MPLA and AddaVax® Adjuvants Fail to Promote Intramuscular LaAg Vaccine Protectiveness against Experimental Cutaneous Leishmaniasis

There is so far no vaccine approved for human leishmaniasis, mainly because of the lack of appropriate adjuvants. This study aimed to evaluate in mice the capacity of a mixture of monophosphoryl lipid A (MPLA) and AddaVax® adjuvants in enhancing the efficacy of a Leishvacin®-like vaccine comprised of Leishmania amazonensis whole antigens (LaAg). For that, mice were immunized with LaAg plus MPLA/AddaVax® by the intramuscular route (i.m.) prior to challenge with 2 × 105 and 2 × 106 living parasites. Immunization with LaAg alone reduced the lesion growth of the 2 × 105-challenged mice only in the peak of infection, but that was not accompanied by reduced parasite load, and thus not considered protective. Mice given a 2 × 106 -challenge were not protected by LaAg. The association of LaAg with MPLA/AddaVax® was able to enhance the cutaneous hypersensitivity response compared with LaAg alone. Despite this, there was no difference in proliferative cell response to antigen ex vivo. Moreover, regardless of the parasite challenge, association of LaAg with MPL/AddaVax® did not significantly enhance protection in comparison with LaAg alone. This work demonstrated that MPL/AddaVax® is not effective in improving the efficacy of i.m. LaAg vaccine against cutaneous leishmaniasis.

Dietary and Plasmodium challenge effects on cuticular hydrocarbons in Anopheles albimanus

The cuticular hydrocarbon (CHC) profile reflects the insect’s physiological states. These states include age, sex, reproductive stage, or gravidity. Environmental factors such as diet, relative humidity, or exposure to insecticides also affect the CHCs composition in mosquitoes. In this work, the CHC profile was analyzed in two Anopheles albimanus phenotypes with different degrees of susceptibility to Plasmodium: the susceptible-White and resistant-Brown phenotypes. The effects of the CHC profile were considered under a carbon-rich diet (sugar), a protein-rich diet (blood), and an infectious challenge (blood containing Plasmodium berghei ookinetes). The CHCs were analyzed by gas chromatography coupled with either mass spectrometry or flame ionization detection, identifying 19 CHCs with chain lengths ranging from 20 to 37 carbons. The qualitative and quantitative changes observed in the CHCs composition were dependent on the diet and parasite challenge, and independent of the phenotype. The exception was the challenged condition, where significant differences between the phenotypes were observed in Z-12 pentacosane, hexacosane 9-octyl, methyl-nonacosane, and methyl-hentriacontane. Since the lipid metabolism in Anopheles mosquitoes has been shown crucial for Plasmodium development, the changes in the CHC profiles associated with infection could have multiple effects on mosquito fitness and impacts on disease transmission.

Evaluating the relationship between fecal egg count, FAMACHA score, and weight in dewormed and non-dewormed Katahdin rams during a parasite challenge

The objective of this study was to evaluate and to estimate the relationship between fecal egg counts (FECs) and FAMACHA score and the body weight of growing Katahdin rams during a parasite challenge. One of the largest factors negatively influencing reproduction and economics in the sheep industry is gastrointestinal nematode (GIN) parasites. Due to anthelmintic resistance of these parasites, animals are selected for parasite resistance using FEC and FAMACHA scores. Data were used from the Virginia Tech Southwest Agricultural Research and Extension Center Ram Test in Glade Spring, VA, from the year 2012 to 2018 in which animals were tested in 14-d intervals for 70 d. Mixed models for repeated weight measurements were made from backward stepwise selection to evaluate the relationships between weight and GIN FEC. A total of 576 animals within 23 contemporary groups derived from test year and pasture group were analyzed. Ram, contemporary group, and consignor were considered random effects, and fixed effects were birth type, test day, age, age squared, starting weight, FEC, and FAMACHA score. Pairwise contrasts were used in the statistical analysis of parameters and their interactions. Weight and age were found to have a quadratic relationship. Increased FEC was associated with weight loss at a rate of 0.00030 kg/FEC (P < 0.0001). Animals dewormed at any point during the trial weighed less than those that were not and increased with test day to a maximum difference of 4.66 kg (P < 0.001). FAMACHA score was found to be significant (P < 0.05), but a direct relationship with weight was not conclusive. Overall, rams with severe enough parasite load to require deworming had lesser weights, which could impact the profitability of sheep production and reinforced the need to select animals that had greater innate parasite resistance.

