RII Resistance Research Articles

Artemisinin and malaria: Current understandings of drug activation, action, and resistance

Malaria is a disease that can be cured with antimalarial drugs if treated early and appropriately. However, parasites resistant to a new drug generally emerge within a few years after large-scale applications. Artemisinin (ART or Qinghaosu) combination therapies (ACTs) have become the major treatments for malaria after the emergence of parasites resistant to almost all classes of antimalarial drugs. Parasites with delayed parasite clearance (DPC) after ART or ACT therapies have also been reported in Southeast Asia, raising concerns of total failure of ART and its derivatives. Many classes of antimalarial drugs have been introduced to successfully treat malaria infections, including chloroquine, piperaquine, primaquine, mefloquine (MQ), pyrimethamine, sulfadoxine, ART and derivatives, etc. Regrettably, many of these drugs have been abandoned by many countries in malaria endemic regions due to the emergence of drug resistant parasites. According to World Health Organization, parasite responses to a drug can be classified into four categories (S, RI, RII, and RIII): Sensitivity (S) to a drug is defined as clearance of asexual parasitemia within seven days of the first day of treatment without recrudescence; Resistance RI is defined as clearance of asexual parasitemia as in sensitive parasites, followed by recrudescence; RII resistance is indicated by marked reduction of asexual parasitemia, but no clearance; and RIII resistance shows no marked reduction of asexual parasitemia. Currently, RII and RIII resistance to chloroquine, pyrimethamine, and other drugs have been widely reported; but residence to ART remains largely at R1 level. ART resistance was initially defined as parasites with half parasite clearance time (PC1/2)>5 h under a standard ART treatment regimen (three-day artesunate treatment at 2–4 mg kg - 1 d - 1). A second measurement is in vitro ring survival assay (RSA) that was developed based on the observation that the ring stages of some parasite strains could survive a short period of ART treatment. Another indicator of increasing ART tolerance is the elevated rate of recrudescence after ART or ACT treatments. The generation of highly reactive radicals via endoperoxide cleavage is critical for ART activation. Both free ferrous iron and heme have been proposed to be the predominant iron sources for ART activation. The heme required for ART activation can be derived from the parasite’s heme biosynthesis pathway at the early ring stage and/or from hemoglobin digestion at later stages. A large number of parasite molecules have been found to bind or interact with ART, most notably the Plasmodium falciparum ATPase 6 (PfATP6 or SERCA), phosphatidylinositol-3-kinase (PfPI3K), chloroquine resistance transporter (PfCRT), and multiple drug resistance 1 (PfMDR1). Recently, a gene encoding a parasite Kelch protein (“K13”) with a six-blade propeller domain was identified as a potential molecular marker of ART resistance in vivo (DPC>5 h) and in vitro (RSA). Various antimalarial drugs such as meflouine and piperaquine have been used as partner drugs in ACTs. However, parasites resistant to these partner drugs have also been reported, which may explain the reported slow parasite clearance after ACT treatment. The success of ACTs in treating malaria infections has generated optimism and proposals for malaria eradication by mass drug administration (MDA), and successes have been achieved from several studies. However, the impact of MDA on malaria transmission in the long term, especially in low- and moderate-transmission settings, and the potential consequences of developing drug resistance, requires careful evaluation. There are a large number of studies and publications on these related subjects, and it is impossible to include or cite all the publications in this review. Additionally, some of the issues discussed here are still being debated, requiring further investigation.

Mapping response of Plasmodium falciparum to some anti-malarial drugs in Anambra State, Nigeria

The chemotherapeutic performance of chloroquine, Mefloquine, pyrimethamine/sulphadoxine (Fansidar® and Maloxine®) pyrimethamine/sulphadoxyrazine (Metakelfine® ) and halofantrine (Halfan®) was investigated in 180 malaria patients using the in vivo extended field tests protocol of the World Health Organization. There was total clearance of parasittaemia (100%) with halofantrine on Day3 (D3) after the initial day of study (D0), with no recrudescence on Day7 and Day14. the parasite was therefore fully sensitive to halofantrine. Parasitological failure, defined as failure of parasitaemia to decrease by 75% of the D0 value by Day3 or presence of any detectable parasitaemia on Day7 ranged from 12.5% for Metakelfine® to 35.00% for Maloxine®. Failures were largely Type 1 (RI) and to a much lesser extent Types 11 (RII) and 11 (RIII). The RII resistance varied from 2.11% for chloroquine to 12.5% for pyrimethamine/sulphdoxypyrazine. Considering these therapeutic results, the higher cost per treatment with drugs other than chloroquine and the low prevalence of RII level chloroquine-resistant Plasmodium falciparum (CRPF), chloroquine still remains useful as the primary therapy for malaria in the area. The Nigerian Journal of Parasitology Vol. 24 2003: 47-52

