Structural and immunological differences in Plasmodium falciparum sexual stage transmission-blocking vaccines comprised of Pfs25-EPA nanoparticles.

Development of a malaria vaccine that blocks transmission of different parasite stages to humans and mosquitoes is considered critical for elimination efforts. A vaccine using Pfs25, a protein on the surface of zygotes and ookinetes, is under investigation as a transmission-blocking vaccine (TBV) that would interrupt parasite passage from mosquitoes to humans. The most extensively studied Pfs25 TBVs use Pichia pastoris-produced recombinant forms of Pfs25, chemically conjugated to a recombinant carrier protein, ExoProtein A (EPA). The recombinant form of Pfs25 first used in humans was identified as Pfs25H, which contained a total of 14 heterologous amino acid residues located at the amino- and carboxyl-termini including a His6 affinity tag. A second recombinant Pfs25, identified as Pfs25M, was produced to remove the heterologous amino acid residues and conjugated to EPA (Pfs25M-EPA). Here, monomeric Pfs25M was characterized biochemically and biophysically for identity, purity, and integrity including protein structure to assess its comparability with Pfs25H. Although the biological activities of Pfs25H and Pfs25M, whether generated by monomeric forms or conjugated nanoparticles, appeared similar, fine-mapping studies with two transmission-blocking monoclonal antibodies detected structural and immunological differences. In addition, evaluation of antisera generated against conjugated Pfs25H or Pfs25M nanoparticles in nonhuman primates identified polyclonal IgG that recognized these structural differences.

Applications of the Premack Principle: A Review of the Literature.

The Premack principle states that any Response A can reinforce any other Response B if the independent rate of A is greater than the independent rate of B. This theory demonstrates reinforcer relativity, where the relative probabilities of responses can be more impactful than preference. Applying the Premack principle involves arranging the environment to restrict access to certain responses based on relative probabilities of a set of given responses. Though the Premack principle is described in modern behavior analytic texts, Konarski et al. identified a lack of empirical evidence to support its application. The purpose of the current paper is to systematically review the extant literature using the Premack principle and evaluate how and if researchers have applied reinforcer relativity as described by Premack and the subsequent effectiveness of these procedures. Additionally, we make recommendations for practitioners and future researchers based on our findings.

A comparison of different antibiotic regimens for the treatment of naturally acquired shigellosis in rhesus and pigtailed macaques (Macaca mulatta and nemestrina).

BACKGROUND: Shigella spp. are common enteric pathogens in captive non-human primates. Treatment of symptomatic infections involves supportive care and antibiotic therapy, typically with an empirical choice of antibiotic. METHODS: Twenty-four clinically ill, Shigella PCR-positive animals were randomly assigned to one of four treatment groups: single-dose ceftiofur crystalline free acid (CCFA), single-dose azithromycin gavage, a 5-day tapering azithromycin dose, or 7-day course of enrofloxacin. We hypothesized that all antimicrobial therapies would have similar efficacy. RESULTS: Animals in all groups cleared Shigella, based on fecal PCR, and had resolution of clinical signs 2 weeks after treatment. Eight out of nine clinically ill and PCR-positive animals tested negative by fecal culture. CONCLUSIONS: Single-dose CCFA, single-dose azithromycin, and a 5-day tapering course of azithromycin all performed as well as a 7-day course of enrofloxacin in eliminating Shigella infection. Fecal PCR may be a better diagnostic than culture for Shigella.

The use of midazolam as an appetite stimulant and anxiolytic in the common marmoset (Callithrix jacchus).

BACKGROUND: Food avoidance secondary to disease or stress can lead to weight loss and rapid deterioration of clinical condition in the common marmoset (Callithrix jacchus). Currently, there are no data supporting the use of any pharmaceuticals as an appetite stimulant in this species; however, benzodiazepines are frequently used for this purpose in other species. METHODS: Six marmosets were used in a crossover study design to evaluate the benzodiazepine midazolam as an appetite stimulant and anxiolytic. Total food intake (TFI) and latency to eat (LTE) were measured following administration of oral and injectable midazolam in non-anxious and anxious states. RESULTS: Injectable midazolam increased TFI and decreased LTE in anxious marmosets, but had no effect in non-anxious animals. Oral midazolam had no effect on appetite in either state. CONCLUSIONS: Injectable midazolam may be an effective treatment for anxiety-induced inappetence in marmosets. Individual response to both oral and injectable midazolam may vary.

Behavior Momentum Theory and Humans: A Review of the Literature.

Behavioral Momentum Theory (BMT) is often described as analogous to Newton's (1687) laws of motion. That is to say, similar to an object in motion continuing in motion unless acted upon by a force, responses occurring in a static environment will continue to occur at the same rate, unless presented with a disruptor (Nevin, Tota, Torquato, & Shull, Journal of the Experimental Analysis of Behavior, 53, 359-379, 1990). When evaluating response rates through a behavioral momentum framework, responding continuing after a change in reinforcer conditions is said to persist. Previous research conducted with nonhuman animals indicates greater response persistence following conditions with either higher reinforcer rates or higher reinforcer magnitudes (Nevin, Journal of the Experimental Analysis of Behavior, 21(3), 389-408, 1974; Nevin et al., Journal of the Experimental Analysis of Behavior, 53, 359-379, 1990). Although BMT's implications extend across human and nonhuman species, this literature review attempts to provide practitioners and researchers information regarding response persistence across various conditions with human participants.

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.

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.