Hitting a Moving Target: A Model for Malaria Elimination in the Presence of Population Movement

South Africa is committed to eliminating malaria with a goal of zero local transmission by 2018. Malaria elimination strategies may be unsuccessful if they focus only on vector biology, and ignore the mobility patterns of humans, particularly where the majority of infections are imported. In the first study in Mpumalanga Province in South Africa designed for this purpose, a metapopulation model is developed to assess the impact of their proposed elimination-focused policy interventions. A stochastic, non-linear, ordinary-differential equation model is fitted to malaria data from Mpumalanga and neighbouring Maputo Province in Mozambique. Further scaling-up of vector control is predicted to lead to a minimal reduction in local infections, while mass drug administration and focal screening and treatment at the Mpumalanga-Maputo border are predicted to have only a short-lived impact. Source reduction in Maputo Province is predicted to generate large reductions in local infections through stemming imported infections. The mathematical model predicts malaria elimination to be possible only when imported infections are treated before entry or eliminated at the source suggesting that a regionally focused strategy appears needed, for achieving malaria elimination in Mpumalanga and South Africa.     

Clinical Malaria Transmission Trends and Its Association with Climatic Variables in Tubu Village,Botswana: A Retrospective Analysis

Good knowledge on the interactions between climatic variables and malaria can be very useful for predicting outbreaks and preparedness interventions. We investigated clinical malaria transmission patterns and its temporal relationship with climatic variables in Tubu village, Botswana. A 5-year retrospective time series data analysis was conducted to determine the transmission patterns of clinical malaria cases at Tubu Health Post and its relationship with rainfall, flood discharge, flood extent, mean minimum, maximum and average temperatures. Data was obtained from clinical records and respective institutions for the period July 2005 to June 2010, presented graphically and analysed using the Univariate ANOVA and Pearson cross-correlation coefficient tests. Peak malaria season occurred between October and May with the highest cumulative incidence of clinical malaria cases being recorded in February. Most of the cases were individuals aged >5 years. Associations between the incidence of clinical malaria cases and several factors were strong at lag periods of 1 month; rainfall (r = 0.417), mean minimum temperature (r = 0.537), mean average temperature (r = 0.493); and at lag period of 6 months for flood extent (r = 0.467) and zero month for flood discharge (r = 0.497). The effect of mean maximum temperature was strongest at 2-month lag period (r = 0.328). Although malaria transmission patterns varied from year to year the trends were similar to those observed in sub-Saharan Africa. Age group >5 years experienced the greatest burden of clinical malaria probably due to the effects of the national malaria elimination programme. Rainfall, flood discharge and extent, mean minimum and mean average temperatures showed some correlation with the incidence of clinical malaria cases.     

2012—2019年上海市某三甲医院境外输入性传染病病例特征分析

本研究分析近年来上海市境外输入性传染病的病例特点,为上海市输入性传染病的防控提供依据。对上海市某三甲医院2012—2019年报告的所有法定及重点监测传染病中确定为境外感染的305例传染病病例进行回顾性分析。采用WPS Office 2019和 SPSS17.0软件对所收集病例的病种、数量、输入时间、病例人口学特征以及输入地区等进行整理分析。结果显示,2012—2019年该院报告境外输入性传染病11种,分别为疟疾、登革热、肺结核、麻疹、甲型肝炎、戊型肝炎、伤寒、人类免疫缺陷病毒(human immunodeficiency virus,HIV)感染、黄热病、白喉、隐性梅毒。确诊的305例病例中,疟疾226例,占74.10%;登革热68例,占22.30%;其他9种疾病共11例,占3.6%。疟疾、登革热全年均有输入,其中6月、9月和11月为疟疾输入高峰,6～8月为登革热输入高峰,肺结核、麻疹、甲型肝炎、戊型肝炎、伤寒、HIV感染、黄热病、白喉、隐性梅毒无明显季节性分布特征。输入性病例中,中国籍多于外籍,男性多于女性,以青壮年为主;主要职业为商业服务和工人;主要输入地为非洲。本研究结果提示境外输入性传染病以疟疾、登革热等虫媒传染病为主,病种呈现多样化的变化趋势,输入高峰主要在夏秋季。应加强非洲、东南亚劳务和旅游人群的健康教育,做好病例监管和防蚊、灭蚊,减少二代病例。     

Molecular surveillance and temporal monitoring of malaria parasites in focal Vietnamese provinces

