Increase In Parasite Density Research Articles

Quality Assurance of Rapid Diagnostic Tests for Malaria in Routine Patient Care in Rural Tanzania

Histidine-rich protein II (HRP2)-based malaria rapid diagnostic tests (RDTs) have shown high sensitivity and specificity for detecting Plasmodium falciparum malaria in a variety of study settings. However, RDTs are susceptible to heat and humidity and variation in individual performance, which may affect their use in field settings. We evaluated sensitivity and specificity of RDTs during routine use for malaria case management in peripheral health facilities. From December 2007 to October 2008, HRP2-based ParaHIT-f RDTs were introduced in 12 facilities without available microscopy in Rufiji District, Tanzania. Health workers received a single day of instruction on how to perform an RDT and thick blood smear. Job aids, Integrated Management of Childhood Illness guidelines, and national malaria treatment algorithms were reviewed. For quality assurance (QA), thick blood smears for reference microscopy were collected for 2 to 3 days per week from patients receiving RDTs; microscopy was not routinely performed at the health facilities. Slides were stained and read centrally within 72 hours of collection by a reference microscopist. When RDT and blood smear results were discordant, blood smears were read by additional reference microscopists blinded to earlier results. Facilities were supervised monthly by the district laboratory supervisor or a member of the study team. Ten thousand six hundred fifty (10,650) patients were tested with RDTs, and 51.5% (5,488/10,650) had a positive test result. Blood smear results were available for 3,914 patients, of whom 40.1% (1,577/3,914) were positive for P. falciparum malaria. Overall RDT sensitivity was 90.7% (range by facility 85.7-96.5%) and specificity was 73.5% (range 50.0-84.3%). Sensitivity increased with increasing parasite density. Successful implementation of RDTs was achieved in peripheral health facilities with adequate training and supervision. Quality assurance is essential to the adequate performance of any laboratory test. Centralized staining and reading of blood smears provided useful monitoring of RDT performance. However, this level of QA may not be sustainable nationwide.

Budding ofTaenia crassicepsCysticerci In Vitro Is Promoted by Crowding in Addition to Hormonal, Stress, and Energy-Related Signals

Taenia crassiceps cysticerci (cysts) reproduce by budding. The cysts' production of buds was measured in vitro to explore parasite and environmental-related factors involved in the extreme individual variation in parasite loads of inbred mice. Cysts were placed in in vitro culture for 10 days at initial parasite densities of 1, 5, 10 cysts/well in 1 ml of RPMI Medium 1640 without serum. Results showed that there is considerable intrinsic initial variation among inoculated cysts in their production of buds and that increasing parasite density (crowding) stimulates the overall production of buds and recruit into budding most of the cysts. Identical cultures were then subjected to various treatments such as heating and exposure to peroxide to induce stress, or to 17ß-estradiol, insulin, glucose, or insulin+glucose to supplement putatively limiting hormonal and energy resources. All treatments increased budding but the parasites' strong budding response to crowding alone overshadows the other treatments.

Platelets, Aspirin, and Malaria

Thrombocytopenia, a common manifestation of malaria, is associated with increased parasite density and poor outcome. Platelets produce microbicidal peptides active against a variety of bacteria. Now, researchers in Australia have investigated whether these blood components play a role in host defense against …

Challenges in Routine Implementation and Quality Control of Rapid Diagnostic Tests for Malaria–Rufiji District, Tanzania

Rapid diagnostic tests (RDTs) represent an alternative to microscopy for malaria diagnosis and have shown high sensitivity and specificity in a variety of study settings. Current World Health Organization (WHO) guidelines for quality control of RDTs provide detailed instructions on pre-field testing, but offer little guidance for quality assurance once RDTs are deployed in health facilities. From September 2006 to April 2007, we introduced a histidine-rich protein II (HRP2)-based RDT (Paracheck) for suspected malaria cases five years of age and older in nine health facilities in Rufiji District, Tanzania, to assess sensitivity and specificity of RDTs in routine use at rural health facilities. Thick blood smears were collected for all patients tested with RDTs and stained and read by laboratory personnel in each facility. Thick smears were subsequently reviewed by a reference microscopist to determine RDT sensitivity and specificity. In all nine health facilities, there were significant problems with the quality of staining and microscopy. Sensitivity and specificity of RDTs were difficult to assess given the poor quality of routine blood smear staining. Mean operational sensitivity of RDTs based on reference microscopy was 64.8%, but varied greatly by health facility, range 18.8-85.9%. Sensitivity of RDTs increased with increasing parasite density. Specificity remained high at 87.8% despite relatively poor slide quality. Institution of quality control of RDTs based on poor quality blood smear staining may impede reliable measurement of sensitivity and specificity and undermine confidence in the new diagnostic. There is an urgent need for the development of alternative quality control procedures for rapid diagnostic tests that can be performed at the facility level.