COMPARISON OF SULFADOXINE-PYRIMETHAMINE WITH AND WITHOUT CHLOROQUINE FOR UNCOMPLICATED MALARIA IN NIGERIA

While resistance to older antimalarials is increasingly common, newer antimalarials are still not widely available or affordable in much of Africa. Older antimalarials used in combination might be adequately effective in treating uncomplicated malaria. The objective of this study was to determine whether the combination of sulfadoxine-pyrimethamine (SP) and chloroquine (CQ) is superior to SP alone in the treatment of uncomplicated Plasmodium falciparum malaria in Nigerian patients. We recruited subjects with malaria, defined as the presence of fever and parasitemia > 2,000/microL, from the outpatient department of a Nigerian teaching hospital. We alternately assigned 280 subjects to receive SP with or without CQ. We assessed clinical and parasitologic responses on days 1, 2, 3, 7, and 14. A total of 114 in the SP + CQ group and 116 in the SP group completed the study. By day 3, 97 (75%) in the SP + CQ group and 52 (42%) in the SP group had cleared their parasitemia (P < 0.001); by day 14, 112 (98%) and 67 (58%), respectively, had cleared their parasitemia (P < 0.001). By day 3, 82 (63%) in the SP + CQ group and 20 (16%) in the SP group were symptom free (P < 0.001). When a modified World Health Organization clinical classification system was used, adequate clinical response occurred in 99 (87%) and 61 (53%) of those in the SP + CQ and SP groups, respectively. RI, RII, and RIII resistance to SP + CQ was 7.9%, 3.5%, and 1.8%, respectively, whereas resistance to SP was 23%, 17%, and 5%, respectively. Combined SP + CQ is superior to SP alone for treatment of uncomplicated malaria in Nigerian patients and may prolong the usefulness of these readily available and affordable drugs.

COMPARISON OF THE PARASITOLOGIC EFFICACY OF AMODIAQUINE AND SULFADOXINE-PYRIMETHAMINE IN THE TREATMENT OF PLASMODIUM FALCIPARUM MALARIA IN THE BUNGOMA DISTRICT OF WESTERN KENYA

The efficacy of amodiaquine (AQ) and sulfadoxine-pyrimethamine (SP) was assessed in 310 symptomatic children from western Kenya with uncomplicated Plasmodium falciparum malaria. A non-blinded, randomized, 14-day study was performed and parasitologic criteria were used. Of 310 patients included, 238 (77%) completed the study: 120 received AQ and 118 received SP. In those treated with AQ, there were sensitive (S) infections in 107 patients (89.2%, 95% confidence interval [CI] = 82.2, 94.1%), RI resistance in 10 (8.3%, 95% CI = 4.1, 14.8%), RII resistance in 1 (0.8%, 95% CI = 0, 4.6%), and RIII resistance in 2 (1.7%, 95% CI = 0.2, 5.9%). In those treated with SP, there were S infections in 74 patients (62.7%, 95% CI = 53.3, 71.4%), RI resistance in 21 (17.8%, 95% CI = 11.4, 25.9%), RII resistance in 11 (9.3%, 95% CI = 4.7, 16.1%), and RIII resistance in 12 (10.2%, 95% CI = 5.4, 17.1%). Resistance rates were consistently higher in the SP-treated patients (P < 0.001). Resistance to SP in this area has reached such levels that it should no longer be the first-line treatment. Alternative treatment, such as SP plus AQ combination treatment or artemisinin combination treatment, is urgently needed.

