Aotus nancymaae model predicts human immune response to the placental malaria vaccine candidate VAR2CSA

Placental malaria vaccines (PMVs) are being developed to prevent severe sequelae of placental malaria (PM) in pregnant women and their offspring. The leading candidate vaccine antigen VAR2CSA mediates parasite binding to placental receptor chondroitin sulfate A (CSA). Despite promising results in small animal studies, recent human trials of the first two PMV candidates (PAMVAC and PRIMVAC) generated limited cross-reactivity and cross-inhibitory activity to heterologous parasites. Here we immunized Aotus nancymaae monkeys with three PMV candidates (PAMVAC, PRIMVAC and ID1-ID2a_M1010) adjuvanted with Alhydrogel, and exploited the model to investigate boosting of functional vaccine responses during PM episodes as well as with nanoparticle antigens. PMV candidates induced high levels of antigen-specific IgG with significant cross-reactivity across PMV antigens by enzyme-linked immunosorbent assay. Conversely, PMV antibodies recognized native VAR2CSA and blocked CSA adhesion of only homologous parasites and not of heterologous parasites. PM episodes did not significantly boost VAR2CSA antibody levels or serum functional activity; nanoparticle and monomer antigens alike boosted serum reactivity but not functional activities. Overall, PMV candidates induced functional antibodies with limited heterologous activity in Aotus monkeys, similar to responses reported in humans. The Aotus model appears suitable for preclinical downselection of PMV candidates and assessment of antibody boosting by PM episodes.

Acute Pulmonary Embolism in an Intensive Care Unit Setting in Sierra Leone

INTRODUCTION

In Sierra Leone, the lack of information on pulmonary embolism (PE) limits the access to evidence-based standard of diagnostic work-up and management of the disease. The objective of this study was to describe the clinical characteristics and management of acute pulmonary embolism in our setting and to determine whether the pre-test probability scoring algorithms were used prior to Computed Tomography Pulmonary Angiogram (CTPA) request.

METHODS

This retrospective observational study was conducted on CTPA-confirmed PE patients admitted to the Intensive Care Unit, Choithrams Memorial Hospital, in Freetown, Sierra Leone between July 2014 to June 2019. Clinical data, and pertinent investigations related to PE were determined. CTPA findings were correlated with the patient's hemodynamic status. The calculated pretest clinical probability scores (PCPS) for each patient were compared to the CTPA results.

RESULTS

CTPA-confirmed PE in the study cohort was 79, with a rate of 16 new PE per year. The frequency of PE was 1.9% of the total hospital admission per year. The mean age was 64.1 ± 17.9 years, median age was 63.3years (range: 23-89 years), with 55.7% of the cohort being females. Dyspnea (78.5%) and tachycardia (69.6%) were the commonest signs and symptoms documented, with immobilization (34.2%) being the prevalent risk factor, while hypertension (48.1%) was the most common co-morbidity. The PCPS algorithm was underutilized, as "Wells Score" was documented in only 9.5% while "modified Geneva score" was never used by hospital physicians. PE with hemodynamic stability was significantly more common than PE with unstable hemodynamic status [55 (69.6%) vs 24 (30.4%), p=0.015]. All patients were managed only with anticoagulants. The overall in-hospital mortality was 17.7%.

CONCLUSION

Since PCPS was hardly calculated by doctors in the diagnosis of PE, the study showed that the diagnostic algorithm for suspected PE was infrequently used in clinical practice. The use of empirical judgement by doctors in requesting for CTPA may have accounted for low rate in the diagnosis of PE per year. The establishment of P.E registry in Sierra Leone is imperative.

Efficient infection of non-human primates with purified, cryopreserved Plasmodium knowlesi sporozoites

Background

Plasmodium falciparum (Pf) sporozoite (SPZ) vaccines are the only candidate malaria vaccines that induce > 90% vaccine efficacy (VE) against controlled human malaria infection and the only malaria vaccines to have achieved reproducible VE against malaria in adults in Africa. The goal is to increase the impact and reduce the cost of PfSPZ vaccines by optimizing vaccine potency and manufacturing, which will benefit from identification of immunological responses contributing to protection in humans. Currently, there is no authentic animal challenge model for assessing P. falciparum malaria VE. Alternatively, Plasmodium knowlesi (Pk), which infects humans and non-human primates (NHPs) in nature, can be used to experimentally infect rhesus macaques (Macaca mulatta) to assess VE.