Mimotope-based antigens as potential vaccine candidates in experimental murine cysticercosis

Human cysticercosis is a public health problem caused by Taenia solium metacestodes; thus, eradication of T. solium transmission by vaccination is an urgent requirement. The Cc48 mimotope from T. solium cysticerci was tested expressed in phage particles (mCc48) and chemically synthesized (sCc48) as a vaccine candidate in experimental murine cysticercosis. For this, BALB/c mice were immunized with mCc48 (G1; n = 40), sCc48 (G2; n = 40) and phosphate-buffered saline (PBS) (G3; n = 40, positive control) and challenged with Taenia crassiceps metacestodes. Another PBS group without parasite challenge was used as a negative control (G4; n = 40). Mice were sacrificed 15, 30, 45 and 60 days post-infection for cysticerci and serum collection. Immunization efficacy was determined by cysticerci counting. Serum samples were tested by ELISA to verify antibody (IgM, IgG, IgA and IgE) and cytokine (IFNγ and IL-4) levels. The sCc48 achieved the highest rates of protection and efficacy (90 and 98%, respectively). The group immunized with mCc48 presented the highest reactivity for IgM, IgG and IgE. All groups presented IL-4, but IFNγ was quite variable among groups. The protection induced by sCc48 synthetic peptide supports further studies of this mimotope as a potential vaccine candidate against cysticercosis.

Effect of Gastrointestinal Nematodes on Reproduction and Lamb Growth in Australian Merino Sheep

Environmental conditions in Uruguay favour the development of gastrointestinal nematodes (GIN) throughout the year, with clinical or subclinical manifestations that cause significant economic losses. The aim of this study was to evaluate the effect of the GIN on fertility, fecundity, reproductive rate and lamb growth in Australian Merino sheep grazing on basalt fields. The study was carried out in a farm located in north of Uruguay. Sixty-eight Merino ewes facing a natural parasite challenge were divided into two groups. Control group was doused with active anthelmintic that have proven efficacy to minimize the effects of parasitic and the parasitized group that did not receive anthelmintic, except rescue dosages. Stool sample of each sheep was collected monthly for egg counts (EPG) of GIN using McMaster technique and nematode genders were identified from infective larvae obtained in cultures by Roberts O’ Sullivan technique. Artificial insemination and ewes were mated for new service, and pregnancy condition was diagnosed by ultrasound. Lambing control was made and lambs were weighed at birth and marking. The evolution of EPG values showed significant differences between groups at the end of gestation and lactation. Haemonchus spp. was the main gender of nematodes found, followed by Trichostrongylus spp. Fertility was 95 % versus 90 %; fecundity 87 % versus 63 % and reproductive rate 73 % versus 47 % for the control group and the parasitized one respectively. No significant differences were recorded in birth-weight. However market-weight and lamb daily gain were lower in the parasitized group. The effect of natural infection GIN was evident in lower reproductive performance of Australian Merino sheep.

