Larval Load Research Articles

Mitigation Strategies against Food Safety Contaminant Transmission from Black Soldier Fly Larva Bioconversion.

The black soldier fly larva, Hermetia illucens, can efficiently convert organic waste into biomatter for use in animal feed. This circularity comes with a risk of contaminating downstream consumers of the larval products with microbes, heavy metals, and other hazards potentially present in the initial substrate. This review examines research on mitigation techniques to manage these contaminants, from pretreatment of the substrate to post-treatment of the larvae. While much research has been done on such techniques, little of it focused on their effects on food safety contaminants. Cheap and low-technology heat treatment can reduce substrate and larval microbial load. Emptying the larval gut through starvation is understudied but promising. Black soldier fly larvae accumulate certain heavy metals like cadmium, and their ability to process certain hazards is unknown, which is why some government authorities are erring on the side of caution regarding how larval bioconversion can be used within feed production. Different substrates have different risks and some mitigation strategies may affect larval rearing performance and the final products negatively, so different producers will need to choose the right strategy for their system to balance cost-effectiveness with sustainability and safety.

Screening of Popular Maize Hybrids against fall Armyworm, Spodoptera frugiperda

Fall armyworm (Spodoptera frugiperda) was the member of noctuidae family which has got economic importance as polyphagous and extreme pest of many important crops, including maize in India and elsewhere. In this context, screening experiment was conducted by using 15 different maize cultivars viz., CP 818, NK 6240, GPMH 1110, GH 0727, 900 M Gold, NK 6801, SM- 2, S- 4717, GK 3207, KMH 225, KMH 8333, Sunny NMH 777, 30 B07, PMH 2244 and Kaveri minchu in MARS, Dharwad. The results revealed that PMH 2244 was recorded the least mean larval load (0.67 larvae per plant) compared to rest of the cultivars. Among fifteen different cultivars screened, Kaveri minchu recorded the highest mean leaf damage score (4.62) whereas, the hybrid PMH 224 recorded the least mean leaf damage score (0.73). The cultivars, PMH 2244, NK 6801 and 900 M Gold were recorded with the least egg mass (0.33 per plant) whereas, the hybrids SM- 2 and Kaveri minchu were recorded with the highest egg mass of 0.63 and 0.61 per plant, respectively. Biophysical parameters of plant such as plant height, leaf area, stem girth and trichome density have been implicated in maize resistance to the fall armyworm. All the plant characters except leaf area which are mentioned above showed significant negative correlation with fall armyworm infestation whereas, leaf area was found significantly positive correlation.

Effect of Date of Sowing on Incidence of Fall Armyworm, Spodoptera frugiperda in Maize

Fall armyworm (Spodoptera frugiperda) is a member of the Noctuidae family which has economic importance as a polyphagous and extreme pest of many important crops, including maize in India and elsewhere. In this context, an experiment regarding the influence of different dates of sowing on the incidence of fall armyworm was conducted in MARS, Dharwad. The results revealed that the least mean larval load of fall armyworm was recorded in crop sown during the July 2nd fortnight (0.75 larvae per plant) and the highest was recorded in crop sown during the August 2nd fortnight (1.53 larvae per plant). Whereas, the lowest mean leaf damage score of 2.95 was observed in crop sown during 2nd fortnight of July and the highest was recorded in the crop sown during 2nd fortnight of August (4.82).

Seasonal abundance of stem-boring insects associated with the invasive Senecio madagascariensis in its native range (KwaZulu-Natal, South Africa) and their potential for biological control

