Chloroquine-resistant Plasmodium falciparum malaria in Ethiopia

Therapeutic efficacies of artemether-lumefantrine and dihydroartemisinin-piperaquine for the treatment of uncomplicated Plasmodium falciparum and chloroquine and dihydroartemisinin-piperaquine for uncomplicated Plasmodium vivax infection in Ethiopia

BACKGROUND

Routine monitoring of anti-malarial drugs is recommended for early detection of drug resistance and to inform national malaria treatment guidelines. In Ethiopia, the national treatment guidelines employ a species-specific approach. Artemether-lumefantrine (AL) and chloroquine (CQ) are the first-line schizonticidal treatments for Plasmodium falciparum and Plasmodium vivax, respectively. The National Malaria Control and Elimination Programme in Ethiopia is considering dihydroartemisinin-piperaquine (DHA/PPQ) as an alternative regimen for P. falciparum and P. vivax.

METHODS

The study assessed the clinical and parasitological efficacy of AL, CQ, and DHA/PPQ in four arms. Patients over 6 months and less than 18 years of age with uncomplicated malaria mono-infection were recruited and allocated to AL against P. falciparum and CQ against P. vivax. Patients 18 years or older with uncomplicated malaria mono-infection were recruited and randomized to AL or dihydroartemisinin-piperaquine (DHA/PPQ) against P. falciparum and CQ or DHA/PPQ for P. vivax. Patients were followed up for 28 (for CQ and AL) or 42 days (for DHA/PPQ) according to the WHO recommendations. Polymerase chain reaction (PCR)-corrected and uncorrected estimates were analysed by Kaplan Meier survival analysis and per protocol methods.

RESULTS

A total of 379 patients were enroled in four arms (n = 106, AL-P. falciparum; n = 75, DHA/PPQ- P. falciparum; n = 142, CQ-P. vivax; n = 56, DHA/PPQ-P. vivax). High PCR-corrected adequate clinical and parasitological response (ACPR) rates were observed at the primary end points of 28 days for AL and CQ and 42 days for DHA/PPQ. ACPR rates were 100% in AL-Pf (95% CI: 96-100), 98% in CQ-P. vivax (95% CI: 95-100) at 28 days, and 100% in the DHA/PPQ arms for both P. falciparum and P. vivax at 42 days. For secondary endpoints, by day three 99% of AL-P. falciparum patients (n = 101) cleared parasites and 100% were afebrile. For all other arms, 100% of patients cleared parasites and were afebrile by day three. No serious adverse events were reported.

CONCLUSION

This study demonstrated high therapeutic efficacy for the anti-malarial drugs currently used by the malaria control programme in Ethiopia and provides information on the efficacy of DHA/PPQ for the treatment of P. falciparum and P. vivax as an alternative option.

Therapeutic efficacy of dihydroartemisinin-piperaquine for the treatment of uncomplicated Plasmodium vivax malaria in Seacha area, Arbaminch Zuria District, South West Ethiopia

BACKGROUND

Declining efficacy of chloroquine against Plasmodium vivax malaria has been documented in Ethiopia. Thus, there is a need to assess the efficacy of alternative schizontocidal anti-malarials such as dihydroartemisinin-piperaquine (DHA-PPQ) in P. vivax malaria-infected patients. This study was conducted to evaluate the therapeutic efficacy of DHA-PPQ drug in South West Ethiopia.

METHODS

This is a single-arm, prospective therapeutic efficacy study in patients with uncomplicated P. vivax malaria. The study was conducted from May 2021 to August 2021, based on the standard World Health Organization study protocol for surveillance of anti-malarial therapeutic efficacy. The study endpoint was adequate clinical and parasitological response on day 42.

RESULTS

A total of 86 patients with uncomplicated vivax malaria were enrolled. Of these, 79 patients completed the scheduled follow up; all showing adequate clinical and parasitological responses to day 42, with a successful cure rate of 100% (95% CI 96-100). Parasitaemias were cleared rapidly (86% by day 1 and 100% by day 3), as were clinical symptoms (100% by day 1). Gametocyte carriage decreased from 44% on Day 0 to 1% on day 1 and 0% on Day 2. Mean haemoglobin concentrations increased between day 0 (mean 12.2 g/dL) and day 42 (mean 13.3 g/dL). Treatment was well tolerated and no severe adverse events were observed.