Methods

Sanaria has, therefore, produced purified, vialed, cryopreserved PkSPZ and conducted challenge studies in several naïve NHP cohorts. In the first cohort, groups of three rhesus macaques each received doses of 5 × 10², 2.5 × 10³, 1.25 × 10⁴ and 2.5 × 10⁴ PkSPZ administered by direct venous inoculation. The infectivity of 1.5 × 10³ PkSPZ cryopreserved with an altered method and of 1.5 × 10³ PkSPZ cryopreserved for four years was tested in a second and third cohort of rhesus NHPs. The lastly, three pig-tailed macaques (Macaca nemestrina), a natural P. knowlesi host, were challenged with 2.5 × 10³ PkSPZ cryopreserved six years earlier.

Results

In the first cohort, all 12 animals developed P. knowlesi parasitaemia by thick blood smear, and the time to positivity (prepatent period) followed a non-linear 4-parameter logistic sigmoidal model with a median of 11, 10, 8, and 7 days, respectively (r² = 1). PkSPZ cryopreserved using a modified rapid-scalable method infected rhesus with a pre-patent period of 10 days, as did PkSPZ cryopreserved four years prior to infection, similar to the control group. Cryopreserved PkSPZ infected pig-tailed macaques with median time to positivity by thin smear, of 11 days.

Conclusion

This study establishes the capacity to consistently infect NHPs with purified, vialed, cryopreserved PkSPZ, providing a foundation for future studies to probe protective immunological mechanisms elicited by PfSPZ vaccines that cannot be established in humans.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-022-04261-z.

Determinants of Malaria Protective Immunity in Mice Immunized with Live Sporozoites during Trimethoprim-Sulfamethoxazole Prophylaxis

HIV and malaria geographically overlap. Trimethoprim–sulfamethoxazole (TMP-SMX) is a drug widely used in HIV-exposed uninfected and infected children in malaria-endemic areas, and is known to have antimalarial effects. Further study in terms of antimalarial impact and effect on development of malaria-specific immunity is therefore essential. Using rodent malaria models, we previously showed that repeated Plasmodium exposure during TMP-SMX administration, or chemoprophylaxis vaccination (CVac), induces CD8 T-cell–dependent preerythrocytic immunity. However, humoral immune responses have been shown to be important in models of preerythrocytic immunity. Herein, we demonstrate that antibody-mediated responses contribute to protective immunity induced by CVac immune sera using TMP-SMX in models of homologous, but not heterologous, parasite species. Clinical studies must account for potential anti-Plasmodium antibody induced during TMP-SMX prophylaxis.

Dynamics and Outcomes of Plasmodium Infections in Grammomys surdaster (Grammomys dolichurus) Thicket Rats versus Inbred Mice

Investigations of malaria infection are often conducted by studying rodent Plasmodium species in inbred laboratory mice, but the efficacy of vaccines or adjunctive therapies observed in these models often does not translate to protection in humans. This raises concerns that mouse malaria models do not recapitulate important features of human malaria infections. African woodland thicket rats (Grammomys surdaster) are the natural host for the rodent malaria parasite Plasmodium berghei and the suspected natural host for Plasmodium vinckei vinckei. Previously, we reported that thicket rats are highly susceptible to diverse rodent parasite species, including P. berghei, Plasmodium yoelii, and Plasmodium chabaudi chabaudi, and are a more stringent model to assess the efficacy of whole-sporozoite vaccines than laboratory mice. Here, we compare the course of infection and virulence with additional rodent Plasmodium species, including various strains of P. berghei, P. yoelii, P. chabaudi, and P. vinckei, in thicket rats versus laboratory mice. We present evidence that rodent malaria parasite growth typically differs between the natural versus nonnatural host; G. surdaster limit infection by multiple rodent malaria strains, delaying and reducing peak parasitemia compared with laboratory mice. The course of malaria infection in thicket rats varied depending on parasite species and strain, resulting in self-cure, chronic parasitemia, or rapidly lethal infection, thus offering a variety of rodent malaria models to study different clinical outcomes in the natural host.

Prevalence, Awareness and Risk Factors of Hypertension among Health Workers at the Connaught Teaching Hospital, Sierra Leone

BACKGROUND

Hypertension among the health workforce is a major public health problem due to its high prevalence and dire consequences. This study aimed to determine the prevalence of hypertension, awareness, and related cardiovascular risk factors among health workers in a Teaching Hospital in Sierra Leone.

