A Listeria monocytogenes-Based Vaccine Formulation Reduces Vertical Transmission and Leads to Enhanced Pup Survival in a Pregnant Neosporosis Mouse Model.

Dennis Imhof,Anna Oevermann,William Robert Pownall,Camille Monney,Andrew Hemphill

doi:10.3390/vaccines9121400

Abstract

The apicomplexan parasite Neospora caninum is the worldwide leading cause of abortion and stillbirth in cattle. An attenuated mutant Listeria monocytogenes strain (Lm3Dx) was engineered by deleting the virulence genes actA, inlA, and inlB in order to avoid systemic infection and to target the vector to antigen-presenting cells (APCs). Insertion of sag1, coding for the major surface protein NcSAG1 of N. caninum, yielded the vaccine strain Lm3Dx_NcSAG1. The efficacy of Lm3Dx_NcSAG1 was assessed by inoculating 1 × 105, 1 × 106, or 1 × 107 CFU of Lm3Dx_NcSAG1 into female BALB/c mice by intramuscular injection three times at two-week intervals, and subsequent challenge with 1 × 105 N. caninum tachyzoites of the highly virulent NcSpain-7 strain on day 7 of pregnancy. Dose-dependent protective effects were seen, with a postnatal offspring survival rate of 67% in the group treated with 1 × 107 CFU of Lm3Dx_NcSAG1 compared to 5% survival in the non-vaccinated control group. At euthanasia (25 days post-partum), IgG antibody titers were significantly decreased in the groups receiving the two higher doses and cytokines recall responses in splenocyte culture supernatants (IFN-γ, IL-4, and IL-10) were increased in the vaccinated groups. Thus, Lm3Dx_NcSAG1 induces immune-protective effects associated with a balanced Th1/Th2 response in a pregnant neosporosis mouse model and should be further assessed in ruminant models.

Highlights

Neospora caninum is a cyst-forming, intracellular apicomplexan parasite closely related to Toxoplasma gondii, causing significant diseases in farm animals
N. caninum exhibits a life cycle with three major infectious stages: (I) sporozoites encapsulated in oocysts that are generated in their definitive host and shed into the environment via feces; (II) rapidly proliferating tachyzoites, that cause acute disease in the intermediate host and are vertically transmitted to fetuses, which may lead to abortion or disease; (III) slowly dividing bradyzoites, which form tissue cysts, that can persist for years in the intermediate host without inducing any clinical symptoms [1]
We report on a challenge experiment to demonstrate proof-of-principle for the efficacy of Lm3Dx_NcSAG1 in a standardized pregnant neosporosis mouse model

Summary

Introduction

Neospora caninum is a cyst-forming, intracellular apicomplexan parasite closely related to Toxoplasma gondii, causing significant diseases in farm animals. N. caninum is an economically significant parasite, especially in cattle, due to its ability to persist within an infected animal, causing repeated abortions and stillbirth [1]. Infection of N. caninum in cattle frequently leads to the birth of persistently infected calves, which can transmit the parasite to the generation. N. caninum exhibits a life cycle with three major infectious stages: (I) sporozoites encapsulated in oocysts that are generated in their definitive host and shed into the environment via feces; (II) rapidly proliferating tachyzoites, that cause acute disease in the intermediate host and are vertically transmitted to fetuses, which may lead to abortion or disease; (III) slowly dividing bradyzoites, which form tissue cysts, that can persist for years in the intermediate host without inducing any clinical symptoms [1]. The inherent immunomodulation that takes place during pregnancy triggers recrudescence and reconversion to tachyzoites, and vertical transmission can lead to abortion and stillbirth [1]

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Conclusion