Parasitic mite and trematode abundance are associated with reduced reproductive output and physiological condition of freshwater mussels

Although historically understudied, parasites may play an important role in freshwater invertebrate population ecology and evolution. We quantified abundance of parasitic mites and trematodes in the freshwater mussel Pyganodon grandis, in a southeastern Alabama stream (USA), to assess parasite impact on adult mussel physiological condition and reproductive output. We used stepwise multiple regression analyses to assess the effects of mussel size and parasites on reproduction and condition. Multiple regression analysis found no multivariate models that predicted reproductive output or physiological condition. However, univariate models revealed that increased parasite densities predict reduced mussel reproductive output and physiological condition. These findings suggest that parasites may have important negative consequences for freshwater mussels. We hypothesize that elevated parasite loads may reduce mussel fitness in impounded or nutrient-enriched streams with high densities of intermediate hosts (chironomid midges).

Adverse birth outcomes in a malarious area

To determine factors associated with fetal growth, preterm delivery and stillbirth in an area of high malaria transmission in Southern Malawi, a cross-sectional study of pregnant women attending and delivering at two study hospitals was undertaken. A total of 243 (17.3%) babies were preterm and 54 (3.7%) stillborn. Intra-uterine growth retardation (IUGR) occurred in 285 (20.3%), of whom 109 (38.2%) were low birthweight and 26 (9.1%) preterm. Factors associated with IUGR were maternal short stature [adjusted odds ratio (AOR) 1.6, 95% confidence interval (CI) 1.0-2.5]; primigravidae (AOR 1.9, 95% CI 1.4-2.7); placental or peripheral malaria at delivery (AOR 1.4, 95% CI 1.0-1.9) and maternal anaemia at recruitment (Hb<8 g/dl) (AOR 1.9, 95% CI 1.3-2.7). Increasing parasite density in the placenta was associated with both IUGR (P=0.008) and prematurity (P=0.02). Factors associated with disproportionate fetal growth were maternal malnutrition [mid-upper arm circumference (MUAC)<23 cm, AOR 1.9, 95% CI 1.0-3.7] and primigravidae (AOR 1.8, 95% CI 1.0-3.1). Preterm delivery and stillbirth were associated with <5 antenatal care visits (AOR 2.2, 95% CI 1.3-3.7 and AOR 3.1, 95% CI 1.4-7.0 respectively) and stillbirth with a positive Venereal Disease Research Laboratory (VDRL) test (AOR 4.7, 95% CI 1.5-14.8). Interventions to reduce poor pregnancy outcomes must reduce the burden of malaria in pregnancy, improve antenatal care and maternal malnutrition.

Relationship between malaria infection intensity and rainfall pattern in Entebbe peninsula, Uganda.

This study was to assess malaria prevalence in relation to rainfall pattern in different localities of Entebbe Municipality, Uganda. A cross sectional study was conducted amongst the local community residing in the area from January 2003 to January 2004 to investigate the incidence and intensity of malaria infection. Thick and thin blood smears were made from each patient with fever (body temperature >or= 37.5 degrees C). The slides were examined microscopically for malaria parasites. A total of 616 residents aged 2 to 50 years were registered in the study by name, age, sex and residential location. Spearman correlation coefficient (r) was used to evaluate relationship between parasite density, age and body temperature on one hand and rainfall plus parasite density on the other hand. A direct relationship was observed between malaria transmission and monthly rainfall in Entebbe Municipality. About 69.8% of the patients had fever. Parasite density fluctuated according to monthly rainfall pattern. Two peaks of high parasite density was observed, each peak coinciding with a peak rainfall pattern of the bimodal annual rain seasons. There was a negative but significant correlation (r = -0.09271; p < 0.0214) between parasite density and age, suggesting that mature individuals clear parasites more effectively than children. Furthermore, we observed a bimodal peak of mean parasite density in children and adults; peak in children is higher than of adults, each peak coinciding with rainfall pattern. There is also a significant positive correlation between parasite density and body temperature (r = 0.1927; p = 0.0001). However, there is no significant variation in mean parasite densities in the different locations of Entebbe Municipality. Our study confirms rainfall pattern and age influence parasite density and are important determinants of malaria infection and transmission in Entebbe Municipality. Increased parasite density in children is a useful indicator for monitoring intensity of infection. This information is valuable in policy formulation for control of malaria during periods of intense transmission.