In the past decade substantial reduction in malaria morbidity and mortality has been observed through well-implemented case management and vector control strategies. India has also achieved a significant reduction in malaria burden in 2018 and has committed to eliminate malaria by 2030. The Mandla Malaria Elimination Demonstration Project (MEDP) was started in 2017 in 1233 villages of District Mandla to demonstrate malaria elimination in a tribal district with hard-to-reach areas was possible using active and passive surveillance, case management, vector control, and targeted information, education and communication campaigns. An operational plan was developed to strengthen the existing surveillance and malaria elimination systems, through fortnightly active case detection to ensure that all cases including those that are introduced into the communities are rapidly identified and treated promptly. The plan also focused on the reduction of human-mosquito contact through the use of Long-Lasting Insecticial Nets (LLINs) and Indoor Residual Spray (IRS). The operational plan was modified in view of the present COVID-19 pandemic by creating systems of assistance for the local administration for COVID-related work while ensuring the operational integrity of malaria elimination efforts. The use of MEDP study design and operational plan, with its built-in management control systems, has yielded significant (91%) reduction of indigenous cases of malaria during the period from June 2017 to May 2020. The malaria positivity rate was 0.33% in 2017–18, 0.13% in 2018–19, and 0.06% in 2019–20. Mass screening revealed 0.18% malaria positivity in September–October 2018, followed by 0.06% in June 2019, and 0.03% in December 2019, and these were mostly asymptomatic cases in the community. The project has been able to sustain the gains of the past three years during the ongoing COVID-19 pandemic. This paper provides the study design and the operational plan for malaria elimination in a high-burden district of Central India, which presented difficulties of hard to reach areas, forest malaria, and complex epidemiology of urban and rural malaria. The lessons learned could be used for malaria elimination efforts in rest of the country and other parts of South Asia with comparable demography and epidemiology.     

Could Malaria Control Programmes be Timed to Coincide with Onset of Rainfall?

Malaria cases in South Africa’s Northern Province of Limpopo have surpassed known endemic KwaZulu Natal and Mpumalanga Provinces. This paper applies statistical methods: regression analysis and impulse response function to understand the timing of impact and the length that such impacts last. Climate data (rainfall and temperature) are obtained from South African Weather Services (SAWs); global data from the European Centre for Medium-Range Weather Forecasts (ECMWF), while clinical malaria data came from Malaria Control Centre in Tzaneen (Limpopo Province). Data collected span from January 1998 to July 2007. Signs of the coefficients are positive for rainfall and temperature and negative for their exponents. Three out of five independent variables consistently maintain a very high statistical level of significance. The coefficients for climate variables describe an inverted u-shape: parameters for the exponents of rainfall (?0.02, ?0.01, ?0.02, ?0.00) and temperature (?46.61, ?47.46, ?48.14, ?36.04) are both negative. A one standard deviation rise in rainfall (rainfall onset) increases malaria cases, and the effects become sustained for at least 3 months and conclude that onset of rainfall therefore triggers a ‘malaria season’. Malaria control programme and early warning system should be intensified in the first 3 months following the onset of rainfall.     

Urban and suburban malaria in Rondônia (Brazilian Western Amazon) II. Perennial transmissions with high anopheline densities are associated with human environmental changes

Longitudinal entomological surveys were performed in Vila Candelária and adjacent rural locality of Bate Estaca concomitantly with a clinical epidemiologic malaria survey. Vila Candelária is a riverside periurban neighborhood of Porto Velho, capital of the state of Rond?nia in the Brazilian Amazon. High anopheline densities were found accompanying the peak of rainfall, as reported in rural areas of the region. Moreover, several minor peaks of anophelines were recorded between the end of the dry season and the beginning of the next rainy season. These secondary peaks were related to permanent anopheline breeding sites resulting from human activities. Malaria transmission is, therefore, observed all over the year. In Vila Candelária, the risk of malaria infection both indoors and outdoors was calculated as being 2 and 10/infecting bites per year per inhabitant respectively. Urban malaria in riverside areas was associated with two factors: (1) high prevalence of asymptomatic carriers in a stable human population and (2) high anopheline densities related to human environmental changes. This association is probably found in other Amazonian urban and suburban communities. The implementation of control measures should include environmental sanitation and better characterization of the role of asymptomatic carriers in malaria transmission.     