Decreasing clinical efficacy of chloroquine in Ankazobe, Central Highlands of Madagascar

The clinical efficacy of chloroquine was assessed in the Primary Health Centre of Ankazobe, Central Highlands of Madagascar. This study shows an increase in the level of chloroquine resistance with the appearance of early treatment failures and RIII resistance. Furthermore, the prevalence of clinical treatment failures is approaching the level of 25%, at which WHO recommends a change of first-line drug.

The drug sensitivity and transmission dynamics of human malaria on Nias Island, North Sumatra, Indonesia.

Nias Island, off the north-western coast of Sumatra, Indonesia, was one of the first locations in which chloroquine-resistant Plasmodium vivax malaria was reported. This resistance is of particular concern because its ancient megalithic culture and the outstanding surfing conditions make the island a popular tourist destination. International travel to and from the island could rapidly spread chloroquine-resistant strains of P. vivax across the planet. The threat posed by such strains, locally and internationally, has led to the routine and periodic re-assessment of the efficacy of antimalarial drugs and transmission potential on the island. Active case detection identified malaria in 124 (17%) of 710 local residents whereas passive case detection, at the central health clinic, confirmed malaria in 77 (44%) of 173 cases of presumed 'clinical malaria'. Informed consenting volunteers who had malarial parasitaemias were treated, according to the Indonesian Ministry of Health's recommendations, with sulfadoxine-pyrimethamine (SP) on day 0 (for P. falciparum) or with chloroquine (CQ) on days 0, 1 and 2 (for P. vivax). Each volunteer was then monitored for clinical and parasite response until day 28. Recurrent parasitaemia by day 28 treatment was seen in 29 (83%) of the 35 P. falciparum cases given SP (14, 11 and four cases showing RI, RII and RIII resistance, respectively). Recurrent parasitaemia was also observed, between day 11 and day 21, in six (21%) of the 28 P. vivax cases given CQ. Although the results of quantitative analysis confirmed only low prevalences of CQ-resistant P. vivax malaria, the prevalence of SP resistance among the P. falciparum cases was among the highest seen in Indonesia. When the parasites present in the volunteers with P. falciparum infections were genotyped, mutations associated with pyrimethamine resistance were found at high frequency in the dhfr gene but there was no evidence of selection for sulfadoxine resistance in the dhps gene. Night-biting mosquitoes were surveyed by human landing collections and tested for sporozoite infection. Among the five species of human-biting anophelines collected, Anopheles sundaicus was dominant (68%) and the only species found to be infective--two (1.2%) of 167 females being found carrying P. vivax sporozoites. The risk of malarial infection for humans on Nias was considered high because of the abundance of asymptomatic carriers, the reduced effectiveness of the available antimalarial drugs, and the biting and infection 'rates' of the local An. sundaicus.

Plasmodium vivax clinically resistant to chloroquine in Colombia.

Chloroquine-resistant Plasmodium vivax has been the subject of numerous case reports and prospective studies from Oceania and Asia. In contrast, only case reports exist from the Americas. We performed a prospective study with 28-day follow-up of clinical responses to chloroquine in 2 P. vivax-endemic regions of Colombia. Three (11%) of 27 patients failed to respond to treatment with the standard regimen of chloroquine (1,500 mg of base over 3 days). One patient demonstrated RI resistance on Day 26; one patient demonstrated RI resistance due to recrudescence of blood stages on Day 11; and one patient demonstrated RII resistance of blood stages by never displaying clearing of peripheral parasitemia. All patients were successfully treated with primaquine, which has some blood stage efficacy against P. vivax, combined with a second course of chloroquine. Clinical resistance of P. vivax to chloroquine is present in Colombia and should be monitored in the Americas.

Reduced levels of chloroquine resistant &lt;i&gt;Plasmodium falciparum&lt;/i&gt; in selected &lt;i&gt;foci&lt;/i&gt; for the South West Province, Cameroon

To evaluate the state of chloroquine resistant malaria in the South West Province of Cameroon. To estimate the prevalence of different species of Plasmodium in the area. A cross sectional study. South West Province of Cameroon. 326 febrile patients. Chloroquine resistance studies using the WHO seven-day standard in vivo test. Speciation of malaria by polymerase chain reaction. Prevalence of falciparum malaria by light microscopy of thick blood smears. Prevalence of chloroquine resistance ranged from 4.3 to 13.2%. A total of six cases showed RIII resistance, and three cases showed RII resistance. Plasmodium falciparum was the predominant species, 96.8% of those testing positive for P. falciparum, 6.3% of cases showed mixed infections of P. falciparum and P. malariae. P. ovale accounted for 3% of cases. P. falciparum resistance to chloroquine may not be on the increase compared to earlier reports from the South West Province. The results have important implications in treatment of malaria in view of the low cost of chloroquine.

