Development of a loop-mediated isothermal amplification (LAMP) assay for the detection of Anaplasma marginale

Detection of Babesia bovis using loop-mediated isothermal amplification (LAMP) with improved thermostability, sensitivity and alternative visualization methods

Bovine babesiosis is one of the most economically important tick-borne diseases in tropical and subtropical countries. A conventional microscopic diagnosis is typically used because it is inexpensive and expeditious. However, it is highly dependent on well-trained microscopists and tends to be incapable of detecting subpatent and chronic infections. Here, we developed a novel nucleic acid-based amplification method using loop-mediated isothermal amplification (LAMP) in conjunction with a colori-fluorometric dual indicator for the rapid and accurate detection of Babesia bovis based on the mitochondrial cytochrome b gene. We aimed to improve the thermostability, sensitivity, specificity, and alternative visualization of LAMP-based methods. We assessed its diagnostic performance compared to two conventional PCR agarose gel electrophoresis (PCR-AGE) methods. The thermostability of LAMP reaction mixtures and DNA templates in variable conditions was also assessed. In addition, we evaluated alternative visualization methods using different light sources including neon, LED, and UV lights. We found that the LAMP-neon was ten times more sensitive than the PCR-AGE, while the LAMP-LED and LAMP-UV were 1,000 times more sensitive. The current LAMP method showed no cross-amplification with uninfected cattle DNA or other common blood parasites in cattle, including Babesia bigemina, Theileria orientalis, Anaplasma marginale, and Trypanosoma evansi. In addition, the developed LAMP method has good thermostability and the potential for on-site utility as B. bovis DNA could still be detected up to 72 h after initial preparation. Our findings suggested that the developed LAMP method provides an alternative approach for B. bovis detection with sensitivity higher than PCR-AGE diagnostics, high specificity, and the flexibility to use neon, LED, and UV light sources for positive signal observations.

Natural levels of Rhipicephalus microplus infestation and Anaplasma marginale infection in Angus and Ultrablack calves

Infections by Anaplasma marginale and infestations by Rhipicephalus microplus occur endemically in Brazil, representing an obstacle to expanding the use of taurine breeds, which are more susceptible. In this study, the levels of infection by A. marginale and infestation by R. microplus were monitored in 31 calves that were either purebred or had a high degree of taurine blood: 17 Angus (100% taurine) and 14 Ultrablack (ca. 82% taurine and 18% Zebu). The animals were evaluated on 13 occasions at 12-day intervals. The levels of A. marginale infection were determined by quantification of DNA copy number (CN) by qPCR, and ticks were monitored by two methods: counting adult females (≥ 4.5 mm) and scoring the level of tick infestation considering all visible instars in the animals' bodies. No significant effects were observed between the means of CN of A. marginale, tick counts and scores among Angus and Ultrablack animals. The repeatability estimates for CN of A. marginale, tick counts and tick scores were 0.53, 0.12 and 0.16, respectively. The correlations between CN and tick counts and scores were close to zero, whereas the correlations between tick assessment methods were 0.57. The absence of differences between the two genetic groups indicates, under the conditions of the present study, that the low degree of Zebu blood did not influence the levels of infection by A. marginale or infestation by R. microplus. The results also suggest that the evaluation of the levels of infestation by ticks using scores can provide information closer to the real infestation rate considering that it uses all the visible instars of the parasites.

Polymerase chain reaction and loop-mediated isothermal amplification targeting lic13162, lic20239, and lipL32 genes for leptospirosis diagnosis

Leptospirosis is a zoonotic disease caused by pathogenic species of Leptospira. Due to the similarity with clinical signs of other febrile diseases, early diagnosis remains challenging. Real-time PCR has been used for direct detection of Leptospira, but it requires thermocyclers and highly trained personnel. Loop-mediated isothermal amplification (LAMP) is a simple and rapid DNA-based assay. Therefore, here we have developed PCR and LAMP assays targeting two novel genes, lic13162 and lic20239, and also lipL32 gene to detect pathogenic Leptospira. Analytical and diagnostic performances were compared with bacterial isolates (including different Leptospira species and serovars) and clinical samples. The results demonstrated that PCR assays targeting lic13162 and lic20239 were successful to amplify Leptospira, but LAMP not. However, both PCR and LAMP targeting lipL32 could detect pathogenic Leptospira. LAMP lipL32 could be performed in 30 min with a detection limit of 156 cells/mL. Diagnostic performance of lipL32-LAMP presented 84.2% sensitivity and 93.2% specificity. In conclusion, lipL32 PCR and LAMP are effective methods to detect pathogenic Leptospira directly from clinical samples.