ABSTRACT Fireweed, Senecio madagascariensis Poiret (Asteraceae), is a target for biological control in Australia and Hawaii. Candidate agents recorded in KwaZulu-Natal Province, South Africa, the region of origin of the invasive populations, include stem-boring insects. The seasonal abundance of stem borers associated with S. madagascariensis populations was studied at four field sites in the KwaZulu-Natal Midlands region, during 2017/18. DNA barcoding was used to differentiate and link insect taxa with their endophagous larvae. Monthly sampling revealed that stem-boring larvae comprised largely Diptera (42% of specimens) and Curculionidae (38.9%), with Lepidoptera (19.8%) the least abundant. Differences in larval herbivore loads between sites were statistically significant, with the warmer and drier sites supporting 59% higher larval numbers. DNA barcoding focused on Curculionidae and Lepidoptera, which took precedence due to restricted host ranges. Of the four lineages of weevil larvae recorded, 95% of sequenced specimens comprised two maternal lineages of Gasteroclisus tricostalis (Thunberg). Collectively, G. tricostalis was detected across nine months of the year, with peaks in abundance in autumn and summer. Similarly, of the three lineages of lepidopteran larvae recorded, 83% of sequenced specimens comprised Metamesia elegans (Walsingham) (Tortricidae). Metamesia elegans was collected across six months of the year, with an autumn peak. These results support the prioritisation of G. tricostalis and M. elegans as the most promising stem-boring agents for S. madagascariensis. The higher seasonal abundance of G. tricostalis, together with the good track record of weevils in weed biocontrol, suggest that it should take precedence in subsequent laboratory host-range assessments.

Assessment ofthe efficacy of thymol against Toxocara vitulorum in experimentally infected rats.

The effect of thymol and ivermectin on the development and embryonation of Toxocara vitulorum (T. vitulorum) eggs, as well as their migration in albino rats was investigated both in vitro and in vivo. A total of forty male albino rats were divided into four groups for an in vivo experiment. The first group was uninfected; the second group was infected but left untreated; the third group was infected and received thymol at a dose of 40mg/kg; and the fourth group was infected and received ivermectin (0.2mg/kg). In vitro, thymol inhibited the development of Toxocara larvae within the eggs. However, ivermectin, produced inconsistent results. The in vivo results indicated that the recovery rates of Toxocara larvae from the liver and lungs on day 7 post-infection were significantly lower in the thymol or ivermectin-treated groups than in the infected untreated control. Albumin levels were significantly increased in the thymol-treated group as compared to thepositive control and ivermectin groups.Nitric oxide, IL-4, and IFN- levels in the serum of the thymol or ivermectin-treated groups were significantly lower than that of thepositive control group. Histopathological examination demonstrated that thymol and ivermectin were effective in reducing larval load, reducing the number and size of granulomas in the absence of larvae, and improving tissuearchitecture. The current study concluded that thymol possessed anti-Toxocara activity in a rat model. Additionally, thymol possessed ovicidal properties and may be used as a disinfectant.

Clinical and blood count findings in dogs naturally infected with Dirofilaria immitis.

Dirofilaria immitis is a nematode that infects canids worldwide as well as other mammalian species, including humans. Worms and dogs are well adapted to one another, making dogs the best urban host for the parasite. Nevertheless, 30% of dogs do not sufficiently present microfilaremia, that is, the low larval load impairs transmission by mosquitoes and diagnosis by its detection in the blood samples. Therefore, the canine diagnosis must always include a microfilaria test and serological tests to detect adult worm antigens. To describe the clinical findings in naturally infected dogs in Rio de Janeiro, 34 dogs were included in the study. All dogs were evaluated for history, anamnesis, physical examination, complete blood count (CBC), D. immitis testing for antigens (ELISA test SNAP 4Dx Plus®), and microfilarial burden. The most frequent complaint from the owners was coughing (14.7%, 5/34). The most common CBC finding was eosinophilia (29.4%), followed by thrombocytopenia (26.5%) and neutrophilia (14.7%). Of the 34 animals, 91.2% were microfilaremic, with a mean count of 11.939 microfilaria/mL. Veterinarians working in areas endemic to D. immitis should always undergo screening tests and pulmonary auscultation, and increased expiratory sounds, even in the absence of coughing, can be considered a sign of the disease, along with eosinophilia, thrombocytopenia, and neutrophilia.