THE IMPACT OF AGE, TEMPERATURE, AND PARASITE DENSITY ON TREATMENT OUTCOMES FROM ANTIMALARIAL CLINICAL TRIALS IN KAMPALA, UGANDA

Antimalarial drug treatment policy in sub-Saharan Africa is generally guided by the results of clinical drug efficacy studies in patients with uncomplicated Plasmodium falciparum malaria. The selection criteria used to enroll these patients often vary and may have a significant impact on treatment outcomes. In Kampala, Uganda, we investigated the impact of age, baseline temperature, and pre-treatment parasite density on estimates of treatment efficacy using a statistical modeling approach in 2,138 patients enrolled in six clinical trials involving seven different treatment regimens. Decreasing age, increasing temperature, and increasing parasite density were all independent predictors of an increased risk of treatment failure across all treatment groups. Compared with an unrestrictive approach to subject selection, enrolling only patients fulfilling selection criteria recommended by the World Health Organization (age < 5 years old, documented fever, and parasite density < 200,000/microL) increased the risk of treatment failure by 25-60% for the different treatment regimens. Caution should be taken when comparing results from drug efficacy studies with different subject selection criteria.

Density-dependence and within-host competition in a semelparous parasite of leaf-cutting ants

BackgroundParasite heterogeneity and within-host competition are thought to be important factors influencing the dynamics of host-parasite relationships. Yet, while there have been many theoretical investigations of how these factors may act, empirical data is more limited. We investigated the effects of parasite density and heterogeneity on parasite virulence and fitness using four strains of the entomopathogenic fungus, Metarhizium anisopliae var. anisopliae, and its leaf-cutting ant host Acromyrmex echinatior as the model system.ResultsThe relationship between parasite density and infection was sigmoidal, with there being an invasion threshold for an infection to occur (an Allee effect). Although spore production was positively density-dependent, parasite fitness decreased with increasing parasite density, indicating within-host scramble competition. The dynamics differed little between the four strains tested. In mixed infections of three strains the infection-growth dynamics were unaffected by parasite heterogeneity.ConclusionsThe strength of within-host competition makes dispersal the best strategy for the parasite. Parasite heterogeneity may not have effected virulence or the infection dynamics either because the most virulent strain outcompeted the others, or because the interaction involved scramble competition that was impervious to parasite heterogeneity. The dynamics observed may be common for virulent parasites, such as Metarhizium, that produce aggregated transmission stages. Such parasites make useful models for investigating infection dynamics and the impact of parasite competition.

The Role of Kola Nut (Cola Nitida) in the Etiology of Malaria Morbidity

The contribution of kola nut in mimicking malaria-like morbidity in apparently healthy volunteers was evaluated. Thirty-five grams of Cola nitida was given to each of the 48 volunteers who were known not to have taken kola nut or coffee in the previous one month for three consecutive days. The blood samples of these volunteers were enumerated for malaria parasites before serving them the kola nut. The sampling of blood was repeated on the 2nd and 3rd days for the presence of malaria parasites. Blood samples were also taken from known kola nut addicts (those that eat kola nut on daily basis). It was found that 16 (33.3%) of the volunteers had malaria parasites in their blood at the inception of the study while 32 (66.7%) had no detectable parasites. Four days after, 10 (20.8%) of the volunteers that did not show detectable parasites on the first day now had parasites. Those that showed detectable parasite before taking the kola had significant increase in parasite density. Statistical analysis showed a strong relationship between parasite increase and eating of the kola nut (Chi-squared, X 2 = 14.83, p > 0.0001 at 95% confidence limit). The volunteers reported clinical symptoms of sleeplessness, lack of concentration, dizziness, and weakness observable in malaria patients. There was no association between malaria parasite presence and clinical complaints (X 2 = 3.75, df = 1, p = 0.05). It was found that 11 people without the malaria parasite in their blood before and after taking the kola nut complained of various malaria symptoms confirming that kola nut can mimic malaria-like symptoms. In conclusion, it can be said that kola nut taken at a high concentration (about 35 g/day) will mimic malaria-like symptoms. This quantity will leave a high level of caffeine and cyanide in the circulation so that people with a low level of malaria parasite in them will notice active infection which otherwise may have been controlled by the host immune system. Lastly, the observed phenomenon can affect drug pressure and induce resistance to antimalarial drugs. The mechanism of kola nut action that influences malaria-like morbidity is discussed.

