Seroepizootiology and molecular diagnosis of Neospora caninum infection in cattle in Serbia

Abstract

Neospora caninum is a relatively recently recognized protozoan parasite of animals. It has been studied only since 1988, until when it was misdiagnosed as Toxoplasma gondii, due to the morphological similarity of the agents. Today, neosposoris in cattle is known as a disease of growing importance worldwide, causing abortions and large economic losses if epidemic abortions occur. The first investigations of the prevalence of N. caninum infection in cattle in Serbia were not carried out before 2008, and no data exist on the potential damaging effects of neoporosis on cattle husbandry in Serbia. In this study we examined the seroprevalence of the infection in a representative sample of cows from the entire territory of Serbia as well as the epizootiological factors that may play a role in the emergence and spread of infection. Sera originating from a total of 1496 cattle were tested by competitive ELISA assay for the presence of N. caninum-specific antibodies. It was shown that the seroprevalence was 7.2%, ranging from a low to a moderate (2.2 to 12%) prevalence accross all twelve epizootiological areas of Serbia. At least one seropositive animal was detected on 10.7% of farms. Results of the cELISA, i.e. the degree of inhibition in seropositive individuals, ranged from 40.3 to 91.8%, mean = 71.9 ± 17.1%, median = 79.9%, which means that almost one half of the seropositive cows had specific antibodies in high titres, or high values of inhibition of more than 80%. Possible association of the infection with biologically plausible risk factors including herd size, breed, husbandry methods, feeding practices (use of silage), origin of replacement stock, presence and number of dogs, occurrence of abortions in the herd, average annual rainfall and region, was analyzed by univariate analysis, and variables significant at P≤0.25 were included in multivariate logistic regression models. The results showed that the single risk factor for infection in individual animals was keeping cows in loafing barns (OR=3.31, 95% CI=1.95-5.60, P lt 0.001), while risk factors for the presence of infection on farms were the use of loafing barns (OR=18.49, 95% CI=5.40-63.36, P lt 0.001), and herd size gt 100 animals (OR=24.08 95% CI=3.85-150.50, P=0.001). In addition to a comprehensive insight into the current state of N. caninum infection in cattle in Serbia, the results of this research on infection risk factors both at the individual and farm level in our country suggest preventive measures that can be applied to improve animal health and reduce economic losses, thereby improving livestock production...

Infekcija parazitom Neospora caninum izučava se od 80-ih godina prošlog veka, do kada je zbog sličnosti agensa sa Toxoplasma gondii bila pogrešno dijagnostikovana. Danas je neosporoza goveda širom sveta bolest rastućeg značaja, koja kod reproduktivnih kategorija izaziva pobačaje, smrtnost teladi i velike ekonomske gubitke ako se javi u epizootskoj formi. Početna istraživanja prevalence infekcije N. caninum kod goveda u Srbiji datiraju od 2008. godine, mećutim nema podataka o gubicima koje neosporoza potencijalno prouzrokuje u govedarstvu Srbije. U ovom radu ispitali smo seroprevalencu ove infekcije na reprezentativnom uzorku krava sa cele teritorije Srbije i analizirali epizootiološke faktore koji mogu imati ulogu u pojavi i širenju infekcije kod goveda u našoj zemlji, što bi moglo da rezultira predlogom razvoja mera prevencije i posledičnog unapređenja stočarske proizvodnje. Takođe, izvršili smo optimizaciju metoda molekularne dijagnostike infekcije N. caninum i sagledali mogućnosti primene molekularnih metoda u dijagnostici neosporoze. Serumi poreklom od ukupno 1496 goveda ispitani su kompetitivnim ELISA testom na prisustvo N. caninum specifičnih antitela. Pokazano je da seroprevalenca iznosi 7,2%, sa niskim do umerenim (od 2,2 do 12%) stepenom prokuženosti u svih dvanaest epizootioloških područja Srbije. Infekcija je ustanovljena na 10,7% ispitanih farmi. Rezultati cELISA testa za seropozitivne jedinke, tj. vrednosti stepena inhibicije kretale su se od 40,3 – 91,8%, srednje vrednosti 71,9±17,1%, i medijane 79,9%, što znači da je praktično polovina seropozitivnih krava imala specifična antitela u visokom titru, tj. visoke vrednosti stepena inhibicije od preko 80%. Ispitivanje epizootioloških faktora u smislu faktora rizika za infekciju N. caninum urađeno je primenom logističke regresione analize. Povezanost infekcije sa potencijalno relevantnim epizootiološkim faktorima (veličina stada, dominantno zastupljena rasa, način gajenja, način držanja u štali, upotreba silaže u ishrani, poreklo grla za remont stada, prisustvo i broj pasa, pojava pobačaja u stadu, prosečna godišnja količina padavina, region) prvo je ispitana univarijantnom logističkom regresijom, i varijable značajne na nivou P≤0,25 uključene su u multivarijantni regresioni model...