METHODS

This was a cross-sectional descriptive study conducted among 250 health workers. A modified World Health Organization Non-Communicable Disease (WHO NCD) questionnaire was used to collect information on the socio-demographic characteristics, anthropometric, and lifestyle variables.

RESULTS

The prevalences of hypertension and pre-hypertension were 37.2% and 22.4% respectively. The level of hypertension awareness was 36.6 %. The univariate logistic regression showed a significant crude odds ratio for gender, age, marital status, smokers, alcohol, extra sugar to tea/coffee, years of employment, weight, Waist Circumference, Hip Circumference, and Waist-Hip-Ratio (WHR) in the prediction of hypertension. The multivariate logistic regression revealed that male sex (AOR = 1.89; C.I 95%: [0.01- >20], p = 0.002), duration of employment (AOR = 0.36; C.I 95%: [0.17- 0.94], p = 0.01), and Waist Circumference (WC) (AOR = 1.46; C.I 95%: [0.58 - 3.68], p = 0.017), were positive predictors of hypertension. Males were about 2 times more likely to have hypertension, (AOR = 1.89; C.I 95%: [0.01- >20]). Participants with abnormal Waist Circumference (WC) were 1.5 times more likely to have hypertension (AOR = 1.46; C.I 95%: [0.58 - 3.68]).

CONCLUSION

The prevalence of hypertension in this study population was slightly higher than the 34.8% reported for the general population even though this study population is relatively younger. The level of awareness was low. This calls for the implementation of an effective workplace health education program to improve lifestyle and reduce the risk of cardiovascular diseases.

The Effect of Plasmodium on the Outcome of Ebola Virus Infection in a Mouse Model

Following the Ebola virus epidemic in West Africa, several studies investigated whether there was an effect of Plasmodium coinfection on survival in Ebola virus (EBOV) disease patients. Different effects of coinfection were found in different patient cohorts. To determine whether an effect of Plasmodium coinfection on EBOV survival may exist, we modeled coinfection of Plasmodium yoelii and mouse-adapted EBOV (MA-EBOV) in CD1 mice. Subsequent infection with MA-EBOV at different time points after P. yoelii infection did not have any significant effect on survival.

γδ T Cells Are Required for the Induction of Sterile Immunity during Irradiated Sporozoite Vaccinations

Whole-sporozoite vaccines confer sterilizing immunity to malaria-naive individuals by unknown mechanisms. In the first PfSPZ Vaccine trial ever in a malaria-endemic population, Vδ2 γδ T cells were significantly elevated and Vγ9/Vδ2 transcripts ranked as the most upregulated in vaccinees who were protected from Plasmodium falciparum infection. In a mouse model, absence of γδ T cells during vaccination impaired protective CD8 T cell responses and ablated sterile protection. γδ T cells were not required for circumsporozoite protein-specific Ab responses, and γδ T cell depletion before infectious challenge did not ablate protection. γδ T cells alone were insufficient to induce protection and required the presence of CD8α⁺ dendritic cells. In the absence of γδ T cells, CD8α⁺ dendritic cells did not accumulate in the livers of vaccinated mice. Altogether, our results show that γδ T cells were essential for the induction of sterile immunity during whole-organism vaccination.

Grammomys surdaster, the Natural Host for Plasmodium berghei Parasites, as a Model to Study Whole-Organism Vaccines Against Malaria

AbstractInbred mice are commonly used to test candidate malaria vaccines, but have been unreliable for predicting efficacy in humans. To establish a more rigorous animal model, we acquired African woodland thicket rats of the genus Grammomys, the natural hosts for Plasmodium berghei. Thicket rats were acquired and identified as Grammomys surdaster by skull and teeth measurements and mitochondrial DNA genotyping. Herein, we demonstrate that thicket rats are highly susceptible to infection by P. berghei, and moderately susceptible to Plasmodium yoelii and Plasmodium chabaudi: 1-2 infected mosquito bites or 25-100 sporozoites administered by intravenous injection consistently resulted in patent parasitemia with P. berghei, and resulted in patent parasitemia with P. yoelii and P. chabaudi strains for at least 50% of animals. We then assessed efficacy of whole-organism vaccines to induce sterile immunity, and compared the thicket rat model to conventional mouse models. Using P. berghei ANKA radiation-attenuated sporozoites, and P. berghei ANKA and P. yoelii chemoprophylaxis vaccination approaches, we found that standard doses of vaccine sufficient to protect laboratory mice for a long duration against malaria challenge, are insufficient to protect thicket rats, which require higher doses of vaccine to achieve even short-term sterile immunity. Thicket rats may offer a more stringent and pertinent model for evaluating whole-organism vaccines.