Mutations in the pfmdr1, dhfr and dhps genes of Plasmodium falciparum are associated with in-vivo drug resistance in West Papua, Indonesia

This study (conducted in 1996–1999) examines the association of mutations in pfmdr1, dihydrofolate reductase ( dhfr) and dihydropteroate synthase ( dhps) genes of Plasmodium falciparum with in-vivo drug resistance in West Papua, Indonesia. Initially, 85 patients infected with P. falciparum were treated with chloroquine, of whom 21 were cleared of parasites, 49 had parasitaemias classified as RI, RII or RIII resistance and 1 patient had recrudescent parasitaemia. Fansidar ® (pyrimethamine-sulfadoxine) was the second-line treatment and 18 patients were cleared of parasites and 31 had continuing infections classified as RI, RII or RIII resistance and 1 patient had recrudescent parasitaemia. The pfmdr1, dhfr and dhps genes were examined for mutations previously shown to be associated with resistance to these drugs. In this study, mutations in pfmdr1 were associated with chloroquine resistance and mutations in both dhfr and dhps were associated with Fansidar resistance in vivo. Interestingly, Gly-437 in dhps along with Arg-59/Asn-108 in dhfr were associated with RI, RII and RIII resistance whereas Glu-540 was highly associated with only RII and RIII Fansidar resistance. This finding supports the hypothesis that the molecular basis of RI, RII and RIII Fansidar resistance involves an accumulation of mutations in both dhfr and dhps. These results suggest that mutations in both dhfr and dhps genes are a good predictor of potential Fansidar treatment failure.

Towards an Understanding of the Mechanism of Pyrimethamine-Sulfadoxine Resistance in Plasmodium falciparum : Genotyping of Dihydrofolate Reductase and Dihydropteroate Synthase of Kenyan Parasites

The antifolate combination of pyrimethamine (PM) and sulfadoxine (SD) is the last affordable drug combination available for wide-scale treatment of falciparum malaria in Africa. Wherever this combination has been used, drug-resistant parasites have been selected rapidly. A study of PM-SD effectiveness carried out between 1997 and 1999 at Kilifi on the Kenyan coast has shown the emergence of RI and RII resistance to PM-SD (residual parasitemia 7 days after treatment) in 39 out of 240 (16.25%) patients. To understand the mechanism that underlies resistance to PM-SD, we have analyzed the dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS) genotypes of 81 patients. Fifty-one samples were obtained, before treatment, from patients who remained parasite free for at least 7 days after treatment. For a further 20 patients, samples were obtained before treatment and again when they returned to the clinic with parasites 7 days after PM-SD treatment. Ten additional isolates were obtained from patients who were parasitemic 7 days after treatment but who were not sampled before treatment. More than 65% of the isolates (30 of 46) in the initial group had wild-type or double mutant DHFR alleles, and all but 7 of the 47 (85%) had wild-type DHPS alleles. In the paired (before and after treatment) samples, the predominant combinations of DHFR and DHPS alleles before treatment were of triple mutant DHFR and double mutant DHPS (41% [7 of 17]) and of double mutant DHFR and double mutant DHPS (29% [5 of 17]). All except one of the posttreatment isolates had triple mutations in DHFR, and most of these were "pure" triple mutants. In these isolates, the combination of a triple mutant DHFR and wild-type DHPS was detected in 6 of 29 cases (20.7%), the combination of a triple mutant DHFR and a single mutant (A437G) DHPS was detected in 4 of 29 cases (13.8%), and the combination of a triple mutant DHFR and a double mutant (A437G, L540E) DHPS was detected in 16 of 29 cases (55.2%). These results demonstrate that the triply mutated allele of DHFR with or without mutant DHPS alleles is associated with RI and RII resistance to PM-SD. The prevalence of the triple mutant DHFR-double mutant DHPS combination may be an operationally useful marker for predicting the effectiveness of PM-SD as a new malaria treatment.