Relationship between parasite density and fever risk in a community exposed to a low level of malaria transmission in Madagascar highlands.

To establish a simple definition of a malaria attack based on blood parasite density and other explanatory covariates, a cohort study was conducted from 1993 to 1996 in the Madagascar highlands undergoing a low seasonal transmission of falciparum malaria. Using logistic regression, the explanatory variables found to be significantly related to the risk of fever are parasite density, age, season, and year. However, and in contrast with other studies, we found no evidence of a clear cutoff in parasite density values consistent with the concept of "pyrogenic threshold" despite a gradual increase of the risk of fever with increasing parasite density. Furthermore, the model evidenced an individual-dependent relationship at a given age. This point was in accordance with the immunological data recorded from the participants. The investigators conclude that the parasite density to distinguish malaria attacks from other causes of fever is not reliable in a context of low falciparum transmission.

Malaria in the first 6 months of life in urban African infants with anemia.

A total of 446 infants in the first 6 months of life who presented at an urban children's hospital with complaints of any illness whatsoever were recruited into a study with the aim of determining the contribution of malaria to infant morbidity in a malaria-endemic urban area in Nigeria. Sixty-eight of the infants were in their first month of life and 79, 77, 61, 97, and 64 were in their second, third, fourth, fifth and sixth month of life, respectively. Overall, 107 (24.0%) infants were clinically diagnosed as having malaria. This included 3 who were in the first month of life, 12 in the second, 15 in the third, 17 in the fourth, 33 in the fifth, and 27 in the sixth months of life (4.4, 15.2, 19.5, 27.9, 34.0, and 42.1%, respectively). Laboratory investigations confirmed 35 (32.7%) of those clinically diagnosed and 86 (25.4%) of those not clinically diagnosed (n = 339) as having malaria parasitemia, giving an overall malaria parasite rate of 27.1% among the infants. Acute respiratory infection was the major diagnosis (41.3%) among those that were not initially diagnosed as malaria but turned out to have malaria parasitemia followed by gastroenteritis (11.8%) and failure to growth (1.5%). Overall geometric mean parasite density was 202.5 parasites/microL of blood (range, 12-65,317 parasites/microL of blood). The mean hematocrit of infants with parasites (33.0%) was significantly lower (P < 0.005) than that of infants without parasites (35.1%). The mean hematocrit of infants with malaria parasites in each age group was lower than that of infants without malaria parasites in the corresponding age group. Among the infants with malaria parasites, those aged 2 to 2.9 months recorded the lowest mean hematocrit (30.1%), and those aged < 1 month recorded the highest mean hematocrit (42.7%). Axillary temperature increased and hematocrit decreased with increase in parasite density. The percentage of infants with anemia likewise increased as the parasite density increased. Plasmodium falciparum was present in all infected infants, but mixed infection with P. malariae was present in only 2.5% of infections. Analysis of our data suggests an urgent need for health education of caretakers and for training of clinicians for increased awareness of malaria as an important cause of illness and anemia in infants aged < 6 months so as to reduce children's wasting due to an easily preventable and treatable disease.

The effect of trematode infection on amphibian limb development and survivorship.

The causes of amphibian deformities and their role in widespread amphibian declines remain conjectural. Severe limb abnormalities were induced at high frequencies in Pacific treefrogs (Hyla regilla) exposed to cercariae of a trematode parasite (Ribeiroia sp.). The abnormalities closely matched those observed at field sites, and an increase in parasite density caused an increase in abnormality frequency and a decline in tadpole survivorship. These findings call for further investigation of parasite infection as a cause of amphibian deformities in other sites and species.

The role of low level Plasmodium falciparum parasitaemia in anaemia among infants living in an area of intense and perennial transmission.