Development of a loop-mediated isothermal amplification (LAMP) assay targeting the mitochondrial cytochrome b gene for the rapid detection of alveolar echinococcosis in hepatic nodules of horses

Alveolar echinococcosis, which is caused by a larval-stage infection of Echinococcus multilocularis, is a zoonosis with public health importance. Recently, alveolar echinococcosis in slaughtered horses has been reported in Japan and Poland. In terms of public health, a highly sensitive and specific diagnostic method is essential for early detection during meat inspection. In this study, the loop-mediated isothermal amplification (LAMP) assay was developed and validated to target the mitochondrial cytochrome b (cob) gene of E. multilocularis. Forty-one hepatic solid nodules obtained from each horse were evaluated based on histopathological examination and cob-targeted PCR and then submitted to the LAMP assay. The optimal condition of the developed LAMP assay was 64℃ for 30 min. The results of the developed LAMP assay were completely consistent with those of cob PCR. In addition, the detection limit for the number of copies of the cob gene was 135 copies/μL in the LAMP assay. These findings suggest that the ability of the LAMP assay developed in this study is equivalent to that of the conventional PCR testing. The LAMP assay developed in this study can be used as an alternative to PCR testing for the routine genetic diagnosis of alveolar echinococcosis in horses.

Recombinase polymerase amplification (RPA) with lateral flow detection for three Anaplasma species of importance to livestock health

Anaplasma marginale, A. ovis, and A. phagocytophilum are the causative agents of bovine anaplasmosis, ovine anaplasmosis, and granulocytic anaplasmosis, respectively. The gold standard for diagnosis of post-acute and long-term persistent infections is the serological cELISA, which does not discriminate between Anaplasma species and requires highly equipped laboratories and trained personnel. This study addresses the development of a rapid, isothermal, sensitive, species-specific RPA assays to detect three Anaplasma species in blood and cELISA A. marginale-positive serum samples. Three RPA primer and probe sets were designed targeting msp4 genes of each Anaplasma species and the internal control (GAPDH gene) for each assay. The limit of detection of gel-based or RPA-basic assays is 8.99 × 10⁴ copies/µl = A. marginale, 5.04 × 10⁶ copies/µl = A. ovis, and 4.58 × 10³ copies/µl = A. phagocytophilum, and for each multiplex lateral flow or RPA-nfo assays is 8.99 × 10³ copies/µl of A. marginale, 5.04 × 10³ copies/µl of A. ovis, 4.58 × 10³ copies/µl of A. phagocytophilum, and 5.51 × 10³ copies/µl of internal control (GAPDH). Although none of the 80 blood samples collected from Oklahoma cattle were positive, the RPA-nfo assays detected all A. marginale cattle blood samples with varying prevalence rates of infection, 83% of the 24 cELISA A. marginale-positive serum samples, and all A. phagocytophilum cell culture samples. Overall, although early detection of three Anaplasma species was not specifically addressed, the described RPA technique represents an improvement for detection of three Anaplasma in regions where access to laboratory equipment is limited.

The potential of diagnostic point-of-care tests (POCTs) for infectious and zoonotic animal diseases in developing countries: Technical, regulatory and sociocultural considerations