Trimethoprim-Sulfamethoxazole Prophylaxis During Live Malaria Sporozoite Immunization Induces Long-Lived, Homologous, and Heterologous Protective Immunity Against Sporozoite Challenge

Trimethoprim-sulfamethoxazole (TMP-SMX) is widely used in malaria-endemic areas in human immunodeficiency virus (HIV)-infected children and HIV-uninfected, HIV-exposed children as opportunistic infection prophylaxis. Despite the known effects that TMP-SMX has in reducing clinical malaria, its impact on development of malaria-specific immunity in these children remains poorly understood. Using rodent malaria models, we previously showed that TMP-SMX, at prophylactic doses, can arrest liver stage development of malaria parasites and speculated that TMP-SMX prophylaxis during repeated malaria exposures would induce protective long-lived sterile immunity targeting pre-erythrocytic stage parasites in mice. Using the same models, we now demonstrate that repeated exposures to malaria parasites during TMP-SMX administration induces stage-specific and long-lived pre-erythrocytic protective anti-malarial immunity, mediated primarily by CD8⁺ T-cells. Given the HIV infection and malaria coepidemic in sub-Saharan Africa, clinical studies aimed at determining the optimum duration of TMP-SMX prophylaxis in HIV-infected or HIV-exposed children must account for the potential anti-infection immunity effect of TMP-SMX prophylaxis.

Chloroquine neither eliminates liver stage parasites nor delays their development in a murine Chemoprophylaxis Vaccination model

Chemoprophylaxis Vaccination (CVac) confers long lasting sterile protection against homologous parasite strains in humans, and involves inoculation of infectious sporozoites (SPZ) under drug cover. CVac using the drug chloroquine (CQ) induces pre-erythrocytic immunity in humans that includes antibody to SPZ and T-cell responses to liver stage (LS) parasites. The mechanism by which CVac with CQ induces strong protective immunity is not understood as untreated infections do not confer protection. CQ kills blood stage parasites, but its effect on LS parasites is poorly studied. Here we hypothesized that CQ may prolong or perturb LS development of Plasmodium, as a potential explanation for enhanced pre-erythrocytic immune responses. Balb/c mice with or without CQ prophylaxis were infected with sporozoite forms of a luciferase-expressing rodent parasite, Plasmodium yoelii-Luc (Py-Luc). Mice that received primaquine, a drug that kills LS parasites, served as a positive control of drug effect. Parasite burden in liver was measured both by bioluminescence and by qRT-PCR quantification of parasite transcript. Time to appearance of parasites in the blood was monitored by microscopic analysis of Giemsa-stained thick and thin blood smears. The parasite load in livers of CQ-treated and untreated mice did not significantly differ at any of the time points studied. Parasites appeared in the blood smears of both CQ-treated and untreated mice 3 days after infection. Taken together, our findings confirm that CQ neither eliminates LS parasites nor delays their development. Further investigations into the mechanism of CQ-induced protection after CVac are required, and may give insights relevant to drug and vaccine development.

HIV treatments reduce malaria liver stage burden in a non-human primate model of malaria infection at clinically relevant concentrations in vivo

We have previously shown that the HIV protease inhibitor lopinavir-ritonavir (LPV-RTV) and the antibiotic trimethoprim sulfamethoxazole (TMP-SMX) inhibit Plasmodium liver stages in rodent malarias and in vitro in P. falciparum. Since clinically relevant levels are better achieved in the non-human-primate model, and since Plasmodium knowlesi is an accepted animal model for the study of liver stages of malaria as a surrogate for P. falciparum infection, we investigated the antimalarial activity of these drugs on Plasmodium knowlesi liver stages in rhesus macaques. We demonstrate that TMP-SMX and TMP-SMX+LPV-RTV (in combination), but not LPV-RTV alone, inhibit liver stage parasite development. Because drugs that inhibit the clinically silent liver stages target parasites when they are present in lower numbers, these results may have implications for eradication efforts.

