Geospatial analysis of Plasmodium falciparum serological indicators: school versus community sampling in a low-transmission malaria setting

BACKGROUND

Due to low numbers of active infections and persons presenting to health facilities for malaria treatment, case-based surveillance is inefficient for understanding the remaining disease burden in low malaria transmission settings. Serological data through the detection of IgG antibodies from previous malaria parasite exposure can fill this gap by providing a nuanced picture of where sustained transmission remains. Study enrollment at sites of gathering provides a potential approach to spatially estimate malaria exposure and could preclude the need for more intensive community-based sampling.

METHODS

This study compared spatial estimates of malaria exposure from cross-sectional school- and community-based sampling in Haiti. A total of 52,405 blood samples were collected from 2012 to 2017. Multiplex bead assays (MBAs) tested IgG against P. falciparum liver stage antigen-1 (LSA-1), apical membrane antigen 1 (AMA1), and merozoite surface protein 1 (MSP1). Predictive geospatial models of seropositivity adjusted for environmental covariates, and results were compared using correlations by coordinate points and communes across Haiti.

RESULTS

Consistent directional associations were observed between seroprevalence and environmental covariates for elevation (negative), air temperature (negative), and travel time to urban centers (positive). Spearman's rank correlation for predicted seroprevalence at coordinate points was lowest for LSA-1 (ρ = 0.10, 95% CI: 0.09-0.11), but improved for AMA1 (ρ = 0.36, 95% CI: 0.35-0.37) and MSP1 (ρ = 0.48, 95% CI: 0.47-0.49).

CONCLUSIONS

In settings approaching P. falciparum elimination, case-based prevalence data does not provide a resolution of ongoing malaria transmission in the population. Immunogenic antigen targets (e.g., AMA1, MSP1) that give higher population rates of seropositivity provide moderate correlation to gold standard community sampling designs and are a feasible approach to discern foci of residual P. falciparum transmission in an area.

Plasmodium falciparum pfhrp2 and pfhrp3 Gene Deletions and Relatedness to Other Global Isolates, Djibouti, 2019-2020

Deletions of pfhrp2 and paralogue pfhrp3 (pfhrp2/3) genes threaten Plasmodium falciparum diagnosis by rapid diagnostic test. We examined 1,002 samples from suspected malaria patients in Djibouti City, Djibouti, to investigate pfhrp2/3 deletions. We performed assays for Plasmodium antigen carriage, pfhrp2/3 genotyping, and sequencing for 7 neutral microsatellites to assess relatedness. By PCR assay, 311 (31.0%) samples tested positive for P. falciparum infection, and 296 (95.2%) were successfully genotyped; 37 (12.5%) samples were pfhrp2+/pfhrp3+, 51 (17.2%) were pfhrp2+/pfhrp3-, 5 (1.7%) were pfhrp2-/pfhrp3+, and 203 (68.6%) were pfhrp2-/pfhrp3-. Histidine-rich protein 2/3 antigen concentrations were reduced with corresponding gene deletions. Djibouti P. falciparum is closely related to Ethiopia and Eritrea parasites (pairwise G_ST 0.68 [Ethiopia] and 0.77 [Eritrea]). P. falciparum with deletions in pfhrp2/3 genes were highly prevalent in Djibouti City in 2019-2020; they appear to have arisen de novo within the Horn of Africa and have not been imported.

Antibody dynamics in children with first or repeat Plasmodium falciparum infections

Immunoglobulin (Ig) production during and after infection with Plasmodium parasites is one of the greatest adaptive immune defenses the human host has against this parasite. Infection with P. falciparum has been shown to induce different B cell maturation responses dependent upon the age of the patient, number of previous exposures, and severity of the disease. Described here are dynamics of Ig responses to a panel of 32 P. falciparum antigens by patients followed for 42 days and classified individuals as showing characteristics of an apparent first P. falciparum infection (naïve) or a repeat exposure (non-naïve). Six parameters were modeled to characterize the dynamics of IgM, IgG1, IgG3, and IgA for these two exposure groups with differences assessed among Ig isotypes/subclasses and unique antigens. Naïve patients had significantly longer periods of time to reach peak Ig titer (range 4–7 days longer) and lower maximum Ig titers when compared with non-naïve patients. Modeled time to seronegativity was significantly higher in non-naïve patients for IgM and IgA, but not for the two IgG subclasses. IgG1 responses to Rh2030, HSP40, and PfAMA1 were at the highest levels for non-naïve participants and may be used to predict previous or nascent exposure by themselves. The analyses presented here demonstrate the differences in the development of the Ig response to P. falciparum if the infection represents a boosting response or a primary exposure. Consistency in Ig isotype/subclasses estimates and specific data for P. falciparum antigens can better guide interpretation of seroepidemiological data among symptomatic persons.