S2244 Unusual Presentation of Strongyloides with Microscopic Colitis

Introduction: Strongyloides is an endemic helminth in the tropical regions of the world. It has varied presentation from asymptomatic infection to having hyper-infection syndrome and disseminated disease. We present a case of Strongyloides with microscopic colitis- whether they coexist or lead to one another. Case Description/Methods: A 57 year old male presented with multiple episodes of bilious, non-projectile vomiting and bilateral pedal edema for 15 days. He has past history for L5-S1 radiculopathy for which he was given steroids for 3 months and they were tapered off in that period. Antiemetics were started, but there was no relief. His routine blood investigations were normal except for low serum albumin. Contrast enhanced CT Abdomen was normal. Upper GI endoscopy was normal, biopsies from second part of duodenum was taken. Colonoscopy was done;the mucosa was normal and segmental biopsies were taken. Stool examination and duodenal mucosa showed presence of the larva of Strongyloides. Histopathoplogy of colonic mucosa showed features of microscopic colitis; lamina propria in the ileum and caecum showed inflammatory infiltrate and lymphoid aggregates with eosinophils. Transverse colon stroma showed mixed inflammatory infiltrate with many eosinophils and occasional lymphoid aggregates. Oral ivermectin was started and given for 5 days. Along with anti-helminthic, oral budesonide was also given for microscopic colitis. His symptoms improved and was doing well on follow up. Discussion: S.stercorails has the unique ability to complete its life cycle within the host through an asexual autoinfective cycle, allowing infection to persist in the host indefinitely. Immunocompromised state can precipitate hyperinfection syndrome. Hallmark of hyperinfection syndrome is the increase in the larvae in the stool or the sputum leading to gastrointestinal and pulmonary symptoms. GI symptoms include abdominal pain, nausea, diarrhoea and rarely intestinal obstruction and GI hemorrhage. Our patient didn’t develop any of these symptoms while on steroids. On the other hand, microscopic colitis presents with chronic diarrhoea. These symptoms were also not present. Our patient had symptoms due to increased larval load leading to repeated episodes of vomiting. There is scant literature if Strongyloides leads to microscopic colitis. Bacterial infection leading to microscopic colitis is known but parasitic cause is not known yet.Figure 1.: A: Normal stomach with food residue. B: Normal appearing mucosa of the ascending colon. C: Homogeneous eosinophilic deposits of amyloid in submucosal blood vessels of the small bowel (conventional haematoxylin and eosin-stained section 20x) D: Reddish-orange appearance of amyloid protein deposit in submucosal blood vessels of small bowel (congo red-stained section 20x).

Effect of sex and genotype of the host on the anthelmintic efficacy of albendazole microcrystals, in the CBi-IGE Trichinella infection murine model.

Albendazole (ABZ) is an anthelmintic pharmaceutical commonly used in the treatment of nematode infections. It is a Class II drug poorly water-soluble, with very low bioavailability, a feature particularly limiting to treat the trichinellosis chronic phase. Microcrystals obtained by controlled precipitation using hydroxyethyl cellulose and chitosan have previously been shown to improve ABZ biopharmaceutical properties. This investigation aimed to test the systems' in vivo efficacy in the CBi-IGE murine model of Trichinella spiralis infection in the infection's different phases and parasite’ stages. Treatment in the enteral phase led to a 90% decrease in the larval muscle load, probably due to its effect on T. spiralis female fecundity. Both microcrystal systems given in the migratory phase halved muscle load in males, a response not observed in females. The chitosan-based microcrystals proved to be the best when administered in the chronic phase of the infection – an increased proportion of L1 dead larvae was found compared to controls, except in CBi+-treated females. Males and females from the highly susceptible CBi+ line presented a significantly different treatment response in this phase. In vivo efficacy depended on the host genotype and sex and was related to the parasite cycle stage in which the formulations were administered.

Technical basis for the small-scale production of black soldier fly, Hermetia illucens (L. 1758), meal as fish feed in Benin

Promoting black soldier fly (BSF) rearing in Benin to replace fishmeal in fish diet could reduce fish production costs. This study aims to set up a breeding technique of BSF as a protein source. BSF reproduction has been carried out in sunlight. Two densities (8500 individuals/m 3 and 10,500 individuals/m 3 ) associated with 2 attractants (soybean and pineapple waste) were tested on imago egg-laying. A larvarium with a prepupae self-harvesting system was designed and its efficiency was evaluated by testing 3 densities of larval rearing (1 larva/g, 2 larva/g, 3 larva/g). Two diets, VGD (soybean meal ​+ ​euphorbia leaves and seeds ​+ ​colza oil) and FOD (soybean meal ​+ ​fish offal) were formulated to optimize polyunsaturated fatty acid profile of prepupae to meet nutritional requirements of tilapia. Best oviposition was obtained with 8500 individuals/m 3 with pineapple waste and optimal larval load density was 2 larva/g. Prepupae fed with VGD accumulated C18:2n-6 (10.1%) which is essential for tilapia. Prepupae fed with FOD contained C20:5n-3 (2.20%), a fatty acid beneficial to humans. The lowest production cost of BSF meal was estimated at $1.84/Kg and was obtained with the FOD diet. BSF can easily be reared under local conditions throughout the year. Its nutritional qualities are very interesting to meet Nile tilapia requirements. • Reproduction and larval breeding of BSF are easily carried out in natural conditions in Benin. • Larval rearing containers are easy to design and have prepupae self-harvesting system. • From agricultural by-products, BSF meal can be enriched with essential fatty acids to feed tilapia. • Black soldier fly breeding guidelines in Benin are available.

