Hammondia heydorni -like oocysts shed by a naturally infected dog and Neospora caninum NC-1 cannot be distinguished

Abstract

This study describes transmission experiments using Hammondia heydorni-like oocysts isolated in 1996 from a naturally infected dog. The isolate was designated as H. heydorni-Berlin-1996. Examination of sera from infected intermediate hosts showed immunoblot reactions that resembled patterns observed after Neospora caninum NC-1 infection. Furthermore, N. caninum DNA could be demonstrated in tissue samples (e.g. heart, brain) of experimentally infected intermediate hosts and in oocyst preparations from H. heydorni-Berlin-1996. The isolated oocysts did not induce any detectable disease in any of the inoculated adult intermediate hosts (goats, sheep, gerbils, guinea pigs, multimammate rats, BALB/c mice, SCID mice), even upon immunosuppression. Furthermore, neither histological lesions nor parasite stages could be identified in the tissues of all fetuses recovered from two multimammate rats that had been infected prior to pregnancy. An experiment with one dog fed a second time on infected intermediate host tissue indicated that immunity may prevent repeated oocyst shedding in N. caninum-infected dogs. In addition, the study clearly demonstrates that N. caninum can be readily transmitted by dogs that have ingested exclusively skeletal muscles of infected intermediate hosts. Therefore, the study has consequences for the recommendations for farmers to prevent postnatal transmission of N. caninum to cattle. It indicates that feeding of any tissues of potential intermediate hosts (including sheep, goats, rodents) to final hosts may induce the shedding of oocysts in these hosts and thus pose a risk for post-natal infection of cattle. With respect to oocyst morphology and the infectivity of muscle tissues for final hosts, no differences were seen in comparison with observations made in the past on Isospora bigemina/I. heydorni/H. heydorni. Therefore, earlier studies made on I. bigemina/I. heydorni/H. heydorni have to be re-evaluated critically to determine whether they may have included N. caninum or other protozoan parasites that use dogs as final hosts and have an oocyst morphology resembling that of I. bigemina/I. heydorni/H. heydorni.

Epidemiology and Control of Neosporosis andNeospora caninum

“…This could be explained by analogy to T. gondii, for which it is well known that naïve definitive hosts are crucial for the life cycle (105). In N. caninum, the situation seems to be similar, as dogs shed no or only few oocysts after being fed repeatedly with infectious material (120,191,397). Additionally, higher oocyst numbers are shed by young dogs (10 to 14 weeks old) than by older dogs (2 to 3 years old) (191).…”

“…Tissue cysts and bradyzoites can survive up to 2 weeks at refrigeration temperature (4°C) but are killed by freezing (155,267). Oocysts were orally infective to cattle (111,190,443), goats and sheep (397), and rodents such as mice, gerbils (Meriones unguiculatus), and guinea pigs (Cavia porcellanus) (134,294,397). Transplacental transmission has been induced experimentally in cattle, dogs, sheep, goats, monkeys, cats, and mice and occurs naturally in many hosts (133).…”

“…This seasonality may be biologically linked to the whelping season of the putative definitive hosts in Texas, coyotes and gray foxes. Since, naïve or young dogs are more submissive definitive hosts for N. caninum than are older or immune dogs (120,191,397), the same may also be true for young coyotes and gray foxes. Further studies are needed to explain the observations with Texas beef calves.…”

Hammondia heydornioocysts in the faeces of a greyhound in New Zealand

“…A great deal of discussion has occurred in recent times over the relationship between H. heydorni and N. caninum (Dubey et al 2002) (Mehlhorn and Heydorn 2000) and it is unfortunate 80 that no type material of H. heydorni exists in order to substantiate claims on its biological properties (Schares et al 2001). Fortunately, the molecular biology of N. caninum is now well defined and a number of genetic loci have been isolated and characterised by a variety of PCR methodologies.…”

Quantification of vertical transmission of Neospora caninum in dairy cows in Minas Gerais, Brazil

“…This was shown in a murine model, using isolates from an asymptomatic calf that was naturally infected (ROJO-MONTEJO et al, 2009). Thus, it is also possible that the herds from farms A and B were infected with a low virulence strain of N. caninum (SCHARES et al, 2001). This would partly explain the results obtained previously from dairy cattle in the southern region of the state of Minas Gerais, where infection by N. caninum presents high prevalence, but there is no significant association with occurrences of abortion, and the frequency of congenital transmission is relatively low (GUEDES et al, 2008).…”