Malaria in the Pare area of Tanzania. V. Malaria 20 years after the end of residual insecticide spraying

A malariometric survey, including serology, was done in the South Pare area of the former Pare-Taveta Malaria Scheme, Tanzania, 10 years after the previous survey and 20 years after the end of residual insecticide spraying. Although the densities of the vectors and their infectivity rates have for 10 years equalled those found before malaria control, malaria in the human population is still significantly less. The chief factor in this delayed resurgence is thought to be the increasing use of antimalaria drugs by the population.     

Malaria in Kenya's western highlands

Records from tea estates in the Kericho district in Kenya show that malaria reemerged in the 1980s. Renewed epidemic activity coincided with the emergence of chloroquine-resistant Plasmodium falciparum malaria and may have been triggered by the failure of antimalarial drugs. Meteorologic changes, population movements, degradation of health services, and changes in Anopheles vector populations are possible contributing factors. The highland malaria epidemics of the 1940s were stopped largely by sporontocidal drugs, and combination chemotherapy has recently limited transmission. Antimalarial drugs can limit the pool of gametocytes available to infect mosquitoes during the brief transmission season.     

Malaria transmission after five years of vector control on Bioko Island,Equatorial Guinea

Background

Cytoplasmic incompatibility (CI) is induced in nature by Wolbachia bacteria, resulting in conditional male sterility. Previous research demonstrated that the two Wolbachia strains (w AlbA and w AlbB) that naturally co-infect the disease vector mosquito Aedes albopictus (Asian tiger mosquito) can be replaced with the w Pip Wolbachia strain from Culex pipiens. Since Wolbachia-based vector control strategies depend upon the strength and consistency of CI, a greater understanding is needed on the CI relationships between w Pip, w AlbA and w AlbB Wolbachia in Ae. albopictus.

Methods

This work consisted of a collaborative series of crosses carried out in Italy and in US to study the CI relationships between the “w Pip” infected Ae. albopictus strain (ARw P) and the superinfected SR strain. The Ae. albopictus strains used in Italian tests are the w Pip infected ARw P strain (ARw P_IT), the superinfected SR strain and the aposymbiotic AR strain. To understand the observed pattern of CI, crossing experiments carried out in USA focused on the study of the CI relationships between ARw P (ARw P_US) and artificially-generated single infected lines, in specific HTA and HTB, harbouring only w AlbA and w AlbB Wolbachia respectively.

Results

The paper reports an unusual pattern of CI observed in crossing experiments between ARw P and SR lines. Specifically, ARw P males are able to induce full sterility in wild type females throughout most of their lifetime, while crosses between SR males and ARw P females become partially fertile with male aging. We demonstrated that the observed decrease in CI penetrance with SR male age, is related to the previously described decrease in Wolbachia density, in particular of the w AlbA strain, occurring in aged superinfected males.

Conclusions

The results here reported support the use of the ARw P Ae. albopictus line as source of “ready-made sterile males”, as an alternative to gamma radiation sterilized males, for autocidal suppression strategies against the Asian tiger mosquito. In addition, the age dependent CI weakening observed in the crosses between SR males and ARw P females simplifies the downstream efforts to preserve the genetic variability within the laboratory ARw P colonies, to date based on the antibiotic treatment of wild captured superinfected mosquitoes, also reducing the costs.

     

Effect of indoor residual spraying of DDT and bendiocarb on the feeding patterns of Anopheles pseudopunctipennis in Mexico

Intense and persistent use of DDT for malaria control has increased resistance and induced exophilic behavior of Anopheles pseudopunctipennis. An evaluation of bendiocarb and DDT to control this species in Sinaloa, Mexico, showed that, in spite of DDT-resistance, both insecticides produced similar effects. Feeding patterns were analyzed to explain these results. Resting mosquitoes were collected over the dry and wet seasons. Anophelines were tested in an ELISA to determine the source of the meals. The human blood index (HBI) ranged from 3.3 to 6.8% in DDT- and from 12.7 to 26.9% in bendiocarb-sprayed houses. Irritability and repellency in DDT-sprayed houses could explain the reduced HBI. In contrast, bendiocarb produced higher mortality. These effects could have affected different components of the vectorial capacity and similarly reduced malaria.     

Malaria in highlands of Ecuador since 1900

A recent epidemic of malaria in the highlands of Bolivia and establishment of multiple Anopheles species mosquitoes in the highlands of Ecuador highlights the reemergence of malaria in the Andes Mountains in South America. Because malaria was endemic to many highland valleys at the beginning of the 20th century, this review outlines the 20th century history of malaria in the highlands of Ecuador, and focuses on its incidence (e.g., geographic distribution) and elimination from the northern highland valleys of Pichincha and Imbabura and the role of the Guayaquil to Quito railway in creating highland larval habitat and inadvertently promoting transportation of the vector and parasite. Involvement of control organizations in combating malaria in Ecuador is also outlined in a historical context.     