Antibodies to PfSEA-1 block parasite egress from RBCs and protect against malaria infection

Novel vaccines are urgently needed to reduce the burden of severe malaria. Using a differential whole-proteome screening method, we identified Plasmodium falciparum schizont egress antigen-1 (PfSEA-1), a 244-kilodalton parasite antigen expressed in schizont-infected red blood cells (RBCs). Antibodies to PfSEA-1 decreased parasite replication by arresting schizont rupture, and conditional disruption of PfSEA-1 resulted in a profound parasite replication defect. Vaccination of mice with recombinant Plasmodium berghei PbSEA-1 significantly reduced parasitemia and delayed mortality after lethal challenge with the Plasmodium berghei strain ANKA. Tanzanian children with antibodies to recombinant PfSEA-1A (rPfSEA-1A) did not experience severe malaria, and Kenyan adolescents and adults with antibodies to rPfSEA-1A had significantly lower parasite densities than individuals without these antibodies. By blocking schizont egress, PfSEA-1 may synergize with other vaccines targeting hepatocyte and RBC invasion.

HIV nonnucleoside reverse transcriptase inhibitors and trimethoprim-sulfamethoxazole inhibit plasmodium liver stages

BACKGROUND

Although nonnucleoside reverse transcriptase inhibitors (NNRTIs) are usually part of first-line treatment regimens for human immunodeficiency virus (HIV), their activity on Plasmodium liver stages remains unexplored. Additionally, trimethoprim-sulfamethoxazole (TMP-SMX), used for opportunistic infection prophylaxis in HIV-exposed infants and HIV-infected patients, reduces clinical episodes of malaria; however, TMP-SMX effect on Plasmodium liver stages requires further study.

METHODS

We characterized NNRTI and TMP-SMX effects on Plasmodium liver stages in vivo using Plasmodium yoelii. On the basis of these results, we conducted in vitro studies assessing TMP-SMX effects on the rodent parasites P. yoelii and Plasmodium berghei and on the human malaria parasite Plasmodium falciparum.

RESULTS

Our data showed NNRTI treatment modestly reduced P. yoelii liver stage parasite burden and minimally extended prepatent period. TMP-SMX administration significantly reduced liver stage parasite burden, preventing development of patent parasitemia in vivo. TMP-SMX inhibited development of rodent and P. falciparum liver stage parasites in vitro.

CONCLUSIONS

NNRTIs modestly affect liver stage Plasmodium parasites, whereas TMP-SMX prevents patent parasitemia. Because drugs that inhibit liver stages target parasites when they are present in lower numbers, these results may have implications for eradication efforts. Understanding HIV drug effects on Plasmodium liver stages will aid in optimizing treatment regimens for HIV-exposed and HIV-infected infected patients in malaria-endemic areas.

Plasmodium yoelii-infected A. stephensi inefficiently transmit malaria compared to intravenous route

It was recently reported that when mosquitoes infected with P. berghei sporozoites feed on mice, they deposit approximately 100–300 sporozoites in the dermis. When we inoculate P. yoelii (Py) sporozoites intravenously (IV) into BALB/c mice, the 50% infectious dose (ID₅₀) is often less than 3 sporozoites, indicating that essentially all Py sporozoites in salivary glands are infectious. Thus, it should only take the bite of one infected mosquito to infect 100% of mice. In human subjects, it takes the bite of at least 5 P. falciparum-infected mosquitoes to achieve 100% blood stage infection. Exposure to 1–2 infected mosquitoes only leads to blood stage infection in approximately 50% of subjects. If mosquitoes carrying Py sporozoites inoculate 100–300 sporozoites per bite, and 1 to 2 mosquito bites achieve 50% blood stage infection rates, then this would suggest that the majority of sporozoites inoculated by mosquitoes into the dermis are not responsible for a productive infection, or that a significant number of sporozoite-infected mosquitoes do not inoculate any sporozoites. The objective of this study was to determine if this is the case. We therefore studied the infectivity to mice of the bites of 1, 2, 4, or 5–8 Py-infected mosquitoes. The bite of one Py sporozoite-infected mosquito caused blood stage infection in 41.4% (12/29) of mice, two bites infected 66.7% (22/33), four bites infected 75% (18/24), and five to eight bites infected 100% (21/21). These findings demonstrate that inoculation of sporozoites by mosquito bite is much less efficient than IV inoculation of Py sporozoites by needle and syringe. Such data may have implications for determining the best route and dose of administration to humans of our attenuated P. falciparum sporozoite vaccine, the scientific basis of which is immunity by bites from irradiated infected mosquitoes, and suggest that the challenge is to develop a method of administration that approximates IV inoculation, not one that mimics mosquito bite.

