Cryptosporidium infection in calves from a rural area of Buenos Aires, Argentina.

Dairy calves less than 1 month of age are commonly infected with Cryptosporidium spp. The objective of the present study was to evaluate the prevalence of Cryptosporidium spp. among dairy calves <or=30 days old, with and without diarrhoea, in a rural area of Buenos Aires, Argentina. A total of 280 calves were studied. For each calf a single faecal sample was obtained and processed by water-ether concentration. The microscopic search was carried out using a modified Ziehl-Neelsen's acid fast method. The population was stratified according to days of life. The samples were classified according to macroscopic characteristics. The intensity of infection was estimated semiquantitatively according to the average number of oocysts in 20 randomly selected fields observed at 1, 000 x. Analysis of a single sample of each 280 calves revealed that 48 calves eliminated oocysts. The overall prevalence of cryptosporidial infection was 17%. The analysis of the macroscopic characteristics of the faeces of all the studied calves showed that 57.1% were diarrhoeic. The 100% of the infected calves were <or=14 days old. The prevalence according to age group was: 37.5% for <or=7 days, and 21.4% for >or=8<or=14 days. Both normal and diarrhoeic faeces with blood were negative for Cryptosporidium spp. The 37.5% of diarrhoeic faeces without blood were positive, showing a presence of mucus of 83.3%. The 66.7% of samples with mucus showed an average of 10 oocysts/field. The relationship between intensity of infection and age group showed that 66.7% of positive samples from calves <or=7 days old, presented an average of >10 oocysts/field. This study shows that Cryptosporidium spp. is one of the causes of calf neonatal diarrhoea in a rural area of Buenos Aires, Argentina. The highest intensity of infection reported for the <or=7-day-old group demonstrates that these animals are, from an epidemiological point of view, an important source of contamination of water and soil of the area.