Influence ofNeospora caninumintra-specific variability in the outcome of infection in a pregnant BALB/c mouse model

Abstract

Previous assays in pregnant animals have demonstrated the effect of different host factors and timing of infection on the outcome of neosporosis during pregnancy. However, the influence of Neospora caninum isolate itself has been poorly investigated. Here, we compared the effects on clinical outcome and vertical transmission observed in a pregnant mouse model following infection with 10 different N. caninum isolates. The isolates in our study included the Nc-Liv isolate and nine N. caninum isolates obtained from calves. Female BALB/c mice were inoculated with 2 × 106 tachyzoites at day 7 of pregnancy. Morbidity and mortality, in both dams and offspring during the course of infection, and transmission to progeny at day 30 postpartum were evaluated. The serum IgG1 and IgG2a production in dams were also examined. All dams showed elevated IgG1 and IgG2a responses, confirming N. caninum infection, although signs of disease were only exhibited in dams infected with 4 of the 10 isolates (Nc-Spain 4H, Nc-Spain 5H, Nc-Spain 7 and Nc-Liv). In neonates, clinical signs were observed in all N. caninum-infected groups, and neonatal mortality rates varied from greater than 95% with the isolates mentioned above to less than 32.5% with the other isolates. Vertical transmission rates, as assessed by parasite PCR-detection in neonate brains, also varied from 50% to 100% according to the isolate implicated. These results confirm the wide pathogenic and transmission variability of N. caninum. The intra-specific variability observed herein could help us explain the differences in the outcome of the infection in the natural host.

Dose-dependent effects of experimental infection with the virulent Neospora caninum Nc-Spain7 isolate in a pregnant mouse model

“…This mirrors findings reported in previous studies using the same pregnant mouse model and isolate (Regidor-Cerrillo et al, 2010;Collantes-Fernández et al, 2012;Dellarupe et al, 2014), and those employing the virulent isolate Nc-Liv (Marugán-Hernández et al, 2011;Dellarupe et al, 2014;Pastor-Fernández et al, 2015). Importantly, reduction of tachyzoite numbers by a factor 20 (from 2 × 10 6 to 10 5 ) did not alter median survival time, parasite burden and immune responses in both pregnant and non-pregnant mice, and was still causing 100% of pup mortality until day 30 pp.…”

“…In addition, very different outcomes have been observed between non-pregnant and pregnant mice (reviewed in Monney and Hemphill, 2014). BALB/c mice are the most widely employed mouse breed for studies on Neospora infection biology (López-Pérez et al, 2010;Regidor-Cerrillo et al, 2010;Dellarupe et al, 2014) and as proof-of-concept model for the assessment of drugs (e.g., Debache et al, 2011;Debache and Hemphill, 2012;Schorer et al, 2012;Ojo et al, 2014). Most notably, the pregnant BALB/c model has demonstrated various degrees of efficacy for a number of vaccine candidates (e.g., Aguado-Martínez et al, 2009;Debache et al, 2009;Zhang et al, 2010;Marugán-Hernández et al, 2011;Monney et al, 2012;Rojo-Montejo et al, 2012), and enabled researchers to assess the effects of parasite infection and respective vaccines on both progeny and dams (López-Pérez et al, 2008).…”

“…For that purpose, pregnant BALB/c mice were experimentally infected with 2 × 10 6 , 10 5 , 10 4 , 10 3 or 10 2 N. caninum tachyzoites. Challenge was carried out using the Nc-Spain7 isolate, which had been earlier obtained from an asymptomatic calf (Regidor-Cerrillo et al, 2008). This isolate has a controlled low number of passages in cell culture and its high degree of virulence has been demonstrated in vitro (RegidorCerrillo et al, 2011) andin vivo (Regidor-Cerrillo et al, 2010;Caspe et al, 2012;Collantes-Fernández et al, 2012;Dellarupe et al, 2014;Regidor-Cerrillo et al, 2014;Arranz-Solís et al, 2015).…”

Neosporosis in animals—The last five years

“…Little is known of the strain variation with respect to their virulence. In limited studies some N. caninum strains were more virulent to mice than others and showed also differences during in vitro cultivation (García-Melo et al, 2009Rojo-Montejo et al, 2009a,b;Regidor-Cerrillo et al, 2010b. It is not yet known, whether virulence in mice could reflect the effect an N. caninum infection in other host.…”

A vaccine formulation combining rhoptry proteins NcROP40 and NcROP2 improves pup survival in a pregnant mouse model of neosporosis

“…Second, several studies have focused on non-pregnant mouse models Monney and Hemphill, 2014), for which the regulation of immunity is obviously not equal to those found during pregnancy. Third, the BALB/c model employed here ensures a 100% congenital transmission and 0% of survival of the offspring in the non-vaccinated mice (López-Pérez et al, 2008;Dellarupe et al, 2014), which is highly dependent of the type of isolate used for challenge, since differences in isolate virulence have been demonstrated (Atkinson et al, 1999;Collantes-Fernández et al, 2006;Regidor-Cerrillo et al, 2010). Fourth, direct comparisons with studies carried out in mouse models for T. gondii infection must be carefully considered despite the common phylogenetic origin of T. gondii and N. caninum, since relevant genetic dissimilarities that affect their infection biology have been recently elucidated (Reid et al, 2012).…”