On the Efficacy and Safety of Vaccination with Live Tachyzoites of Neospora caninum for Prevention of Neospora-Associated Fetal Loss in Cattle

Abstract

bInfection of cattle with Neospora caninum may result in abortion or the birth of a congenitally infected calf. Vaccination with live N. caninum protects against experimental infection of cattle and mice, and the naturally attenuated Nc-Nowra strain of N. caninum is of particular interest as a potential vaccine candidate. Vaccination of heifers prior to breeding with live Nc-Nowra tachyzoites by either the subcutaneous or the intravenous route reduced the rate of abortion and the presence of the parasite in calves as determined by PCR and serology after infection of cows with a virulent isolate. Protected fractions were 55.6% to 85.2% depending on the route of vaccination and growth conditions of the vaccine strain, with cryopreserved Nc-Nowra tachyzoites being less effective, with a 25.9% protected fraction. Vaccination appeared to reduce the rate of pregnancy after artificial insemination in some groups compared to nonvaccinated, nonchallenged controls. One animal that was vaccinated but not challenged experienced an abortion, but Nc-Nowra could not be detected in any of the cows in this group or their progeny. This study confirms that live vaccination can be an effective method of preventing neosporosis in cattle and yet highlights the technical hurdle of preservation of live parasites that must be overcome for a vaccine to be commercially successful.

The effect of a live Neospora caninum tachyzoite vaccine in naturally infected pregnant dairy cows

“…In another study, it was demonstrated that live vaccination protects against fetal death, all cows immunized intravenously 9 weeks prior to artificial insemination and challenged at 70 days of pregnancy had viable no infected offspring (Williams et al, 2007). Partial protection effect against infection of the offspring, varying from 25.9% to 85.2% depending on the route of vaccination and growth conditions of the parasites, had been shown when cows were vaccinated at 63-75 days before pregnancy and challenged at 139 days of pregnancy (Weber et al, 2013). Compared to these studies, our design differs because vaccination was performed at mid-term under field conditions where the dams were seropositive following natural infection.…”

“…It has been considered that an effective vaccine against neosporosis should either be aimed to prevent infection in uninfected animals, or to prevent abortion or vertical transmission in infected animals (Innes et al, 2002). Previous studies demonstrated that vaccination of naïve cows with live tachyzoites was protective against experimental challenge (Williams et al, 2007;Rojo-Montejo et al, 2013;Weber et al, 2013;Hecker et al, 2013;Reichel et al, 2014;Monney and Hemphill, 2014). The Israeli N. caninum NcIs491 isolate, obtained from brain tissue of an aborted fetus, can be easily grown in culture and is suggested to be of low pathogenicity to laboratory animals including gerbils (Fish et al, 2007) and mice (unpublished results), in comparison with the NC-1 strain (Lindsay et al, 1995;Rettigner et al, 2004).…”

Vertical transmission in experimentally infected sheep despite previous inoculation with Neospora caninum NcNZ1 isolate

“…In three cattle studies (Williams et al, 2007(Williams et al, , 2000Innes et al, 2001), where the dams were inoculated with live tachyzoites prior to mating, there was no evidence of vertical transfer to the calves using serology, immunohistochemistry and PCR for the detection of N. caninum infection. In contrast, low levels of abortion or detection of N. caninum have been reported in 3 other studies where cows were inoculated prior to pregnancy (Weston, 2011;Hecker et al, 2013;Weber et al, 2013). Thus, protection against vertical transmission in cattle following inoculation prior to pregnancy is not absolute.…”

Control options forNeospora caninum– is there anything new or are we going backwards?

“…Hope had been expressed that efficacious and economically viable vaccines would become available for the control of N. caninum infections and abortions when, in addition to a commercially available inactivated vaccine (Neoguard™), highly efficacious live vaccine candidates showed promise Weber et al 2013). However, these vaccine candidates may yet be a few years from reaching the market place.…”