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This study was conducted in order to investigate the prevalence of bacterial and protozoal intestinal pathogens in camel calves up to twelve weeks of age in Northern Kenya. A point prevalence study was conducted to describe the existing intestinal pathogens according to age groups and health status and to compare their occurrence between two camel management systems. A longitudinal study was carried out in the ranch management system in order to strengthen the findings of the point prevalence study and to describe the age prevalence of the existing pathogens more comprehensively.
Point prevalence study
Of the 229 individual camel calves sampled in both management systems, 67.7% were healthy, 23.1% diseased, exhibiting diarrhoea, 6.6% convalescent and 2.2% dead. A higher percentage of camel calves suffering from diarrhoea were found in pastoralist herds (31.9%) as compared to ranch herds (19.2%). Looking at the age prevalence of camel calves suffering from diarrhoea there was a peak within the second and third week of age in both management systems.
Of 197 individual camel calves investigated for parasitic infections, 6.6% were shedding Isospora sp. and Strongyloides sp. while only 4.6% were excreting Strongyle sp. eggs.
Isospora sp. excretion was more prevalent in calves in pastoralist herds (12.9%) as compared to ranch herds (3.7%). Strongyloides sp. and Strongyle sp. were both more frequently isolated from pastoralist herds (9.7% and 6.5%) than from ranch herds (4.4% and 3.7%). Isospora sp. was found in 23% of calves suffering from diarrhoea. 92% of all calves shedding Isospora sp. suffered from diarrhoea. Excretion of Isospora sp. infection was most prevalent from the second week till the seventh week of age but no shedding was diagnosed at an older age.
Klebsiella pneumoniae was isolated in 26.9% (n=119) of calves sampled. In 19.1% (n=226), Salmonella sp. was isolated, while in 97.5% (n=200) E. coli was present. The point prevalences of K. pneumoniae and Salmonella sp. were particularly high in the first three weeks of age. No K. pneumoniae was isolated from camel calves older than six weeks while Salmonella sp. infection was constantly present up to the twelfth week of age. E. coli was constantly present in all age groups. There was no difference in K. pneumoniae point prevalences between the two management systems. Point prevalence of Salmonella sp. infections was similar in both management systems with a peak during the first three weeks of age. No Salmonella sp. was detected in ranch herds after the ninth week of age while there was constant excretion of the pathogen in pastoralist herds.
For the longitudinal study, a total of 323 samples were taken from 86 individual camel calves belonging to ranch herds. Category A camel calves (60.5%) were never recorded with diarrhoea while Category B camel calves (39.5%) were recorded with diarrhoea at least once during the observation period. In Category B 7% were dead calves with previous diarrhoea history.
The highest prevalence of calves recorded with diarrhoea was between weeks three and 12. The youngest calf sampled showing signs of diarrhoea was two days old, while the oldest was 132 days old.
The longitudinal study underlined the findings of intestinal pathogens in the point prevalence study. Infection with Isospora sp. was detected in camel calves from the second till the fourth week of age with a peak around the third week of age. All samples positive for Isospora sp. were taken from calves falling into Category B. Similar to the infection with Strongyle sp., there was a higher Strongyloides sp. prevalence with an older age in the camel calves. Both parasites were detected in calves falling into the two categories with a higher prevalence in Category B.
Klebsiella pneumoniae was more prevalent in young calves during their first ten weeks of age and less common in older camel calves. Comparing the two categories, there was a higher prevalence of K. pneumoniae infection in camel calves falling into Category B (25.3 %) as compared to Category A (12.5%).
Salmonella sp. prevalence was high with the beginning of the second week of age slowly decreasing towards an older age. The prevalence of Salmonella sp. infection was higher in camel calves falling into Category B (43.6%) than in Category A (22.7%).
Infections with E.coli were found in both categories and within the different age groups.
Additional differentiation of pathogens
Sequence analysis of the SSU rRNA gene and ITS 1 confirmed that the Isospora sp. isolates from this study belonged to the species Isospora orlovi and that the sequences were identical to isolates from Dubai.
Out of 32 K. pneumoniae positive camel calves a total of 62 K. pneumoniae were isolated, incl. multiple and repeat isolations. 42 of the 62 isolates were typed and 18 capsular antigens types identified: K2, K3, K5, K11, K13, K16, K26, K28, K31, K34, K36, K38, K54, K55, K60, K61, K64, K81, six isolates were untypable. According to Pearsons Chi-Square (p<0.05), there was no significant relation (p=0.18) between health status and capsular type of K. pneumoniae present. Of the 62 K. pneumoniae isolates, 62.9% originated from calves that had either suffered from diarrhoea or were found dead. In one third of the dead camel calves (n=9) K. pneumoniae was the only noteworthy pathogen present. Capsular type 28 and type 2 were involved in two cases, while in one case no capsular typing was carried out. Klebsiella pneumoniae isolates were resistant to Amoxicillin, Sulphonamide-TMP and Tetracycline but sensitive to Streptomycin.
Out of the 144 Salmonella sp. isolated 86.1% and 13.9% were from calves belonging to the ranches and pastoralist herds, respectively. Salmonella bovismorbificans was the most common serotype with 32.6%, followed by S. butantan (21.5%), S. typhimurium (11.1%), S. kiambu (9.0%) and S. muenchen (7.6%). Salmonella typhimurium and S. adelaide were the only two serotypes found in both management systems. Comparing the distribution of Salmonella sp. according to health status a total of 38.9%, 31.3%, 22.2% and 7.6% originated from healthy, diseased, convalescent and dead camel calves, respectively. The only Salmonella sp. associated commonly (81%) with calf disease and present in camel calves of both management systems was S. typhimurium.
Out of 531 E. coli isolates, a total of 255 were analysed for virulence-associated genes. In 78 isolates virulence-associated genes were detected: eae (13.7%), astA (10.6%), hlyEHEC (4.3%) and stx (2.0%). None was positive for elt Ia/Ib and est Ia/Ib. 83.5% of the isolates originated from calves belonging to ranch herds and 16.5% from calves kept in pastoralist herds. While eae and astA were found in E. coli isolates from both management systems, hlyEHEC and stx were only found in isolates from ranch herds. The majority (92%) of the virulence-associated genes were found in camel calves kept in ranch herds. Virulence-associated genes were equally found in camels being healthy (57.7%), with diarrhoea or convalescent (42.3%). No virulence-associated genes were detected in dead camel calves. There was no indication that E. coli plays an important role in the diarrhoea-complex of camel calves up to twelve weeks of age. Escherichia coli serotype O157:H7 was not isolated from the camel calves in the studied age group.