Children under one year of age in an area of intense and perennial Plasmodium falciparum transmission were followed up for one year to establish to what extent chronic, low parasitaemia was associated with severe anaemia. There was a significant increase in the prevalence of anaemia (PCV < or = 25%) with increase in parasite density. PCV levels were related not only to concurrent parasite density but also decreased with densities measured one month previously. At any point in time, the mean PCV level in infants with low parasitaemia (< 1000 parasites/microliter) was higher than that of infants with intermediate (1000-9999/microliter) and high parasite densities (> or 10000/microliter). After the age of 7 months, infants with low parasite densities tend to recover, probably as a result of developing immunity. At the age of 12 months, they have similar PCV levels to infants with no detectable parasitaemia by microscopy. The maintenance of low parasite density appears crucial to the survival of infants in malaria endemic areas. The findings suggest that interventions which lower parasite densities in areas of intense transmission reduce the development of severe malarial anaemia and thus malaria-related mortality and morbidity in infants.

Rapid Manual Diagnosis of Plasmodium falciparum Malaria Using ParaSight-F Dipsticks Applied to Human Blood and Urine.

Rapid, simple and accurate methods are required for the diagnosis of malaria in travelers. Studies have reported field evaluation of a dipstick antigen-capture assay based on qualitative detection of Plasmodiumfalciyarm (Pf) histidine-rich protein I1 (PfHRP-11) in peripheral blood for diagnosis of ef infection (Parasight-F test, Becton Dickinson Advanced Diagnostics).’.* The dipstick, a preparation of nitrocellulose and glass fiber, is pretreated with a mouse monoclonal antibody (mAb) against PfHRP-11, which is applied across the stick in a line across about 1 cm from the base of the stick.A second dotted line of PfHRP-I1 antigen is incorporated in the dipstick about 3 mm above the line of mAb as a reagent control. The dipstick is placed in a drop of hemolyzed blood. Following this process, drops of developing and clearing reagents are applied at the base of the dipstick. A positive test result (indicating the presence of PfHRP-11) is evident when a thin, solid pink band appears on the dipstick. The sensitivity of the test, when compared with microscopic examination, increases with increasing parasite density to reach almost 100% for densities greater than 100 pf/l~.L.’ Since it is known that some Plasmodium antigens can be detected in the urine of parasitemic individual^,^ we conducted a pilot study to assess the sensitivity of the dipstick test when applied to human urine. We compared the results of blood slide examination by microscopy with the results of the dipstick test in both the blood and urine samples of 53 healthy adults living in a highly endemic area of Papua New G ~ i n e a . ~ Examiners were blinded to the results of the other tests.

Studies on the characteristics of parasitism ofPlutella xylostella (Lep.: Plutellidae) by a larval parasiteDiadegma semiclausum (Hym.: Ichneumonidae)

Laboratory experiments were conducted to study the characteristics of parasitism of diamondback moth,Plutella xylostella (L.), a worldwide pest of crucifers, by a larval parasite,Diadegma semiclausum Hellen. Results showed that the greater the host larval density, the lesser was the percentage of larvae parasitized. The area of discovery decreased with increasing parasite density, but k-value remained practically unchanged. Parasitism reduced food consumption in parasitised larvae. No difference was observed in duration of larval instars between the parasitized and healthy larvae. As the frequency of superparasitism increased, the proportion of production of female progeny also increased. Presence of parasite larva within the host larva deterred superparasitism greater than the presence of parasite egg. Presence of larva of eitherD. semiclausum or another larval parasite,Cotesia plutellae Kurdjumov, within host larva deterred multiparasitism by either species greater than the presence of egg of either parasite species.Diadegma semiclausum was much more aggressive thanC. plutellae in parasitisingP. xylostella larvae.

