of 1500 mg. All 30 patients were cured, with a mean asexual parasite clearance time of 47.6 hours and mean fever clearance time of 36.6 hours. Post-dosing side-effects occurred in 6 patients consisting of mild to moderate headache, dizziness and abdominal muscle spasm. Drug-induced hemolysis did not occur in two G6PD deficient patients. Twenty-three out of 28 isolates tested (82%) were resistant to amodiaquine, 3 (11%) were resistant to the sulfadoxine-pyrimethamine combination, and all were sensitive to chloroquine, quinine and mefloquine by in vitro microtests. The study confirms the efficacy of halofantrine hydrochloride as a blood schizonticide in falciparum malaria.

Oral clindamycin in the treatment of acute uncomplicated falciparum malaria.

Clinical trials on oral clindamycin as an antimalarial in hospitalized patients and residents of endemic communities were conducted in the Philippines between May 1984 and December 1985. Seven and 9 qualified subjects in hospital were treated with 300 mg (regimen A) and 600 mg (regimen B) respectively, twice daily for 5 days. Eighteen patients seen at a rural health unit were given the lower dosage. On the basis of the 28-day extended in vivo test of WHO, P. falciparum in all but one patient showed susceptibility to the drug as a blood schizontocide hence, the clinical cure of malaria. Side effects were few and self-limiting. Ten other patients on regimen A were cured within the 7- and/or 28-day extended test period. Clindamycin per se is currently one of the few alternatives in the treatment of clinically moderate drug-resistant malaria.

Chemotherapy: principles in practice--a case study of the Philippines.

This paper reports on the principles that form the basis of chemotherapy and examines the operational considerations that affect their practice in a developing country like the Philippines, where malaria endemicity is synonymous with difficult topography, poor public health infrastructure, and alternative means of obtaining medication. The practice of using microscopic diagnosis for radical treatment is followed routinely and uniformly. Where policy dictates that all fever cases be screened, the result is an overload of the system and a corresponding delay in the slide-examination rate which makes such microscopic diagnosis cease to serve as a basis for prompt radical treatment and control in transmission.

Observation on biting midge infestations on Mamburao Beach, Mimdoro, Philippines.

The occurrence of biting midge infestation involving the species Leptoconops (Styloconops) spinosifrons Carter 1921 (Diptera, Ceratopogonidae) is reported from a beach resort in Mindoro Island, Philippines. The flies are most active between 0700 and 0900 hours, and again, between 1600 and 1800 hours; they are most abundant in the shoreline and sand beach area.