Investigations into the role of rats as intermediate hosts for Neospora caninum in Chennai, India

Serological and molecular detection of Toxoplasma gondii and Neospora caninum in free-ranging rats from Nagpur, India

Toxoplasma gondii and Neospora caninum are cyst-forming coccidian parasites that infect both wild and domestic non-felids as intermediate hosts, with rodents serving as important reservoir hosts during their life cycles. This study was aimed at investigating T. gondii and N. caninum infections and identifying factors favouring T. gondii infection in free-ranging rats from India. A total of 181 rodents were trap-captured, and blood and brain samples were subsequently collected for serological and molecular examination of T. gondii and N. caninum. Antibodies against T. gondii and N. caninum were detected by MAT/NAT and IFAT in 13.8% (25/181) and 1.65% (3/181) of rodents, respectively. All three N. caninum samples positive by NAT/IFAT were also positive for ELISA, while for T. gondii, 19 of 25 MAT/IFAT positive samples were also positive for ELISA. The antibody titers (MAT/NAT/IFAT) of rodents seropositive for T. gondii ranged from 25 to 400, while those of rats seropositive for N. caninum ranged from 25 to 100. Also, using PCR, DNA from T. gondii (B1 gene) and N. caninum (NC5 gene) was found in 2.76% (5/181) of brain samples and 0.55% (1/181) of brain samples. All PCR positive samples were also seropositive. No mixed infections were observed in the serological and molecular detections. A Chi-square analysis revealed that older rats and rats living in urban areas are significantly associated with T. gondii infection; however, rodent species, gender, location, habitat types, and seasonality were statistically nonsignificant. Overall, this study demonstrated that T. gondii was widely distributed while N. caninum was less prevalent among free-ranging rats in the studied area.

Global prevalence of Neospora caninum in rodents: A systematic review and meta-analysis

BACKGROUND

Neosporosis has been considered a cause of abortion in dairy and beef cattle worldwide. Rodents are reservoir hosts for several infectious diseases. It is necessary to determine the prevalence of Neospora caninum in rodents to improve the current understanding of the transmission dynamics of Neospora as well as its life cycle and risk of transmission to livestock. Therefore, the objective of the present study was to estimate the pooled global prevalence of N. caninum in different rodent species.

METHODS

Published studies on the prevalence of N. caninum in different rodent species were searched in the MEDLINE/PubMed, ScienceDirect, Web of Science, Scopus and Google Scholar and the reference lists of the retrieved articles until July 30, 2022. The eligible studies were selected using inclusion and exclusion criteria. The extracted data were verified and analysed using the random-effect meta-analysis.

RESULT

For this meta-analysis, a total of 4372 rodents from 26 eligible studies were included. The global prevalence of N. caninum in rodents was estimated at 5% (95% CI 2%-9%), with the highest prevalence in Asia (12%; 95% CI 6%-24%) and lowest prevalence in America (3%; 95% CI 1%-14%) and Europe (3%; 95% CI 1%-6%). N. caninum was more prevalent in females (4%; 95% CI 2%-9%) than in males (3%; 95% CI 1%-11%). The most common diagnostic test was polymerase chain reaction (PCR) (21 studies). The pooled prevalence of N. caninum in rodents based on the diagnostic method was as follows: immunohistochemistry: 11% (95% CI 6%-20%), NAT: 5% (95% CI 4%-7%), IFAT: 5% (95% CI 2%-13%) and PCR: 3% (95% CI 1%-9%).

CONCLUSION

The results of this study showed a relatively low but widespread prevalence of N. caninum infection in rodents.

Risk factors for Neospora caninum, bovine viral diarrhoea virus, and Leptospira interrogans serovar Hardjo infection in smallholder cattle and buffalo in Lao PDR

Smallholder large ruminant production in Lao People's Democratic Republic (Laos) is characterised by low reproductive efficiency. To determine if common abortifacient bovid infectious diseases are involved, a serological investigation was conducted. Sera was collected from stored and fresh cattle (n = 390) and buffalo (n = 130) samples from 2016-18 from, and then examined for associations in a retrospective risk factor study of 71 herds. The sera were assayed for antibodies to Neospora caninum, bovine viral diarrhoea virus (BVDV), Leptospira interrogans serovar Hardjo and Brucella abortus using commercially available enzyme-linked immunosorbent assay kits. These pathogens were detected in buffalo samples at 78.5% (95% CI 71.4-85.6), 0%, 2.3% (95% CI 0-4.9) and 0%, respectively, and in cattle at 4.4% (95% CI 2.4-6.4), 7.7% (95% CI 3.1-12.3), 12.8% (95% CI 9.5-16.1) and 0.26% (95% CI 0-0.8), respectively. Exposure of buffalo to N. caninum was positively associated with buffalo age, with a predicted seropositivity at birth of 52.8%, increasing to 97.2% by 12 years of age (p = 0.037). Exposure of cattle to L. interrogans serovar Hardjo was more prevalent in females compared to males, was associated with higher titres of BVDV, and was more prevalent in the wet season compared to the dry season. Exposure of cattle to BVDV was more prevalent in males compared to females, the wet and dry seasons were comparable, and was associated with rising antibody titres against N. caninum and L. interrogans serovar Hardjo. The risk factor survey identified that the probability of herds being N. caninum positive increased with farmer age, if farmers believed there were rodents on farm, and if farmers weren't aware that canids or rodents could contaminate bovid feed on their farm. The probability of a herd being positive to L. interrogans serovar Hardjo increased on farms where multiple cows shared the same bull, where farmers had lower husbandry knowledge, and on farms that used water troughs. The probability of a herd being BVDV seropositive increased with increasing herd size and increasing titres to N. caninum. The benchmarking of bovid exposure to emerging abortifacient pathogens and identification of their risk factors potentially informs disease prevention strategies, supporting efforts to establish a biosecure beef supply for enhanced smallholder livestock productivity, public health and food security in Laos and surrounding countries.