Feasibility of direct venous inoculation of the radiation-attenuated Plasmodium falciparum whole sporozoite vaccine in children and infants in Siaya, western Kenya.

PfSPZ Vaccine, composed of radiation-attenuated, aseptic, purified, cryopreserved Plasmodium falciparum sporozoites, is administered by direct venous inoculation (DVI) for maximal efficacy against malaria. A critical issue for advancing vaccines that are administered intravenously is the ability to efficiently administer them across multiple age groups. As part of a pediatric safety, immunogenicity, and efficacy trial in western Kenya, we evaluated the feasibility and tolerability of DVI, including ease of venous access, injection time, and crying during the procedure across age groups. Part 1 was an age de-escalation, dose escalation trial in children aged 13 months-5 years and infants aged 5-12 months; part 2 was a vaccine efficacy trial including only infants, using the most skilled injectors from part 1. Injectors could use a vein viewer, if needed. A total of 1222 injections (target 0.5 mL) were initiated by DVI in 511 participants (36 were 5-9-year-olds, 65 were 13-59-month-olds, and 410 infants). The complete volume was injected in 1185/1222 (97.0%) vaccinations, 1083/1185 (91.4%) achieved with the first DVI. 474/511 (92.8%) participants received only complete injections, 27/511 (5.3%) received at least one partial injection (<0.5 mL), and in 10/511 (2.0%) venous access was not obtained. The rate of complete injections by single DVI for infants improved from 77.1% in part 1 to 92.8% in part 2. No crying occurred in 51/59 (86.4%) vaccinations in 5-9-year-olds, 25/86 (29.1%) vaccinations in 13-59-month-olds and 172/1067 (16.1%) vaccinations in infants. Mean administration time ranged from 2.6 to 4.6 minutes and was longer for younger age groups. These data show that vaccination by DVI was feasible and well tolerated in infants and children in this rural hospital in western Kenya, when performed by skilled injectors. We also report that shipping and storage in liquid nitrogen vapor phase was simple and efficient. (Clinicaltrials.gov NCT02687373).

Viral vectors in malaria vaccine development.

Traditional vaccine technologies have resulted in an impressive array of efficacious vaccines against a variety of infectious agents. However, several potentially deadly pathogens, including retroviruses and parasites, have proven less amenable to the application of traditional vaccine platforms, indicating the need for new approaches. Viral vectors represent an attractive way to deliver and present vaccine antigens that may offer advantages over traditional platforms. Due to their ability to induce strong cell-mediated immunity (CMI) in addition to antibodies, viral vectors may be suitable for infectious agents, such as malaria parasites, where potent CMI is required for protection. Poxvirus-vectored malaria vaccines have been the most extensively studied in the clinic, achieving significant reductions in liver-stage parasite burden. More recently, adenovirus-vectored malaria vaccines have entered clinical testing. The most promising approach - heterologous prime-boost regimens, in which different viral vectors are sequentially paired with each other or with DNA or recombinant protein vaccines - is now being explored, and could provide high-grade protection, if findings in animal models are translatable to humans. Significant barriers remain, however, such as pre-existing immunity to the vector particle and an unexplained safety signal observed in one trial suggesting an increased risk of HIV acquisition in volunteers with pre-existing immunity to the vector.

Surface-associated antigens of Brugia malayi L2 and L3 parasites during vector-stage development.

Surface and metabolic labeling procedures were used to characterize the composition and the time of expression of Brugia malayi L2 and L3 surface-associated molecules as the larvae develop within the mosquito vector. Larvae were harvested from mosquito tissues at 5 (early L2), 8 (late L2) and 11 (L3) days post-infection and labeled with 125I-Iodo-Gen. The results of one-dimensional analysis showed that there is a progressive increase in the complexity of peptides associated with the surface of developing larvae, culminating in the expression of 7 major labeled components on L3s. Both L2 and L3 parasites have surface-associated components of 42, 35, 33, 19 and 17 kDa. Between days 8 and 11 of development in the insect vector, Brugia malayi undergoes the L2 to L3 molt and acquires additional major immunogenic peptides of 40 and 22 kDa. Two-dimensional analyses of extracts from 125I-labeled L2s and L3s revealed that the major 35-, 33-, 19- and 17-kDa molecules are part of a peptide complex that forms a 'ladder' between 17 and 150 kDa. To gain information on the times during which the major surface-associated molecules are produced by the parasite, larvae were labeled with [35S]methionine either in situ as they developed within the mosquito or during culture after exiting the vector. For in situ labeling, [35S]methionine was introduced into the hemolymph of infected mosquitoes by micro-injection at days 2, 5 and 8 post-infection and the larvae were allowed to develop for an additional 3 days. The results of 1- and 2-dimensional analyses of [35S]methionine-labeled extracts from vector-stage or post-vector-stage larvae indicate that the molecules associated with the surface of B. malayi L3s are synthesized between day 5 and day 11 of development in the insect host. Immediately after the larvae exit the vector, the synthesis of the 40 and 22-kDa peptides is drastically reduced or terminated.

