Plasmodium Vivax Malaria Transmission Research Articles

Surveillance of Plasmodium vivax transmission using serological models in the border areas of China\u2013Myanmar

BackgroundTo understand the Plasmodium vivax malaria transmission intensity and to assess the effectiveness of prevention and control measures taken along the China–Myanmar border, a catalytic model was used to calculate the seroconversion rate, an important indicator of malaria transmission intensity with high sensitivity, which is particularly useful in areas of low transmission.MethodsFive counties in Yunnan Province bordering Myanmar were selected as survey sites, and subjects were obtained in each county by stratified random sampling in 2013–2014. Fingerstick blood was collected from each subject and tested for antibodies to P. vivax Merozoite Surface Protein 1-19 (PvMSP1-19) using indirect ELISA. A catalytic conversion model was used to assess the transmission intensity of P. vivax malaria based on the maximum likelihood of generating a community seroconversion rate.ResultsA total of 3064 valid blood samples were collected. Antibody levels were positively correlated with age. The seroconversion rate (SCR) values for each village were Luoping (0.0054), Jingqiao (0.0061), Longpen (0.0087), Eluo (0.0079), Banwang (0.0042) and Banbie (0.0046), respectively.ConclusionOverall, the intensity of P. vivax malaria transmission in the border areas of Yunnan Province is low and not entirely consistent across counties. Consecutive serological surveys are needed to provide a sensitive evaluation of transmission dynamics and can help to confirm areas where infection is no longer present.

Malaria risk map for India based on climate, ecology and geographical modelling.

Mapping the malaria risk at various geographical levels is often undertaken considering climate suitability, infection rate and/or malaria vector distribution, while the ecological factors related to topography and vegetation cover are generally neglected. The present study abides a holistic approach to risk mapping by including topographic, climatic and vegetation components into the framework of malaria risk modelling. This work attempts to delineate the areas of Plasmodium falciparum and Plasmodium vivax malaria transmission risk in India using seven geo-ecological indicators: temperature, relative humidity, rainfall, forest cover, soil, slope, altitude and the normalized difference vegetation index using multi-criteria decision analysis based on geographical information system (GIS). The weight of the risk indicators was assigned by an analytical hierarchical process with the climate suitability (temperature and humidity) data generated using fuzzy logic. Model validation was done through both primary and secondary datasets. The spatio-ecological model was based on GIS to classify the country into five zones characterized by various levels of malaria transmission risk (very high; high; moderate; low; and very low. The study found that about 13% of the country is under very high malaria risk, which includes the malaria- endemic districts of the states of Chhattisgarh, Odisha, Jharkhand, Tripura, Assam, Meghalaya and Manipur. The study also showed that the transmission risk suitability for P. vivax is higher than that for P. falciparum in the Himalayan region. The field study corroborates the identified malaria risk zones and highlights that the low to moderate risk zones are outbreak-prone. It is expected that this information will help the National Vector Borne Disease Control Programme in India to undertake improved surveillance and conduct target based interventions.

Effects of climate change on Plasmodium vivax malaria transmission dynamics: A mathematical modeling approach

Malaria is a major public health concern and an economic burden around the world. Currently, malaria has been declared as endemic in 91 countries. Every year more than 200 million cases of malaria are reported and more than US$2 billion has been invested in malaria control. Recent climate change caused by global warming has affected the pattern of malaria outbreak and expanded the endemic regions. In this study, we develop a malaria transmission model associated with climate-dependent parameters. We analyze the impact of climate change on malaria transmission using climate data based on Representative Concentration Pathways (RCP) scenarios. We investigate the potential risk of malaria outbreaks through the computation of seasonal reproduction number and vectorial capacity under RCP scenarios and perform a sensitivity analysis of the model parameters. Our region of focus is the northern part of South Korea where Plasmodium vivax malaria is currently endemic. Our results show that climate change will increase the risk of massive malaria outbreaks in the area. Furthermore, based on the actual incidence data, we estimate the parameter values that reflect the level of controls implemented recently in Korea. We found that the current level of controls is not sufficient to mitigate the effect of climate change on malaria outbreaks and a combination of stronger control measures such as at least a 10% increase of control for humans combined with a 5% increase of control for adult mosquitoes should be implemented to reduce the risk of malaria outbreaks.

Imported malaria in northern Italy: epidemiology and clinical features observed over 18 years in the Teaching Hospital of Brescia.