Asymptomatic Malaria in Refugees Living in a Non-Endemic South African City

Background

Asymptomatic malaria infection in refugees is both a threat to the lives of the individuals and the public in the host country. Although South Africa has been experiencing an unprecedented influx of refugees since 1994, data on malaria infection among refugees is lacking. Such information is critical since South Africa is among the countries that have planned to eliminate malaria. The objective of this study was to determine prevalence of asymptomatic malaria infection among a refugee population living in a city of KwaZulu-Natal province, South Africa.

Methods and Findings

A survey was conducted on adult refugee participants who attended a faith-based facility offering social services in a city of KwaZulu-Natal province, South Africa. The participants were screened for the presence of malaria using rapid diagnostic tests and microscopy. Demographic data for the participants were obtained using a closed ended questionnaire. Data was obtained for 303 participants consisting of 51.5% females and 47.5% males, ranging from 19 to 64 years old. More than 95% of them originated from sub-Saharan African countries. Two hundred and ninety participants provided a blood sample for screening of malaria. Of these, 3.8% tested positive for rapid diagnostic test and 5.9% for microscopy. The majority of malaria infections were due to Plasmodium falciparum.

Conclusions

The study confirms the presence of asymptomatic malaria infections among a refugee population residing in a city of KwaZulu-Natal province that is not endemic for malaria. The results have important implications for both public health and malaria control in South Africa, particularly since the country has decided to eliminate malaria by 2018. To achieve this goal, South Africa needs to expand research, surveillance and elimination activities to include non-endemic areas, particularly with high refugee populations. We further recommend use of powerful diagnostic tests such as PCR for these interventions.     

Surveillance for malaria elimination in Swaziland: a national cross-sectional study using pooled PCR and serology

Background

To guide malaria elimination efforts in Swaziland and other countries, accurate assessments of transmission are critical. Pooled-PCR has potential to efficiently improve sensitivity to detect infections; serology may clarify temporal and spatial trends in exposure.

Methodology/Principal Findings

Using a stratified two-stage cluster, cross-sectional design, subjects were recruited from the malaria endemic region of Swaziland. Blood was collected for rapid diagnostic testing (RDT), pooled PCR, and ELISA detecting antibodies to Plasmodium falciparum surface antigens. Of 4330 participants tested, three were RDT-positive yet false positives by PCR. Pooled PCR led to the identification of one P. falciparum and one P. malariae infection among RDT-negative participants. The P. falciparum-infected participant reported recent travel to Mozambique. Compared to performing individual testing on thousands of samples, PCR pooling reduced labor and consumable costs by 95.5%. Seropositivity was associated with age ≥20 years (11·7% vs 1·9%, P<0.001), recent travel to Mozambique (OR 4.4 [95% CI 1.0–19.0]) and residence in southeast Swaziland (RR 3.78, P<0.001).

Conclusions

The prevalence of malaria infection and recent exposure in Swaziland are extremely low, suggesting elimination is feasible. Future efforts should address imported malaria and target remaining foci of transmission. Pooled PCR and ELISA are valuable surveillance tools for guiding elimination efforts.     

Malaria in Brazil: what happens outside the Amazonian endemic region

Brazil, a country of continental proportions, presents three profiles of malaria transmission. The first and most important numerically, occurs inside the Amazon. The Amazon accounts for approximately 60% of the nation’s territory and approximately 13% of the Brazilian population. This region hosts 99.5% of the nation’s malaria cases, which are predominantly caused by Plasmodium vivax (i.e., 82% of cases in 2013). The second involves imported malaria, which corresponds to malaria cases acquired outside the region where the individuals live or the diagnosis was made. These cases are imported from endemic regions of Brazil (i.e., the Amazon) or from other countries in South and Central America, Africa and Asia. Imported malaria comprised 89% of the cases found outside the area of active transmission in Brazil in 2013. These cases highlight an important question with respect to both therapeutic and epidemiological issues because patients, especially those with falciparum malaria, arriving in a region where the health professionals may not have experience with the clinical manifestations of malaria and its diagnosis could suffer dramatic consequences associated with a potential delay in treatment. Additionally, because the Anopheles vectors exist in most of the country, even a single case of malaria, if not diagnosed and treated immediately, may result in introduced cases, causing outbreaks and even introducing or reintroducing the disease to a non-endemic, receptive region. Cases introduced outside the Amazon usually occur in areas in which malaria was formerly endemic and are transmitted by competent vectors belonging to the subgenus Nyssorhynchus (i.e., Anopheles darlingi, Anopheles aquasalis and species of the Albitarsis complex). The third type of transmission accounts for only 0.05% of all cases and is caused by autochthonous malaria in the Atlantic Forest, located primarily along the southeastern Atlantic Coast. They are caused by parasites that seem to be (or to be very close to) P. vivax and, in a less extent, by Plasmodium malariae and it is transmitted by the bromeliad mosquito Anopheles (Kerteszia) cruzii. This paper deals mainly with the two profiles of malaria found outside the Amazon: the imported and ensuing introduced cases and the autochthonous cases. We also provide an update regarding the situation in Brazil and the Brazilian endemic Amazon.     