CONCLUSION

In summary, treatment with DHA-PPQ demonstrated excellent efficacy for uncomplicated P. vivax, with no recurrences to day 42, and no safety concerns. This treatment, which is also effective against P. falciparum, appears to be an ideal alternative for P. vivax as part of the malaria elimination programme.

Beyond eves and cracks: An interdisciplinary study of socio-spatial variation in urban malaria transmission in Ethiopia

During the past century, the global trend of reduced malaria transmission has been concurrent with increasing urbanization. Although urbanization has traditionally been considered beneficial for vector control, the adaptation of malaria vectors to urban environments has created concerns among scientific communities and national vector control programs. Since urbanization rates in Ethiopia are among the highest in the world, the Ethiopian government developed an initiative focused on building multi-storied units organized in condominium housing. This study aimed to develop an interdisciplinary methodological approach that integrates architecture, landscape urbanism, medical anthropology, and entomology to characterize exposure to malaria vectors in this form of housing in three condominiums in Jimma Town. Mosquitoes were collected using light trap catches (LTCs) both indoor and outdoor during 2019's rainy season. Architectural drawings and ethnographic research were superposed to entomological data to detect critical interactions between uses of the space and settlement conditions potentially affecting malaria vector abundance and distribution. A total of 34 anopheline mosquitoes comprising three species (Anopheles gambiae s.l, An. pharoensis and An. coustani complex) were collected during the three months of mosquito collection. Anopheles gambiae s.l, the principal malaria vector in Ethiopia, was the predominant species of all the anophelines collected. Distribution of mosquito breeding sites across scales (household, settlement, urban landscape) is explained by environmental conditions, socio-cultural practices involving modification of existing spaces, and systemic misfits between built environment and territory. Variations in mosquito abundance and distribution in this study were mainly related to standard building practices that ignore the original logics of the territory, deficiency of water and waste disposal management systems, and adaptations of the space to fit heterogeneous lifestyles of residents. Our results indicate that contextualizing malaria control strategies in relation to vector ecology, social dynamics determining specific uses of the space, as well as building and territorial conditions could strengthen current elimination efforts. Although individual housing remains a critical unit of research for vector control interventions, this study demonstrates the importance of studying housing settlements at communal level to capture systemic interactions impacting transmission at the household level and in outdoor areas.

Case Report: Primaquine Failure for Radical Cure of Plasmodium vivax Malaria in Gambella, Ethiopia

Failures of primaquine for the treatment of relapsed Plasmodium vivax malaria is a serious challenge to malaria elimination in Ethiopia, where P. vivax accounts for up to 40% of malaria infections. We report here occurrence of a total of 15 episodes of primaquine treatment failure for radical cure in three historical P. vivax malaria patients from Gambella, Ethiopia, during 8-16 months of follow-up in 1985-1987. The total primaquine doses received were 17.5 mg/kg, 25.8 mg/kg, and 35.8 mg/kg, respectively. These total doses are much higher than in previous reports of patients with treatment failure in Ethiopia and East Africa. The possibility of new infection was excluded for these cases as the treatment and follow-up were carried out in Addis Ababa, a malaria-free city. Recrudescences were unlikely, considering the short duration pattern of the recurrences. The cytochrome P450 2D6 (CYP2D6) status for these patients is unknown, but polymorphisms have been described in Ethiopia and may have contributed to primaquine treatment failures. It is suggested that further studies be carried out in Ethiopia to determine the prevalence and distribution of primaquine treatment failures in different ethnic groups, considering the impact of CYP2D6 polymorphisms and the potential value of increasing the primaquine dose to avoid relapse.

Malaria epidemiology and interventions in Ethiopia from 2001 to 2016

BACKGROUND

Ethiopia is one of the African countries where Plasmodium falciparum and P. vivax co-exist. Monitoring and evaluation of current malaria transmission status is an important component of malaria control as it is a measure of the success of ongoing interventions and guides the planning of future control and elimination efforts.

