Introduction

Cryptosporidiosis is an intestinal parasitic infection caused by protozoans of the genus Cryptosporidium (Apicomplexa: Cryptosporiidae). Unlike other coccidia, Cryptosporidium spp. oocysts are infectious from the moment excreted by an infected individual and can infect another host through ingestion. They have a cosmopolitan distribution and are considered opportunistic parasites, causing severe digestive disorders in young individuals. They affect many domestic and wild animals, as well as humans¹.

Dogs and cats are common pets because they can develop a bond with humans. However, they are also exposed to numerous parasite infections, representing a risk of transmission to other animals and humans². Dogs may be naturally infected by C. canis³, C. parvum⁴, C. meleagridis⁵, and C. muris⁶. Infection is typically asymptomatic, but can cause severe clinical manifestations including watery diarrhea, fever, and pathologies of the respiratory system, liver, and pancreas, especially in immunocompromised animals^7,8.

Canine cryptosporidiosis is widely distributed. It has been reported worldwide in dogs in private homes, in kennels, in shelters and in stray dogs; reports are largely from urban areas but it has been reported in some rural communities^9,10,11. Little data exists in Mexico on the epidemiological traits of this disease in dog populations in urban and rural areas and communities, which would help to better understand the infection transmission and maintenance process in other domestic animals, livestock and humans.

The present study objective was to quantify Cryptosporidium spp. frequency and identify risk factors associated with the infection in dogs from rural environments associated with dairy farms and from an urban area in Aguascalientes, Mexico.

Material and methods

The study was carried out in the state of Aguascalientes, Mexico (21°37', 22°01' N; 101°52', 102°35' W). Altitude in the region ranges from 1,765 and 2,400 m asl, average annual temperature is 17.4 °C, and annual average rainfall is 526 mm, mostly in the summer¹².

Dairy farm sampling sites

Samples were collected at 30 dairy farms in 10 of the state’s municipalities. In each municipality, three farms with at least one domestic dog were sampled; only farms where owners could provide the necessary facilities were included.

Municipality codes: Pabellón de Arteaga (PA), Asientos (ASI), San José de Gracia (SJG), Cosío (COS), Tepezalá (TEP), Rincón de Romos (RR), San Francisco de los Romo (SFR), Calvillo (CAL), Jesús María (JM), Aguascalientes (AGS) and El Llano (ELL).

Figure 1: Location of sampled dairy farms (numbered 1, 2, 3 in each municipality) and CCABA 

Results

Overall Cryptosporidium spp. infection frequency in the sampled dogs was 20.5 % (64/312; CI95% 16-25). Frequency in urban dogs was 9 % (13/144; CI95% 5-15), and in farm dogs it was 30 % (51/168; CI95% 23-38).

Infection frequency among farm dogs was highest in Jesús María municipality (58 %) and lowest in Cosío municipality (15 %) (Table 1). All the municipalities contained positive animals, whereas 70 % of the farms did (21/30). The average number of dogs per farm was 5.6, and density was 2 to 12 dogs.

Most of the studied dogs were young (≤18 mo of age), and infection frequency was highest in this age group (Table 2). Farm dogs exhibited a higher frequency (37 %) than urban dogs (12 %). In both populations, females were more frequently positive than males. Feces samples described as diarrheal had a higher frequency (31 %) than those described as firm (11 %). In farm dogs, frequency by food type was 22 % for dry food, 32 % for prepared food and 36% for a combination of these. Farm dogs that had their own water had a higher frequency than those that shared water with other animals. Frequency was nearly the same in vaccinated (usually against rabies) and unvaccinated dogs, but those that had not been dewormed exhibited a higher frequency.

Risk analysis identified the variable of diarrheal feces in urban dogs (OR, 3.2; CI95% 1.06-9.79 P<0.03) and farm dogs (OR, 2.7; CI95% 1.36-5.49 P<0.001) as related to infection frequency diagnosed by parasitological analysis. No other analyzed variable exhibited a significant association.