Molecular cloning of a gene expressed during early embryonic development in Onchocerca volvulus.

Little attention has been paid to the reproductive biology of filarial nematode parasites as a possible target for immunological or chemotherapeutic intervention. An interruption of the reproductive process would, in addition to breaking the cycle of transmission, reduce the morbidity associated with certain filarial infections. As part of our efforts to define molecules that have important functions during filarial embryogenesis, antibodies against embryo-associated proteins were used to identify a 6308-bp cDNA sequence (ovt1) from an Onchocerca volvulus cDNA expression library. The ovt1 cDNA contained an open reading frame that coded for 2022 amino acids. The deduced amino acid sequence was highly hydrophilic, alpha-helical in nature and included two leucine zipper domains. OVT1 also contained a single Arg-Gly-Asp (RGD) site. The results of Southern blot analyses demonstrated that an ovt1-like gene occurs in a number of different species of filarial nematodes. In situ hybridization experiments to identify tissues that contain ovt1 transcripts showed that ovt1 was transcribed at high levels in the late morula/early blastocyst stage of embryonic development. Transcripts for ovt1 were also detected in O. volvulus larvae and in the hypodermal cells of adult parasites. Two fragments of ovt1 were expressed as fusion proteins and the fusion proteins were used to produce antibodies in rabbits. Both antibodies recognized a native protein with an apparent molecular mass of 230 kDa in extracts from gravid female O. volvulus. In addition, the antibodies reacted with a restricted number of lower-molecular mass bands which may represent the products of post-transcriptional or post-translational processing. The predicted coiled-coil structure and the sites of transcription suggest that OVT1 may be a component of the extracellular matrix.

Primaquine for prophylaxis against malaria among nonimmune transmigrants in Irian Jaya, Indonesia.

A comparison of primaquine versus chloroquine for prophylaxis among nonimmune transmigrants from Java and Bali in the hyperendemic Arso region of Irian Jaya, Indonesia was conducted. Forty-five subjects received 0.5 mg of primaquine base/kg of body weight every other day, and 54 people in the same village received weekly 5 mg of chloroquine base/kg for 16-19 weeks beginning in December 1992. Plasmodium falciparum accounted for 18 of 30 infections with chloroquine, and four of five infections among subjects receiving primaquine. Plasmodium vivax was found in 12 people taking chloroquine but in just one person taking primaquine. The risk of malaria among people taking chloroquine relative to that among subjects taking primaquine was 3.96 (P = 0.014) for P. falciparum and 10.56 (P = 0.012) for P. vivax. Primaquine was better tolerated than chloroquine. The minimal protective efficacy for primaquine prophylaxis was 74% against P. falciparum and 90% against P. vivax among nonimmune children and adults living in Irian Jaya. These findings require confirmation with randomized, double-blinded, and placebo-controlled trials.

Plasmodium falciparum mdr1 mutations and in vivo chloroquine resistance in Indonesia.

Mutations in the Pfmdr1 gene are reported to be associated with chloroquine resistance in some Plasmodium falciparum isolates. A polymerase chain reaction/restriction fragment length polymorphism method was used for the detection of Pfmdr1 mutations in chloroquine-resistant field isolates of P. falciparum collected in Irian Jaya. The frequency of Pfmdr1 mutations was significantly higher in chloroquine-resistant P. falciparum parasites than background frequencies observed in the same location. The 7G8 mutation was identified in some parasites although always in a mixed genotype status. Chloroquine-resistant P. falciparum specimens were characterized using the World Health Organization 28-day criteria, supplemented by demonstrating adequate chloroquine absorption and genetic analysis.

Malaria in a nonimmune population after extended chloroquine or primaquine prophylaxis.