Efficacy of Coragen 20 SC against Lepidopteran Pest in Greengram and Its Compatibility with Bacillus thuringiensis Isolates

Background: Green gram, Vigna radiata (L.) R. Wilczek is third most important pulse crop cultivated in India. The two key insect pest viz., pod borer, Helicoverpa armigera Hubner and Tobacco leaf caterpillar, Spodoptera litura Fabricius inflicts heavy yield loss in greengram. As these are polyphagous insect pest and the crop is a short duration crop, immediate management strategy such as chemical control is very much essential to check its yield loss. The current study reports the efficacy of novel insecticide i.e. Coragen® 20 SC against above cited two insect pest in greengram. Further its effect on non-target insects and its influence on growth and survival of Bacillus thuringiensis were evaluated. Methods: Field experiments were conducted to evaluate the efficacy of Coragen® 20 SC (at four doses viz., 75 ml ha-1, 100 ml ha-1, 125 ml ha-1 150 ml ha-1), chlorpyriphos 20 EC @ 2.5 l ha-1 and emamectin benzoate 5 SG @ 220 g ha-1 against H. armigera and S. litura during kharif 2018 and 2019. Based on larval load per plant, the percent reduction in larval counts was estimated based on Henderson and Tilton method. The benefit cost ratio (BCR) was worked out for each respective year based on seed yield and net returns. Result: Coragen® 20 SC at 125 ml ha-1 and 150 ml ha-1 had resulted in highest percent reduction in larval population over control. Simultaneously, the highest BCR during kharif 2018 (6.29, 4.21) and 2019 (5.95, 5.64) were recorded from above 2 treatments. Further, Coragen® 20 SC showed compatibility with 5 Bt isolates evaluated, i.e Bt growth didn’t inhibited in nutrient agar containing field dose of Coragen 20 SC.

ASSESSMENT OF NEUROINFLAMMATORY AND NEURODEGENERATIVE ALTERATIONS IN THE BRAIN IN A MOUSE MODEL OF VISCERAL LARVA MIGRANS

Neurotoxocariasis is a parasitic zoonosis resulting from the intrusion of the larvae of dogroundworm Toxocara canis into the central nervous system (CNS), leading to severe CNS insults,and provoking different neurological manifestations ranging from headache to convulsionsand paresis. This work assessed the probable occurrence of neuroinflammatory and neuro-degenerativealterations in the brain tissues of T. canis infected mice and evaluated the changes inbrain parasite loads over the course of infection. The total larval loads in the brain, histopathological,immunohistochemical (MMP-3 & MMP-9) examination as well as determination of NFcellinfiltration around larvae in brain tissues of mice, expressions of all the investigated markersof neuroinflammation and neurodegeneration showed an ascending pattern throughout thecourse of the infection and were directly proportional to the increase in the brain larval loads.

ASSESSMENT OF NEUROINFLAMMATORY AND NEURODEGENERATIVE ALTERATIONS IN THE BRAIN IN A MOUSE MODEL OF VISCERAL LARVA MIGRANS

Neurotoxocariasis is a parasitic zoonosis resulting from the intrusion of the larvae of dogroundworm Toxocara canis into the central nervous system (CNS), leading to severe CNS insults,and provoking different neurological manifestations ranging from headache to convulsionsand paresis. This work assessed the probable occurrence of neuroinflammatory and neuro-degenerativealterations in the brain tissues of T. canis infected mice and evaluated the changes inbrain parasite loads over the course of infection. The total larval loads in the brain, histopathological,immunohistochemical (MMP-3 & MMP-9) examination as well as determination of NFcellinfiltration around larvae in brain tissues of mice, expressions of all the investigated markersof neuroinflammation and neurodegeneration showed an ascending pattern throughout thecourse of the infection and were directly proportional to the increase in the brain larval loads.