MAIN TEXT

We evaluated changes in malaria control policy in Ethiopia, and reviewed dynamics of country-wide confirmed and clinical malaria cases by Plasmodium species and reported deaths for all ages and less than five years from 2001 to 2016. Districts level annual parasite incidence was analysed to characterize the malaria transmission stratification as implemented by the Ministry of Health. We found that Ethiopia has experienced major changes from 2003 to 2005 and subsequent adjustment in malaria diagnosis, treatment and vector control policy. Malaria interventions have been intensified represented by the increased insecticide treated net (ITN) and indoor residual spraying (IRS) coverage, improved health services and improved malaria diagnosis. However, countrywide ITN and IRS coverages were low, with 64% ITN coverage in 2016 and IRS coverage of 92.5% in 2016 and only implemented in epidemic-prone areas of > 2500 m elevation. Clinical malaria incidence rate dropped from an average of 43.1 cases per 1000 population annually between 2001 and 2010 to 29.0 cases per 1000 population annually between 2011 and 2016. Malaria deaths decreased from 2.1 deaths per 100 000 people annually between 2001 and 2010 to 1.1 deaths per 100 000 people annually between 2011 to 2016. There was shrinkage in the malaria transmission map and high transmission is limited mainly to the western international border area. Proportion of P. falciparum malaria remained nearly unchanged from 2000 to 2016 indicating further efforts are needed to suppress transmission.

CONCLUSIONS

Malaria morbidity and mortality have been significantly reduced in Ethiopia since 2001, however, malaria case incidence is still high, and there were major gaps between ITN ownership and compliance in malarious areas. Additional efforts are needed to target the high transmission area of western Ethiopia to sustain the achievements made to date.

Anti-malarial treatment outcomes in Ethiopia: a systematic review and meta-analysis

BACKGROUND

Ethiopia is among countries with a high malaria burden. There are several studies that assessed the efficacy of anti-malarial agents in the country and this systematic review and meta-analysis was performed to obtain stronger evidence on treatment outcomes of malaria from the existing literature in Ethiopia.

METHODS

A systematic literature search using the preferred reporting items for systematic review and meta-analysis (PRISMA) statement was conducted on studies from Pubmed, Google Scholar, and ScienceDirect databases to identify published and unpublished literature. Comprehensive meta-analysis software was used to perform all meta-analyses. The Cochrane Q and the I 2 were used to evaluate heterogeneity of studies. Random effects model was used to combine studies showing heterogeneity of Cochrane Q p < 0.10 and I 2  > 50.

RESULTS

Twenty-one studies were included in the final analysis with a total number of 3123 study participants. Treatment outcomes were assessed clinically and parasitologically using World Health Organization guidelines. Adequate clinical and parasitological response was used to assess treatment success at the 28th day. Overall, a significant high treatment success of 92.9% (95% CI 89.1-96.6), p < 0.001, I 2  = 98.39% was noticed. However, treatment success was higher in falciparum malaria patients treated with artemether-lumefantrine than chloroquine for Plasmodium vivax patients [98.1% (97.0-99.2), p < 0.001, I 2  = 72.55 vs 94.7% (92.6-96.2), p < 0.001, I 2  = 53.62%]. Seven studies reported the adverse drug reactions to anti-malarial treatment; of 822 participants, 344 of them were exposed to adverse drug reactions with a pooled event rate of 39.8% (14.1-65.5), p = 0.002.

CONCLUSIONS

On the basis of this review, anti-malarial treatment success was high (92.9%) and standard regimens showed good efficacy against Plasmodium falciparum (98.1%) and P. vivax (94.7%) infections in Ethiopia, but associated with high rates of adverse drug reactions (ADRs). However, these ADRs were not serious enough to discontinue anti-malarial treatment. The results of this study suggest that the current anti-malarial medications are effective and safe; however, greater priority should be placed on the discovery of new anti-malarial drugs to achieve successful outcomes as resistance seems inevitable since cases of anti-malarial drug resistance have been reported from other areas of the world.

Combining long-lasting insecticidal nets and indoor residual spraying for malaria prevention in Ethiopia: study protocol for a cluster randomized controlled trial

BACKGROUND

Long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) are the main malaria prevention interventions in Ethiopia. There is conflicting evidence that the combined application of both interventions is better than either LLINs or IRS used alone. This trial aims to investigate whether the combination of LLINs (PermaNet 2.0, Vestergaard Frandsen, Lausanne, Switzerland) with IRS using propoxur will enhance the protective benefits and cost-effectiveness of the interventions against malaria and its effect on mosquito behavior, as compared to each intervention alone.