Extended chemoprophylaxis against endemic malaria raises concern with regard to susceptibility after ceasing use of the drug. In this study, we measured attack rates of malaria among adult men for 28 weeks after they ended one year of prophylaxis using either weekly chloroquine (5 mg base/kg, n = 20), daily primaquine (0.5 mg base/kg, n = 30), or a placebo of primaquine (n = 41). The 28-week incidence densities, times to parasitemia, parasite densities, and symptoms of primary post-prophylaxis infections were not significantly different among the former primaquine, chloroquine, and placebo groups. However, the incidence of Plasmodium falciparum infection in the post-chloroquine group was significantly greater than in the post-primaquine group during the first (P = 0.03) and second (P = 0.02) months post-prophylaxis. Six of 10 primary P. falciparum and three of 10 P. vivax infections occurred in the former chloroquine group within one month after ending prophylaxis and the mean time to infection was 30-35 days. In contrast, only one P. falciparum and no P. vivax infections occurred during the first month after ending primaquine prophylaxis. The mean time to first parasitemia by either species of malaria parasite in this group was 72-77 days. There was no indication that daily use of primaquine for one year placed subjects at greater risk of malaria infection or to more severe clinical symptoms of malaria than subjects who had taken placebo or chloroquine, despite the potential for some degree of immunity to have been acquired in these latter two groups during the year-long prophylaxis period. The results do suggest that chloroquine suppressed P.falciparum infections until drug levels decreased, and that primaquine had effectively prevented the establishment of liver-stage parasites.

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.

Chloroquine-resistant Plasmodium vivax in transmigration settlements of West Kalimantan, Indonesia.

Malariometric surveys were conducted during July 1996 in native Dayak villages and predominantly Javanese transmigration settlements in Ketapang district of West Kalimantan, Indonesia. Malaria prevalence ranged from 0.9% to 2.7% in Dayak villages and from 1% to 20% in the transmigration settlements. Plasmodium falciparum accounted for 67% of the cases among Dayaks but P. vivax was dominant among transmigrants, accounting for more than 72% of the infections. Chloroquine sensitivity/resistance was assessed by 28-day in vivo testing of uncomplicated malaria infections and measurement of chloroquine blood levels in cases where parasitemias reappeared within the 28-day test period. Resistance was based on the appearance of asexual parasites against chloroquine plus desethylchloroquine levels exceeding the minimally effective whole blood concentrations proposed for sensitive parasite strains (P. vivax, 100 ng/ml; P. falciparum, 200 ng/ml). All parasitemias cleared initially within four days of beginning supervised chloroquine therapy (25 mg base/kg over a 48-hr period), but asexual parasites reappeared within 28 days in 27 of 52 P. vivax and three of 12 P. falciparum cases. Chloroquine blood levels at the time of recurrent parasitemias revealed resistance in 12 of the 27 P. vivax cases and in one of the three P. falciparum cases. Genotypes of nine of the 12 recurrent P. vivax isolates matched with their primary isolates and ruled out reinfection. These findings establish the presence of chloroquine-resistant P. vivax on the island of Borneo. The pattern of malaria and the high frequency of chloroquine resistance by P. vivax at the West Kalimantan location may relate to demographic, ecologic, agricultural, and socioeconomic changes associated with transmigration.

Chloroquine/doxycycline combination versus chloroquine alone, and doxycycline alone for the treatment of Plasmodium falciparum and Plasmodium vivax malaria in northeastern Irian Jaya, Indonesia.

Combination therapy is one method of overcoming the global challenge of drug-resistant Plasmodium falciparum malaria. We conducted a hospital-based 28-day in vivo test comparing chloroquine/doxycycline to chloroquine or doxycycline alone for treating P. falciparum and Plasmodium vivax malaria in Irian Jaya, Indonesia. Eighty-nine patients with uncomplicated falciparum malaria were randomized to standard dose chloroquine (n = 30), doxycycline (100 mg every 12 hours [7 days], n = 20), or chloroquine with doxycycline (n = 39); corresponding numbers for vivax malaria (n = 63) were 23, 16, 24. Endpoints were parasite sensitivity (S) or resistance (RI/RII/RIII). Of the 105 evaluable patients, chloroquine/doxycycline cured (S) 20/22 (90.9% [95% CI 78.9-100%]) patients with P. falciparum malaria; 2/22 (9.1% [0-21%]) were RIII resistant. Doxycycline cured 11/17 (64.7% [42.0-87.4%]) patients, and chloroquine 4/20 (20% [2.5-37.5%]). Against P. vivax, chloroquine/doxycycline cured (S) 12/17 (70.6% [48.9-92.2%]) patients, doxycycline 4/12 (33.3% [6.6-59.9%]), and chloroquine 5/17 (29.4% [7.7-51.1%]). Chloroquine/doxycycline was effective against P. falciparum but only modestly effective against P. vivax. These findings support the use of chloroquine/doxycycline as an inexpensive alternative to mefloquine for treating chloroquine-resistant P. falciparum but not chloroquine-resistant P. vivax in this setting.