Impact of DDT indoor residual spraying on Phlebotomus argentipes in a kala-azar endemic village in eastern Uttar Pradesh.

Data on the operational efficacy of DDT indoor residual spraying against Phlebotomus argentipes, the vector of kala-azar in India, are scarce. We therefore undertook a study of the impact on kala-azar and its vector of DDT indoor residual spraying in the Varanasi district of eastern Uttar Pradesh. Preliminary results indicate that after two rounds of DDT spraying in one village no P. argentipes were found during the peak vector season; in contrast, a large number of these sandfies were collected in the unsprayed comparison village.     

Assessment of nonoccupational exposure to DDT in the tropics and the north: relevance of uptake via inhalation from indoor residual spraying

Background

People who live in dwellings treated with indoor residual spraying (IRS) of DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane] for disease–vector control in the tropics and indigenous populations in the Arctic who comsume marine mammals experience high nonoccupational exposure to DDT. Although the use of DDT in IRS is rising, the resulting nonoccupational exposure is poorly characterized.

Objectives

We have provided a comparative assessment of exposure to DDT and its metabolites in the general population of the tropical and northern regions and in highly exposed populations in these regions.

Methods

We compiled > 600 average or median DDT concentrations from the peer-reviewed literature, representing > 23,000 individual measurements in humans, food, air, soil, and dust. We use Monte Carlo sampling of distributions based on these data to estimate distributions of population- and route-specific uptake. We evaluate our exposure estimates by comparing them with biomonitoring data.

Results

DDT concentrations are highest in people living in IRS-treated houses and lowest in the northern general population, differing by a factor of about 60. Inuits and the general population in the tropics have similar concentrations. Inhalation exposure explains most of the difference in concentration between the highly exposed and the general population in the Tropics. Calculated exposure levels are consistent with human biomonitoring data.

Conclusions

Nonoccupational inhalation exposure is a relevant exposure pathway for people living in homes treated by IRS of DDT. Continued monitoring of time trends and DDE to DDT ratios in the Tropics and in the North is needed to identify a possible slowdown in concentration decline and the influence of ongoing DDT use.     

Residues of DDT in a Norwegian fruitgrowing district two and four years after the termination of DDT usage

This study describes the extent of DDT contamination in a typical fruit growing district in Norway two and four years after the DDT ban. Residues of DDT in man, dairy cows and soil were about five to one hundred times higher than in the control groups, while residues found in samples from the marine biota were the same or moderately higher (Figure 3). The residues of DDT in cows, gulls and parts of the marine samples showed a significant decrease from 1972 to 1974, while the level in soil was almost constant. The amount of DDE had increased considerably in 1974 for all the species except for the gull, although not to the same degree. The distribution of DDE, DDD and DDT in soil were almost constant during the two years of sampling.     

Measurement of insecticides for house spraying

In view of the economic and operational importance in malaria eradication campaigns of correctly measuring the insecticides used, tests have been made in Mexico to compare the accuracy of two manual procedures, one volumetric and the other gravimetric. For volumetric measurement a calibrated, metal measuring-can of sheet metal is used, and for gravimetric measurement a specially designed Roman balance. Altogether 1022 volumetric and 1411 gravimetric tests were made. The results, given in this paper, show that the volumetric measurement entails too great a margin of error to be acceptable, but that the Roman balance is both sufficiently accurate and practical and economical.     

Malaria in the African highlands: past, present and future.

Many of the first European settlers in Africa sought refuge from the heat and diseases of the plains by moving to the cool and salubrious highlands. Although many of the highlands were originally malaria free, there has been a progressive rise in the incidence of the disease over the last 50 years, largely as a consequence of agroforestry development, and it has been exacerbated by scarce health resources. In these areas of fringe transmission where the malaria pattern is unstable, epidemics may be precipitated by relatively subtle climatic changes. Since there is little immunity against the disease in these communities, outbreaks can be devastating, resulting in a substantial increase in morbidity and death among both children and adults. We present here the results obtained using a mathematical model designed to identify these epidemic-prone regions in the African highlands and the differences expected to occur as a result of projected global climate change. These highlands should be recognized as an area of special concern. We further recommend that a regional modelling approach should be adopted to assess the extent and severity of this problem and help improve disease surveillance and the quality of health care delivered in this unstable ecosystem.     