METHODS/DESIGN

This 2 x 2 factorial cluster randomized controlled trial is being carried out in the Adami Tullu district in south-central Ethiopia for about 116 weeks from September 2014 to December 2016. The trial is based on four arms: LLINs + IRS, LLINs alone, IRS alone and control. Villages (or clusters) will be the unit of randomization. The sample size includes 44 clusters per arm, with each cluster comprised of approximately 35 households (about 175 people). Prior to intervention, all households in the LLINs + IRS and LLINs alone arms will be provided with LLINs free of charge. Households in the LLINs + IRS and IRS alone arms will be sprayed with carbamate propoxur once a year just before the main malaria transmission season throughout the investigation. The primary outcome of this trial will be a malaria incidence based on the results of the rapid diagnostic tests in patients with a fever or history of fever attending health posts by passive case detection. Community-based surveys will be conducted each year to assess anemia among children 5-59 months old. In addition, community-based malaria prevalence surveys will be conducted each year on a representative sample of households during the main transmission season. The cost-effectiveness of the interventions and entomological studies will be simultaneously conducted. Analysis will be based on an intention-to-treat principle.

DISCUSSION

This trial aims to provide evidence on the combined use of LLINs and IRS for malaria prevention by answering the following research questions: Can the combined use of LLINs and IRS significantly reduce the incidence of malaria compared with the use of either LLINs or IRS alone? And is the reduced incidence justifiable compared to the added costs? Will the combined use of LLINs and IRS reduce vector density, infection, longevity and the entomological inoculation rate? These data are crucial in order to maximize the impact of vector control interventions on the morbidity and mortality of malaria.

TRIAL REGISTRATION

PACTR201411000882128 (8 September 2014).

Efficacy of artemether-lumefantrine therapy for the treatment of uncomplicated Plasmodium falciparum malaria in Southwestern Ethiopia

BACKGROUND

The development and spread of chloroquine-resistant Plasmodium falciparum threatens the health of millions of people and poses a major challenge to the control of malaria. Monitoring drug efficacy in 2-year intervals is an important tool for establishing rational anti-malarial drug policies. This study addresses the therapeutic efficacy of artemether-lumefantrine (AL) for the treatment of Plasmodium falciparum in southwestern Ethiopia.

METHODS

A 28-day in vivo therapeutic efficacy study was conducted from September to December, 2011, in southwestern Ethiopia. Participants were selected for the study if they were older than 6 months, weighed more than 5 kg, symptomatic, and had microscopically confirmed, uncomplicated P. falciparum. All 93 eligible patients were treated with AL and followed for 28 days. For each patient, recurrence of parasitaemia, the clinical condition, and the presence of gametoytes were assessed on each visit during the follow-up period. PCR was conducted to differentiate re-infection from recrudescence.

RESULTS

Seventy-four (83.1 %) of the study subjects cleared fever by day 1, but five (5.6 %) had fever at day 2. All study subjects cleared fever by day 3. Seventy-nine (88.8 %) of the study subjects cleared the parasite by day 1, seven (7.9 %) were blood-smear positive by day 1, and three (3.4 %) were positive by day 2. In five patients (5.6 %), parasitaemia reappeared during the 28-day follow-up period. From these five, one (1.1 %) was a late clinical failure, and four (4.5 %) were a late parasitological failure. On the day of recurrent parasitaemia, the level of chloroquine/desethylchloroquine (CQ-DCQ) was above the minimum effective concentration (>100 ng/ml) in one patient. There were 84 (94.4 %) adequate clinical and parasitological responses. The 28-day, PCR-uncorrected (unadjusted by genotyping) cure rate was 84 (94.4 %), whereas the 28-day, PCR-corrected cure rate was 87 (97.8 %). Of the three re-infections, two (2.2 %) were due to P. falciparum and one (1.1 %) was due to P. vivax. From 89 study subjects, 12 (13.5 %) carried P. falciparum gametocytes at day 0, whereas the 28-day gametocyte carriage rate was 2 (2.2 %).

CONCLUSIONS

Years after the introduction of AL in Ethiopia, the finding of this study is that AL has been highly effective in the treatment of uncomplicated P. falciparum malaria and reducing gametocyte carriage in southwestern Ethiopia.