Symptomatic Plasmodium vivax Infection in Rwanda

We report a Plasmodium vivax infection in a Rwandan child misdiagnosed with Plasmodium falciparum and administered artemether-lumefantrine. Antigen detection revealed an absence of P falciparum histidine-rich protein 2 (HRP2) and presence of Plasmodium vivax lactate dehydrogenase. Nested and real-time polymerase chain reactions verified that the sample only contained P vivax deoxyribonucleic acid.

Plasmodium falciparum pfhrp2 and pfhrp3 Gene Deletions from Persons with Symptomatic Malaria Infection in Ethiopia, Kenya, Madagascar, and Rwanda

Histidine-rich protein 2 (HRP2)–based rapid diagnostic tests detect Plasmodium falciparum malaria and are used throughout sub-Saharan Africa. However, deletions in the pfhrp2 and related pfhrp3 (pfhrp2/3) genes threaten use of these tests. Therapeutic efficacy studies (TESs) enroll persons with symptomatic P. falciparum infection. We screened TES samples collected during 2016–2018 in Ethiopia, Kenya, Rwanda, and Madagascar for HRP2/3, pan-Plasmodium lactate dehydrogenase, and pan-Plasmodium aldolase antigen levels and selected samples with low levels of HRP2/3 for pfhrp2/3 genotyping. We observed deletion of pfhrp3 in samples from all countries except Kenya. Single-gene deletions in pfhrp2 were observed in 1.4% (95% CI 0.2%–4.8%) of Ethiopia samples and in 0.6% (95% CI 0.2%–1.6%) of Madagascar samples, and dual pfhrp2/3 deletions were noted in 2.0% (95% CI 0.4%–5.9%) of Ethiopia samples. Although this study was not powered for precise prevalence estimates, evaluating TES samples revealed a low prevalence of pfhrp2/3 deletions in most sites.

Missed Plasmodium falciparum and Plasmodium vivax Mixed Infections in Ethiopia Threaten Malaria Elimination

Plasmodium falciparum and Plasmodium vivax are co-endemic in Ethiopia. This study investigated whether mixed infections were missed by microscopy from a 2017 therapeutic efficacy study at two health facilities in Ethiopia. All patients (N = 304) were initially classified as having single-species P. falciparum (n = 148 samples) or P. vivax infections (n = 156). Dried blood spots were tested for Plasmodium antigens by bead-based multiplex assay for pan-Plasmodium aldolase, pan-Plasmodium lactate dehydrogenase, P. vivax lactate dehydrogenase, and histidine-rich protein 2. Of 304 blood samples, 13 (4.3%) contained both P. falciparum and P. vivax antigens and were analyzed by polymerase chain reaction for species-specific DNA. Of these 13 samples, five were confirmed by polymerase chain reaction for P. falciparum/P. vivax co-infection. One sample, initially classified as P. vivax by microscopy, was found to only have Plasmodium ovale DNA. Plasmodium falciparum/P. vivax mixed infections can be missed by microscopy even in the context of a therapeutic efficacy study with multiple trained readers.

Framework for Characterizing Longitudinal Antibody Response in Children After Plasmodium falciparum Infection

Human Plasmodium infection produces a robust adaptive immune response. Time courses for 104 children followed for 42 days after initiation of Plasmodium falciparum chemotherapy were assayed for antibody levels to the five isotypes of human immunoglobulins (Ig) and 4 subclasses of IgG for 32 P. falciparum antigens encompassing all 4 parasite stages of human infection. IgD and IgE against these antigens were undetectable at 1:100 serum concentration, but other Ig isotypes and IgG subclasses were consistently observed against all antigens. Five quantitative parameters were developed to directly compare Ig response among isotypes and antigens: C_max, maximum antibody level; Δ_C, difference between C_max and the antibody level at Day 0; t_max, time in days to reach C_max; t_1/2, Ig signal half-life in days; t_neg, estimated number of days until complete loss of Ig signal. Classical Ig patterns for a bloodborne pathogen were seen with IgM showing early t_max and IgG production highest among Ig isotypes. However, some unexpected trends were observed such as IgA showing a biphasic pattern for many antigens. Variability among these dynamics of Ig acquisition and loss was noted for different P. falciparum antigens and able to be compared both quantitatively and statistically. This parametrization methodology allows direct comparison of Ig isotypes produced against various Plasmodium antigens following malaria infection, and the same methodology could be applied to other longitudinal serologic studies from P. falciparum or different pathogens. Specifically for P. falciparum seroepidemiological studies, reliable and quantitative estimates regarding the IgG dynamics in human populations can better optimize modeling efforts for serological outputs.

