Development and evaluation of diagnostic tools to identify infectious stages for the study of horizontal transmission risks in ruminant neosporosis, toxoplasmosis and sarcocystiosis

• Forschungsstelle: COST
• Projektnummer: C02.0030
• Projekttitel Englisch: Development and evaluation of diagnostic tools to identify infectious stages for the study of horizontal transmission risks in ruminant neosporosis, toxoplasmosis and sarcocystiosis

Schlüsselwörter (Englisch)

Ruminant; abortion; neospora; toxoplasma; diagnosis

Forschungsprogramme (Englisch)

COST-Action 854 - Protozoal reproduction losses in farm ruminants

Kurzbeschreibung (Englisch)

See abstract

Partner und Internationale Organisationen (Englisch)

AT, BE, BG, CZ, FR, DE, EL, IE, IL, IT, LT, NL, NO, PL, PT, ES, SE, CH, UK

Abstract (Englisch)

A major aim of this Action was to integrate research on protozoal reproduction losses in farm ruminants across Europe and to maximize exploitation of technologies for developing better control measures. Our Swiss contribution included several lines of research. One focused on the use of toltrazuril to experimentally control congenital neosporosis in mouse dams. As a first finding, toltrazuril-treatment significantly reduced pre- and perinatal losses due to experimental N. caninum-infection when compared to non-treated dams in their first gestation. Besides reducing abortion and infertility rates in pregnant mice, toltrazuril-treatment also affected directly the infection course in the fetuses, best demonstrated by the lack of postnatal death in offspring of toltrazuril-treated mothers versus postnatal death of some of the newborns of non-treated mothers. Although infected dams may remain carriers of the parasite, they seem not to act as sources of infection for the fetus in later pregnancies, conversely to the situation found in naturally infected cattle. For Neospora caninum, the dog is known to act as definitive host although its potential role as infection source for bovines still remains unelucidated. The aim of one of our studies was to compile first epidemiological data on the prevalence and incidence of N. caninum in Swiss dogs acting as definitive hosts. As all fecal samples investigated so far were negative for N. caninum, we concluded that dogs do not play a significant role in the transmission dynamics of the parasite. Neospora caninum antibody assays are vital tools to support results of clinical investigations and they are indispensable in epidemiological studies. We improved the serodiagnostic performance by developing a highly sensitive and species-specific N. caninum immunoblot. The economic importance of a Neospora infection in cattle at farm level is attributable to costs associated with abortion, premature culling, reduced daily weight gain, reduced slaughter live-weights, decreased milk production and higher veterinary treatment costs. As resources for national control programs are limited, it is indispensable to fully understand the population dynamics and economical consequences of control options to support the decision making process of policy makers. We thus designed a study that aimed to assess the impact of the following control strategies on the seroprevalence of N. caninum infection in the Swiss dairy cattle population: (a) Testing and culling of seropositive breeding bovines; (b) Discontinued breeding of offspring from seropositive cows; (c) Medical treatment of calves born from seropositive cows; (d) Vaccination of susceptible (non-infected) or infected cattle. A dynamic deterministic simulation model was developed to assess the impact of these different temptative control strategies on the prevalence of Neospora caninum Swiss dairy cattle. Thus, a policy of annual culling of all seropositive cattle in the population reduced (sero)-prevalence effectively and rapidly from 12% to less than 1% in the first year of simulation. We also designed a study to estimate the current losses due to N. caninum in dairy cattle in Switzerland and to assess the costs and benefits of different potential control strategies. A Monte Carlo simulation spreadsheet model was developed to estimate the direct costs caused by N. caninum with and without control strategies and to estimate the costs of selected control strategies as listed above. The economically best control strategy at present would therefore be 'testing and culling of all seropositive female cattle' while - taking into account other factors such as acceptability of a strategy - the strategy 'discontinued breeding with offspring from seropositive cows' would probably be preferential. However, medication - once available in the future - was shown to express the highest benefit-cost ratio (3.68). It might be recommendable to postpone decisions on a national Neospora control campaign until more data on the efficacy of substances that are currently under evaluation, and their protocol, become available.

Datenbankreferenzen (Englisch)

Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. [phone] Swiss Project-Number: C02.0030