Evaluation of the indirect fluorescent antibody test as a diagnostic tool for East Coast fever in eastern Zambia

Molecular and serological prevalence of corridor disease (buffalo associated Theileria parva infection) in cattle populations at the livestock/game interface of KwaZulu-Natal province, South Africa

Theileria parva are intracellular protozoal parasites responsible for three disease syndromes in cattle, namely East Coast fever (ECF), Corridor disease (CD) and Zimbabwean theileriosis. The increase in reports of CD outbreaks in recent years has raised questions about the probability of adaptation of buffalo-derived T. parva strains in cattle herds adjacent to game reserves. A cross-sectional study was conducted from March 2016 to December 2018 to investigate the extent of occurrence of T. parva infections in cattle in the CD-controlled area of KwaZulu-Natal Province. Blood samples were collected from 1137 cattle from 14 herds and analysed by quantitative real-time PCR (qPCR) and indirect fluorescent antibody test (IFAT) to determine the prevalence of T. parva. A total of 484 samples from 4 of the 14 herds were further tested on qPCR for the presence of T. taurotragi infections. The data were analysed using descriptive statistics and a chi-square test was used to assess association between variables. The overall prevalence of T. parva was 1.3% (95%CI:1-2%) and 19.9% (95%CI:17-22%) on qPCR and IFAT, respectively. The qPCR positive samples were detected in March and May while IFAT positive samples were detected in all seasons sampled, with higher numbers during summer months. The Pearson Chi-squared test showed that T. parva prevalence rates based on both qPCR and IFAT were positively associated with herds with previous history of CD outbreaks (χ2 = 8.594, p = 0.003; χ2 = 69.513, p < 0.001, respectively). The overall prevalence of T. taurotragi was 39.4% (95% CI: 35-44%) with the herd-level prevalence ranging between 35.0% and 43.4%. Possible cross-reaction of T. parva IFAT to T. taurotragi was detected on few samples, however, there was no significant association between T. taurotragi infections and IFAT positivity (χ2 = 0.829, p = 0.363). Results from this study demonstrated the extent of occurrence of subclinical carriers and the level of exposure to T. parva infections in cattle populations at a livestock/game interface area of KwaZulu-Natal Province. The molecular and seroprevalence rates were low when compared with other areas where cattle-adapted T. parva infections are endemic. The adaptation of buffalo-derived T. parva in cattle population resulting in cattle-cattle transmissions seem to be unlikely under the current epidemiological state.

An endpoint visualization loop-mediated isothermal amplification (LAMP) for detecting bubaline theileriosis

Background

Tropical theileriosis is a significant disease affecting the health and production levels of buffaloes in India. It is caused by an apicomplexan—Theileria annulata. The timely and accurate detection of infection is vital for implementing a mass vaccination or control programme in a given area under outbreak. Most of the literature concerned with diagnosis of theileriosis revolves around cattle, and practically, there are very limited assays available for detecting bubaline theileriosis. Loop-mediated isothermal amplification (LAMP) assay certainly amplifies the targeted deoxyribosenucleic acid (DNA) with a comparatively higher efficacy, rapidity and sensitivity. Alongside, minimal use of sophisticated instruments in performing LAMP assay is certainly an add on. The present study describes the application of LAMP assay in diagnosing tropical theileriosis in buffaloes alongside, its comparison with polymerase chain reaction (PCR) and blood microscopical examination.

Results

No cross-reaction was seen with DNA of other haemoprotozoan. LAMP was compared with blood microscopy and PCR. LAMP detected infection in 27 out of 100 buffaloes, while blood microscopy and PCR detected disease in 16 and 24 buffaloes, respectively.

Conclusion

The sensitivity, specificity and kappa value prediction of LAMP were found to be much higher than the PCR and blood microscopy. The present communication reports the first use of LAMP in detecting theileriosis in buffaloes in the world.

Rapid diagnosis of Theileria annulata by colorimetric loop-mediated isothermal amplification (LAMP) assay

Theileria annulata the causative agent of bovine tropical theileriosis (BTT) is globally distributed. Rapid and accurate detection of the parasite is essential for the implementation and evaluation of mass drug administration and planned vaccination programs for controlling BTT. Loop mediated isothermal amplification (LAMP) amplifies targeted nucleic acid with a high efficacy, sensitivity and rapidity under isothermal conditions. In the present study, the internal transcriber space (ITS) gene of T. annulata was targeted for the development of a LAMP assay using pH-sensitive dye (phenol red) for enhanced visual detection of amplification. This method employed a set of specially designed four primers that recognized six distinct regions on the targeted gene. No amplification was detected with the DNA of other tested haemoprotozoans. Positive LAMP products were identified by a colour change from pink to yellow, and then rechecked by specific ladder pattern upon agarose gel electrophoresis. LAMP was able to detect infection in 63 out of 85 animals compared with blood microscopy, simple PCR and nested PCR which detected infection in 40, 49 and 64 animals, respectively. No difference in detection was seen in the colorimetric assay and the classical UV based LAMP assay.