Even though malaria incidence is decreasing worldwide, travel-related cases reported in Europe have remained stable in recent years. In Italy, incidence had increased in the 1990s, reaching a peak in 1999; a slow decline was then reported over the subsequent decade. To our knowledge, few published data are available on imported malaria in Italy since 2010. In this article we aimed to analyse trends in imported malaria in the teaching hospital of Brescia, northern Italy, over the last 18 years. All malaria cases diagnosed from 1999 to 2016 in Spedali Civili Hospital, Brescia, were retrospectively identified. Demographic, clinical and travel-related data were described. A total of 1200 cases of imported malaria were diagnosed in Brescia during the study period. Among them, 225 were children. A trend of increasing paediatric cases was identified over the study period, while cases in adults were stable. Most cases were diagnosed between August and October. Patients were most likely exposed in sub-Saharan Africa (87.2%). The main reported travel reason was travelling to visit friends and relatives (66.0%). A significantly higher risk of severe malaria was observed in non-immune patients and children visiting friend and relatives (P < 0.001 and P = 0.006, respectively). Our study reveals a relatively stable incidence in imported malaria cases with a peak during the summertime. A large and increasing paediatric burden of disease was identified. Imported malaria requires attention since in Italy a potential reappearance of autochthonous Plasmodium vivax malaria transmission cannot be excluded. Preventive action and physician awareness should be especially directed to children visiting friends and relatives in endemic countries and to non-immune patients since they both represent high-risk groups for severe malaria.

Health systems readiness and management of febrile outpatients under low malaria transmission in Vanuatu.

BackgroundVanuatu, an archipelago country in Western Pacific harbouring low Plasmodium falciparum and Plasmodium vivax malaria transmission, has been implementing a malaria case management policy, recommending parasitological testing of patients with fever and anti-malarial treatment for test-positive only patients. A health facility survey to evaluate the health systems readiness to implement the policy and the quality of outpatient management for patients with fever was undertaken.MethodsA cross-sectional, cluster sample survey, using a range of quality-of-care methods, included all health centres and hospitals in Vanuatu. The main outcome measures were coverage of health facilities and health workers with commodities and support interventions, adherence to test and treatment recommendations, and factors influencing malaria testing.ResultsThe survey was undertaken in 2014 during the low malaria season and included 41 health facilities, 67 health workers and 226 outpatient consultations for patients with fever. All facilities had capacity for parasitological diagnosis, 95.1 % stocked artemether-lumefantrine and 63.6 % primaquine. The coverage of health workers with support interventions ranged from 50 to 70 %. Health workers’ knowledge was high only regarding treatment policy for uncomplicated P. falciparum malaria (83.4 %). History taking and clinical examination practices were sub-optimal. Some 35.0 % (95 % CI 23.4–48.6) of patients with fever were tested for malaria, of which all results were negative and only one patient received anti-malarial treatment. Testing was significantly higher for patients age 5 years and older (OR = 2.33; 95 % CI 1.48–5.02), seen by less qualified health workers (OR = 2.73; 95 % CI 1.48–5.02), health workers who received malaria case management training (OR = 2.39; 95 % CI 1.28–4.47) and patients with increased temperature (OR = 2.56; 95 % CI 1.17–5.57), main complaint of fever (OR = 5.82; 95 % CI 1.26–26.87) and without runny nose (OR = 3.75; 95 % CI 1.36–10.34). Antibiotic use was very high (77.4 %) with sub-optimal dispensing and counselling practices.ConclusionsHealth facility and health worker readiness to implement policy is higher for falciparum than vivax malaria. Clinical and malaria testing practices are sub-optimal, however adherence to test negative results is nearly universal. Use of antibiotics is irrational. Quantitative and qualitative improvements of ongoing interventions are needed to re-inforce clinical practices in this area characterized by difficult access, human resource shortages but aspiring towards malaria elimination.

Quantifying effect of geographic location on epidemiology of Plasmodium vivax malaria.

Recent autochthonous transmission of Plasmodium vivax malaria in previously malaria-free temperate regions has generated renewed interest in the epidemiology of this disease. Accurate estimates of the incubation period and time to relapse are required for effective malaria surveillance; however, this information is currently lacking. By using historical data from experimental human infections with diverse P. vivax strains, survival analysis models were used to obtain quantitative estimates of the incubation period and time to first relapse for P. vivax malaria in broad geographic regions. Results show that Eurasian strains from temperate regions have longer incubation periods, and Western Hemisphere strains from tropical and temperate regions have longer times to relapse compared with Eastern Hemisphere strains. The diversity in these estimates of key epidemiologic parameters for P. vivax supports the need for elucidating local epidemiology to inform clinical follow-up and to build an evidence base toward global elimination of malaria.