Sterile protection against Plasmodium knowlesi in rhesus monkeys from a malaria vaccine: comparison of heterologous prime boost strategies

Using newer vaccine platforms which have been effective against malaria in rodent models, we tested five immunization regimens against Plasmodium knowlesi in rhesus monkeys. All vaccines included the same four P. knowlesi antigens: the pre-erythrocytic antigens CSP, SSP2, and erythrocytic antigens AMA1, MSP1. We used four vaccine platforms for prime or boost vaccinations: plasmids (DNA), alphavirus replicons (VRP), attenuated adenovirus serotype 5 (Ad), or attenuated poxvirus (Pox). These four platforms combined to produce five different prime/boost vaccine regimens: Pox alone, VRP/Pox, VRP/Ad, Ad/Pox, and DNA/Pox. Five rhesus monkeys were immunized with each regimen, and five Control monkeys received a mock vaccination. The time to complete vaccinations was 420 days. All monkeys were challenged twice with 100 P. knowlesi sporozoites given IV. The first challenge was given 12 days after the last vaccination, and the monkeys receiving the DNA/Pox vaccine were the best protected, with 3/5 monkeys sterilely protected and 1/5 monkeys that self-cured its parasitemia. There was no protection in monkeys that received Pox malaria vaccine alone without previous priming. The second sporozoite challenge was given 4 months after the first. All 4 monkeys that were protected in the first challenge developed malaria in the second challenge. DNA, VRP and Ad5 vaccines all primed monkeys for strong immune responses after the Pox boost. We discuss the high level but short duration of protection in this experiment and the possible benefits of the long interval between prime and boost.

The Effects of radiation on the safety and protective efficacy of an attenuated Plasmodium yoelii sporozoite malaria vaccine

We are developing a radiation attenuated Plasmodium falciparum sporozoite (PfSPZ) malaria vaccine. An important step was to determine the minimum dose of irradiation required to adequately attenuate each sporozoite. This was studied in the Plasmodium yoelii rodent model system. Exposure to 100 Gy completely attenuated P. yoelii sporozoites (PySPZ). Next we demonstrated that immunization of mice intravenously with 3 doses of 750 PySPZ that had received 200 Gy, double the radiation dose required for attenuation, resulted in 100% protection. These results support the contention that a radiation attenuated sporozoite vaccine for malaria will be safe and effective at a range of radiation doses.

Protection of rhesus monkeys by a DNA prime/poxvirus boost malaria vaccine depends on optimal DNA priming and inclusion of blood stage antigens

Background

We have previously described a four antigen malaria vaccine consisting of DNA plasmids boosted by recombinant poxviruses which protects a high percentage of rhesus monkeys against Plasmodium knowlesi (Pk) malaria. This is a multi-stage vaccine that includes two pre-erythrocytic antigens, PkCSP and PkSSP2(TRAP), and two erythrocytic antigens, PkAMA-1 and PkMSP-1(42kD). The present study reports three further experiments where we investigate the effects of DNA dose, timing, and formulation. We also compare vaccines utilizing only the pre-erythrocytic antigens with the four antigen vaccine.

Methodology

In three experiments, rhesus monkeys were immunized with malaria vaccines using DNA plasmid injections followed by boosting with poxvirus vaccine. A variety of parameters were tested, including formulation of DNA on poly-lactic co-glycolide (PLG) particles, varying the number of DNA injections and the amount of DNA, varying the interval between the last DNA injection to the poxvirus boost from 7 to 21 weeks, and using vaccines with from one to four malaria antigens. Monkeys were challenged with Pk sporozoites given iv 2 to 4 weeks after the poxvirus injection, and parasitemia was measured by daily Giemsa stained blood films. Immune responses in venous blood samples taken after each vaccine injection were measured by ELIspot production of interferon-γ, and by ELISA.