Large‐scale prerain vegetation green‐up across Africa

Information on the response of vegetation to different environmental drivers, including rainfall, forms a critical input to ecosystem models. Currently, such models are run based on parameters that, in some cases, are either assumed or lack supporting evidence (e.g., that vegetation growth across Africa is rainfall‐driven). A limited number of studies have reported that the onset of rain across Africa does not fully explain the onset of vegetation growth, for example, drawing on the observation of prerain flush effects in some parts of Africa. The spatial extent of this prerain green‐up effect, however, remains unknown, leaving a large gap in our understanding that may bias ecosystem modelling. This paper provides the most comprehensive spatial assessment to‐date of the magnitude and frequency of the different patterns of phenology response to rainfall across Africa and for different vegetation types. To define the relations between phenology and rainfall, we investigated the spatial variation in the difference, in number of days, between the start of rainy season (SRS) and start of vegetation growing season (SOS); and between the end of rainy season (ERS) and end of vegetation growing season (EOS). We reveal a much more extensive spread of prerain green‐up over Africa than previously reported, with prerain green‐up being the norm rather than the exception. We also show the relative sparsity of postrain green‐up, confined largely to the Sudano‐Sahel region. While the prerain green‐up phenomenon is well documented, its large spatial extent was not anticipated. Our results, thus, contrast with the widely held view that rainfall drives the onset and end of the vegetation growing season across Africa. Our findings point to a much more nuanced role of rainfall in Africa's vegetation growth cycle than previously thought, specifically as one of a set of several drivers, with important implications for ecosystem modelling.     

Temperature and population density determine reservoir regions of seasonal persistence in highland malaria

A better understanding of malaria persistence in highly seasonal environments such as highlands and desert fringes requires identifying the factors behind the spatial reservoir of the pathogen in the low season. In these ‘unstable’ malaria regions, such reservoirs play a critical role by allowing persistence during the low transmission season and therefore, between seasonal outbreaks. In the highlands of East Africa, the most populated epidemic regions in Africa, temperature is expected to be intimately connected to where in space the disease is able to persist because of pronounced altitudinal gradients. Here, we explore other environmental and demographic factors that may contribute to malaria''s highland reservoir. We use an extensive spatio-temporal dataset of confirmed monthly Plasmodium falciparum cases from 1995 to 2005 that finely resolves space in an Ethiopian highland. With a Bayesian approach for parameter estimation and a generalized linear mixed model that includes a spatially structured random effect, we demonstrate that population density is important to disease persistence during the low transmission season. This population effect is not accounted for in typical models for the transmission dynamics of the disease, but is consistent in part with a more complex functional form of the force of infection proposed by theory for vector-borne infections, only during the low season as we discuss. As malaria risk usually decreases in more urban environments with increased human densities, the opposite counterintuitive finding identifies novel control targets during the low transmission season in African highlands.     

Should the use of DDT be revived for malaria vector control?