A waterborne outbreak of hepatitis E virus transmission in southwestern Vietnam.

A hepatitis outbreak affecting primarily adults occurred in southwestern Vietnam, along the Hau river bordering Cambodia, in June and July 1994. One month after the outbreak, sera and epidemiologic information were collected from 150 subjects: 50 patient cases, 50 matched, healthy community controls, and 50 geographic controls living 50 km upriver. The prevalence of immunoglobulin G (IgG) to hepatitis E virus (HEV) was significantly (P < 0.001) higher (76%) among cases than among the matched (38%) and geographic (38%) control populations. Immunoglobulin M to HEV was detected by enzyme-linked immunosorbent assay and Western blot in 16% of sera collected from patients one month after the outbreak. Hepatitis E virus RNA was detected with the polymerase chain reaction in 6% of sera from patients; RNA was not detected in either control group. These results indicate that HEV was the etiologic agent responsible for the outbreak. Children were under-represented among clinical cases. River water served as the principal source for drinking and bathing among most (96%) of the case and control study populations. Boiling of drinking water was negatively associated (P < 0.05) with IgG anti-HEV seropositivity. Unusually heavy rainfall likely contributed to conditions that favored the outbreak. This is the first recognized outbreak of epidemic HEV transmission in Indo-China.

The emerging syndrome of envenoming by the New Guinea small-eyed snake Micropechis ikaheka.

The New Guinea small-eyed or ikaheka snake, Micropechis ikaheka, which occurs throughout New Guinea and some adjacent islands, is feared by the indigenes. The first proven human fatality was in the 1950s and this species has since been implicated in many other cases of severe and fatal envenoming. Reliable attribution of envenoming to this species in victims unable to capture or kill the snake recently became possible by the use of enzyme immunoassay. Eleven cases of proven envenoming by M. ikaheka, with two fatalities, were identified in Papua New Guinea and Irian Jaya. Five patients showed no clinical signs of envenoming. The other six patients showed symptoms typical of envenoming by other Australasian elapids: mild local swelling, local lymphadenopathy, neurotoxicity, generalized myalgia, spontaneous systemic bleeding, incoagulable blood and passage of dark urine (haemoglobinuria or myoglobinuria). Two patients developed hypotension and two died of respiratory paralysis 19 and 38 h after being bitten. In vitro studies indicate that the venom is rich in phospholipase A2, is indirectly haemolytic, anticoagulant and inhibits platelets, but is not procoagulant or fibrinolytic. It shows predominantly post-synaptic neurotoxic and myotoxic activity. Anecdotally, Commonwealth Serum Laboratories' (CSL) death adder antivenom has proved ineffective whereas CSL polyvalent antivenom may be beneficial. Anticholinesterase drugs might prove effective in improving neuromuscular transmission and should be tested in patients with neurotoxic envenoming.

Live attenuated malaria vaccine designed to protect through hepatic CD8⁺ T cell immunity.

Our goal is to develop a vaccine that sustainably prevents Plasmodium falciparum (Pf) malaria in ≥80% of recipients. Pf sporozoites (PfSPZ) administered by mosquito bites are the only immunogens shown to induce such protection in humans. Such protection is thought to be mediated by CD8(+) T cells in the liver that secrete interferon-γ (IFN-γ). We report that purified irradiated PfSPZ administered to 80 volunteers by needle inoculation in the skin was safe, but suboptimally immunogenic and protective. Animal studies demonstrated that intravenous immunization was critical for inducing a high frequency of PfSPZ-specific CD8(+), IFN-γ-producing T cells in the liver (nonhuman primates, mice) and conferring protection (mice). Our results suggest that intravenous administration of this vaccine will lead to the prevention of infection with Pf malaria.

Report of a consultation on the optimization of clinical challenge trials for evaluation of candidate blood stage malaria vaccines, 18-19 March 2009, Bethesda, MD, USA.