Clinical Pathology, Immunopathology and Advanced Vaccine Technology in Bovine Theileriosis: A Review

Theileriosis is a blood piroplasmic disease that adversely affects the livestock industry, especially in tropical and sub-tropical countries. It is caused by haemoprotozoan of the Theileria genus, transmitted by hard ticks and which possesses a complex life cycle. The clinical course of the disease ranges from benign to lethal, but subclinical infections can occur depending on the infecting Theileria species. The main clinical and clinicopathological manifestations of acute disease include fever, lymphadenopathy, anorexia and severe loss of condition, conjunctivitis, and pale mucous membranes that are associated with Theileria-induced immune-mediated haemolytic anaemia and/or non-regenerative anaemia. Additionally, jaundice, increases in hepatic enzymes, and variable leukocyte count changes are seen. Theileria annulata and Theileria parva induce an incomplete transformation of lymphoid and myeloid cell lineages, and these cells possess certain phenotypes of cancer cells. Pathogenic genotypes of Theileria orientalis have been recently associated with severe production losses in Southeast Asia and some parts of Europe. The infection and treatment method (ITM) is currently used in the control and prevention of T. parva infection, and recombinant vaccines are still under evaluation. The use of gene gun immunization against T. parva infection has been recently evaluated. This review, therefore, provides an overview of the clinicopathological and immunopathological profiles of Theileria-infected cattle and focus on DNA vaccines consisting of plasmid DNA with genes of interest, molecular adjuvants, and chitosan as the most promising next-generation vaccine against bovine theileriosis.

Assessment of the prevalence of Theileria lestoquardi in sheep from the Sudan using serological and molecular methods

Malignant theileriosis of sheep and goats caused by Theileria lestoquardi is considered to be among the most important tick borne diseases in the Sudan. Information on the prevalence of the disease in different parts of the Sudan is limited. The purpose of this study was to estimate the prevalence of the disease in five states of the Sudan using molecular and serological assays. A total of 393 blood and serum samples from clinically asymptomatic sheep were analysed using nested reverse line blot (nRLB) and loop mediated isothermal amplification (LAMP), as well as an enzyme-linked immunosorbent assay (ELISA). The results indicated a sero-prevalence of 33.8% while RLB and LAMP assays revealed molecular prevalences of 29.5 and 22.6% respectively. The prevalence of Theileria lestoquardi varied significantly according to the geographical origin of the infected animals, whereas age and gender did not have a significant effect. RLB data indicated that T. lestoquardi usually occurred as a co-infection with the non-pathogenic Theileria ovis. Using RLB as a gold standard, a sensitivity of 68.1% and a specificity of 96.4% were recorded for LAMP and a sensitivity of 75.9% and a specificity of 83.8% for ELISA. The Kappa coefficient between nRLB and LAMP indicated a significant level of agreement (0.692), but only moderate concordance (0.572) between nRLB and ELISA. The results of the present study confirm and extend earlier findings regarding the widespread of T. lestoquardi infections in sheep in the Sudan. The data provide evidence that should enable the veterinary authorities to deploy appropriate control measures.

Seroprevalence of bovine theileriosis in northern China

Background

Bovine theileriosis is a common disease transmitted by ticks, and can cause loss of beef and dairy cattle worldwide. Here, an indirect enzyme-linked immunosorbent assay (iELISA) based on Theileria luwenshuni surface protein (TlSP) was developed and used to carry out a seroepidemiological survey of bovine theileriosis in northern China.

Methods

We used the BugBuster Ni-NTA His•Bind Purification Kit to purify recombinant TlSP (rTlSP), which was subsequently analyzed by Western Blotting to evaluate cross-reactivity with other pathogen-positive sera. The iELISA method based on rTlSP was successfully developed. Sera from 2005 blood samples were tested with the rTlSP-iELISA method, and blood smears from these samples were observed by microscopy.