Malaria Risk and Prevention in Asian Migrants to Angola

The number of Asian migrants working in sub-Saharan developing countries like Angola has been increasing. Their malaria risk, prevention, and care-seeking practices have not been characterized. A cross-sectional survey was conducted in 733 Chinese and Southeast Asian migrants in Angola. Respondents were interviewed and provided blood samples. Samples were analyzed to detect Plasmodium antigen and characterize host anti-Plasmodium response. Positive samples were genotyped using the pfs47 marker. Most respondents (72%; 95% CI: 68-75) reported using bed nets, but less than 1% reported using chemoprophylaxis. Depending on the assay, 1-4% of respondents had evidence of active malaria infection. By contrast, 55% (95% CI: 52-59) were seropositive for Plasmodium antibodies. Most infections were Plasmodium falciparum, but infection and/or exposure to Plasmodium vivax and Plasmodium malariae was also detected. Seroprevalence by time in Angola showed most exposure occurred locally. One respondent had sufficiently high parasitemia for pfs47 genotyping, which showed that the infection was likely locally acquired despite recent travel to home country. Asian migrants to Angola are at substantial risk of malaria. Employers should consider enhanced malaria prevention programs, including chemoprophylaxis; embassies should encourage prevention practices. Angolan healthcare workers should be aware of high malaria exposure in Asian migrants.

Capture and Detection of Plasmodium vivax Lactate Dehydrogenase in a Bead-Based Multiplex Immunoassay

Laboratory detection of malaria antigens has proved valuable for research and epidemiological purposes. We recently developed a bead-based multiplex antigen assay for pan-Plasmodium and Plasmodium falciparum targets. Here, we report integration of a Plasmodium vivax-specific target to this multiplex panel: P. vivax lactate dehydrogenase (PvLDH). Within the multiplex panel, assay signal for purified PvLDH antigen titrated into the single-digit picogram range. Against a panel of polymerase chain reaction (PCR)-confirmed samples from acute P. vivax infections (n = 36), sensitivity was 91.7% in using PvLDH detection for identifying the presence of parasites. Specificity against a panel of persons with no Plasmodium infection (n = 44) was 100%, and specificity against a panel of PCR-confirmed P. falciparum, Plasmodium malariae, or Plasmodium ovale infections (n = 164) was 90.2%. Addition of this PvLDH capture and detection system into the multiplex antigen panel will now allow for sensitive screening for species identification of both P. falciparum and P. vivax in the laboratory.

2771. Seroprotection against Measles, Rubella, Tetanus, and Diphtheria Among Children in Haiti—2017

Background

Measles, rubella, and maternal and neonatal tetanus have been verified to be eliminated in Haiti, but a diphtheria outbreak has been ongoing since 2014. To evaluate progress toward maintaining vaccine preventable disease (VPD) elimination and control, we conducted the first survey to estimate immunity to these VPDs among children in Haiti.

Methods

We conducted a nationally representative, two-stage cluster survey in 2017, stratifying Haiti into 2 regions: (1) West Region, the highly urban West department that includes one-third of Haiti’s population; (2) Non-West Region (all other departments). We sampled 4,286 households to recruit at least 910 children aged 5–7 years. We obtained vaccination history and dried blood spots from one eligible child per household. Antibody concentrations to VPDs were measured on a multiplex bead assay. We compared seroprotection and vaccination coverage estimates.

Results

Among 1146 enrolled children, tetanus (83%, 95% CI: 80%–86%) and diphtheria (83%, 95% CI: 81%–85%) seroprotection were higher than coverage with ≥3 doses of tetanus and diphtheria containing vaccine (DTP3) (68%, 95% CI: 61%–74%). No participants had antibody concentrations consistent with long-term immunity to tetanus or diphtheria. Measles (87%, 95% CI: 85%–89%) and rubella (84%, 95% CI: 81%–87%) seroprotection were higher than or similar to coverage with at least one dose of measles-rubella (MR) vaccine (84%, 95% CI: 80%–87%) (Figure 1). MR second-dose coverage was 20% (95% CI: 16%–24%). Seroprotection in the West Region was lower than in the non-West region for all VPDs.