Development and optimization of first generation malaria vaccine candidates has been facilitated by the existence of a well-established Plasmodium falciparum clinical challenge model in which infectious sporozoites are administered to human subjects via mosquito bite. While ideal for testing pre-erythrocytic stage vaccines, some researchers believe that the sporozoite challenge model is less appropriate for testing blood stage vaccines. Here we report a consultation, co-sponsored by PATH MVI, USAID, EMVI and WHO, where scientists from all institutions globally that have conducted such clinical challenges in recent years and representatives from regulatory agencies and funding agencies met to discuss clinical malaria challenge models. Participants discussed strengthening and harmonizing the sporozoite challenge model and considered the pros and cons of further developing a blood stage challenge possibly better suited for evaluating the efficacy of blood stage vaccines. This report summarizes major findings and recommendations, including an update on the Plasmodium vivax clinical challenge model, the prospects for performing experimental challenge trials in malaria endemic countries and an update on clinical safety data. While the focus of the meeting was on the optimization of clinical challenge models for evaluation of blood stage candidate malaria vaccines, many of the considerations are relevant for the application of challenge trials to other purposes.

A DNA prime-modified vaccinia virus ankara boost vaccine encoding thrombospondin-related adhesion protein but not circumsporozoite protein partially protects healthy malaria-naive adults against Plasmodium falciparum sporozoite challenge.

The safety, immunogenicity, and efficacy of DNA and modified vaccinia virus Ankara (MVA) prime-boost regimes were assessed by using either thrombospondin-related adhesion protein (TRAP) with a multiple-epitope string ME (ME-TRAP) or the circumsporozoite protein (CS) of Plasmodium falciparum. Sixteen healthy subjects who never had malaria (malaria-naive subjects) received two priming vaccinations with DNA, followed by one boosting immunization with MVA, with either ME-TRAP or CS as the antigen. Immunogenicity was assessed by ex vivo gamma interferon (IFN-gamma) enzyme-linked immunospot assay (ELISPOT) and antibody assay. Two weeks after the final vaccination, the subjects underwent P. falciparum sporozoite challenge, with six unvaccinated controls. The vaccines were well tolerated and immunogenic, with the DDM-ME TRAP regimen producing stronger ex vivo IFN-gamma ELISPOT responses than DDM-CS. One of eight subjects receiving the DDM-ME TRAP regimen was completely protected against malaria challenge, with this group as a whole showing significant delay to parasitemia compared to controls (P = 0.045). The peak ex vivo IFN-gamma ELISPOT response in this group correlated strongly with the number of days to parasitemia (P = 0.033). No protection was observed in the DDM-CS group. Prime-boost vaccination with DNA and MVA encoding ME-TRAP but not CS resulted in partial protection against P. falciparum sporozoite challenge in the present study.

Interactions between malaria parasites infecting the same vertebrate host.

Several species of malarial protozoans commonly parasitize the same host population and often the same individual host. This paper reviews the evidence for interactions among such host-sharing parasites. Field studies measuring the cross-sectional prevalence of malarial species often record fewer mixed infections than expected by chance, suggesting that one parasite has excluded another or suppressed its parasitaemia to undetectable levels. Prevalences may vary reciprocally between seasons, with one species increasing in prevalence while another decreases, despite parallel increases in the transmission rates of both, again suggesting suppression of one species by another. However, longitudinal studies of individual hosts indicate that malarial parasites may also favourably affect the host environment for each other, perhaps due to their depressive effect on the immune system: this is shown by the recrudescence of a latent malarial species immediately before or after the parasitic wave of another species. The suppression hypothesis is supported by data derived from the simultaneous inoculation of two Plasmodium species into laboratory animals; many studies have shown that one or both species are suppressed. This may be mediated by competition for host cells or nutrients, or by heterologous immunity. However, the suppressed species rebounds after the other species has abated, and may show a prolonged infection. Experimental evidence that one species can facilitate the recrudescence of another is minimal, but this may reflect the paucity of investigations of this phenomenon. Laboratory studies show only minor cross-resistance between host-sharing species, which is consistent with the hypothesis that their co-occurrence has led to antigenic divergence or that species showing strong heterologous resistance cannot co-exist in the same host population. Such complementarity occurs not only with the host immune response but also with many other life-history characteristics of host-sharing parasites, such as host cell preference. I conclude that malarial species have been important in each other's evolution, particularly in the tropics where multi-species complexes are common.

Natural regulation of rhesus monkey populations in Kathmandu, Nepal. Rhesus monkey groups near Kathmandu, Nepal, show demographic patterns of intrinsic population stability.