Therapeutic efficacy of chloroquine for treatment of Plasmodium vivax malaria cases in Halaba district, South Ethiopia

BACKGROUND

Chloroquine is an anti-malarial drug being used to treat Plasmodium vivax malaria cases in Ethiopia. However, emergence of chloroquine resistant strains of the parasite has challenged the current efficacy of the drug. Therefore, the aim of this study was to assess the effectiveness of chloroquine against P. vivax strains in one of the malaria endemic areas of Ethiopia, namely Halaba district, located in South Nations and Nationalities Peoples Region (SNNPR) of South Ethiopia

RESULTS

Among 87 malaria patients enrolled in the study, only 80 of them completed the 28-days follow-up. Seven of them dropped from the study for different reasons. Among those study participants that completed their follow-up, 69 were classified under the category of adequate clinical and parasitological response (ACPR). However, the remaining 11 cases were considered as under treatment failure mainly due to recurrence of parasitemia on day 7 (four patients), day 14 (six patients), and day 21 (one patient). The age of all cases of treatment failures was found to be less than 20 years. The load of parasitemia of patients with treatment failure on day of admission (4709.4/μl) was higher than day of recurrence (372.37/μl). Parasite reduction ratio (PRR) of treatment failure cases was 12.6/μl.

CONCLUSION

This report revealed the rise in treatment failure (13% [95% CI = 0.074 - 0.217]) as compared to earlier reports from Ethiopia. It signals the spreading of chloroquine resistant P. vivax (CRPv) strains to malaria endemic areas of Ethiopia. It is recommended that all concerned bodies should act aggressively before further expansion of the current drug resistant malaria.

Confirmed vivax resistance to chloroquine and effectiveness of artemether-lumefantrine for the treatment of vivax malaria in Ethiopia

Chloroquine (CQ) is still the drug of choice for the treatment of vivax malaria in Ethiopia, whereas artemether-lumefantrine (AL) is for falciparum malaria. In this setting, clinical malaria cases are treated with AL. This necessitated the need to assess the effectiveness of AL for the treatment of Plasmodium vivax with CQ as a comparator. A total of 57 (80.3%) and 75 (85.2%) cases treated with CQ or AL, respectively, completed the study in an outpatient setting. At the end of the follow-up period of 28 days, a cumulative incidence of treatment failure of 7.5% (95% confidence interval [CI] = 2.9-18.9%) for CQ and 19% (95% CI = 11-31.6%) for AL was detected. CQ resistance was confirmed in three of five CQ treatment failures cases. The effectiveness of AL seems lower than CQ; however, the findings were not conclusive, because the AL evening doses were not supervised.

Spatial and temporal variations of malaria epidemic risk in Ethiopia: factors involved and implications

The aim of this study was to describe spatial and temporal variations in malaria epidemic risk in Ethiopia and to examine factors involved in relation to their implications for early warning and interpretation of geographical risk models. Forty-eight epidemic episodes were identified in various areas between September 1986 and August 1993 and factors that might have led to the events investigated using health facility records and weather data. The study showed that epidemics in specific years were associated with specific geographical areas. A major epidemic in 1988 affected the highlands whereas epidemics in 1991 and 1992 affected highland-fringe areas on the escarpments of the Rift Valley and in southern and north-western parts of the country. Malaria epidemics were significantly more often preceded by a month of abnormally high minimum temperature in the preceding 3 months than based on random chance, whereas frequency of abnormally low minimum temperature prior to epidemics was significantly lower than expected. Abnormal increases of maximum temperature and rainfall had no positive association with the epidemics. A period of low incidence during previous transmission seasons might have aggravated the events, possibly due to low level of immunity in affected populations. Epidemic risk is a dynamic phenomenon with changing geographic pattern based on temporal variations in determinant factors including weather and other eco-epidemiological characteristics of areas at risk. Epidemic early warning systems should take account of non-uniform effects of these factors by space and time and thus temporal dimensions need to be considered in spatial models of epidemic risks.

Incidence of malaria among children living near dams in northern Ethiopia: community based incidence survey

OBJECTIVE

To assess the impact of construction of microdams on the incidence of malaria in nearby communities in terms of possibly increasing peak incidence and prolonging transmission.

DESIGN

Four quarterly cycles of malaria incidence surveys, each taking 30 days, undertaken in eight at risk communities close to dams paired with eight control villages at similar altitudes but beyond flight range of mosquitoes.