Over-expression of ERT(ESX/ESE-1/ELF3), an ets-related transcription factor, induces endogenous TGF-beta type II receptor expression and restores the TGF-beta signaling pathway in Hs578t human breast cancer cells.

The epithelium-specific transcription factor, ERT/ESX/ESE-1/ELF3, binds to the TGF-beta RII promoter in a sequence specific manner and regulates its expression. In this study, we investigated whether ERT could regulate endogenous TGF-beta RII expression in Hs578t breast cancer cells. Analyses of the Hs578t parental cell line revealed low RII mRNA expression and resistance to the growth inhibitory effects of TGF-beta. Infection of this cell line with a retroviral construct expressing ERT induced higher levels of endogenous RII mRNA expression and protein expression relative to cells infected with chloramphenicol acetyltransferase (CATneo) as a control. Relative to control cells, the ERTneo-expressing Hs578t cells show approximately a 50% reduction in cell growth in the presence of exogenous TGF-beta1, as well as a fourfold higher induction of activation in transient transfection assays using the 3TP-luciferase reporter construct. When transplanted into athymic mice, ERT-expressing Hs578t cells showed decreased and delayed tumorigenicity compared with control cells. This data strongly suggests that ERT plays an important role as a transcriptional activator of TGF-beta RII expression, and that deregulated ERT expression may play a critical role in rendering Hs578t human breast cancer cells insensitive to TGF-beta's growth inhibitory effects.

Chemotherapy of malaria and resistance to antimalarial drugs in Guayana area, Venezuela.

Resistance to antimalarial chemotherapy is one of the greatest difficulties for the control of malaria transmission. Seventy patients with Plasmodium falciparum malaria were included in a study of resistance to chloroquine and sulfadoxine-pyrimethamine therapy. Resistance levels RI, RII, and RIII were established. Eighteen infections (51%) cleared after chloroquine treatment and did not recur within 28 days of follow-up; these were classified as sensitive. Ten infections (29%) were resistant at the RI level. Resistance at level RII was observed in 5 (14%) cases, and RIII resistance was demonstrated in 2 infections (6%). With sulfadoxine-pyrimethamine, 28 (80%) infections were classified as sensitive. Six infections (17%) showed resistance at level RII, and 1 (3%) infection was resistant at the RI level. Resistance at level RIII was not observed. In a microtest for chloroquine and sulfadoxine-pyrimethamine sensitivity in vitro, schizont development was accomplished successfully in 70 blood samples. In vitro resistance to chloroquine was demonstrated in 15 of 70 (21%) of all isolates. Eight of 70 (11%) of all isolates showed resistance to sulfadoxine-pyrimethamine. Diversity of response of P. falciparum to the studied antimalarial drugs in the Guayana area of Venezuela is considered a problem restricting the control of malaria in this geographical area. A constant evaluation program monitoring P. falciparum drug sensitivity is necessary for preserving the efficacy of the established treatment.

In vivo responses to antimalarials by Plasmodium falciparum and Plasmodium vivax from isolated Gag Island off northwest Irian Jaya, Indonesia.

There is renewed interest in the rich nickel and cobalt deposits of Pulau Gag, an isolated but malarious island off the northwest coast of Irian Jaya. In preparation for an expanded workforce, an environmental assessment of malaria risk was made, focusing upon malaria prevalence in the small indigenous population, and the in vivo sensitivity of Plasmodium falciparum and P. vivax to chloroquine (CQ) and sulfadoxine/pyrimethamine (S/P), the respective first- and second-line drugs for uncomplicated malaria in Indonesia. During April-June 1997, mildly symptomatic or asymptomatic malaria infections were found in 24% of 456 native residents. Infections by P. falciparum accounted for 60% of the cases. Respective day 28 cure rates for CQ (10 mg base/kg on days 0 and 1; 5 mg/kg on day 2) in children and adults were 14% and 55% (P < 0.005). Type RII and RIII resistance characterized only 5% of the CQ failures. Re-treatment of 36 P. falciparum CQ treatment failures with S/P (25 mg/kg and 1.25 mg/kg, respectively) demonstrated rapid clearance and complete sensitivity during the 28-day follow-up period. More than 97% of the P. vivax malaria cases treated with CQ cleared parasitemia within 48 hr. Three cases of P. vivax malaria recurred between days 21 and 28, but against low drug levels in the blood. The low frequency of RII and RIII P. falciparum resistance to CQ, the complete sensitivity of this species to S/P, and the absence of CQ resistance by P. vivax are in contrast to in vivo and in vitro test results from sites on mainland Irian Jaya.

