A simplified Barbervax® vaccination regimen in lambs to evoke immunological protection to Haemonchus contortus

Mucosal Immunity of Major Gastrointestinal Nematode Infections in Small Ruminants Can Be Harnessed to Develop New Prevention Strategies

Gastrointestinal parasitic nematode (GIN) infections are the cause of severe losses to farmers in countries where small ruminants such as sheep and goat are the mainstay of livestock holdings. There is a need to develop effective and easy-to-administer anti-parasite vaccines in areas where anthelmintic resistance is rapidly rising due to the inefficient use of drugs currently available. In this review, we describe the most prevalent and economically significant group of GIN infections that infect small ruminants and the immune responses that occur in the host during infection with an emphasis on mucosal immunity. Furthermore, we outline the different prevention strategies that exist with a focus on whole and purified native parasite antigens as vaccine candidates and their possible oral-nasal administration as a part of an integrated parasite control toolbox in areas where drug resistance is on the rise.

Fasciola hepatica antioxidant and protease-inhibitor cocktail recombinant vaccines administered five times elicit potent and sustained immune responses in sheep but do not confer protection

Our laboratory's vaccine development strategy against the livestock parasite Fasciola hepatica centres around disrupting key biological processes by combining groups of antigens with similar/complementary functional actions into a single vaccine cocktail. In this study the focus was on antioxidant protein vaccines and a protease inhibitor vaccine aimed at disrupting the parasite's ability to defend against oxidative stress and protease-inhibitor balance, respectively. Two combinations of recombinantly expressed antioxidants were assessed, namely peroxiredoxin (rFhPrx), thioredoxin (rFhTrx) and thioredoxin-glutathione reductase (rFhTGR) (Group 1) and rFhPrx, rFhTrx, and two superoxide dismutases (rFhSOD1 and rFhSOD3) (Group 2). The protease inhibitor vaccine cocktail included representatives of each of the key secreted protease inhibitor families, namely a Kunitz-type inhibitor (rFhKT1), a serpin (rFhSrp1) and a stefin, (rFhStf1) (Group 3). The vaccine combinations were formulated in adjuvant Montanide 61VG administered at five timepoints; two before experimental challenge with 60 F. hepatica metacercariae and three after infection. The vaccine combinations did not reduce the liver fluke burden, and only Group 2 displayed a marginal reduction in egg viability (8.2%). Despite previous results showing an effect of liver fluke vaccines on overall weight gain in infected animals, no significant (P value >0.05) impact on weight gain was observed in this study. Antibodies were elicited against all the vaccine antigens within the cocktails and were maintained at high levels to the end of the trial, due to our strategy of continuing vaccine administration after infection. However, these responses were not boosted by the challenge F. hepatica infection. A comparative analysis with previous vaccine data using a protease inhibitor vaccine found no repeat of the promising outcomes associated with this vaccine, indicating that the addition of rFhSrp1 to the vaccine cocktail did not improve vaccine efficacy. Assessment of liver pathology across the two trials using a modified liver enzyme score (glutamate dehydrogenase to platelet ratio) at eight weeks post infection suggests an association with liver fluke burden above 45 flukes, which could be used to predict liver pathology in future trials. The results reported in this study highlight the ambiguousness in liver fluke vaccine development and the difficulty in obtaining consistent and repeatable protection. This work stresses the need for repetition of trials and the use of sufficiently sized groups to assess vaccine efficacy with adequate statistical power.

How to train your myeloid cells: a way forward for helminth vaccines?

Soil-transmitted helminths affect approximately 1.5 billion people worldwide. However, as no vaccine is currently available for humans, the current strategy for elimination as a public health problem relies on preventive chemotherapy. Despite more than 20 years of intense research effort, the development of human helminth vaccines (HHVs) has not yet come to fruition. Current vaccine development focuses on peptide antigens that trigger strong humoral immunity, with the goal of generating neutralizing antibodies against key parasite molecules. Notably, this approach aims to reduce the pathology of infection, not worm burden, with only partial protection observed in laboratory models. In addition to the typical translational hurdles that vaccines struggle to overcome, HHVs face several challenges (1): helminth infections have been associated with poor vaccine responses in endemic countries, probably due to the strong immunomodulation caused by these parasites, and (2) the target population displays pre-existing type 2 immune responses to helminth products, increasing the likelihood of adverse events such as allergy or anaphylaxis. We argue that such traditional vaccines are unlikely to be successful on their own and that, based on laboratory models, mucosal and cellular-based vaccines could be a way to move forward in the fight against helminth infection. Here, we review the evidence for the role of innate immune cells, specifically the myeloid compartment, in controlling helminth infections. We explore how the parasite may reprogram myeloid cells to avoid killing, notably using excretory/secretory (ES) proteins and extracellular vesicles (EVs). Finally, learning from the field of tuberculosis, we will discuss how anti-helminth innate memory could be harnessed in a mucosal-trained immunity-based vaccine.