SETTING

Tigray region in northern Ethiopia at altitudes of 1800 to 2225 m.

SUBJECTS

About 7000 children under 10 years living in villages within 3 km of microdams and in control villages 8-10 km distant.

MAIN OUTCOME MEASURES

Incidence of malaria in both communities.

RESULTS

Overall incidence of malaria for the villages close to dams was 14.0 episodes/1000 child months at risk compared with 1.9 in the control villages-a sevenfold ratio. Incidence was significantly higher in both communities at altitudes below 1900 m.

CONCLUSIONS

There is a need for attention to be given to health issues in the implementation of ecological and environmental development programmes, specifically for appropriate malaria control measures to counteract the increased risks near these dams.

Chloroquine resistance of Plasmodium falciparum malaria in Ethiopia and Eritrea

We report on the first 2 years of operation of a new strategy for treatment for P. falciparum malaria patients who were not cured by a standard course of chloroquine. Any such patient who returned to a malaria treatment and detection post within 2 weeks was treated daily under supervision with chloroquine. Patients whose parasitaemia had not decreased below 25% of the initial level by day 3 or cleared completely by day 7 were given sulphadoxine/pyrimethamine (Fansidar). Of 39824 patients treated initially with chloroquine, 4% returned to the malaria post within 2 weeks of treatment; 87% of these were chloroquine resistant and treated with Fansidar and 28% of the returning patients were RIII resistant. Resistance was associated with geographical area, initial parasite density and age. Earlier studies had shown resistance to be confined to border areas, but we found that it was highest in the centre of the region, notably in the lowlands of the Shewa and Arsi provinces, and lowest in the west. Although imported cases have been held responsible for the development of resistance in border areas, other factors are likely to be important in the middle of the region. The implications of these findings for a treatment policy of P. falciparum malaria in the region are discussed.

Chloroquine-resistant Plasmodium falciparum isolates from the Sudan lack two mutations in the pfmdr1 gene thought to be associated with chloroquine resistance

Isolates of Plasmodium falciparum from 3 areas of the Sudan were recovered from cryopreservation in London and their chloroquine sensitivity was determined in vitro. Chloroquine resistance was detected in 6/6 isolates from Khartoum, 1/4 from Sennar and 3/3 from Gadarif, indicating that resistance is spreading. All the isolates were sensitive to mefloquine. Studies using blood spots on glass fibre discs and the polymerase chain reaction did not detect two mutations in the pfmdr1 gene, thought to be correlated with chloroquine-resistance, in any of the isolates studied.

Correlation between in vivo and in vitro response of chloroquine-resistant Plasmodium falciparum in Calabar, south-eastern Nigeria

Since chloroquine-resistant Plasmodium falciparum (CRPF) has emerged in Nigeria, we monitored the susceptibility of the parasite strain to a standard chloroquine (C25) dose in our Children's Emergency Unit. Chloroquine (CQ) is the drug of choice for malaria chemotherapy in Nigeria. The WHO 7-day in vivo evaluation and Rieckmann's microtitre technique (in vitro test) were used. 33 children of mean age 4.9 years were enrolled in the study. 27 (81.8%) of the in vitro cultures were successful. 16 (59.3%) of the successful isolates still showed schizogony at CQ concentration of 5.7 pmol/well and above. 28 (84.8%) of the children completed the in vivo study. 15 (53.6%) were parasitaemic on day 7 and/or day 14 and were regarded as parasitologic failures. The isolates from 14 of these children showed corresponding in vitro resistance of CQ concentrations equal to or above 5.7 pmol/well. The proportion of RIII (= 13.3%) appears to have increased as compared to 5.9% recorded in 1987. We conclude that there appears to be a good correlation between in vivo evaluation of parasitologic failures (53.6%) and in vitro resistance (59.3%). It thus appears that CRPF is definitely increasing in South-Eastern Nigeria. This can be expected not only to complicate malaria chemotherapy in the Children's Emergency Unit of the University of Calabar Teaching Hospital, but will contribute immensely to the deterioration of malaria therapy and control in Nigeria.