Vaccination with chimeric protein induces protection in murine model against ascariasis

An estimated 400 million people are infected by parasites of the genus Ascaris and the existing control measures are inefficient. Vaccine development using B cell antigens is a promising strategy for increased protection against this parasite. The present study aimed at developing a chimeric protein capable of conferring protection against infection by Ascaris sp. For this purpose, we performed B-cell epitope predictions on previously described vaccine candidate proteins from Ascaris suum and the corresponding peptides were used to construct a chimeric protein. Female BALB / c mice were immunized subcutaneously in three doses at 10 day intervals with a vaccine formulation comprised of the chimeric protein together with monophosphoryl lipid A (MPLA). Control groups included protein alone, MPLA, or PBS. After challenge infection, animals vaccinated with chimeric protein plus MPLA showed a reduction of 73.54% of larval load in the lung compared to control group animals. Animals immunized with chimeric protein plus MPLA also display higher IgG response and a reduction in lung inflammation. Our study highlights how chimeric proteins containing more than one B cell epitope can enhance immune protection against helminthic infection and offer new approaches to the development of Ascaris vaccines.

Lactobacillus spp. attenuate antibiotic-induced immune and microbiota dysregulation in honey bees

Widespread antibiotic usage in apiculture contributes substantially to the global dissemination of antimicrobial resistance and has the potential to negatively influence bacterial symbionts of honey bees (Apis mellifera). Here, we show that routine antibiotic administration with oxytetracycline selectively increased tetB (efflux pump resistance gene) abundance in the gut microbiota of adult workers while concurrently depleting several key symbionts known to regulate immune function and nutrient metabolism such as Frischella perrera and Lactobacillus Firm-5 strains. These microbial changes were functionally characterized by decreased capped brood counts (marker of hive nutritional status and productivity) and reduced antimicrobial capacity of adult hemolymph (indicator of immune competence). Importantly, combination therapy with three immunostimulatory Lactobacillus strains could mitigate antibiotic-associated microbiota dysbiosis and immune deficits in adult workers, as well as maximize the intended benefit of oxytetracycline by suppressing larval pathogen loads to near-undetectable levels. We conclude that microbial-based therapeutics may offer a simple but effective solution to reduce honey bee disease burden, environmental xenobiotic exposure, and spread of antimicrobial resistance.

Estimation of the number of Anisakis larvae in commercial fish using a descriptive model based on real‐time PCR

Seafood parasitation by Anisakis (Anisakidae) larvae has been reported in most of the oceans and seas worldwide. The presence of these nematodes in commonly consumed fish represents a potential hazard for consumers as they can provoke gastrointestinal symptoms and allergic reactions. In the present work, the capacity of a SYBR Green qPCR protocol to quantify Anisakis larvae in commercial fish was evaluated using experimentally spiked samples with different numbers (0-50) of A. simplex third-stage larvae (L3). To verify the agreement of the obtained results, 25 naturally infected fish specimens of Atlantic blue whiting underwent a parallel visual inspection. The logarithmic behavior of the Cq data obtained from the experimentally spiked samples allowed the development of a descriptive mathematical model that correlates the Cq value with the number of Anisakis larvae (R2 = 0.9908, CV = 2.37%). In the commercial blue whiting specimens there was a high correlation between the results of the molecular technique and the visual inspection (R2 = 0.9912); the Bland-Altman analysis showed that 94% of the differences were within the limits of agreement (-4.98 and 6.68), indicating the reliability of the descriptive mathematical model based on the SYBR Green qPCR technique. The descriptive function presented based on the SYBR Green qPCR assay is promising as a sensitive and accurate tool for measuring the Anisakis larval load in commercial fish, with a potential application not only in the food industry but also in prevention programs for public health. © 2020 Society of Chemical Industry.