Optimal Control Strategy of Plasmodium vivax Malaria Transmission in Korea

ObjectiveTo investigate the optimal control strategy for Plasmodium vivax malaria transmission in Korea. MethodsA Plasmodium vivax malaria transmission model with optimal control terms using a deterministic system of differential equations is presented, and analyzed mathematically and numerically. ResultsIf the cost of reducing the reproduction rate of the mosquito population is more than that of prevention measures to minimize mosquito-human contacts, the control of mosquito-human contacts needs to be taken for a longer time, comparing the other situations. More knowledge about the actual effectiveness and costs of control intervention measures would give more realistic control strategies. ConclusionMathematical model and numerical simulations suggest that the use of mosquito-reduction strategies is more effective than personal protection in some cases but not always.

Estimated effect of climatic variables on the transmission of Plasmodium vivax malaria in the Republic of Korea.

Background: Climate change may affect Plasmodium vivax malaria transmission in a wide region including both subtropical and temperate areas.Objectives: We aimed to estimate the effects of climatic variables on the transmission of P. vivax in temperate regions.Methods: We estimated the effects of climatic factors on P. vivax malaria transmission using data on weekly numbers of malaria cases for the years 2001–2009 in the Republic of Korea. Generalized linear Poisson models and distributed lag nonlinear models (DLNM) were adopted to estimate the effects of temperature, relative humidity, temperature fluctuation, duration of sunshine, and rainfall on malaria transmission while adjusting for seasonal variation, between-year variation, and other climatic factors.Results: A 1°C increase in temperature was associated with a 17.7% [95% confidence interval (CI): 16.9, 18.6%] increase in malaria incidence after a 3-week lag, a 10% rise in relative humidity was associated with 40.7% (95% CI: –44.3, –36.9%) decrease in malaria after a 7-week lag, a 1°C increase in the diurnal temperature range was associated with a 24.1% (95% CI: –26.7, –21.4%) decrease in malaria after a 7-week lag, and a 10-hr increase in sunshine per week was associated with a 5.1% (95% CI: –8.4, –1.7%) decrease in malaria after a 2-week lag. The cumulative relative risk for a 10-mm increase in rainfall (≤ 350 mm) on P. vivax malaria was 3.61 (95% CI: 1.69, 7.72) based on a DLNM with a 10-week maximum lag.Conclusions: Our findings suggest that malaria transmission in temperate areas is highly dependent on climate factors. In addition, lagged estimates of the effect of rainfall on malaria are consistent with the time necessary for mosquito development and P. vivax incubation.

Characterization of Plasmodium vivax malaria transmission at the border of Panamá and Costa Rica

Few studies have described the factors associated with Plasmodium vivax transmission dynamics in endemic regions from Panamá. Malaria transmission dynamics produced by P. vivax were characterized at the border between Panamá and Costa Rica. In the municipality of Barú, an observational, descriptive and cross-sectional study was undertaken to measure the annual parasite index (API), slide positivity index (SPR), and the annual blood examination rate (ABER). The most frequent symptoms and signs in malaria patients were recorded. The anopheline species were identified in the area and the preferred larval habitats, the density of larval populations in the larval habitats and the bites/human/night were characterized. Of a total of 10,401 thick smear blood samples, 83 were positive for P. vivax. Of these, 84% came from rural areas and 79% were from economically active individuals. The median and average ages were 36 and 30 years, respectively, and 58.5% of the malaria cases were male. API was 4.1/1,000 inhabitants; SPR was 0.8% and ABER was 51.9%. Of the diagnosed cases, 54% showed blood parasitemias ranging between 100-2,000 parasites/μl. The majority of the cases were observed in May and June. Two mosquito vector species were identified-- Anopheles albimanus and An. punctimacula. These observations indicate the advisibility of continued entomological studies, strengthening of epidemiological surveillance, consideration of additional risk factors and evaluation of work performance in the border region. This will require coordination with health authorities of both countries to control malaria in this region.

The abundance and host-seeking behavior of culicine species (Diptera: Culicidae) and Anopheles sinensis in Yongcheng city, people's Republic of China