Indoor residual spraying with DDT was the principle method by which malaria transmission was eradicated or greatly reduced in many countries between the late 1940s and 1970s. Since then, decreasing use of DDT has been associated with a resurgence of malaria in India, Sri Lanka, former Soviet Central Asia, Zanzibar, Venezuela and several other Latin American countries. In India and Zanzibar, DDT resistance in vectors, as well as a decline in spray coverage, are probable causes of reduced effectiveness of DDT in recent decades. In southern Europe, eradication of malaria transmission was achieved by DDT spraying in the 1940s and 50s and eradication has been sustained by adequate treatment of imported human malaria cases. In the highlands of Madagascar and South Africa, recent reversion to DDT spraying has been successful in stemming resurgences of malaria. Continued use of DDT for vector control, but not for agriculture, is approved by the Stockholm Convention on Persistent Organic Pollutants. DDE residues in breast milk have been associated with DDT anti-malaria spraying in South Africa, but it is not known whether this is harmful. A claimed association of DDE residues with breast cancer have not been substantiated. There is a recent report of association of DDE residues with probability of premature birth; the possible relevance of this to anti-malarial use of DDT should be investigated. In Colombia, testing of the DDT stockpile for suspensibility, DDT resistance in Anopheles darlingi and investigation of the present affordability of widespread spraying with DDT, compared with alternative chemicals, are recommended.     

Imported Malaria in Korea: a 13-Year Experience in a Single Center

The incidence of imported malaria has been increasing in Korea. We reviewed data retrospectively to evaluate the epidemiology, clinical features, and outcomes of imported malaria from 1995 to 2007 in a university hospital. All patients diagnosed with imported malaria were included. Imported malaria was defined as a positive smear for malaria that was acquired in a foreign country. A total of 49 patients (mean age, 35.7 year; M : F = 38 : 11) were enrolled. The predominant malarial species was Plasmodium falciparum (73.5%), and the most frequent area of acquisition was Africa (55.1%), followed by Southeast Asia (22.4%) and South Asia (18.4%). Fourteen-patients (30.6%) suffered from severe malaria caused by P. falciparum and 1 patient (2.0%) died of multiorgan failure. Most of the patients were treated with mefloquine (79.2%) or quinine (10.2%); other antimalarial agents had to be given in 13.2% treated with mefloquine and 44.4% with quinine due to adverse drug events (ADEs). P. falciparum was the most common cause of imported malaria, with the majority of cases acquired from Africa, and a significant number of patients had severe malaria. Alternative antimalarial agents with lower rates of ADEs might be considered for effective treatment instead of mefloquine and quinine.     

Relations between Anopheles darlingi breeding habitats, rainfall, river level and malaria transmission rates in the rain forest of Suriname

Irregular peaks of P.falciparum malaria incidence were monitored in Suriname during 1982-86. An attempt is made to correlate these fluctuations of malaria rates with rainfall and river level in relation to the periodic availability of breeding habitats for the malaria vector Anopheles darlingi Root. Densities of adult female An.darlingi were recorded in the Upper-Marowijne region of Suriname, in a focus of malaria along the Marowijne River. Peaks in biting densities correlated well with periods of (i) high water level in the long rainy season, (ii) low water level in the long dry season, and (iii) abundant rainfall in the short rainy season. Critical levels of river-height and rainfall were defined which could explain most of the monthly fluctuations in malaria parasite incidence observed in this area.     

A sticky situation: the unexpected stability of malaria elimination

Malaria eradication involves eliminating malaria from every country where transmission occurs. Current theory suggests that the post-elimination challenges of remaining malaria-free by stopping transmission from imported malaria will have onerous operational and financial requirements. Although resurgent malaria has occurred in a majority of countries that tried but failed to eliminate malaria, a review of resurgence in countries that successfully eliminated finds only four such failures out of 50 successful programmes. Data documenting malaria importation and onwards transmission in these countries suggests malaria transmission potential has declined by more than 50-fold (i.e. more than 98%) since before elimination. These outcomes suggest that elimination is a surprisingly stable state. Elimination''s ‘stickiness’ must be explained either by eliminating countries starting off qualitatively different from non-eliminating countries or becoming different once elimination was achieved. Countries that successfully eliminated were wealthier and had lower baseline endemicity than those that were unsuccessful, but our analysis shows that those same variables were at best incomplete predictors of the patterns of resurgence. Stability is reinforced by the loss of immunity to disease and by the health system''s increasing capacity to control malaria transmission after elimination through routine treatment of cases with antimalarial drugs supplemented by malaria outbreak control. Human travel patterns reinforce these patterns; as malaria recedes, fewer people carry malaria from remote endemic areas to remote areas where transmission potential remains high. Establishment of an international resource with backup capacity to control large outbreaks can make elimination stickier, increase the incentives for countries to eliminate, and ensure steady progress towards global eradication. Although available evidence supports malaria elimination''s stickiness at moderate-to-low transmission in areas with well-developed health systems, it is not yet clear if such patterns will hold in all areas. The sticky endpoint changes the projected costs of maintaining elimination and makes it substantially more attractive for countries acting alone, and it makes spatially progressive elimination a sensible strategy for a malaria eradication endgame.     

