A highly sensitive DNA bead-based suspension array for the detection and species identification of bovine piroplasms

Coxiella burnetii infection persistence in a goat herd during seven kidding seasons after an outbreak of abortions: the effect of vaccination

Coxiella burnetii infection was monitored during seven kidding seasons (2017-2023) in a dairy goat herd that after an outbreak of Q fever abortions was vaccinated with an inactivated phase I vaccine. Due to the high infection rate just after the outbreak, only the replacement stock was vaccinated during the first three kidding seasons, and when the average herd immunity had decreased (fourth kidding season onwards), the whole herd was vaccinated. Vaginal swabs, feces, and milk were analyzed by PCR to monitor infection, and dust and aerosols were analyzed to measure C. burnetii environmental contamination. One year after the onset of the outbreak, a significant reduction in C. burnetii shedding loads was observed, but the percentage of shedding animals remained high until the third kidding season. By the seventh kidding season, no shedders were detected. The bacterial load excreted was significantly lower in vaccinated compared with unvaccinated animals, and in yearlings compared with multiparous. C. burnetii was detected by PCR in aerosols collected inside the animal premises throughout the study period except in the last season; whereas, aerosols collected outdoors tested negative in the last three kidding seasons. Viable C. burnetii was detectable in environmental dust collected inside the barn until the third kidding season following the outbreak. These results indicate that after an outbreak of Q fever, the risk of infection for humans and susceptible animals can remain high for at least three kidding seasons when the number of C. burnetii animal shedders is still high, even when bacterial excretion is low.

IMPORTANCE

Q fever is a zoonosis distributed worldwide. Ruminants are the main reservoir, and infection can cause high rates of abortion. After entering a farm, Coxiella burnetii infection can persist in the animal population over several lambing/kidding periods. Once infection is established in a herd, vaccination with the inactivated Phase I vaccine significantly reduces bacterial shedding, but although at low levels, excretion may continue to occur for several lambing/kidding seasons. The time that C. burnetii remains viable in the farm environment after an outbreak of Q fever determines the period when risk of infection is high for the people in close contact. This work showed that this period extends at least three kidding seasons after the outbreak. These results provided valuable information on the epidemiology of C. burnetii infection in goat herds and may help to develop guidelines for controlling the disease and reducing infection risk for susceptible people and animals.

Establishment and application of a qPCR diagnostic method for Theileria annulata

Bovine theileriosis caused by several Theileria species including Theileria annulata, Theileria parva, Theileria orientalis, Theileria mutans, and Theileria sinensis is a significant hemoprotozoan tick-borne disease. Among these, Theileria species, T. annulata, which causes tropical theileriosis (TT), is regarded as one of the most pathogenic and is responsible for high mortality. At present, most conventional diagnostic methods for tropical theileriosis are time-consuming and laborious and cannot distinguish newfound T. sinensis in China. Therefore, a high sensitivity and specificity real-time quantitative PCR method based on the TA19140 target molecule was developed, and the method was found to be specific for T. annulata. No cross-reaction was observed with T. sinensis, T. orientalis, Babesia bovis, Babesia bigemina, or Hyalomma anatolicum which is negative for T. annulata. A total of 809 field samples from different regions of China were analyzed by using the developed qPCR and conventional PCR. The positive samples for T. annulata detected by real-time qPCR and conventional PCR were 66/809 (8.16%) and 20/809 (2.47%), respectively, and all positive amplicons by qPCR were confirmed by Sanger sequencing. The results showed that the developed qPCR for the T. annulata 19,140 gene was more sensitive than conventional PCR. In addition, we first discovered that TA19140 was mainly expressed at the schizont and merozoite stages of T. annulata by relative quantification. The protein encoded by the TA19140 gene may be used as a potential diagnostic antigen for tropical theileriosis. In conclusion, a real-time quantitative PCR diagnostic method targeting the TA19140 gene was successfully established and could be used for both the quantitative and qualitative analysis of T. annulata infection from cattle and vector ticks, which will greatly help to control and diagnosis of tropical theileriosis.