Study of Trichinella patagoniensis in wild boars

Trichinellosis is a zoonotic disease, which represents a significant public health concern in some South American countries, such as Argentina and Chile. Its impact is essentially due to absence of adequate control measures on meat from game animals, as well as the presence of illegal slaughterhouses and the trade of meat products without being tested for this parasite. In Argentina, trichinellosis is an endemic disease. At present, Trichinella spiralis, Trichinella patagoniensis, Trichinella pseudospiralis, and Trichinella britovi have been detected in animals from Argentina. Until now, T. patagoniensis had only been found in mountain cougars (Puma concolor) in Argentina but there is limited information available. The present study intends to determine susceptibility, serological response and distribution of muscle larvae in wild boars infected with T. patagoniensis, T. spiralis and T. pseudospiralis. For each of the Trichinella species five wild boars were inoculated with 20,000 muscle larvae. Except for two specimens which died during the experiment, the animals were euthanized 19 weeks post infection (pi). Blood samples were collected throughout the study in order to determine the antibody kinetics. Also, nine muscle samples from each specimen were taken and analysed for determination of larval distribution. Additionally, four muscle samples were used to obtain muscle juices. Wild boars infected with T. patagoniensis showed little to no larvae in the muscle samples analysed while animals infected with T. spiralis and T. pseudospiralis had a significantly high larval load in all the samples analysed. Optical density (OD) values remained above the cut-off value throughout the experiment. This is the first study to characterize the biological aspects of T. patagoniensis in wild boars.

Immunogenicity and protection induced by recombinant Toxocara canis proteins in a murine model of toxocariasis

Toxocariasis, a natural helminth infection of dogs and cats caused by Toxocara canis and T. cati, respectively, that are transmitted to mammals, including humans. Infection control is based currently on periodic antihelmintic treatment and there is a need for the development of vaccines to prevent this infection. Materials and Methods: Eight potential vaccine candidate T. canis recombinant proteins were identified by in silico (rTcGPRs, rTcCad, rTcVcan, rTcCyst) and larval proteomics (rTES26, rTES32, rMUC-3 and rCTL-4) analyses. Immunogenicity and protection against infectious challenge for seven of these antigens were determined in a murine model of toxocariasis. C57BL/6 female mice were immunized with each of or combinations of recombinant antigens prior to challenge with 500 T. canis embryonated eggs. Levels of specific antibodies (IgG, IgG1, IgG2a and IgE) in sera and cytokines (IL-5, INF-ɣ and IL-10) produced by antigens-stimulated splenocytes, were measured. Presence of specific antibodies to the molecules was measured in sera of T. canis-seropositive dogs and humans. Results: All seven molecules were immunogenic in immunized mice; all stimulated significantly elevated levels of specific IgG, IgG1 or IgG2a and six were associated with elevated levels of specific IgE; all induced elevated production of IFN- ɣ and IL-10 by splenocytes, but only the in silico-identified membrane-associated recombinants (rTcCad, rTcVcan, and rTcCyst) induced significantly increased IL-5 production. Vaccination with two of the latter (rTcCad and rTcVcan) reduced larval loads in the T. canis challenged mice by 54.3% and 53.9% (P < 0.0001), respectively, compared to unimmunized controls. All seven recombinants were recognized by T. canis-seropositive dog and human sera. Conclusion: The identification of vaccine targets by in silico analysis was an effective strategy to identify immunogenic T. canis proteins capable of reducing larval burdens following challenge with the parasite. Two recombinant proteins, rTcCad and rTcVcan, were identified as promising vaccine candidates for canine toxocariasis.