The resistance of falciparum malaria in Africa to 4-aminoquinolines and antifolates

Falciparum malaria cannot be eradicated from sub-Saharan Africa with present technology. The mainstay of malaria control in this situation is treatment of fever cases with chloroquine, aiming principally at reduction of mortality. The efficacy of this policy is now endangered because of the appearance and spread of chloroquine-resistance on the African continent. The present review examines laboratory and field research on the resistance of African P.falciparum to chloroquine, amodiaquine, pyrimethamine, proguanil, chlorproguanil and the combination sulfadoxine-pyrimethamine. Drug-resistance in malaria may be assessed with in vivo and in vitro technology. In vivo tests are simple, but the results are difficult to compare because of the influence of immunity. In vitro tests provide a more precise epidemiological tool, but their analysis should be undertaken with consideration of their technical limitations. For parasitological, immunological and epidemiological reasons, a one-to-one correlation between in vivo and in vivo grading of resistance is usually not found. Extended in vivo tests may be at least as sensitive as in vitro tests for detecting rare resistant parasites. On the other hand, the standardized grading of higher levels of in vivo resistance is arbitrary, and it is doubtful, whether such distinction has any clinical relevance. The 4-aminoquinolines (chloroquine and amodiaquine) presumably act by interfering with vital functions in the acid vesicles of parasites. Recent experiments indicate that resistance may be related to an increased rate of efflux of chloroquine from the parasite. It is caused by mutation, and at least three genetic levels of resistance have been identified. The blood stages of resistant plasmodia seem to have a biological advantage over sensitive ones, an observation that raises some hitherto unanswered questions. In the 1970s, a low degree of resistance to chloroquine was found in African P. falciparum in several localities. Resistance to the standard dose of chloroquine of 25 mg/kg was found in 1978 in tourists, who had sojourned in Kenya and Tanzania. Since then, chloroquine-resistance has spread centrifugally with increasing rapidity from an original focus in Northern Tanzania or Southern Kenya. The rate of increase in the proportion of resistant infections has generally been more rapid in the areas, where resistance has been introduced recently than in the original epifocus. The rate of increase is also generally more rapid in urban than in rural areas, an observation that can be ascribed to differences in drug pressure.(ABSTRACT TRUNCATED AT 400 WORDS)

Chloroquine-resistant Plasmodium falciparum in eastern Sudan

In vivo testing of the sensitivity of Plasmodium falciparum to chloroquine was carried out in 61 falciparum malaria patients with acute symptoms, in Eastern Sudan. In 26 patients (42%), P. falciparum was resistant to chloroquine. Nine patients (15%) had RI resistance, seven (11%) had RII resistance while ten (16%) had RIII resistance. The persistance of parasitaemia and symptoms were highly correlated in patients with RIII responses. In 21 patients in vitro testing of chloroquine sensitivity was carried out simultaneously with the in vivo testing using the World Health Organization microtest. In vivo and in vitro testing were also highly correlated. Isolates from 12 patients with proven in vivo resistance, grew in vitro in the presence of chloroquine concentrations above 0.8 X 10(-6) mol/l blood. Resistant strains have either been spread by refugees across the borders from Ethiopia or have developed indigenously. Mounting drug pressure, mass movement of non-immune refugees and loss of immunity among local inhabitants, due to the drought, are in favour of development of an indigenous focus. Epidemics with intense transmission caused by heavy rains following the drought could have greatly enhanced the emergence and spread of resistant strains.

Susceptibility of Plasmodium falciparum to chloroquine and mefloquine in Somalia

A field study was conducted in the Malable area, in Somalia, to assess the susceptibility of Plasmodium falciparum to chloroquine and mefloquine. The in vivo response of P. falciparum to standard therapeutic regimen of chloroquine was studied in 16 children (1-12 years) using the standard WHO in vivo field test. All subjects were parasite free by day 3 and no recrudescence occurred during a 7-d follow-up. In the 24 h micro in vitro tests for chloroquine, 29 of 39 tests performed were successful. Of the 29 isolates, 3 showed distinct resistance and 2 were borderline. The drug concentration yielding 99% (EC99) inhibition was 1.64 x 10(-6) M, indicating low grade resistance. For mefloquine, 11 of 20 tests gave interpretable results and were sensitive, although with some heterogeneity. The EC50 and EC99 of 0.24 x 10(-6) M and 1.31 x 10(-6) M respectively indicate sensitivity.