Immunoprotection Efficacy of Con A-Purified Proteins against Haemonchus contortus in Goats

Parasitic nematodes are important pathogens that infect animals, causing significant economic losses globally. Current repeated treatments have led to widespread anthelmintic resistance in nematode populations, so vaccine development offers an alternative control approach. However, only one effective vaccine (named Barbervax) has been developed to protect animals against one of the most pathogenic nematodes of ruminants—Haemonchus contortus (the barber’s pole worm). This vaccine contains a dominant component, Concanavalin A (Con A) purified H11 antigen, which has been shown to induce high levels (>85%) of immune protection in sheep breeds, but in goat breeds, the immunoprotection test of this native protein is still lacking. Here, we evaluated the protective efficacy of low-dose Con A-purified proteins for controlling the H. contortus infection in goats. Four-month-old Boer goats were equally divided into two vaccinated groups of 5 μg and 10 μg native proteins, and one adjuvant control. Each goat was immunized subcutaneously thrice and then challenged with 7000 infective third-stage larvae (L3s). The fecal egg count (FEC), degree of anemia, antibody levels of serum and abomasum mucosa, as well as worm burdens, were detected in experimental goats. Our results showed that both 5 μg and 10 μg vaccinated groups induced the effective protection in goats, reduced mean FEC by 71.8% and 68.6%, and mean worm burdens by 69.8% and 61.6%, respectively, compared to the adjuvant control. In addition, we detected that the serum antibody responses to the Con A-purified proteins were dominated by the IgG subtype, but the mucosal antibody responses were not detected. These data demonstrate Con A-purified proteins induced effective immunoprotection in goats, and underline their significance for controlling this widespread parasite.

Investigation of the combined efficacy of two Haemonchus contortus vaccines in weaner Merino sheep

This study was conducted to investigate whether co-administration of Barbervax® (Bvax) with Haemonchus contortus surface larval antigen (HcsL3) would increase the protective efficacy and duration of protection against H. contortus infection in weaner Merino sheep. A total of 132 10-month-old weaned Merino ewe lambs were randomly allocated into six treatment groups (n = 22). Sheep were vaccinated four times with either Barbervax® (Bvax), H. contortus L3 surface larval antigen (HcsL3), combined vaccination (Bvax + HcsL3), Bvax + AlOH, HcsL3 + Saponin or remained as unvaccinated controls. Aluminium hydroxide (AlOH) and saponin adjuvants were included in HcsL3 and Bvax vaccines respectively. The first three vaccinations were given at 4 week intervals and the fourth vaccination provided as booster, 9 weeks later. All animals were treated with Zolvix™ (monepantel 25 mg/mL, Elanco) at the third vaccination and commencing two weeks later, artificially trickle infected with H. contortus L3. Worm egg count (WEC), packed cell volume (PCV), antibody titre and bodyweight were measured throughout the study as was specific antibody directed against each antigen using ELISA. The administration of Bvax and HcsL3, alone or in combination, induced an antibody response against HcsL3 but only the Bvax and the combined treatment elicited an antibody response to the Bvax antigen. The targeting of HcsL3 by each vaccine was confirmed by immunofluorescence staining of H. contortus L3. However, only the booster vaccination in the Bvax treatments reduced WEC to levels below untreated controls. The HcsL3 vaccine did not reduce WEC in this experiment and co-administration with Bvax did not improve the efficacy and duration of protection against H. contortus infection.

Protective efficacy of Barbervax® in Merino weaner sheep trickle infected with five doses of Haemonchus contortus infective larvae

Barbervax® protects sheep against H. contortus infection; however, the level of protection afforded by the vaccine at different levels of larval challenge under field conditions has not been reported. Therefore, this study was designed to investigate the protective efficacy of Barbervax® at increasing doses of trickle infection with H. contortus third stage larvae (L3). Merino lambs (220) were randomly allocated to challenge treatment groups and received Barbervax® vaccinations at approximately 8, 11, 15 and 22 weeks of age or not vaccinated (control group). Animals within each treatment group were subjected to one of five levels of H. contortus L3 trickle infection (0, 300, 600, 1200 and 2400 L3/week in two split doses). Trickle infections started two weeks after the third vaccination (week 0). Worm egg count (WEC), packed cell volume (PCV), antibody titre and bodyweight were measured at week 2 (start of trickle infection), week 5 and then every two weeks for 11 weeks. Vaccinated weaners had a significantly (P < 0.0001) lower faecal WEC than unvaccinated control animals. Vaccination induced significant specific antibody responses that were not influenced by level of trickle infection. Vaccination significantly reduced the number of weaners requiring salvage anthelmintic treatment (9.4% vaccinated weaners versus 33.6% unvaccinated). Vaccine protective index based on WEC was similar at all challenge levels (overall mean> 60%) and at the higher challenge levels did not reduce H. contortus infection to levels that would not require anthelmintic treatment. Therefore, it is suggested that under conditions of high larval challenge the use of Barbervax® should be integrated with other control methods.