Semi-nested, multiplex polymerase chain reaction for detection of human malaria parasites and evidence of Plasmodium vivax infection in Equatorial Guinea.
A semi-nested, multiplex polymerase chain reaction (PCR) based on the amplification of the sequences of the 18S small subunit ribosomal RNA (ssrRNA) gene was tested in a field trial in Equatorial Guinea (a hyperendemic focus of malaria in west central Africa). The method uses a primary PCR amplification reaction with a universal reverse primer and two forward primers specific for the genus Plasmodium and to mammals (the mammalian-specific primer was included as a positive control to distinguish uninfected cases from inhibition of the PCR). The second amplification is carried out with the same Plasmodium genus-specific forward primer and four specific reverse primers for each human Plasmodium species. The PCR amplified products are differentiated by fragment size after electrophoresis on a 2% agarose gel. Four villages from three regions of the island of Bioko (Equatorial Guinea) and two suspected Plasmodium vivax-P. ovale infections from the hospital of Malabo were tested by microscopy and PCR. The PCR method showed greater sensitivity and specificity than microscopic examination and confirmed the existence of a focus of P. vivax infections in Equatorial Guinea suspected by microscopic examination. It also provided evidence of several mixed infections, mainly P. falciparum and P. malariae, the two predominant species causing malaria in Equatorial Guinea. (+info)
Antimalarial activities of various 4-pyridinemethanols with special attention to WR-172,435 and WR-180,409.
Pilot appraisals of the activities of 10 specially selected 2,6-substituted-4-pyridinemethanols against acute Plasmodium falciparum infections in owl monkeys identified three derivatives that were two to three times as active as chloroquine against infections with a 4-aminoquinoline-susceptible strain and, at the same doses, were equally effective against infections with a strain fully resistant to treatment with maximally tolerated doses of chloroquine, quinine, and pyrimethamine. Two of these derivatives, WR-172,435 and WR-180,409, deemed worthy of evaluation in human volunteers, were studied in greater depth in owl monkeys infected with either the multidrug-resistant Smith strain of P. falciparum or the pyrimethamine-resistant Palo Alto strain of P. vivax. These studies showed (i) that at the same total oral dose, 3-day and 7-day treatment schedules were equally effective and slightly superior to a single-dose schedule; (ii) that WR-172,435 was slightly more active than WR-180,409 in each treatment regimen; (iii) that intravenous delivery of WR-180,409 phosphate was feasible and effective; (iv) that both compounds effected control of parasitemia more rapidly than any standard or newly discovered antimalarial drug; and (v) that WR-172,435 and WR-180,409 had therapeutic indexes at least four to eight times those exhibited by chloroquine in infections with 4-aminoquinoline-susceptible strains, indexes retained by these pyridinemethanols against infections with various drug-resistant strains. (+info)
Multispecies Plasmodium infections of humans.
We analyzed point-prevalence data from 19 recent studies of human populations in which either Plasmodium ovale or Plasmodium vivax co-occur with Plasmodium falciparum and Plasmodium malariae. Although the only statistical interactions among, sympatric congeners are pairwise, the frequencies of mixed-species infections relative to standard hypotheses of species sampling independence show no strong relation to overall malaria prevalence. The striking difference between the P. falciparum-P. malariae-P. ovale and the P. falciparum-P. malariae-P. vivax data is that the first typically shows a statistical surplus of mixed-species infections and the second a deficit. This suggests that the number of Plasmodium species present in a human population may be less important in determining the frequencies of mixed-species infections than is the identity of those species. (+info)
Drug resistance in malaria.
Drug resistance in malaria is now widespread and in many parts of the world is making treatment increasingly difficult. This article reviews current knowledge of the mechanisms and extent of resistance of Plasmodium falciparum and P. vivax to the available antimalarial drugs, and the recommendations for treating malaria in regions where resistance is prevalent. (+info)
Differential perpetuation of malaria species among Amazonian Yanomami Amerindians.
To determine whether malaria perpetuates within isolated Amerindian villages in the Venezuelan Amazon, we surveyed malaria infection and disease among 1,311 Yanomami in three communities during a 16-month period. Plasmodium vivax was generally present in each of these small, isolated villages; asymptomatic infection was frequent, and clinical disease was most evident among children less than five years of age (odds ratio [OR] = 6.3, 95% confidence interval [CI] = 1.4-29.2) and among persons experiencing parasitemias > or = 1,000 parasites/mm3 of blood (OR = 45.0, 95% CI = 5.5-370.7). Plasmodium falciparum, in contrast, was less prevalent, except during an abrupt outbreak in which 72 infections resulted in symptoms in all age groups and at all levels of parasitemia, and occasionally were life-threatening. The observed endemic pattern of P. vivax infection may derive from the capacity of this pathogen to relapse, while the epidemic pattern of P. falciparum infection may reflect occasional introductions of strains carried by immigrants or residents of distant villages and the subsequent disappearance of this non-relapsing pathogen. (+info)
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. (+info)
Antimalarial activities of WR-194,965, an alpha-amino-o-cresol derivative.
Pilot appraisals of the activities of WR-194,965 and WR-204,165, two closely related o-cresol derivatives (both Mannich bases), in owl monkeys infected with the multidrug-resistant Vietnam Smith strain of Plasmodium falciparum showed that these compounds had similar levels of efficacy. Total course doses effecting 90% cures (CD(90)s) were 27 and 37 mg/kg of body weight for the respective compounds, values almost identical to the CD(90) of mefloquine (a highly promising 4-quinolinemethanol) against infections with the same strain, and the CD(90)s of chloroquine against infections with 4-aminoquinoline-susceptible strains. Expanded studies of the activities of WR-194,965 against infections with the Smith strain of P. falciparum and Vietnam Palo Alto strain of P. vivax, designed to guide projected evaluations in human volunteers, showed: (i) that the activity of this compound was a function of total dose administered, with single doses as effective as the same amount delivered in three or seven successive daily fractions; (ii) that all regimens effected rapid clearance of parasitemia; and (iii) that based on CD(90)s, this agent was twice as active against infections with the Palo Alto strain of P. vivax as against the Smith strain of P. falciparum. These findings, together with results of preclinical pharmacological studies pursued elsewhere, provided support for studies in human volunteers now underway. (+info)
Antimalarial activities of the 4-quinolinemethanols WR-184,806 and WR-226,253.
WR-184,806 and WR-226,253, two 4-quinolinemethanols structurally similar to WR-142,490 (mefloquine), have been studied in depth in owl monkeys infected with various drug-resistant and drug-susceptible strains of Plasmodium falciparum and P. vivax in an effort to provide support and guidance for projected evaluations in human volunteers. The results of these studies, confirmatory of preliminary appraisals, showed that WR-184,806 was approximately one-third as active as WR-142,490 against infections with a multidrug-resistant strain of P. falciparum, whereas WR-226,253 was twice as active. Additionally, the current studies showed: (i) that both WR-184,806 and WR-226,253 were significantly more active against infections with blood schizonts of P. vivax than against those of P. falciparum; (ii) that their activities against established infections with either Plasmodium species were functions of the total doses delivered, single doses being as effective as three or seven fractional doses given on successive days; (iii) that WR-184,806 could be administered intravenously as the phosphate salt and was curative via this route in single doses; and (iv) that based on comparative curative doses, WR-184,806 was slightly more active and WR-226,253 was seven times more active against infections with a multidrug-resistant strain of P. falciparum than was chloroquine against infections with a 4-aminoquinoline-susceptible strain. (+info)