Conclusions

1) the number of DNA injections, the formulation of the DNA plasmids, and the interval between the last DNA injection and the poxvirus injection are critical to vaccine efficacy. However, the total dose used for DNA priming is not as important; 2) the blood stage antigens PkAMA-1 and PkMSP-1 were able to protect against high parasitemias as part of a genetic vaccine where antigen folding is not well defined; 3) immunization with PkSSP2 DNA inhibited immune responses to PkCSP DNA even when vaccinations were given into separate legs; and 4) in a counter-intuitive result, higher interferon-γ ELIspot responses to the PkCSP antigen correlated with earlier appearance of parasites in the blood, despite the fact that PkCSP vaccines had a protective effect.

Sexually transmitted diseases among randomly selected attenders at an antenatal clinic in The Gambia

One hundred randomly selected women attending a free government antenatal clinic in the town of Bakau, The Gambia, were examined. Vaginal swabs were taken for microscopical examination for Trichomonas vaginalis and for culture on Sabouraud's medium. Cervical swabs were taken for culture of Neisseria gonorrhoeae and Chlamydia trachomatis and, in 50 cases, Herpesvirus hominis; in addition, urethral swabs were taken for culture of N gonorrhoeae. Serum samples were tested for antibodies to Treponema pallidum by the Venereal Diseases Research Laboratory (VDRL) test and T pallidum haemagglutination assay (TPHA), and to C trachomatis and H hominis by microimmunofluorescence. The prevalence of infection with Candida albicans was found to be 35%, T vaginalis 32%, C trachomatis 6.9%, N gonorrhoeae 6.7%, T pallidum 1%, and H hominis 0%. IgG antibodies at a titre of at least 1/16 to C trachomatis serotypes D-K were found in 29.4%, and to serotypes A-C in a further 10.6%. IgG antibodies at a titre of at least 1/16 to H hominis type I were found in 94%, and to type II in 53%, although a proportion of the latter probably represent cross reacting antibodies to type I.

Leishmaniasis in The Gambia. 3. Is its incidence increasing?

During 1982 a further case of visceral leishmaniasis and six cases of cutaneous leishmaniasis were seen at the Medical Research Council Laboratories in The Gambia, suggesting that the incidence of this infection in The Gambia is increasing.

Leishmaniasis in The Gambia. I. A case of cutaneous leishmaniasis and a case of visceral leishmaniasis

Leishmaniasis is thought to be rare in The Gambia but in June 1980 two patients with this infection were seen at Fajara, one with cutaneous leishmaniasis and one with visceral leishmaniasis. A possible diagnosis of visceral leishmaniasis was considered only late in the course of the illness of the second patient who died a few days after specific chemotherapy was started. Visceral leishmaniasis must be considered as a possible cause of fever and splenomegaly in The Gambia and in adjacent parts of West Africa.

A comparison of bottle tops, teaspoons and WHO glucose-electrolyte packets for home made oral rehydration solutions in The Gambia

Three methods of preparation of oral rehydration solution were taught to Gambian mothers and the sodium concentration and osmolality of the solutions prepared were estimated. Most of the solutions made up using WHO glucose-electrolyte mix had a satisfactory sodium content (70 to 120 mmol/l) and osmolality (200 to 350 mosmoles/kg). Of the sugar and salt mixtures using a teaspoon as a measure, 17% were hypertonic (greater than 120 mmol sodium/l) and 24% were hyperosmolar (greater than 350 mosmol/kg). Nearly all the sugar and salt solutions prepared using a soft drink bottle top as a measure had sodium contents of 30-88 mmol/l and none was hyperosmolar. We suggest that wider trials of this simple, widely available measure are indicated.

Effect of a lipid load on blood and urinary carnitine in man

Blood and urine carnitine contents have been determined in patients before and after a lipid load and in patients on haemodialysis. Oral and intravenous lipid administration significantly depressed blood carnitine content and after 500 ml intravenous Intralipid urinary carnitine excretion fell by 43%. Blood carnitine was reduced by 50% by haemodialysis and returned to the pre-dialysis value within 20 h in 5 out of 8 patients. It is concluded that the blood carnitine level is normally controlled over a narrow range. The fall in blood carnitine concentration and urine excretion which follows a lipid load indicate a limiting role for carnitine in lipid utilization in man, and suggest that carnitine supplements could be of value during parenteral nutrition with fats.