Characterisation of brucella isolates from human and animal patients in Narok district of Kenya
Brucellosis is a cosmopolitan zoonotic disease that afflicts man, his domestic animals and wildlife. The smooth members of the genus are the main culprits worldwide. The incidence of the disease in humans, and which directly relates to that in animals, is highly dependent on animal husbandry practices, animal population, animal population density and inter-group interactions. Disease in humans is related to the interaction between humans and animals, living standards, hygiene and food customs. Owing to these reasons, Narok, the district where this study was undertaken, has the full potential for high occurrence of brucellosis both in animals and humans. It is for this reason that this study was undertaken with the aim of recovering Brucella pathogens from man and animals; to gain an insight into the prevalence in animals through sero-survey and where possible to establish the sources of infections to the human patients. The study was carried out in thre,e overlapping phases in which human patients clinically suspected of brucellosis, in the opinion of the clinician, had two 10ml blood samples collected from the radial vein into vacutainer tubes. One sample was collected and preserved in a vacutainer tube containing potassium oxalate while the other sample, for serum harvesting, was collected into a tube without the anticoagulant. Hemoculture of the preserved blood was done into diphasic medium for not less than eight weeks. The human samples for culture were chosen on the basis of a quick Rose Bengal plate test (RBPT) on serum, carried out at the point of sampling. This led to the culture of 397 patients who tested positive and 134 (one in five) of the negative ones, all totalling 531. The total human serum samples were 957. The selection of animal herds was random, using multistage computer methods, and also specific i.e. home herds in which human patients' blood had shown signs of growth or the serum was positive on RBPT. From each home herd, a random sample of 20 cattle, 10 sheep and 10 goats were chosen and each animal had lOml of jugular blood collected into a vacutainer tube. Animals with signs implicative of brucellosis such as lameness, abortion or hygroma had a second 10ml of blood taken for hemoculture as in the human suspects. In all, cattle sera were 1,620, caprine 1,257 and ovine 557. The cultured animal blood were 388 comprising 132 cattle, 196 goats and 50 sheep; out of which 54 cattle, 73 goats and 34 sheep had a history of abortion. The human and animal sera were simultaneously screened at the central Veterinary Investigation Laboratories (Vet Labs), Kabete; using Rose Bengal plate test (RBPT) , Serum agglutination test (SAT) and Complement fixation test (CFT). Thus, the human serum was tested on RBPT twice; at the sampling points and at Vet Labs Kabete. From the 531 cultured human blood samples, Brucella abortus, Yersinia and Campylobacter species were isolated three, eight and 11 times, respectively. From the cultured animal blood, only Campylobacter species were realised in one cow, eight goats and 11 sheep. The 957 human sera yielded a cumulative total of 78 (8.2%) reactors with individual test results being; RBPT 62 (6.5%), SAT 40 (4.2%) and CFT 23 (2.9%). From the 1620 cattle sera tested, 177 (10.9%) cumulative reactors were realised with RBPT picking 75 (4.6%), SAT 136 (8.4%), and CFT 53(3.3%). The 1257 caprine sera had 106 (8.4%) reactors with RBPT picking 38(2.7%), SAT 69(5.5%) and CFT 39(3.1 %), while the ovine reactors were 45(8.1 %) with RBPT picking 23(4.1 %), SAT 19(3.4%) and CFT 16(2.9%), respectively. From the serological results, it is clear that brucellosis is widely distributed in Narok District both in human beings and in animals. Many human cases were misdiagnosed both clinically and serologically probably due to poor interpretation of RBPT results and also due to cross-reactivity as a result of infections by other I organisms such as Yersinia species. Clinical misdiagnosis could be due to inadequate understanding of the possible differentials, while poor interpretation of RBPT readings could be a result of inadequate training. This poor interpretation of RBPT results led to prolonged antibiotic treatment on patients, who otherwise were without brucellosis. Isolation of Yersinia species was accompanied by positive RBPT results, while that of Campylobacter species showed no crossxv reaction. Yersiniosis, campylobacteriosis and probably typhoid, may be a big menace especially in place and times when human resistance is compromised by malnutrition as in this case. These other diseases are directly linked to lack of clean drinking water, poor personal hygiene and absence of toilets. The serological results tend to imply that sheep and goats aborted due to brucellosis as flocks with a high rate of abortion also had higher reactor rates. Also, the serological reactors in the flocks with a high rate of abortion tended to have higher titres than the titres realised in the reactors from flocks with low abortion rate or those that had no abortions at all. Also, the three serological tests used, tended to agree more in groups with high abortion rates than in the groups in which no abortions had been noticed. Campylobacteriosis is another common cause of abortion particularly in small ruminants in which it was isolated only from sero-negative sheep and goats with abortion.