BackgroundThe knowledge of mosquito species diversity and the level of anthropophily exhibited by each species in a region are of great importance to the integrated vector control. Culicine species are the primary vectors of Japanese encephalitis (JE) virus and filariasis in China. Anopheles sinensis plays a major role in the maintenance of Plasmodium vivax malaria transmission in China. The goal of this study was to compare the abundance and host-seeking behavior of culicine species and An. sinensis in Yongcheng city, a representative region of P. vivax malaria. Specifically, we wished to determine the relative attractiveness of different animal baits versus human bait to culicine species and An. sinensis.ResultsCulex tritaeniorhynchus was the most prevalent mosquito species and An. sinensis was the sole potential vector of P. vivax malaria in Yongcheng city. There were significant differences (P < 0.01) in the abundance of both An. sinensis and Cx. tritaeniorhynchus collected in distinct baited traps. The relative attractiveness of animal versus human bait was similar towards both An. sinensis and Cx. tritaeniorhynchus. The ranking derived from the mean number of mosquitoes per bait indicated that pigs, goats and calves frequently attracted more mosquitoes than the other hosts tested (dogs, humans, and chickens). These trends were similar across all capture nights at three distinct villages. The human blood index (HBI) of female An. sinensis was 2.94% when computed with mixed meals while 3.70% computed with only the single meal. 19:00~21:00 was the primary peak of host-seeking female An. sinensis while 4:00~5:00 was the smaller peak at night. There was significant correlation between the density of female An. sinensis and the average relative humidity (P < 0.05) in Wangshanzhuang village.ConclusionsPigs, goats and calves were more attractive to An. sinensis and Cx. tritaeniorhynchus than dogs, humans, and chickens. Female An. sinensis host-seeking activity mainly occurred from 19:00 to 21:00. Thus, we propose that future vector control against An. sinensis and Cx. tritaeniorhynchus in the areas along the Huang-Huai River of central China should target the interface of human activity with domestic animals and adopt before human hosts go to bed at night.

Expression Profile of Prophenoloxidase-Encoding (&lt;I&gt;acppo6&lt;/I&gt;) Gene of Plasmodium vivax-Refractory Strain of Anopheles culicifacies

Anopheles culicifacies is the main vector for transmission of Plasmodium vivax malaria in the Indian subcontinent. A strain of An. culicifacies isolated from its natural niche displayed complete refractoriness to P. vivax by melanotic encapsulation of ookinetes. Prophenoloxidases are key components of the phenoloxidase cascade that leads to recognition and melanization of invading organisms. We isolated and cloned prophenoloxidase-encoding acppo6 gene of An. culicifacies and analyzed its expression profile under various regimens of immune challenge. The acppo6 was differentially expressed during various stages of larval development. The acppo6 transcription was also up-regulated in response to bacteria and Plasmodium vinckei petteri challenge. The transcript levels of the acppo6 gene were higher in naive adult refractory female mosquitoes as compared with female susceptible mosquitoes. Furthermore, the induction of acppo6 in the susceptible strain upon Plasmodium infection was negligible as compared with that of the refractory strain. The observation is suggestive of the role of acppo6 in effectuating a melanotic response in Plasmodium-incompetent naturally occurring refractory An. culicifacies strain.

Mapping and predicting malaria transmission in the People’s Republic of China, using integrated biology-driven and statistical models

The purpose of this study was to deepen our understanding of Plasmodium vivax malaria transmission patterns in the People's Republic of China (P.R. China). An integrated modeling approach was employed, combining biological and statistical models. A Delphi approach was used to determine environmental factors that govern malaria transmission. Key factors identified (i.e. temperature, rainfall and relative humidity) were utilized for subsequent mapping and modeling purposes. Yearly growing degree days, annual rainfall and effective yearly relative humidity were extracted from a 15-year time series (1981-1995) of daily environmental data readily available for 676 locations in P.R. China. A suite of eight multinomial regression models, ranging from the null model to a fully saturated one were constructed. Two different information criteria were used for model ranking, namely the corrected Akaike's information criterion and the Bayesian information criterion. Mapping was based on model output data, facilitated by using ArcGIS software. Temperature was found to be the most important environmental factor, followed by rainfall and relative humidity in the Delphi evaluation. However, relative humidity was found to be more important than rainfall and temperature in the ranking list according to the three single environmental factor regression models. We conclude that the distribution of the mosquito vector is mainly related to relative humidity, which thus determines the extent of malaria transmission. However, in regions with relative humidity >60%, temperature is the major driver of malaria transmission intensity. By integrating biology-driven models with statistical regression models, reliable risk maps indicating the distribution of transmission and the intensity can be produced. In a next step, we propose to integrate social and health systems factors into our modeling approach, which should provide a platform for rigorous surveillance and monitoring progress towards P. vivax malaria elimination in P.R. China.