In Kathmandu valley, two populations of rhesus monkeys which are totally protected, have shown relatively stable numbers over a period of several years. Population stability within heterosexual troops appears to have been maintained through lower birth rates and slightly higher infant and adult mortality rates than in comparable rhesus populations in India which have been subject to trapping. Although the behavioral and physiological mechanisms by which these demographic changes occur are not known, behavioral observations on these populations suggest several possibilities. These data represent the first indication of possible mechanisms for population regulation in natural rhesus populations.

Naturally acquired antibody responses to Plasmodium falciparum merozoite surface protein 4 in a population living in an area of endemicity in Vietnam.

Merozoite surface protein 4 (MSP4) of Plasmodium falciparum is a glycosylphosphatidylinositol-anchored integral membrane protein that is being developed as a component of a subunit vaccine against malaria. We report here the measurement of naturally acquired antibodies to MSP4 in a population of individuals living in the Khanh-Hoa region of Vietnam, an area where malaria is highly endemic. Antibodies to MSP4 were detected in 94% of the study population at titers of 1:5,000 or greater. Two forms of recombinant MSP4 produced in either Escherichia coli or Saccharomyces cerevisiae were compared as substrates in the enzyme-linked immunosorbent assay. There was an excellent correlation between reactivity measured to either, although the yeast substrate was recognized by a higher percentage of sera. Four different regions of MSP4 were recognized by human antibodies, demonstrating that there are at least four distinct epitopes in this protein. In the carboxyl terminus, where the single epidermal growth factor-like domain is located, the reactive epitope(s) was shown to be conformation dependent, as disruption of the disulfide bonds almost completely abolished reactivity with human antibodies. The anti-MSP4 antibodies were mainly of the immunoglobulin G1 (IgG1) and IgG3 subclasses, suggesting that such antibodies may play a role in opsonization and complement-mediated lysis of free merozoites. Individuals in the study population were drug-cured and followed up for 6 months; no significant correlation was observed between the anti-MSP4 antibodies and the absence of parasitemia during the surveillance period. As a comparison, antibodies to MSP1(19), a leading vaccine candidate, were measured, and no correlation with protection was observed in these individuals. The anti-MSP1(19) antibodies were predominantly of the IgG1 isotype, in contrast to the IgG3 predominance noted for MSP4.

Comparative performance of the ParaSight F test for detection of Plasmodium falciparum in malaria-immune and nonimmune populations in Irian Jaya, Indonesia.

A comparison was made of the performance of the ParaSight F test (F test) for detection of Plasmodium falciparum in blood from malaria-immune (410 native Irianese) and nonimmune (369 new transmigrants) populations in Irian Jaya, Indonesia, where malaria is hyperendemic and all four species of human malaria occur. There were highly significant differences between populations in the sensitivity (Irianese, 60% versus transmigrants, 84%; P < 0.001) and specificity (Irianese, 97% versus transmigrants, 84%; P < 0.001) of the F test. The test had comparably high levels of sensitivity for Irianese children aged < or = 10 years, both age groups of transmigrants (76-85%), but low sensitivity for Irianese aged > 10 years (40%), among whom only 7% of parasitaemias < 120 per microliter and 69% of those > 120 per microliter were detected. Specificity was comparably high for transmigrant children aged < or = 10 years and both age groups of Irianese (93-98%). The low specificity for transmigrants aged > 10 years (79%) was due to a preponderance of false positives, frequently identified by microscopy as P. vivax. The results suggest that comparison based on microscopy underestimated the performance of the ParaSight F test and that malaria immune status, irrespective of P. falciparum density, may influence the test's sensitivity.

PIP: The ParaSight F test uses a nonmicroscopic dipstick approach to the rapid detection of Plasmodium falciparum in blood. The performance of this test was assessed in serum samples collected in Irian Jaya, Indonesia, from 410 native Irianese (malaria-immune) and 369 new transmigrants (nonimmune). Of particular interest was the capability of the F test to detect P. falciparum prevalence among children, whose immunity is less than that of adults. There were highly significant differences by population in the F test's sensitivity (60% for Irianese vs. 84% for transmigrants) and specificity (97% for Irianese vs. 84% for transmigrants). The test had high sensitivity levels (76-85%) for Irianese children 10 years of age and under and both child and adult transmigrants, but low sensitivity (40%) for Irianese over 10 years of age. Specificity was comparably high (93-98%) for transmigrant children and both age groups of Irianese. The low specificity (79%) for transmigrants over 10 years of age reflected a preponderance of false positives, frequently identified by microscopy as P. vivax. These findings suggest that microscopy comparisons underestimate the performance of the ParaSight F test and that malaria immune status, regardless of P. falciparum density, may influence the test's sensitivity.