Development of a Multiplex PCR and Magnetic DNA Capture Assay for Detecting Six Species Pathogens of the Genera Anaplasma and Ehrlichia in Canine, Bovine, Caprine and Ovine Blood Samples from Grenada, West Indies

Infections with tick-borne pathogens belonging to Anaplasma/Ehrlichia in various vertebrate hosts are a persistent problem resulting in nonspecific clinical signs during early infection. Diagnosis of single and multi-infections with these pathogens, causing diseases in companion/agricultural animals and people, remains a challenge. Traditional methods of diagnosis, such as microscopy and serology, have low sensitivity and specificity. Polymerase chain reaction (PCR) assays are widely used to detect early-phase infections, since these have high sensitivity and specificity. We report the development and validation of an assay involving PCR followed by magnetic capture method using species-specific oligonucleotides to detect six Anaplasma/Ehrlichia species pathogens in canine, bovine, caprine, and ovine blood samples. Overall, the assay application to 455 samples detected 30.1% (137/455) positives for one or more out of six screened pathogens. Single-pathogen infections were observed in 94.9% (130/137) of the positive samples, while co-infections were detected in 5.1% (7/137). Anaplasma marginale infection in cattle had the highest detection rate (34.4%), followed by canines positive for Anaplasma platys (16.4%) and Ehrlichia canis (13.9%). The assay aided in documenting the first molecular evidence for A. marginale in cattle and small ruminants and Ehrlichia chaffeensis and Ehrlichia ewingii in dogs in the Caribbean island of Grenada.

The Pathology of Pathogenic Theileriosis in African Wild Artiodactyls

The published literature on schizont-"transforming," or pathogenic theileriosis, in African wild artiodactyls is dated and based on limited information. Here the authors review the taxonomy, diagnosis, epidemiology, hematology, pathology, and aspects of control in various species. Molecular studies based on 18S and 16S rRNA gene sequences have shown that African wild artiodactyls are commonly infected with diverse Theileria spp., as well as nontheilerial hemoprotozoa and rickettsia-like bacteria, and coinfections with pathogenic and nonpathogenic Theileria species are often recorded. Although theileriosis is still confusingly referred to as cytauxzoonosis in many species, the validity of a separate Cytauxzoon genus in artiodactyls is debated. The epidemiology of theileriosis is complex; the likelihood of fatal disease depends on the interplay of parasite, vertebrate host, tick vector, and environmental factors. Roan calves (Hippotragus equinus) and stressed animals of all host species are more susceptible to fatal theileriosis. Even though regenerative anemia is common, peripheral blood piroplasm parasitemia does not correlate with disease severity. Other than anemia, common macroscopic lesions include icterus, hemorrhages (mucosal, serosal, and tissue), fluid effusions into body cavities, lung edema, and variably sized raised cream-colored foci of leukocyte infiltration in multiple organs. Histopathologic findings include vasocentric hyperproliferation and lysis of atypical leukocytes with associated intracellular schizonts, parenchymal necrosis, hemorrhage, thromboembolism, and edema. Immunophenotyping is required to establish the identity of the schizont-transformed leukocytes in wild ungulates. Throughout the review, we propose avenues for future research by comparing existing knowledge on selected aspects of theileriosis in domestic livestock with that in African wild artiodactyls.

A review of Theileria diagnostics and epidemiology

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Serological and molecular assays exist for most economic important Theileria species.

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Molecular assays are constantly being improved with regard to sensitivity and specificity.

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The concept of what constitute a Theileria species impacts on accurate diagnostics.

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Analytical specificity of molecular assays are >800 000 parasites/L blood.

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Parasitemia ranges may determine practical limits of detection.

An extensive range of serological and molecular diagnostic assays exist for most of the economically important Theileira species such as T. annulata, T. equi, T. lestoquardi, T. parva, T. uilenbergi and other more benign species. Diagnostics of Theileria is considered with regard to sensitivity and specificity of current molecular and serological assays and their use in epidemiology. In the case of serological assays, cross-reactivity of genetically closely related species reduces the use of the gold standard indirect fluorescent antibody test (IFAT). Development of antigen-specific assays does not necessarily address this problem, since closely related species will potentially have similar antigens. Even so, serological assays remain an important line of enquiry in epidemiological surveys. Molecular based assays have exploded in the last decade with significant improvements in sensitivity and specificity. In this review, the current interpretation of what constitute a species in Theileria and its impact on accurate molecular diagnostics is considered. Most molecular assays based on conventional or real-time PCR technology have proven to be on standard with regard to analytical sensitivity. However, consideration of the limits of detection in regard to total blood volume of an animal indicates that most assays may only detect >400,000 parasites/L blood. Even so, natural parasitaemia distribution in carrier-state animals seems to be above this limit of detection, suggesting that most molecular assays should be able to detect the majority of infected individuals under endemic conditions. The potential for false-negative results can, however, only be assessed within the biological context of the parasite within its vertebrate host, i.e. parasitaemia range in the carrier-state that will support infection of the vector and subsequent transmission.

