Neospora Caninum: Infection and Immunity

Dear Colleagues,

Neospora caninum is an apicomplexan parasite that was misdiagnosed as Toxoplasma gondii until the 1980s, but has subsequently been shown to be responsible for abortion, stillbirth, and birth of weak offspring in dogs, cattle, and many other species. N. caninum and T. gondii are phylogenetically closely related and share many morphological, structural, and biological features, but they also have important differences in terms of pathophysiology and host–parasite interactions. Most notably, canids can act as definitive hosts for N. caninum, which is not infective in humans, while only feline hosts allow sexual development of T. gondii, which has enormous zoonotic potential, showing that the two parasites are distinct biological entities. These similarities and differences have profound implications for the design of management control measures and for the development of new therapeutic options and vaccine candidates.

N. caninum can infect a wide range of domestic and wildlife mammals, but infection in cattle and, more recently, in sheep is of high economic concern. Indeed, N. caninum constitutes one of the major causes of infective reproductive losses in ruminants, most notably, bovines.

Neospora caninum infected animals commonly do not present clinical signs other than occasional abortion, stillbirth, or birth of weak calves, but the parasite is efficiently transmitted from the dam to the offspring, perpetuating the infection in the herd. Therefore, management control options are expensive and difficult to implement. Vaccination is generally considered the most cost-effective strategy to control the disease. However, an inactivated vaccine introduced to the market years ago was withdrawn due to ambiguous results, and despite considerable efforts, no other vaccines have been made available so far. Therapeutic options, such as the use of drugs, have previously not been regarded as attractive alternatives, due to the necessary withdrawal periods for meat and milk consumption and because safe and efficacious compounds have not been available on the market.

Overall, the development of viable prophylactic and therapeutic interventions to combat neosporosis depends largely on deepening the knowledge on the mechanisms underlying the interaction of N. caninum with its hosts. On the cellular level, this includes host cell entry and establishment in the host cell, replication, dissemination to other cells, and stage conversion. On the immunological level, the most relevant aspects are how the host innate defense mechanisms sense the parasite, the roles of parasite virulence factors and antigens, immunomodulation during gestation, and the acquired immune response profiles that are relevant for protection. Since vertical transmission has a central role in maintaining infection in cattle herds, vaccines and drugs must be safe during gestation and must eliminate vertical transmission. Considering the difficulties associated with in vivo experiments using cattle, the definition, characterization, and standardization of pregnant and non-pregnant alternative animal infection models is important in this context. However, alternative models must be critically evaluated in terms of their relevance. This Special Issue “Neospora caninum: infection and immunity” aims to compile original research papers and review articles on these topics to offer a comprehensive overview of the subject.

Dr. Alexandre Leitão
Prof. Andrew Hemphill
Prof. Luis-Miguel Ortega-Mora
Guest Editors

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• invasion
• host cell modification
• proliferation
• egress
• stage conversion
• innate immunity
• acquired immunity
• humoral response
• cytokines
• in vitro and in vivo models
• therapy
• vaccines