Do high levels of C-reactive protein in Tanzanian children indicate malaria morbidity

Children under 6 years of age living in an area of Tanzania highly endemic for malaria were tested for C-reactive protein (CRP) in order to determine how the acute-phase response is related to malaria in children of different ages and to investigate whether serum CRP concentrations might be useful in the qualification of morbidity in such children. The median CRP level in the 629 finger-prick blood samples measured, 6.0 mg/liter, was much higher than that reported in the blood of children in Europe. The CRP concentration was correlated with recent illness reported by the parents. High CRP levels were most strongly associated with Plasmodium falciparum parasitemia in children under 1 year of age. In older children, lower levels of CRP were associated with parasitemia, and fewer children had increased CRP levels attributable to parasitemia. The levels of malaria-attributable CRP appear to track the acquisition of parasitological and clinical tolerance in this area with very high levels of P. falciparum transmission. Determination of CRP levels should be useful in the rapid assessment of the overall burden of morbidity, especially in infants. In areas where malaria is endemic, CRP associated with increased parasite densities provides an objective measure of malaria-specific morbidity. This would be an efficient approach to estimating malaria morbidity risks from small-scale serological surveys.

Dynamics of malaria parasitaemia associated with febrile illness in children from a rural area of Madang, Papua New Guinea

Active community and self-reporting surveillance techniques have been used to describe the dynamics of febrile illness and associated malaria infection in children aged 2 to 15 years from a rural area of Madang Province, Papua New Guinea (PNG). Both history of fever and fever in association with parasitaemia appeared to be reliable indicators of malaria morbidity in this endemic area. Parasite density was observed to be a major determinant of mild malarial disease at both the population level and within an individual. Age-specific prevalence of febrile illness correlated with age-specific patterns of parasite density but not of parasite prevalence. Seasonal changes in fever incidence correlated with parasite density. The transition from afebrile to febrile state within an individual was generally associated with an increase in parasite density. Surveillance and self-reported febrile cases (which differ in severity on the basis of the perceived need for treatment) could be distinguished on the basis of parasite density. Thus surveillance techniques divide clinical malaria in rural PNG into ‘mild’ and ‘very mild’ forms. The age-specific pattern of decline of prevalence of malariaassociated febrile illness and parasite density is best explained by induction of strain-specific anti-disease immunity upon infection with a given strain of Plasmodium falciparum. The fever threshold in self-reporting febrile cases was seen to decrease with age and can be explained by an age-specific decline in anti-toxic immunity.

Malaria in a rural area of Sierra Leone. II. Parasitological and related results from pre- and post-rains clinical surveys.

The prevalence of Plasmodium falciparum in a cohort of over 900 nought to seven-year-old children living in a rural area of Sierra Leone was found to be approximately 61%, both before and after the rainy season. Plasmodium malariae rates measured in the same children were approximately 12%, and P. ovale rates averaged about 1%. Spleen rates averaged 44% for the two surveys; the age prevalence spleen profiles closely matched those for P. falciparum. The overall gametocyte rates for both P. falciparum and P. malariae were roughly one fifth of the prevalence rates for the asexual parasites. However, whilst there was no difference between the P. falciparum gametocyte rates at the two surveys, the P. malariae rate was significantly higher post-rains when compared with the pre-rains result. Spleen size did not increase with increased parasite density. There was a statistically significant difference between the geometric mean P. falciparum trophozoite densities of febrile and afebrile children both before and after the rainy season, but there was little seasonal difference in the means for the febrile children or in those for the afebrile children. Antimalaria antibody levels, measured by ELISA and IFAT, showed no significant differences at either survey. The levels found were high for all age groups, indicating that exposure to malaria begins at birth. Our results indicate that, in the area studied, malaria is hyperendemic and is probably transmitted perennially.

Transcribing and replicating particles in a double-stranded RNA virus from Leishmania

During the replicative cycle of many double-stranded RNA viruses, transcription of particles with a double-stranded RNA genome alternates with replication of particles containing a single-stranded genome. In virions infecting some strains of Leishmania guyanensis the putative transcriptase and replicase activities of the RNA-dependent RNA polymerase were previously detected in vitro. Northern hybridization to RNA of known polarity demonstrates that the single-stranded RNA products are of positive polarity and, by definition, are the products of the viral transcriptase. Re-evaluation of previously published data in the light of these findings suggests that transcription in Leishmania viruses is conservative. Sedimentation in sucrose gradients revealed two types of viral particles; single-stranded RNA particles comprised a small fraction of the virus population and sedimented more slowly than the peak of double-stranded RNA particles. In agreement with the replicative model of other dsRNA viruses, these single-stranded particles co-purified with the viral replicase activity that resulted in double-stranded RNA synthesis. In virus-infected promastigote extracts replicase activity decreased with increasing parasite density in culture, suggesting a correlation between cell division and viral replication.