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INTRODUCTION
Neospora caninum is an intracellular Apicomplexan parasite, in close relationship to Toxoplasma gondii. Due to its similarity to T. gondii, neosporosis has been misdiagnosed for many years 1. Neosporosis, although implicated as a major cause of infectious bovine abortion, is primarily a disease of cattle and dogs. It was first described in dogs in Norway and first isolated from cattle 2. Further reports of neosporosis in Europe, Asia, Middle East, North and South America draw attention on this emergent and relevant disease in cattle 1. To date, farm management practices that reduce the chance of infection are the only methods to fight the disease, existing no effective control methods for neosporosis. Host range and distribution of N. caninum is found in a wide range of host species with ubiquitous distribution with reports on animal exposition to N. caninum and parasite antibodies in pigs, cats, foxes, raccoons, camels, coyotes, rodents, birds and other wild animals. On the other hand, viable parasite isolation has been achieved only from dog, cattle, sheep, water buffalo, European bison and white-tailed deer. The definite hosts are domestic dog, Australian dingo, and coyote, being cattle, sheep, water buffalo, horse, white-tailed deer among others only intermediate hosts 1.
The main neosporosis clinical manifestation in cattle is abortion. Clinical cases may show an epidemic or endemic behavior being the epidemic cases defined as more than 12.5% abortions within 6 to 8 weeks of gestation 3.
Neospora caninum is a cyst-forming parasite and its development involves two asexual stages - tachyzoite and bradyzoite that occur in the intermediate host (e.g. cattle, horse) and definitive hosts (e.g. dog), and one sexual stage that takes place only in the definitive hosts. Tachyzoites divide quickly inside the cells and infect multiple cellular types including placental trophoblasts, myocytes, hepatocytes, neural cells, vascular endothelial cells, renal cells, alveolar macrophages, among others. During the encysted phase of the parasite, the bradyzoites, are able to replicate slowly in tissues from the central nervous system (CNS) and skeletal muscles 4. A definitive host may acquire the infection via ingestion of cysts contained in tissues from infected animals 5 such as placenta from naturally infected cows, an important source of infection for dogs. Although oocysts are eliminated in dogs’ feces and other definitive hosts, to date N. caninum oocysts have been identified in few naturally infected dogs, raising doubts about the shedding frequencies and oocyst viability in canids.
Serum and milk antibody detection have been used in several studies, being apparently serum detection more accurate 1. In South America, reports indicate prevalence of 12.4% in Peru, 14% - 97% in Brazil 6, and 14% - 80% in Argentina with characteristic pathognomonic pathological findings 7. In Chile, N. caninum seropositivity has been reported in dairy cattle in central and southern regions, and the rate varies between 15.7% and 30% 8,9,10. Recent unpublished reports indicate that between 8 to 22% of abortions show lesions compatible with N. caninum in the Los Ríos Region (Personal communication). This study aims to obtain serological information and risk factors for neosporosis on dairy farms that are part of a Government Technical Support Service (SAT) from de O´Higgins region.
MATERIAL AND METHODS
Study type. Seroprevalence study, including a survey and sample collection and analysis.
Study population and study area. The study population was milking cows of farms associated to the Technical Support Service (SAT) program, in the O´Higgins region, in central Chile. This program belongs to the Instituto Nacional de Desarrollo Agropecuario (INDAP) and provides technical support to producers. There were 11 farms associated to the SAT program in the O´Higgins Region, in the communes of Rengo, Las Cabras, Malloa, Quinta de Tilcoco and Peralillo (Figure 1). The cattle population was of 47 animals.
Figure 1 Neospora caninum positive and negative dairy farms in the Libertador Bernardo O´Higgins Region in central Chile.
Climatic conditions. The study area is an example of Mediterranean climate with dry summers and low winter rainfall.
Epidemiological data collection. To evaluate the potentially relevant risk factors, each farm was visited and farmers where interviewed. Nine farmers accepted to participate in this study. The survey was developed based on previously described risk factors for neosporosis 12, including 28 variables in four main areas: animal information, production information, environmental factors and sanitary aspects (Table 1).
Table 1 Information collected through survey, from small farms in the Libertador Bernardo O´Higgins Region, Chile.
| General information | Categories |
|---|---|
| Farm owner name | |
| Contact phone | |
| Farm address | |
| Commune | |
| Official farm ID number | |
| Latitude | |
| Longitude | |
| Herd information | |
| Number of dairy cattle | |
| Number of milking cows | |
| Individual cow information | |
| DIIO (Official traceability ID number) | |
| Cow´s age category | Less than 3 years |
| From 3 to 6 years | |
| More than 6 years | |
| Breed | Holstein / Jersey |
| Crossbreed | |
| Abortion history | Yes / No |
| Repeated heat | Yes / No |
| Herd management/biosecurity | |
| Farm main productive purpose | Agricultural |
| Livestock | |
| Mixed | |
| Other | |
| Management responsible person | |
| Cattle replacement obtained from outside farm | Yes / No |
| Origin of replacement cattle | Own / Buy |
| Presence of dogs in the farm | Yes / No |
| Number of dogs | |
| Acces of other dogs to the farm | Yes / No |
| Owner of other dogs entering to the farm | Known |
| Unknown | |
| Dogs feed | Home made |
| Commercial feed | |
| Dogs can have access to birth/abortion residues | Yes / No |
| Dogs can have access cow´s water sources | Yes / No |
| Dogs can have access cow´s feed | Yes / No |
| Other animal species in the farm | |
| Number of poultry | |
| Number of Horses | |
| Number of cats | |
| Number of other domestic animals | |
| Cattle water source | Drinking water |
| Water well | |
| Open water | |
| Cattle pen floor | Muddy |
| Dry | |
| Herd sanitary conditions | |
| Other diseases present | |
| Brucellosis | Yes / No |
| Tuberculosis | Yes / No |
| Leucosis | Yes / No |
| Deworming | Yes / No |
| Placenta / abortion residues management | |
| Samples information | |
| Total samples collected | |
| Sample ID |
Laboratory methods. Three to five ml of blood from each cow (coccygeal vein) were collected and placed in a vacuum tubes. Samples were taken to the Epidemiology Unit laboratory, at the Faculty of Veterinary Science, University of Chile, where sera was obtained. Identification for antibodies to N. caninum in milking cows’ sera was carried out using the IDEXX NeosporaX2 Test® (IDEXX® Laboratories, Inc., Westbrook, Maine, USA).
