No abstract

A dipstick colloidal dye immunoassay (DIA) was developed for the field diagnosis of Trypanosoma evansi infection using affinity-purified polyclonal antibodies (PcAbs) and the monoclonal antibody (McAb) 8B9. PcAbs were adsorbed onto Palanil Red dye particles and used as dye reagents. Dipsticks were dotted with four different antibodies; normal rabbit and mouse IgGs as negative controls, and anti-T. evansi PcAb and McAb 8B9, which capture trypanosome antigens in the tested samples. Since the dye reagent bound to the captured antigens, the presence of coloured dots on the dipstick identified trypanosome infections. The sensitivity of the DIA was compared with two antigen detection ELISAs (Ag-ELISA); one was PcAb-based and the other was based on a combination of the same Mc- and PcAbs as were employed for the DIA. With a positive serum, the DIA detected trypanosomal antigen up to a dilution of 1:500 for both the PcAb and McAb dots, at which dilution the PcAb- and combination-based Ag-ELISA gave positive OD readings of 0.13 and 0.36, respectively. When 124 field sera were tested, circulating antigens were detected in 51 (41%) samples by the DIA, and 76 (61%) and 49 (40%) samples by the PcAb- and combination-based Ag-ELISAs respectively, of which 48 (63%) and 34 (69%) were also positive by the DIA.

Six 6-month-old bulls were experimentally infected with five different isolates of Trypanosoma evansi; two received the same isolate and the other four received different isolates. The parasitaemias and serum antigen levels were monitored regularly by the haematocrit centrifuge technique (HCT) and antigen-detection ELISA (Ag-ELISA), respectively. Trypanosomal antigen was demonstrated by the Ag-ELISA by 10-14 days post inoculation in four cattle, while parasitaemias were first found to be positive in individual cattle over a longer period of time post inoculation (6-28 days). In two cattle, the Ag-ELISA values were also positive when the animals were found to harbour trypanosomes by the HCT and only turned negative 3 days after treatment, while the ELISA values fluctuated during the experiment in another two bulls. The remaining two cattle never produced positive ELISA results despite positive parasitological results. The antibody titres in all six cattle started to rise around 10 days post inoculation and then stayed high throughout the experiment. It was concluded that the Ag-ELISA would produce some false negative results in the early stages of T. evansi infection owing to variations in the balance of parasitaemia and antibody levels in the circulation, and in the pathogenicity of parasite strains.

Background: Brucellosis is an important re-emerging zoonosis with worldwide distribution. In Thailand, endemic bovine and caprine brucellosis is a serious public health threat. Brucellosis in cattle and buffalo is primarily due to Brucella abortus while Brucella melitensis predominates in sheep and goats. The main factors maintaining the disease in humans and animals are unhygienic food habits, poor animal husbandry processes, lack of awareness and ineffective surveillance systems. Therefore, prevention of human brucellosis would depend on controlling the disease in livestock. The current study aimed to study the epidemiological situation to develop an effective control strategy. Methods: The estimated seropositivity rates at the herd and animal levels were compiled during 2009-2018. The sera were submitted to the National Institute of Animal Health (NIAH) and the Regional Veterinary Research and Development Centers (VRDCs), where serological tests were performed. The testing used screening based on the Rose Bengal test (RBT) followed by confirmatory tests, the complement fixation test (CFT) and the indirect enzyme-linked immunosorbent assay (I-ELISA). The data were collected, the proportion of the estimated seropositivity rate was analyzed. The seropositive animals were followed up and specimens were collected for isolation and PCR identification. Result: The results of the accumulated seropositivity rate of the brucellosis of dairy cattle, beef cattle, buffaloes, goats and sheep at the herd level from 2009 to 2018 was 7.12% (95% CI: 6.99-7.26) and the animal level was 0.92% (95% CI: 0.91-0.93). The species identification presented Brucella abortus five isolates, whereas Brucella melitensis presented 31 isolates from the total of 36 isolates. This information of the serological status and Brucella spp., including diagnostics patterns could be used as base data for better managing the prevention and control measures of brucellosis in Thailand and other countries.