Pyrimethamine-sulfadoxine efficacy and selection for mutations in Plasmodium falciparum dihydrofolate reductase and dihydropteroate synthase in Mali.

To assess pyrimethamine-sulfadoxine (PS) efficacy in Mali, and the role of mutations in Plasmodium falciparum dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS) in in vivo PS resistance, 190 patients with uncomplicated P. falciparum malaria were treated with PS and monitored for 56 days. Mutation-specific polymerase chain reactions and digestion with restriction endonucleases were used to detect DHFR and DHPS mutations on filter paper blood samples from pretreatment and post-treatment infections. Only one case each of RI and RII level resistance and no cases of RIII resistance or therapeutic failure were observed. Post-PS treatment infections had significantly higher rates of DHFR mutations at codons 108 and 59. No significant selection for DHPS mutations was seen. Pyrimethamine-sulfadoxine is highly efficacious in Mali, and while the low level of resistance precludes assessing the utility of molecular assays for in vivo PS resistance, rapid selection of DHFR mutations supports their role in PS failure.

Molecular assays for surveillance of antifolate-resistant malaria

to detect all known DHFR and DHPSmutations, and correlations were determined betweenDHFR and DHPS genotypes and therapeutic responsedefined as sensitive (S), RI, RII, or RIII resistance.A genotype defined by DHFR mutations Asn-108, Ile-51,and Leu-164 combined with DHPS mutations Gly-437,Glu-540, and Gly-581 was detected in 7/8 cases (87·5%) ofRIII resistance, 9/13 cases (69·2%) of RII resistance, 5/13cases (38·5%) of RI resistance, and 0/11 sensitive cases(0·0%) (figure). The Bolivia repeat mutation at codon 30,

Resistance of falciparum malaria to chloroquine and sulfadoxine-pyrimethamine in Afghan refugee settlements in western Pakistan: surveys by the general health services using a simplified in vivo test.

Surveys of drug resistant falciparum malaria were conducted in several Afghan refugee settlements, distributed over a 700 km range in western Pakistan, during the transmission seasons of 1994 and 1995. Symptomatic malaria patients were recruited by a process of passive case detection at the refugees' basic health units. To facilitate follow-up by local health workers, a modified version of the WHO extended in vivo test was adopted in which blood smears were taken from each subject, and clinical symptoms recorded, at weekly intervals. Resistance to chloroquine and sulfadoxine-pyrimethamine was identified in every settlement. The frequency of chloroquine resistance ranged from 18% to 62%. Resistance occurred mostly as RI, with RII resistance never exceeding 11%. Resistance to sulfadoxine-pyrimethamine occurred at much lower frequencies, ranging from 4% to 25%. There was a resumption of clinical symptoms at the onset of parasite recrudescence in over 90% of cases. The policy of using chloroquine as first-line treatment might be changed in favour of sulfadoxine-pyrimethamine in most camps and areas of western Pakistan. The modified in vivo test was almost as accurate as the normal WHO in vivo test in identifying the grade of resistance, and should prove a useful tool for the monitoring of resistance to common antimalarials by district health services.

Chloroquine resistance in Pakistan and the upsurge of falciparum malaria in Pakistani and Afghan refugee populations.