Hygiene Defense Behaviors Used by a Fungus-Growing Ant Depend on the Fungal Pathogen Stages

Parasites and their hosts use different strategies to overcome the defenses of the other, often resulting in an evolutionary arms race. Limited animal studies have explored the differential responses of hosts when challenged by differential parasite loads and different developmental stages of a parasite. The fungus-growing ant Trachymyrmex sp. 10 employs three different hygienic strategies to control fungal pathogens: Grooming the antibiotic-producing metapleural glands (MGs) and planting or weeding their mutualistic fungal crop. By inoculating Trachymyrmex colonies with different parasite concentrations (Metarhizium) or stages (germinated conidia or ungermianted conidia of Metarhizium and Escovopsis), we tested whether ants modulate and change hygienic strategies depending on the nature of the parasite challenge. There was no effect of the concentration of parasite on the frequencies of the defensive behaviors, indicating that the ants did not change defensive strategy according to the level of threat. However, when challenged with conidia of Escovopsis sp. and Metarhizium brunneum that were germinated or not-germinated, the ants adjusted their thygienic behavior to fungal planting and MG grooming behaviors using strategies depending on the conidia germination status. Our study suggests that fungus-growing ants can adjust the use of hygienic strategies based on the nature of the parasites.

Antibody-Mediated Protection againstPlasmodiumSporozoites Begins at the Dermal Inoculation Site

ABSTRACTPlasmodiumsporozoites are injected into the skin as mosquitoes probe for blood. From here, they migrate through the dermis to find blood vessels which they enter in order to be rapidly carried to the liver, where they invade hepatocytes and develop into the next life cycle stage, the exoerythrocytic stage. Once sporozoites enter the blood circulation, they are found in hepatocytes within minutes. In contrast, sporozoite exit from the inoculation site resembles a slow trickle and occurs over several hours. Thus, sporozoites spend the majority of their extracellular time at the inoculation site, raising the hypothesis that this is when the malarial parasite is most vulnerable to antibody-mediated destruction. Here, we investigate this hypothesis and demonstrate that the neutralizing capacity of circulating antibodies is greater at the inoculation site than in the blood circulation. Furthermore, these antibodies are working, at least in part, by impacting sporozoite motility at the inoculation site. Using actively and passively immunized mice, we found that most parasites are either immobilized at the site of injection or display reduced motility, particularly in their net displacement. We also found that antibodies severely impair the entry of sporozoites into the bloodstream. Overall, our data suggest that antibodies targeting the migratory sporozoite exert a large proportion of their protective effect at the inoculation site.IMPORTANCEStudies in experimental animal models and humans have shown that antibodies againstPlasmodiumsporozoites abolish parasite infectivity and provide sterile immunity. While it is well documented that these antibodies can be induced after immunization with attenuated parasites or subunit vaccines, the mechanisms by and location in which they neutralize parasites have not been fully elucidated. Here, we report studies indicating that these antibodies display a significant portion of their protective effect in the skin after injection of sporozoites and that one mechanism by which they work is by impairing sporozoite motility, thus diminishing their ability to reach blood vessels. These results suggest that immune protection against malaria begins at the earliest stages of parasite infection and emphasize the need of performing parasite challenge in the skin for the evaluation of protective immunity.

Temperature modulates the interaction between fungicide pollution and disease: evidence from a Daphnia-microparasitic yeast model

Temperature is expected to modulate the responses of organisms to stress. Here, we aimed to assess the influence of temperature on the interaction between parasitism and fungicide contamination. Specifically, using the cladoceran Daphnia as a model system, we explored the isolated and interactive effects of parasite challenge (yeast Metschnikowia bicuspidata) and exposure to fungicides (copper sulphate and tebuconazole) at two temperatures (17 and 20 °C), in a fully factorial design. Confirming a previous study, M. bicuspidata infection and copper exposure caused independent effects on Daphnia life history, whereas infection was permanently suppressed with tebuconazole exposure. Here, we show that higher temperature generally increased the virulence of the parasite, with the hosts developing signs of infection earlier, reproducing less and dying at an earlier age. These effects were consistent across copper concentrations, whereas the joint effects of temperature (which enhanced the difference between non-infected and infected hosts) and the anti-parasitic action of tebuconazole resulted in a more pronounced parasite × tebuconazole interaction at the higher temperature. Thus, besides independently influencing parasite and contaminant effects, the temperature can act as a modulator of interactions between pollution and disease.