Influence of dose and route of administration on the outcome of infection with the virulent Neospora caninum isolate Nc-Spain7 in pregnant sheep at mid-gestation

Abstract

Experimental infections in pregnant sheep have been focused on studying the effect of the time of challenge on the outcome of N. caninum infection, whereas the impact of the dose and route of challenge has not been studied in depth. Therefore, clinical outcome, immune responses, parasite detection and burden, and lesion severity in placental tissues and foetal brains were investigated in 90-day-pregnant sheep inoculated intravenously with 105 (G1), 104 (G2), 103 (G3), or 102 (G4) tachyzoites or subcutaneously with 104 (G5) tachyzoites of the virulent Nc-Spain7 isolate and an uninfected group (G6). Comparing challenge doses, G1 was the only group that had 100% abortion. Likewise, IFNγ levels in G1 increased earlier than those in other intravenously infected groups, and IgG levels on day 21 post-infection (pi) were higher in G1 than those in other intravenously infected groups. Concerning vertical transmission, G1 shows a higher parasite burden in the foetal brain than did G2 and G3. Comparing routes of administration, no differences in foetal survival rate or parasite load in the foetal brain were found. Although G2 had higher IFNγ levels than G5 on day 10 pi, no differences were found in humoral immune responses. Because the outcome after intravenous infection with 105 tachyzoites was similar to that observed after intravenous infection with 106 tachyzoites used in a previous work (100% abortion and vertical transmission), we conclude that it may be reasonable to use 105 tachyzoites administered by the intravenous route in further experiments when assessing drugs or vaccine candidates.

Effects of challenge dose and inoculation route of the virulent Neospora caninum Nc-Spain7 isolate in pregnant cattle at mid-gestation

“…It is well known that the clinical outcome can vary with the tachyzoite infective dose; therefore, dose-titration studies are also necessary to contribute to the refinement and standardization of a bovine model [21, 22]. Foetal damage is a crucial parameter to be considered in any experimental models of bovine neosporosis [20].…”

“…Methods for DNA extraction from ruminant tissues as well as PCR and qPCR protocols have been previously published in the literature [16, 22, 25]. Automated genomic DNA extraction from 20 to 100 mg of maternal (placentomes), foetal (brain and liver) and calf (brain) tissues was performed with the Maxwell ® 16 System (Promega, Wisconsin, USA), using the commercial Maxwell ® 16 Mouse Tail DNA Purification Kit, following the manufacturer’s recommendations.…”

“…In recent years, the dose-dependent effects of virulent Nc-Spain7 isolate infection have been evaluated in pregnant mouse and ovine models [21, 22]. In dairy cattle, foetal death was reported in 3 of 6 experimentally Nc-Spain7-infected naïve Friesian heifers at mid-gestation during the studied period (up to 7 weeks post-infection) [18].…”

“…However, a titration dose of this isolate has not yet been done in bovine models. In addition, it is known that the route of inoculation can result in different effects in pregnant cattle [11] and sheep [22] at mid-gestation.…”

Toxoplasma gondii and Neospora caninum infections in South American camelids in Switzerland and assessment of serological tests for diagnosis

“…In contrast to T. gondii, N. caninum has no zoonotic character but it is regarded as one of the major causes of abortion in cattle worldwide [2]; besides, it can also cause reproductive failure (i.e. abortion, stillbirths and perinatal mortality) in other ruminant species such as goats [13][14][15], sheep [16] and deer [17]. Furthermore, it represents an important cause of neuromuscular disease and death in dogs [2,13,17].…”