Reverse line blot hybridization with species-specific oligonucleotide probes: application to piroplasm detection

Reverse line blot (RLB) hybridization has become a well-established and widely used method for the multiplex identification of several Babesia and Theileria species in hosts and tick vectors. The procedure is based on the simultaneous PCR amplification of a polymorphic region of the 18S rRNA gene from different piroplasms followed by identification of the individual species by hybridization to species-specific oligonucleotide probes covalently linked to a nylon membrane in a macroarray format.

Risks of suffering tick-borne diseases in sheep translocated to a tick infested area: a laboratory approach for the investigation of an outbreak

This study was designed to investigate an outbreak of high mortality that occurred in naïve Assaf sheep introduced into a Latxa sheep flock in the Basque Country, a region where piroplasmosis is endemic. To identify the causes of this outbreak, a panel of different methods, including traditional pathological, biopathological and parasitological analyses combined with recently developed molecular methods, was used. These novel molecular methods included a multiplex real-time PCR assay to screen for the presence of the most important tick-borne pathogens (piroplasms and anaplasmas), followed by a second species-specific multiplex real-time PCR assay for the identification of Anaplasma-positive samples. The identification of piroplasm-positive samples was carried out by a multiplexed microsphere-based suspension array using a Luminex(®) xMAP technology-based procedure. Anaplasmas and/or piroplasms were detected in 7/10 lambs and 11/13 ewes, with Babesia ovis being detected in 12 of the 23 animals, Theileria ovis in 6 and Anaplasma ovis in 4, both as single and mixed infections. Most of the animals infected with B. ovis had a marked decrease in the values of the red blood cell parameters. Ticks collected from the animals were identified as Riphicephalus bursa, recognised vector of B. ovis. Other haemolytic pathologies (clostridial disease, copper poisoning and leptospirosis) were ruled out and, considering all clinical, laboratory and epidemiological data, babesiosis by B. ovis was diagnosed. A detailed description of the clinical outcome, with ca. 60% of mortality, laboratory results and epidemiological findings are provided. The implications of the introduction of naïve animals into a piroplasmosis endemic area are discussed.

Opportunities for bead-based multiplex assays in veterinary diagnostic laboratories

Bead-based multiplex assays (BBMAs) are applicable for high throughput, simultaneous detection of multiple analytes in solution (from several to 50–500 analytes within a single, small sample volume). Currently, few assays are commercially available for veterinary applications, but they are available to identify and measure various cytokines, growth factors and their receptors, inflammatory proteins, kinases and inhibitors, neurobiology proteins, and pathogens and antibodies in human beings, nonhuman primates, and rodent species. In veterinary medicine, various nucleic acid and protein-coupled beads can be used in, or for the development of, antigen and antibody BBMAs, with the advantage that more data can be collected using approximately the same amount of labor as used for other antigen and antibody assays. Veterinary-related BBMAs could be used for detection of pathogens, genotyping, measurement of hormone levels, and in disease surveillance and vaccine assessment. It will be important to evaluate whether BBMAs are “fit for purpose,” how costs and efficiencies compare between assays, which assays are published or commercially available for specific veterinary applications, and what procedures are involved in the development of the assays. It is expected that many veterinary-related BBMAs will be published and/or become commercially available in the next few years. The current review summarizes the BBMA technology and some of the currently available BBMAs developed for veterinary settings. Some of the human diagnostic BBMAs are also described, providing an example of possible templates for future development of new veterinary-related BBMAs.

Assessment of exposure to piroplasms in sheep grazing in communal mountain pastures by using a multiplex DNA bead-based suspension array

BACKGROUND

Piroplasms are tick-borne hemoprotozoans with a major impact on extensive management systems. Detection of sub-clinical low-level carriers, which can act as source of infection for vector ticks, is key to protect livestock trade and facilitate preventive control programs. The purpose of this study was to develop a method for the detection of ovine piroplasms and to use it in a field study aimed at investigating piroplasms infection in semi-extensive production systems in the Basque Country (northern Spain).

METHODS

A DNA bead-based suspension array using the Luminex xMAP technology that included a generic Theileria-Babesia control probe, 6 species-specific probes, and an internal control probe was developed to detect and identify piroplasms that infect sheep. To monitor piroplasm infection in clinically healthy sheep from 4 flocks that share communal mountain pastures, blood samples were collected during 2 grazing seasons.