Results

The specificity of iELISA was 98.9%, the sensitivity was 98.5%, and the cut-off was selected as 24.6%. Western Blot analysis of rTlSP confirmed that there were cross-reactions with Theileria luwenshuni, Theileria uilenbergi, Theileria ovis, Theileria annulata, Theileria orientalis and Theileria sinensis. The epidemiological survey showed that the highest positive rate of bovine theileriosis was 98.3%, the lowest rate was 84.1%, and the average positive rate was 95.4% by iELISA. With microscopy, the highest positive rate was 38.9%, the lowest rate was 5.1%, and the relative average positive rate was 13.7%.

Conclusions

An rTlSP-iELISA was developed to detect circulating antibodies against bovine Theileria in northern China. This is the first report on the seroprevalence of bovine theileriosis in northern China, and it also provides seroepidemiological data on bovine theileriosis in China.

Tick-borne haemoparasites in African buffalo (Syncerus caffer) from two wildlife areas in Northern Botswana

BACKGROUND

The African buffalo (Syncerus caffer) is a host for many pathogens known to cause economically important diseases and is often considered an important reservoir for livestock diseases. Theileriosis, heartwater, babesiosis and anaplasmosis are considered the most important tick-borne diseases of livestock in sub-Saharan Africa, resulting in extensive economic losses to livestock farmers in endemic areas. Information on the distribution of tick-borne diseases and ticks is scarce in Northern Botswana. Nevertheless, this data is necessary for targeting surveillance and control measures in livestock production at national level.

METHODS

In order to address this gap, we analyzed 120 blood samples from buffalo herds for the presence of common tick-borne haemoparasites causing disease in livestock, collected in two of the main wildlife areas of Northern Botswana: the Chobe National Park (CNP, n=64) and the Okavango Delta (OD, n=56).

RESULTS

Analysis of the reverse line blot (RLB) hybridization assay results revealed the presence of Theileria, Babesia, Anaplasma and Ehrlichia species, either as single or mixed infections. Among the Theileria spp. present, T. parva (60%) and T. mutans (37%) were the most prevalent. Other species of interest were Anaplasma marginale subsp. centrale (30%), A. marginale (20%), Babesia occultans (23%) and Ehrlichia ruminantium (6%). The indirect fluorescent antibody test (IFAT) indicated 74% of samples to be positive for the presence of T. parva antibodies. Quantitative real-time PCR (qPCR) detected the highest level of animals infected with T. parva (81% of the samples). The level of agreement between the tests for detection of T. parva positive animals was higher between qPCR and IFAT (kappa=0.56), than between qPCR and RLB (kappa=0.26) or the latter and IFAT (kappa=0.15).

CONCLUSIONS

This is the first report of tick-borne haemoparasites in African buffalo from northern Botswana, where animals from the CNP showed higher levels of infection than those from OD. Considering the absence of fences separating wildlife and livestock in the CNP and the higher levels of some parasite species in buffalo from that area, surveillance of tick-borne diseases in livestock at the interface in the CNP should be prioritized.

A quantitative risk assessment of bovine theileriosis entering Luapula Province from Central Province in Zambia via live cattle imports from traditional and commercial production sectors

Theileriosis or East Coast Fever (ECF) is an important livestock disease widespread in Zambia except for some provinces such as Luapula. This freedom status has been achieved due to strict livestock movement regulations that only authorise cattle imports from commercial farms implementing strict ECF control regimens. Recent increases in both the demand and price of beef in Zambia are stimulating a policy change towards a more inclusive inter-provincial trade in live cattle. This may also encourage the introduction of breeding cattle from high production pastoral sectors such as Central Province to stimulate the beef industry in disease free low production areas such as the Luapula Province. To estimate and compare the risks linked with those potential introductions of cattle from the traditional or commercial production sectors of the Central Province, a quantitative risk assessment model was developed. This risk comparison was necessary because the traditional livestock production sector accounts for over 79% of breeding cattle trade in Central Province but is characterised by minimalistic tick-borne disease control and a higher prevalence of ECF. We estimate that should the importation of breeding cattle from Central into Luapula Province be permitted, we could expect to import ECF by the introduction of infected animals at a median rate (5th and 95th percentiles) of every 0.44 years (0.12, 2.60), from the traditional sector compared to every 3.57 years (0.37, 103.6) from the commercial sector. Infected ticks would be expected to enter every 3.46 (0.66, 43.8) years via traditional cattle imports. These risks are strongly influenced by the prevalence of infection, performance of pre-transport screening tests, and the effectiveness of pre-transport tick cleansing. This assessment is expected to provide a model for tick borne disease risk assessments in similar settings, as well as inform ECF control, cattle trade, and stock movement policies in Zambia.