Malaria in the southern highlands of Tanzania: a review of hospital records

Outpatient attendance and inpatient admission records were examined to assess malaria situation in ten hospitals in Mbeya and Iringa Regions in southern highlands of Tanzania for a period of fifteen years from 1986-2000. Generally, records were deficient, some hospitals with entire annual records missing for one or several years. However, malaria maintained a high profile as the leading cause of admissions and deaths among hospital attendees. Of the ten hospitals, seven recorded malaria as the leading cause of admissions for at least ten years; in three of these, it was also the top ranking cause of child death. Although the respective magnitude of malaria morbidity and mortality burdens was not directly correlated with altitude (P>0.5), three hospitals (Uwemba, Bulongwa and Ikonda) at above 2,000m, had relatively lower malaria morbidity and mortality burden compared to three worst affected facilities (Ilembula, Chimala and Mbozi) in the lower range of altitude, located in the flat plains. In conclusion, malaria is the major public health problem in the highlands districts of Mbeya and Iringa Regions in Tanzania that need the attention of health authorities and immediate intervention. However, more research is required to establish the true picture of the problem among the communities.     

Ineffectiveness of DDT residual spraying in stopping malaria transmission in the Jordan Valley

The malaria-control campaign in the Jordan Valley-undertaken by the United Nations Relief and Works Agency for Palestine Refugees in the Near East in 1949-has been based solely on DDT residual spraying in the northeastern areas, but in certain southern districts some larvicidal and drainage work has been done.Observations made in the north-east showed that active malaria transmission had occurred in 4 of the 12 villages surveyed in 1951, and in 8 of the 9 villages surveyed in 1952. That the insecticide was effective was demonstrated by the fact that sprayed structures were almost entirely free from anophelines four months after the last spraying, but entomological surveys showed that Anopheles sergenti and A. superpictus (the main malaria vectors) were successfully evading contact with sprayed surfaces by using caves and fissures in hills as daytime resting-places.The author discusses the bearing that the topography of the area and the habits of the population have on the transmission of the disease, and stresses the importance of surveys. He recommends the resumption of antilarval measures in the Jordan Valley.     

Morbidity of schistosomiasis mansoni in the highlands of Madagascar and comparison of current sonographical classification systems

To study the morbidity of schistosomiasis mansoni in the highlands of Madagascar, a cross-sectional study examined the extent to which liver fibrosis occurred in a rural community. The Managil and the Cairo classification systems were used. A second purpose was to investigate the effect of the measurements of 2 different branches of the portal vein (either segmental or sub-segmental branches) on the resulting staging of morbidity using the Cairo classification system. In a rice farmer village, 656 inhabitants (95% of the total population) were parasitologically examined; 561 patients underwent sonographic work-up based on the Managil scoring system, and in 307 randomized patients the outer to outer diameters of both the segmental and the sub-segmental branches of the portal vein were measured and scored by the Cairo classification system. Overall prevalence of schistosomiasis mansoni in the study area in 1994 was 68.3%. Upon sonographic examination and scoring by the Managil system 23.4% of the population showed liver changes (Managil degree I/II/III, 20%/2.5%/0.9%). Measuring the sub-segmental branches only and scoring by the Cairo classification, 19% of the study population were found to have liver changes, none with severe fibrosis. By contrast, 82% were found to have liver changes (Cairo degree 1/2/3, 70%/11%/2%) when the segmental branches were measured. The diameters of the sub-segmental branches were about two-thirds of those of the segmental branches. Both the Cairo- and the Managil-examination protocols have pitfalls. Using the Cairo classification, a considerable systematic error in classifying morbidity is created by measuring different branches of the portal vein.     

Smoking among Macedonian workers five years after the anti-smoking campaign

To assess the efficacy of nationwide anti-smoking campaign, we compared the findings of a study on worker smoking performed in 2005 with our latest cross-sectional study completed in 2010. It included 753 randomly selected workers, of whom 126 office, 108 construction, 93 agricultural, 97 petroleum refinery, 114 textile, 117 food processing workers, and 98 cleaners. Information was collected with a self-administered questionnaire. The prevalence of current smokers among all workers was 35.4 %, ranging from 30.2 % in office workers to 43.5 % in construction workers. It did not significantly differ from the prevalence recorded in 2005 (35.4 % vs. 36.8 %, respectively; P=0.441). Mean pack-years smoked among all smokers was 12.4 ± 2.3, ranging from 10.9 in administrative workers to 13.7 in agricultural workers. We did not find any significant difference in the prevalence of current smokers between male and female workers and between workers aged less or more than 40 years, as well as between workers of higher and lower education. The prevalence of ex-smokers was 10.5 %, ranging from 8.4 % in construction workers to 12.1 % in administrative workers, whereas the prevalence of passive smokers was 29.1 %, ranging from 26.2 % in food processing workers to 32.9 % in agricultural workers. Our findings indicate that the prevalence of current and passive smokers has remained high regardless of the anti-smoking campaign and call for stricter implementation of anti-smoking regulations.