Surveys conducted in Pakistan during the last decade show that falciparum malaria has become resistant to chloroquine in Pakistani and Afghan refugee populations throughout the country. Although RI resistance is common everywhere (with a frequency of 30%-84%), RII is rarer (2%-36%), and RIII resistance has yet to be detected. The national policy is to prescribe chloroquine as first-line treatment of malaria. A repeated in-vivo survey in a sentinel village indicated that prescription of chloroquine can lead to a 15% increase in the frequency of resistance in a single year, and similar trends were observed in other districts. Coinciding with the spread of resistance is a 6-fold increase in the number of falciparum cases recorded nationally between 1982 and 1992 and a parallel, 5-fold increase in the number of cases recorded in the Afghan refugee population. Resistance contributes to this trend in various ways. Firstly, patients with resistant malaria make repeated visits to health centres. In the sentinel village, for example, where resistance was measured at 71%, recrudescent infections inflated by 66% the genuine incidence of new infections recorded at the health centre. Secondly, owing to ineffective treatment, resistant infections are often still patent during the post-transmission season. This may enlarge the 'overwintering' parasite reservoir, leading to a surge of new cases when transmission resumes. Other factors potentially contributing to the upsurge in falciparum include the decrease availability of insecticide for indoor spraying. Despite the problems posed by resistance for case management, the evidence from the vector-control programme among the refugees is that malaria control through well-targeted campaigns of insecticide spraying is still able to reduce the incidence of falciparum malaria to a level that existed before the advent of resistance.

Chloroquine resistance in Pakistan and the upsurge of falciparum malaria in Pakistani and Afghan refugee populations

Surveys conducted in Pakistan during the last decade show that falciparum malaria has become resistant to chloroquine in Pakistani and Afghan refugee populations throughout the country. Although RI resistance is common everywhere (with a frequency of 30%–84%), RII is rarer (2%–36%), and RIII resistance has yet to be detected. The national policy is to prescribe chloroquine as first-line treatment of malaria. A repeated in-vivo survey in a sentinel village indicated that prescription of chloroquine can lead to a 15% increase in the frequency of resistance in a single year, and similar trends were observed in other districts.Coinciding with the spread of resistance is a 6-fold increase in the number of falciparum cases recorded nationally between 1982 and 1992 and a parallel, 5-fold increase in the number of cases recorded in the Afghan refugee population. Resistance contributes to this trend in various ways. Firstly, patients with resistant malaria make repeated visits to health centres. In the sentinel village, for example, where resistance was measured at 71%, recrudescent infections inflated by 66% the genuine incidence of new infections recorded at the health centre. Secondly, owing to ineffective treatment, resistant infections are often still patent during the post-transmission season. This may enlarge the ‘overwintering’ parasite reservoir, leading to a surge of new cases when transmission resumes. Other factors potentially contributing to the upsurge in falciparum include the decreased availability of insecticide for indoor spraying.Despite the problems posed by resistance for case management, the evidence from the vector-control programme among the refugees is that malaria control through well-targeted campaigns of insecticide spraying is still able to reduce the incidence of falciparum malaria to a level that existed before the advent of resistance.

STUDY OF CHLOROQUINE RESISTANCE IN Plasmodium falciparum INFECTION IN NORTH EAST INDIA

During the period April 1993 to July 1993, a total of 410 patients with pyrexia were screened for malarial parasite and 109 (26.5%) cases were found positive for malarial parasite. Of these 109 cases, 91 were positive for Plasmodium falciparum. Of these 91 cases, 43 patients fulfilled the study criteria as per WHO's extended field trial and were included in the analysis. These patients were treated with standard doses of chloroquine. Seven patients each (16.3%) showed RI and RII resistance and 2 patients (4.7%) showed RIII levels of chloroquine resistance.

Short report: gametocytes, chloroquine pressure, and the relative parasite survival advantage of resistant strains of falciparum malaria in west Africa.

Patients with Plasmodium falciparum infections were selected with an in vivo chloroquine sensitivity assay. Fourteen days after treatment, the gametocytes were studied in relation to asexual parasite responses classified as drug-sensitive or showing RI or RII resistance. Gametocyte prevalence and density appeared significantly higher in RII than RI strains and higher in RI than in sensitive strains. This finding on gametocyte variation in vivo may explain why the RII type of chloroquine resistance has became more prevalent than RI everywhere in tropical Africa in the short time since its emergence. The biological and epidemiologic advantage of chloroquine-resistant malaria mediated through gametocytes is discussed in the context of the present drug pressure in Africa.