Data analysis. Within and among farms seroprevalence was calculated. Risk factor survey data was described using standard descriptive epidemiology methods. Afterwards, a simple logistic regression analysis was carried out, to identify risk factors for seropositivity to N. caninum11.
RESULTS
Overall 47 cattle from nine different farms were sampled. Two samples could not be analyzed due to hemolysis. The seroprevalence of 67% (6/9) was found at SAT farm level. Within farm seroprevalence results (Table 2) indicate an average of 55% (considering just the six positive farms). When averaging all nine farms, the prevalence was of 37%.
Table 2 ELISA results for Neospora caninum obtained from cattle in small farms in the Libertador Bernardo O´Higgins Region.
| Farm ID | No. of animals sampled | No. of sero positive cows to N. caninum | Within farm seroprevalence |
|---|---|---|---|
| A | 13 | 7 | 54% |
| B | 5 | 2 | 40% |
| C | 2 | 0 | 0 |
| D | 3 | 0 | 0 |
| E | 3 | 0 | 0 |
| F | 4 | 3 | 75% |
| G | 8a | 2 | 29% |
| H | 3a | 2 | 100% |
| I | 6 | 2 | 33% |
| a: One sample could not be analyzed |
Four variables resulted in a significant association with N. caninum infection with a p<0.05 being these (Table 3): milking cows abortion history (p=0.037, OR=5.09), type of feed provided to dogs (p= 0.0429, OR=6), water consumption from ditches (p=0.034, OR=4.5) and abortion by products sanitary management (p=0.017, OR=7.43). It must be mentioned that some variables had to be removed from the study, such as production purpose (all cattle are dairy animals), repeated heat in cows, with a too low variation among responses, access to shade (all provided access) and sanitary status, with all farms with the same management, provided by INDAP.
DISCUSSION
A recent study reported 23% seroprevalence of N. caninum in farms in the Biobio Region 9, and previously a within farms prevalence of 16 and 30% (in the two sampled farms) was reported in La Araucanía region 8. Within farm seroprevalence of N. caninum found in this study was higher, ranging from 29% to 100%. The differences could possibly be explained by the fact that our study was done with small farms, in a much less technified environment comparing with the studies mentioned before. Moreover, the O´Higgins Region is located 300 km. north of Biobio region and 500 km. north of the Araucanía region, and the environmental and climatic settings are different, having the O´Higgins Region less rainfall. Rainfall is not a factor proven to affect the survival or infectivity of the parasite in the environment, but it has been linked with the occurrences of N. caninum abortions. Average temperatures differ between both regions, being the O´Higgins region approximately two degrees Celsius warmer, a factor described as significant, due to faster sporulation of oocysts in the environment surrounding cattle 12.
Pathological findings have shown evidence that the parasite is present in Chile and abortions with compatible neosporosis findings are being reported (Paredes et al, unpublished data). Here, three of nine farms reported abortions in the last year (33%). Of those three farms that reported abortions, only two of them resulted positive to ELISA (+) for N. caninum antibodies. None of the farms that reported abortions had the abortions examined or tested for any agent. The reported water source for animals was a mixture of drinking water, well water and open water sources like streams of irrigation channels and was significantly correlated to drinking water from open water sources like irrigation ditches as was previously reported 12.
In relation to dog ownership and presence, most of the Neospora ELISA (+) farms owned dogs (80%) and 60% reported feral dogs in the area. Dog presence has been reported as risk factor for neosporosis 13. Nevertheless, this study did not find association with dog presence, with the exception when dogs were fed with homemade food instead of commercial-pet food. A study 8 described that dogs, in rural areas in Southern Chile, were fed commonly with bovine viscera or raw bovine meat. Finally, the lack of management of abortions and abortions by-products was identified as a significant risk factor, a factor previously described as relevant for the epidemiology of the disease 12.
Most of the Neospora ELISA (+) farms owned dogs (80%) and 60% of the farms reported feral dogs in the area. This finding is consistent with reports of dog presence as a risk factor for neosporosis 12. Nevertheless, this study did not find association with the presence of dogs in farms. A positive relationship was only found when dogs were fed with homemade food instead of commercial-pet food. A study (8) described that dogs, in rural areas in Southern Chile, were fed commonly with bovine viscera or raw bovine meat, behaviour that could be linked to these study results. Finally, the lack of management of abortions and abortions by-products was identified as a significant risk factor, a factor previously described as relevant for the epidemiology of the disease.
This study, although limited in size, allowed the researchers to screen a largely marginal community of farmers, providing a sanitary insight to their animals and activities. It must be emphasized that although the study considered only nine farms and 47 animals, these are over 80% of the farms and animals belonging to farmers that participate in the SAT support program in the region, and therefore a relatively large sample of the sanitary status of this farms sub population. These results highlight the need of improving N. caninum surveillance, and the development of preventive measures to avoid losses related with this disease.