From the lab to the river: Determination of ecological hosts of Anodonta anatina

Abstract Coextinction is the simplest form of secondary extinction and freshwater mussels (Bivalvia, Unionida) may be particularly prone to this phenomenon as their life cycle includes an obligatory parasitic larval stage on fish hosts. The main aims of this study were to determine the possible ecological fish hosts of Anodonta anatina (Linnaeus, 1758) in several rivers of the Douro basin in northern Portugal and to assess possible spatial and temporal differences in glochidial (larval) loads. In order to achieve this, electrofishing was conducted from December to April, the fish fauna was characterized, and levels of infestation with A. anatina glochidia were determined. Native cyprinid species, mainly Luciobarbus bocagei (Iberian barbel) and Squalius carolitertii (northern Iberian chub), together with the non‐native Lepomis gibbosus (pumpkinseed sunfish) and Alburnus alburnus (common bleak), were found to have the highest glochidial loads. Clear differences in infestation between rivers and throughout time were detected, with an infestation period from January to March, and with the Tâmega River having the highest prevalence. Anodonta anatina is able to infest a variety of fish species, and this together with earlier studies showed that the metamorphosis into juveniles occurs mainly in native cyprinid species, although non‐native species like common bleak can also be considered suitable hosts. However, the larvae infesting other non‐native species, such as the pumpkinseed sunfish, do not metamorphose and can be considered ‘dead ends’. Overall, the results reported here are important for the conservation of A. anatina (and other unionoid species) because several Iberian rivers (and worldwide) have been subjected to the extirpation of native fish species and the introduction of non‐native fish species. Therefore, careful assessments of fish communities should be conducted to assess possible negative interactions with freshwater mussels.

Bacterial Exposure Mediates Developmental Plasticity and Resistance to Lethal Vibrio lentus Infection in Purple Sea Urchin (Strongylocentrotus purpuratus) Larvae.

Exposure to and colonization by bacteria during development have wide-ranging beneficial effects on animal biology but can also inhibit growth or cause disease. The immune system is the prime mediator of these microbial interactions and is itself shaped by them. Studies using diverse animal taxa have begun to elucidate the mechanisms underlying the acquisition and transmission of bacterial symbionts and their interactions with developing immune systems. Moreover, the contexts of these associations are often confounded by stark differences between “wild type” microbiota and the bacterial communities associated with animals raised in conventional or germ-free laboratories. In this study, we investigate the spatio-temporal kinetics of bacterial colonization and associated effects on growth and immune function in larvae of the purple sea urchin (Strongylocentrotus purpuratus) as a model for host-microbe interactions and immune system development. We also compare the host-associated microbiota of developing embryos and larvae raised in natural seawater or exposed to adult-associated bacteria in the laboratory. Bacteria associated with zygotes, embryos, and early larvae are detectable with 16S amplicon sequencing, but 16S-FISH indicates that the vast majority of larval bacterial load is acquired after feeding begins and is localized to the gut lumen. The bacterial communities of laboratory-cultured embryos are significantly less diverse than the natural microbiota but recapitulate its major components (Alphaproteobacteria, Gammaproteobacteria, and Bacteroidetes), suggesting that biologically relevant host-microbe interactions can be studied in the laboratory. We also demonstrate that bacterial exposure in early development induces changes in morphology and in the immune system. In the absence of bacteria, larvae grow larger at the 4-arm stage. Additionally, bacteria-exposed larvae are significantly more resistant to lethal infection with the larva-associated pathogen Vibrio lentus suggesting that early exposure to high levels of microbes, as would be expected in natural conditions, affects the immune state in later larvae. These results expand our knowledge of microbial influences on early sea urchin development and establish a model in which to study the interactions between the developing larval immune system and the acquisition of larval microbiota.

How general are generalist parasites? The small mammal part of the Lyme disease transmission cycle in two ecosystems in northern Europe.

The pathogens causing Lyme disease are all vectored by generalist tick species found on a wide range of vertebrates, but spatial and annual variation in host use has rarely been quantified. We here compare the load of Ixodes ricinus (the vector) on small mammals and investigate the infection prevalence of Borrelia burgdorferi s.l. (the pathogen) involved in the enzootic transmission cycle of Lyme disease in two contrasting ecosystems in Norway from 2014 to 2016. The most common larval tick host in the eastern region was the bank vole, while the common shrew dominated in the western region of Norway. However, the wood mouse and the bank vole had consistently higher larval tick loads than the common shrew in both ecosystems. Hence, the evidence indicated that species are differently suitable as hosts, regardless of their abundances. The pathogen infection prevalence was similar among small mammal species, but markedly higher in the region with larger small mammal populations and higher tick loads, while the seasonal and annual variation was less marked. Our study indicated that the generalist I. ricinus shows consistent patterns of load on species of small vertebrate hosts, while B. burgdorferi s.l. (B. afzelii) was a true generalist. The similar roles of host species across regions suggest that disease dynamics can be predicted from host community composition, but predicting the role of host community composition for disease dynamics requires a detailed understanding of the different species population limitations under global change.