Is There a Risk of Suburban Transmission of Malaria in Selangor,Malaysia?

Background

The suburban transmission of malaria in Selangor, Malaysia’s most developed and populous state still remains a concern for public health in this region. Despite much successful control efforts directed at its reduction, sporadic cases, mostly brought in by foreigners have continued to occur. In addition, cases of simian malaria caused by Plasmodium knowlesi, some with fatal outcome have caused grave concern to health workers. The aim of this study was to investigate the possibility of local malaria transmission in suburban regions of Selangor, which are adjacent to secondary rainforests.

Findings

A malaria survey spanning 7 years (2006 - 2012) was conducted in Selangor. A total of 1623 laboratory confirmed malaria cases were reported from Selangor’s nine districts. While 72.6% of these cases (1178/1623) were attributed to imported malaria (cases originating from other countries), 25.5% (414/1623) were local cases and 1.9% (31/1623) were considered as relapse and unclassified cases combined. In this study, the most prevalent infection was P. vivax (1239 cases, prevalence 76.3%) followed by P. falciparum (211, 13.0%), P. knowlesi (75, 4.6%), P. malariae (71, 4.4%) and P. ovale (1, 0.06%). Mixed infections comprising of P. vivax and P. falciparum were confirmed (26, 1.6%). Entomological surveys targeting the residences of malaria patients’ showed that the most commonly trapped Anopheles species was An. maculatus. No oocysts or sporozoites were found in the An. maculatus collected. Nevertheless, the possibility of An. maculatus being the malaria vector in the investigated locations was high due to its persistent occurrence in these areas.

Conclusions

Malaria cases reported in this study were mostly imported cases. However the co-existence of local cases and potential Plasmodium spp. vectors should be cause for concern. The results of this survey reflect the need of maintaining closely monitored malaria control programs and continuous extensive malaria surveillance in Peninsula Malaysia.     

Malaria in the United Kingdom

Over the past decade the United Kingdom had the second highest number of cases of imported malaria among European countries. There has been a substantial rise in recorded cases of malaria during the past three years though some of it may be due to improved notification. Fatal cases of malaria in visitors to Africa have averaged 6.5% of reported infections due to Plasmodium falciparum. Attacks of vivax malaria may occur several months after travellers return from a malarious country.     

Climate Drivers on Malaria Transmission in Arunachal Pradesh,India

The present study was conducted during the years 2006 to 2012 and provides information on prevalence of malaria and its regulation with effect to various climatic factors in East Siang district of Arunachal Pradesh, India. Correlation analysis, Principal Component Analysis and Hotelling’s T² statistics models are adopted to understand the effect of weather variables on malaria transmission. The epidemiological study shows that the prevalence of malaria is mostly caused by the parasite Plasmodium vivax followed by Plasmodium falciparum. It is noted that, the intensity of malaria cases declined gradually from the year 2006 to 2012. The transmission of malaria observed was more during the rainy season, as compared to summer and winter seasons. Further, the data analysis study with Principal Component Analysis and Hotelling’s T² statistic has revealed that the climatic variables such as temperature and rainfall are the most influencing factors for the high rate of malaria transmission in East Siang district of Arunachal Pradesh.     

Identification of Plasmodium malariae,a Human Malaria Parasite,in Imported Chimpanzees

It is widely believed that human malaria parasites infect only man as a natural host. However, earlier morphological observations suggest that great apes are likely to be natural reservoirs as well. To identify malaria parasites in great apes, we screened 60 chimpanzees imported into Japan. Using the sequences of small subunit rRNA and the mitochondrial genome, we identified infection of Plasmodium malariae, a human malaria parasite, in two chimpanzees that were imported about thirty years ago. The chimpanzees have been asymptomatic to the present. In Japan, indigenous malaria disappeared more than fifty years ago; and thus, it is most likely inferred that the chimpanzees were infected in Africa, and P. malariae isolates were brought into Japan from Africa with their hosts, suggesting persistence of parasites at low level for thirty years. Such a long term latent infection is a unique feature of P. malariae infection in humans. To our knowledge, this is the first to report P. malariae infection in chimpanzees and a human malaria parasite from nonhuman primates imported to a nonendemic country.