Remote and rural communities in low‐ and middle‐income countries (LMICs) are disproportionately affected by infectious animal diseases due to their close contact with livestock and limited access to animal health personnel). However, animal disease surveillance and diagnosis in LMICs is often challenging, and turnaround times between sample submission and diagnosis can take days to weeks. This diagnostic gap and subsequent disease under‐reporting can allow emerging and transboundary animal pathogens to spread, with potentially serious and far‐reaching consequences. Point‐of‐care tests (POCTs), which allow for rapid diagnosis of infectious diseases in non‐laboratory settings, have the potential to significantly disrupt traditional animal health surveillance paradigms in LMICs. This literature review sought to identify POCTs currently available for diagnosing infectious animal diseases and to determine facilitators and barriers to their use and uptake in LMICs. Results indicated that some veterinary POCTs have been used for field‐based animal disease diagnosis in LMICs with good results. However, many POCTs target a small number of key agricultural and zoonotic animal diseases, while few exist for other important animal diseases. POCT evaluation is rarely taken beyond the laboratory and into the field where they are predicted to have the greatest impact, and where conditions can greatly affect test performance. A lack of mandated test validation regulations for veterinary POCTs has allowed tests of varying quality to enter the market, presenting challenges for potential customers. The use of substandard, improperly validated or unsuitable POCTs in LMICs can greatly undermine their true potential and can have far‐reaching negative impacts on disease control. To successfully implement novel rapid diagnostic pathways for animal disease in LMICs, technical, regulatory, socio‐political and economic challenges must be overcome, and further research is urgently needed before the potential of animal disease POCTs can be fully realized.

A Multiplex PCR Detection Assay for the Identification of Clinically Relevant Anaplasma Species in Field Blood Samples

The genus Anaplasma (Rickettsiales: Anaplasmataceae), which includes the species Anaplasma capra, Anaplasma bovis, Anaplasma ovis, and Anaplasma phagocytophilum, is responsible for a wide variety of infections in both human and veterinary health worldwide. Multiple infections with these four Anaplasma pathogens have been reported in many cases. We introduce a novel multiplex PCR for the simultaneous detection of A. capra, A. bovis, A. ovis, and A. phagocytophilum, based on species-specific primers against the groEL (A. capra and A. bovis), msp4 (A. ovis), and 16S rRNA (A. phagocytophilum) genes. To verify the specificity of the PCR reactions, we evaluated four sets of primers to analyze samples containing different blood pathogens. The sensitivity of the multiplex PCR was evaluated by amplifying 10-fold dilutions of total genomic DNA extracted from sheep blood infected with A. capra, A. bovis, A. ovis, or A. phagocytophilum. The reproducibility of the assay was evaluated by testing 10-fold dilutions of total genomic DNA extracted from sheep blood infected with these pathogens from 10⁰ to 10^–3 ng/μL per reaction in triplicate on three different days. A total of 175 field blood DNA samples were used to evaluate the reproducibility of multiplex PCR compared with the simplex PCRs. PCR primers used in this study were confirmed to be 100% species-specific using blood pathogens previously identified by other methods. The lower limit of detection of the multiplex PCR with good repeatability enabled the detection of A. capra, A. bovis, A. ovis and A. phagocytophilum at concentrations of 3 × 10^–5, 5 × 10^–7, 2 × 10^–5, and 7 × 10^–7 ng/μL, respectively. There was no significant difference between conventional and multiplex PCR protocols used to detect the four Anaplasma species (P > 0.05). The results of the multiplex PCR revealed that the A. capra groEL gene, the A. bovis groEL gene, the A. ovis msp4 gene, and the A. phagocytophilum 16S rRNA gene were reliable target genes for species identification in clinical isolates, being specific for each of the four target Anaplasma species. Our study provides an effective, sensitive, specific, and accurate tool for the rapid differential clinical diagnosis and epidemiological surveillance of Anaplasma pathogens in sheep and goats.

Real-time PCR assay with an endogenous internal amplification control for detection and quantification of Anaplasma marginale in bovine blood

Bovine anaplasmosis is a tick-borne rickettsial disease, causing significant economic losses in many countries. The main causative agent of bovine anaplasmosis is Anaplasma marginale (Rickettsiales, Anaplasmataceae). To date, several PCR assays for A. marginale DNA detection were proposed, but most of them do not provide an internal amplification control, which allows to prevent false-negative results and is required for reliability of the results of pathogen DNA detection by PCR assay. In the present study, a real-time PCR assay based on the species-specific and highly conserved fragment of msp1α gene was developed for detection and quantification of A. marginale in bovine blood. The real-time PCR assay is able to detect as few as one copу of msp1α gene per reaction. To prevent false-negative results, simultaneous amplification and detection of the bovine genomic DNA fragment as an endogenous internal amplification control (IAC) was provided. The assay can be used as a highly specific and sensitive method for detection and quantification of A. marginale in infected cattle, and for the evaluation of the efficacy of anti-rickettsial drugs and anaplasmosis vaccines.