Discussion

The prevalence of Cryptosporidium infection in dogs, be they pets, street dogs or farm dogs, ranges from 1 to 45 %, and is higher in puppies than adults^9-11,15-21. Results can vary in response to characteristics such as experimental design, diagnostic test, geographic region and environmental conditions. The 9 % infection frequency observed here in urban dogs is relatively low, and similar to the 11.5 % reported in pet dogs in Mexico City as determined by FRECU Gum Infection²². The farm dogs exhibited a frequency of 30 %, which is significantly higher than among the urban dogs. In addition, infected farm dogs were widely distributed among the sampled farms, highlighting this parasite’s cosmopolitan nature. Higher frequencies have been previously reported in street dogs and pet dogs in rural communities than in urban dogs⁹. The present study is the first report of Cryptosporidium spp. in dogs at dairy farms. Of note is that cryptosporidiosis is widely distributed in dairy cattle in Aguascalientes, with a significant presence in replacement heifers (40 - 67 %). The only species identified to date is C. parvum^13,23.

In the present results, Cryptosporidium spp. infection frequency was highest in young dogs; this agrees with previous studies^15,22. Infection prevalence tends to decrease in naturally infected puppies as they grow²⁴. However, age is not considered a risk factor for contracting this parasite^25,26, which is also supported by the present data.

Sex had no effect on frequency in the studied populations, although females exhibited higher values than males. The same has been reported elsewhere^25,27,28.

Presence of diarrhea is considered the principal clinical sign if canine cryptosporidiosis⁸. The present results support this in that dogs with diarrheal feces had a higher infection frequency than those with firm feces; it was identified as a risk factor in both urban dogs (OR 3.2) and farm dogs (OR 2.7). Samples came from clinically healthy animals, that is, asymptomatic carriers. Dogs with diarrhea are known to excrete more oocysts than those lacking clinical signs²⁹, making it a recognized risk factor^15,25,27. Asymptomatic dogs or those with sporadic episodes of diarrhea are the source of soil and water contamination in the environments they inhabit. Because oocysts are highly environmentally resist, they represent a significant risk of transmission to humans, and domestic and wild animals. This is the case in rural, agricultural, urban and peridomestic environments¹.

Food type in farm dogs was not identified as a risk factor, which has been reported previously²⁵. However, the studied farm dogs roamed freely about the dairy facilities, providing them easy access to fetuses and placental waste, and allowing them to sporadically hunt birds and rodents. Drinking water is an effective vehicle for Cryptosporidium transmission, especially in humans¹. In the present study, only the use of the recipient form which the dogs drank water was assessed, and this variable was not identified as a risk factor. Another study in which drinking water source was assessed did not find it to be a risk factor²⁵.

Application of a vaccination regime in the farm dogs had no apparent effect on infection frequency since vaccinated and unvaccinated dogs exhibited similar frequencies. In contrast, farm dogs that had received deparasitization treatment had a lower frequency than those that had not received it; nonetheless, this variable was not identified as a risk or a protection factor. The present data suggest that the prevailing environment at dairy farms favors transmission and maintenance of Cryptosporidium spp. infection. Contributing factors include dog density at each farm, their high mobility and their interaction with other domestic and wild animals. The studied urban dogs were largely strays but faced a distinct environmental situation and were therefore less exposed to possible Cryptosporidium spp. infection.

Conclusions and implications

Cryptosporidium spp. infection was identified in both urban and dairy farm dogs. Infection frequency was relatively low in the urban dogs, but high among the farm dogs. Infection distribution was broad throughout the sampled rural areas, reflecting this protozoan’s high infective capacity. Further research is needed on the possible effects of the dog-cattle relationship on this disease’s epidemiology. Both dog populations represent a transmission risk to humans since they can be carriers of both C. canis and C. parvum.