Conclusion

Discordance between DTP3 coverage and seroprotection might be due to underestimating vaccination coverage by recall. Lack of long-term protection against tetanus or diphtheria is consistent with declining antibody concentrations by school-age after the primary DTP series, indicating the need for a booster dose. Seroprotection against measles and rubella viruses was lower than levels needed to prevent transmission, particularly in the West region; re-introduction of either virus could lead to an epidemic. Haiti should reach ≥95% DTP3 and two-dose MR coverage and add tetanus and diphtheria vaccine booster doses per global recommendations.

Disclosures

All authors: No reported disclosures.

Clearance dynamics of lactate dehydrogenase and aldolase following antimalarial treatment for Plasmodium falciparum infection

BACKGROUND

Lingering post-treatment parasite antigen in blood complicates malaria diagnosis through antigen detection. Characterization of antigen clearance dynamics is important for interpretation of positive antigen detection tests.

RESULTS

We used a bead-based serological assay to measure lactate dehydrogenase (LDH), aldolase (Aldo), and histidine-rich protein 2 (HRP2) levels in 196 children with Plasmodium falciparum malaria treated with effective antimalarials and followed for 28 to 42 days as part of therapeutic efficacy studies in Angola. Compared to pre-treatment levels, antigen concentrations two days after treatment declined by 99.7% for LDH, 96.3% for Aldo, and 54.6% for HRP2. After Day 2, assuming a first-order kinetics clearance model, half-lives of the antigens were 1.8 days (95% CI: 1.5-2.3) for LDH, 3.2 days (95% CI: 3.0-3.4) for Aldo, and 4.8 days (95% CI: 4.7-4.9) for HRP2.

CONCLUSIONS

LDH and Aldo show substantially different clearance rates than HRP2, and their presence is largely indicative of active infection.

Lessons learned from an osteoporosis clinical trial in frail long-term care residents

BACKGROUND

Although osteoporosis affects women of all ages, the impact is most pronounced in frail residents in long-term care. Nevertheless, few interventional trials have been performed in this population, and few data on therapeutic alternatives are available in this cohort.

PURPOSE

We describe the challenges and lessons learned in developing and carrying out a trial in frail long-term-care residents.

METHODS

The Zoledronic acid in frail Elders to STrengthen bone (ZEST) study was designed to examine the safety and efficacy of a single-dose therapy for osteoporosis in frail residents in long-term care in the Pittsburgh area. Women with osteoporosis who were 65 years of age and older and currently not on therapy were randomized in a blinded fashion to intravenous zoledronic acid or placebo. Follow-up of each participant was planned for 2 years. All participants received appropriate calcium and vitamin D supplementation.

RESULTS

Seven hundred and thirty-three contacts were made with long-term care residents of nine participating facilities. Of 252 women screened, 181 were eligible, enrolled, and randomized. Multiple barriers to research in long-term-care facilities were encountered but overcome with direct communication, information sessions, in-service trainings, and social events. Lessons learned included designing the study in a manner that avoided placing an additional burden on an already overcommitted facility staff, a two-stage consent process to separate screening from randomization, and a flexible examination schedule to accommodate residents while obtaining the necessary outcome measurements. Furthermore, a mobile unit accessible to participants containing state-of-the-art dual x-ray absorptiometry (DXA), assessment for vertebral fractures, and phlebotomy equipment allows all assessments to be performed on-site at each facility. Serious adverse events are collected from affiliated hospitals in real time with a novel electronic surveillance system.

LIMITATIONS

The major limitation is selection of outcomes that can be assessed at participating facilities and do not require transport of participants to hospitals or clinics.

CONCLUSIONS

Clinical research for osteoporosis can be successfully and safely performed with frail residents in long-term care facilities. Lessons learned from this study may inform future investigations among frail elderly residents of these facilities.

A fork in the road: decision time for behavioral pediatrics

The rapid growth of managed care, and especially that of managed behavioral healthcare organizations (MBHOs), is likely to diminish the role of developmental-behavioral pediatrics and separate care for medical and behavioral problems. Thus, a rethinking of the practice of developmental-behavioral pediatrics is required. This study reviews the structure of MBHOs, identifies barriers to the provision of services by developmental-behavioral pediatricians, describes alternative practice models for consideration, and makes recommendations. The aims of the recommendations are to stimulate an active discussion about these issues, spark an advocacy effort, and ensure the continued participation of developmental-behavioral pediatricians in the care of children with special needs. The study concludes that managed care will push developmental-behavioral pediatricians into integration with primary care group practices or into specialty mental health networks. Immediate discussion, action, and advocacy will be required to ensure a presence in these decisions for developmental-behavioral pediatricians.