The dilution effect of the domestic animal population on the transmission of P. vivax malaria

The diversion of disease carrying insect from humans to animals may reduce transmission of diseases such as malaria. The use of animals to mitigate mosquito bites on human is called ‘zooprophylaxis’. We introduce a mathematical model for Plasmodium vivax malaria transmission with two bloodmeal hosts (humans and domestic animals) to study the effect of zooprophylaxis. After computing the basic reproduction number from the proposed model, we explore how perturbations in the parameters, sensitive to the effects of control measures, affect its value. Zooprophylaxis is shown to determine whether a basic reproduction becomes bigger than an outbreak threshold value or not. Sensitivity analysis shows that increasing the relative animal population size works better in P. vivax malaria control than decreasing the mosquito population when the relative animal population size is larger than a threshold value.

A mathematical model for the transmission of Plasmodium vivax malaria

We have proposed a mathematical model for the transmission of Plasmodium vivax malaria quantitatively, which is adjusted to the infected region, Guadalcanal, in the Solomon Islands. The simulation of a transmission model will be instrumental in planning the malaria control strategy. A characteristic of the life cycle of P. vivax is that a sporozoite injected into the blood stream by a mosquito bite may sometimes stay in a hepatocyte as a hypnozoite. Therefore, we have incorporated a phenomenon of renewed infections caused by a relapse into the transmission model. Also through the simulations we have attempted to evaluate the decline in prevalence caused by the programs of selective mass drug administration (MDA) and vector control such as the distribution of permethrin-treated bednets. The simulations have indicated that the concentrated repetition of MDA at 1-week intervals would reduce the prevalence of vivax malaria swiftly in the beginning and would keep the parasite rate below 1% for a few years but the prevalence would increase thereafter. In contrast, the parasite rate would remain below 1% for a long time if a trial of 1 or 2 times MDA is accompanied with some reduction of the vectorial capacity by the enforcement of vector control. In any case, it is important to beware of relapse cases because even after the execution of MDA it takes a long time to decrease the proportion of hypnozoite carriers.

From the Centers for Disease Control and Prevention. Local transmission of Plasmodium vivax malaria--Houston, Texas, 1994

From the Centers for Disease Control and Prevention. Local transmission of Plasmodium vivax malaria--Houston, Texas, 1994

Local Transmission of Plasmodium vivax Malaria—Houston, Texas, 1994

Malaria was endemic in the United States until the late 1940s; since then, most cases of malaria reported in the United States has been acquired during international travel or has occurred in persons who had resided in countries where malaria is endemic. This report summarizes the investigation of three persons who acquired Plasmodium vivax infection in Houston, Texas, by presumed mosquitoborne transmission during 1994.

Transmission of Plasmodium vivax Malaria — San Diego County, California, 1988 and 1989

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Transmission of Plasmodium Vivax Malaria in San Diego County, California, 1986

Between 18 June and 20 September 1986, 28 cases of Plasmodium vivax malaria were documented in Carlsbad, California, a coastal town north of San Diego. Malaria occurred in 1 local resident who had no risk factors, a second local resident who had traveled to a malarious area 9 months earlier, and 26 Mexican migrant workers (MWs). Among the 28 cases, 27 lived in a square mile marshy area where Anopheles hermsi, a newly described American species of the Anopheles maculipennis group, was known to be breeding. An investigation of MWs residing in the affected area was done to determine the extent of the outbreak and to identify risk factors for acquiring malaria. We interviewed and drew blood from 304 healthy MWs and 17 (65%) of the MWs with malaria. Fluorescent antibody titers to P. vivax greater than or equal to 1:256 occurred in 14 (82%) of the 17 MWs with malaria tested and 9 (3%) of the healthy MWs. The principal risk factor identified for contracting malaria was sleeping outside on a hillside adjacent to the marshy area. Malaria in a local resident with no malaria risk factors and the clustering in time and place of 26 cases suggest that P. vivax malaria was introduced and local transmission was sustained through several generations, producing the largest outbreak of introduced malaria in the United States since 1952.

INDUCED MALARIA OF FOREIGN ORIGIN

IT IS the purpose of this report to describe certain features of induced malaria as observed in the treatment of 243 patients with neurosyphilis. The establishment by the Surgeon General of a center for the treatment of neurosyphilis in a hospital to which numerous patients with naturally acquired malaria had been admitted from overseas provided a unique opportunity to study the transmission of Plasmodium vivax malaria under controlled conditions. It also afforded a means of observing the untreated primary malarial attack with respect to symptoms, complications, course, response to antimalarial therapy and rate of relapse. MATERIAL AND METHODS The 243 patients included in this study were suffering from asymptomatic (77 per cent) or symptomatic (23 per cent) neurosyphilis. One hundred and seventy-five of these patients were white and comprised the chief group for study. The remaining 68 patients were Negroes; 45 of these were given quartan malaria, and an effort