RESULTS

Piroplasms were detected in 48% (214/446) of blood samples, nearly half of them (49.1%, 105/214) as mixed infections. Five different piroplasms were identified: Theileria sp. OT3 in 34.8% of the samples, Theileria ovis in 20.9%, and at lower prevalences Babesia motasi (12.3%), Theileria luwenshuni/OT1 (10.5%) and Babesia ovis (6.3%). Despite differences among flocks associated to differences in management, an increasing trend in the incidence of piroplasm infection with increasing age of animals after increased tick exposure was observed. This increment could be attributed to continued re-infection associated with re-exposure to ticks at grazing. Ticks were collected from animals (4 species) and vegetation (8 species), and associations between tick abundance seasonality and risk of infection with the different piroplasms were established.

CONCLUSION

The multiplex Luminex xMAP procedure is a rapid and high throughput technique that provided highly specific and sensitive identification of single and mixed piroplasm infections in blood of sheep carriers. This study confirmed a situation of endemic stability for piroplasm infection in the region, where infection is present in the absence of clinical signs, and mountain grazing allows for sufficient inoculation rates to maintain such situation.

Development and evaluation of a real-time PCR assay for the quantitative detection of Theileria annulata in cattle

Background

The tick-borne apicomplexan bovine parasite Theileria annulata is endemic in many tropical and temperate areas, including Minorca (Balearic Islands, Spain). Real-time PCR is widely used for the detection of piroplasms but quantification is not commonly considered.

Results

We developed a real-time quantitative PCR (qPCR) assay for the detection and quantification of T. annulata that included an internal amplification control (IAC) to monitor for the presence of potential inhibitors. Specificity, sensitivity, precision, linear range and PCR efficiency were calculated and different methods for transformation of quantification cycle (Cq) values into quantities (Q) were evaluated. The assay was able to detect (100% probability) and quantify (linear response) 100 gene copies, and clinical sensitivity was set at 10 T. annulata per μl of blood. The assay was then validated on 141 bovine blood samples analyzed in parallel by a Luminex® suspension array, showing the utility of the qPCR assay developed here for the detection and quantification of the parasite in field conditions. Once validated it was used to monitor T. annulata parasitaemia throughout a year in 8 carrier animals from a farm in Minorca.

Conclusions

The developed qPCR assay offers a reliable and simple way to quantify T. annulata infection loads, which could prove crucial in studying the role of carrier animals as a source of the infection, or assessing the efficacy of treatment and control measures.

Monitoring piroplasms infection in three cattle farms in Minorca (Balearic Islands, Spain) with previous history of clinical piroplamosis

Bovine piroplasmosis are tick-borne protozoan diseases caused by parasites of the genera Theileria and Babesia. Three Friesian cattle farms (F1-F3) with previous history of clinical piroplamosis were selected in Minorca (Balearic Islands, Spain). Blood samples were collected from 8 to 11 animals every two months throughout a year and, a newly developed multiplex DNA bead-based suspension array based on the Luminex(®) xMAP technology was used to monitor for the presence of piroplasms. The assay incorporated probes for Babesia divergens, Babesia bovis, Babesia bigemina, Babesia major, Babesia occultans, Theileria annulata and Theileria buffeli, and a Catch-all Theileria and Babesia (TB) control probe. An internal amplification control that was detected with a Luminex probe was also included to monitor for inhibition. Infection was detected in 87.5% of the samples, 38.7% as single infections and 48.8% as mixed infections. T. annulata was widespread in Farm F1, with all animals positive over the whole study; albeit less frequently, T. annulata was also detected in Farms F2 and F3. T. buffeli was the overall most prevalent piroplasm, with a wide distribution in Farms F2 and F3 but only occasionally detected in F1. B. bigemina was the most frequent Babesia species, but was absent from Farm F1. B. bovis, previously reported in Minorca, was only sporadically detected in F2 and F3. A further 3 Babesia species not previously found in Minorca were also identified: B. major present in the 3 farms; B. divergens detected once in 2 animals in F2; and B. occultans found in 4 animals in F2 and in 1 Hyalomma marginatum female tick collected from a positive animal. Sequencing confirmed the identity of B. occultans thus extending the distribution of this species to Mediterranean Europe. This study confirmed the endemic situation for piroplasm infection in the region and detected the presence of a large number of chronic asymptomatic carriers. More importantly, 3 Babesia species not previously detected in the region were detected for the first time.