Placentophagia--an alternative way for horizontal transmission of Neospora caninum in cattle?

Abstract

The pathogenic apicomplexan Neospora caninum frequently causes abortions in cattle world-wide. Following the characterization of N. caninum in 1984, the heteroxenous life cycle and the role of dogs as definitive hosts were only discovered recently. McAllister 1xUncovering the biology and epidemiology of Neospora caninum. McAllister, M.M. Parasitol. Today. 1999; 15: 216–217Abstract | Full Text | Full Text PDF | PubMed | Scopus (20)See all References1 reviewed the transmission route and stipulated the role of dogs in N. caninum epidemiology. We are now aware of three modes of N. caninum transmission in cattle: (1) vertical transplacental transmission (vertical propagation), (2) experimental oral inoculation with colostrum spiked with tachyzoites, and (3) oral infection by ingestion of sporulated dog-originated oocysts 1xUncovering the biology and epidemiology of Neospora caninum. McAllister, M.M. Parasitol. Today. 1999; 15: 216–217Abstract | Full Text | Full Text PDF | PubMed | Scopus (20)See all References, 2xExperimental studies on the transmission of Neospora caninum between cattle. Davison, H.C. et al. Res. Vet. Sci. 2001; 70: 63–168CrossRef | Scopus (36)See all References. However, the low prevalence of Hammondia- and Neospora-like coccidia in dogs and the limited numbers of oocysts resulting from experimental infections still puts a question mark on the real importance of dogs in N. caninum epidemiology.Currently, Dijkstra et al.3xDogs shed Neospora caninum oocysts after ingestion of naturally infected bovine placenta but not after ingestion of colostrum spiked with Neospora caninum tachyzoites. Dijkstra, T.H. et al. Int. J. Parasitol. 2001; 31: 747–752CrossRef | PubMed | Scopus (108)See all References3 reported on successful transmission of N. caninum to dogs by feeding them naturally infected bovine placenta (placentophagia) and suggested the possibility of contact between dogs as definitive hosts and placentas from infected cows. The presence of infective stages of N. caninum in placenta also opened up another field for discussion. Placentophagia is a common behavioral feature observed in almost all mammalian groups. There is a lack of explanations for this striking phenomenon, which is evidently a complex feature given the multiple advantages to parturient mammalian mothers 4xPlacentophagia: A biobehavioural enigma. Kristal, M.B. Neuroscience and Biobehavioral Reviews. 1980; 4: 141–150CrossRef | PubMed | Scopus (33)See all References4. Ruminants are not exceptional cases in placentophagia and several ethological studies have documented this behavior. Experiments with cattle demonstrated that parturient cows not only feed on their own placenta, but are also attracted to donor placenta and amniotic fluid 5xTiming of the attraction towards the placenta and amniotic fluid by the parturient cow. Machado, L.C.P. et al. Appl. Anim. Behav. Sci. 1997; 53: 183–192Abstract | Full Text PDF | Scopus (14)See all References5. The opportunity for N. caninum-infected cows to gain contact with placenta from other cows depends on the technology used and the organisation of the calving process, but for many herds this type of contact cannot be excluded. Thus, placentophagia might represent another important route of horizontal transmission of neosporosis among cattle. In published mathematical dynamic models, the long-term maintenance of N. caninum infection in dairy herds by vertical propagation was believed to be impossible, thus supporting the significant role of dogs as definitive hosts 6xMathematical models of Neospora caninum infection in dairy cattle: transmission and options for control. French, N.P. et al. Int. J. Parasitol. 1999; 29: 1691–1704CrossRef | PubMed | Scopus (60)See all References6. Hypothetical transmission by placentophagia explains the high prevalence of N. caninum in herds, which are kept without direct contact with potentially infected dogs, although experimental evidence needs to be confirmed.