Estimation of diagnostic test accuracy without full verification: a review of latent class methods

The performance of a diagnostic test is best evaluated against a reference test that is without error. For many diseases, this is not possible, and an imperfect reference test must be used. However, diagnostic accuracy estimates may be biased if inaccurately verified status is used as the truth. Statistical models have been developed to handle this situation by treating disease as a latent variable. In this paper, we conduct a systematized review of statistical methods using latent class models for estimating test accuracy and disease prevalence in the absence of complete verification.

Loop-mediated isothermal amplification (LAMP) assays for the detection of Theileria annulata infection in China targeting the 18S rRNA and ITS sequences

We have developed two loop-mediated isothermal amplification (LAMP) assays for the detection of Theileria annulata, an economically important cattle disease in China that occurs in subtropical and tropical areas. These assays target the ribosomal RNA (18S rRNA) and ITS LAMP sequences. The primer set for each gene target consists of four primers, and each set recognizes six distinct regions on the target gene to allow for the highly specific detection of T. annulata. The specific ladder bands were amplified from the autologous genomic DNA of four Chinese-laboratory-preserved standard T. annulata stocks, and there were no cross-reactions with the genomic DNA of normal bovine blood and other protozoan species. The LAMP assays were sufficiently sensitive to detect 0.1 pg/μl of genomic DNA. Furthermore, DNA extracted from blood collected from cattle experimentally infected with T. annulata (18-105 days post-infection) was amplified, demonstrating the high sensitivity of these primers. Of the 351 field samples collected from China, 24.5% were positively detected by two LAMP primers, and 18.2% were found to be positive for T. annulata infection by PCR. These results indicate that the LAMP assay could be a potential diagnostic tool for epidemiological studies of T. annulata infection in China.

Identification of Theileria parva and Theileria sp. (buffalo) 18S rRNA gene sequence variants in the African Buffalo (Syncerus caffer) in southern Africa

Theileria parva is the causative agent of Corridor disease in cattle in South Africa. The African buffalo (Syncerus caffer) is the reservoir host, and, as these animals are important for eco-tourism in South Africa, it is compulsory to test and certify them disease free prior to translocation. A T. parva-specific real-time polymerase chain reaction (PCR) test based on the small subunit ribosomal RNA (18S rRNA) gene is one of the tests used for the diagnosis of the parasite in buffalo and cattle in South Africa. However, because of the high similarity between the 18S rRNA gene sequences of T. parva and Theileria sp. (buffalo), the latter is also amplified by the real-time PCR primers, although it is not detected by the T. parva-specific hybridization probes. Preliminary sequencing studies have revealed a small number of sequence differences within the 18S rRNA gene in both species but the extent of this sequence variation is unknown. The aim of the current study was to sequence the 18S rRNA genes of T. parva and Theileria sp. (buffalo), and to determine whether all identified genotypes can be correctly detected by the real-time PCR assay. The reverse line blot (RLB) hybridization assay was used to identify T. parva and Theileria sp. (buffalo) positive samples from buffalo blood samples originating from the Kruger National Park, Hluhluwe-iMfolozi Park, the Greater Limpopo Transfrontier Park, and a private game ranch in the Hoedspruit area. T. parva and Theileria sp. (buffalo) were identified in 42% and 28%, respectively, of 252 samples, mainly as mixed infections. The full-length 18S rRNA gene of selected samples was amplified, cloned and sequenced. From a total of 20 sequences obtained, 10 grouped with previously published T. parva sequences from GenBank while 10 sequences grouped with a previously published Theileria sp. (buffalo) sequence. All these formed a monophyletic group with known pathogenic Theileria species. Our phylogenetic analyses confirm the distinction between Theileria sp. (buffalo) and T. parva and indicate the existence of a single group of T. parva and two Theileria sp. (buffalo) 18S rRNA gene variants in the African buffalo. Despite the observed variation in the full-length parasite 18S rRNA gene sequences, the area in the V4 hypervariable region where the RLB and real-time PCR hybridization probes were developed was relatively conserved. The T. parva specific real-time PCR assay was able to successfully detect all T. parva variants and, although amplicons were obtained from Theileria sp. (buffalo) DNA, none of the Theileria sp. (buffalo) 18S rRNA sequence variants were detected by the T. parva-specific hybridization probes.

True versus apparent malaria infection prevalence: the contribution of a Bayesian approach

Aims

To present a new approach for estimating the “true prevalence” of malaria and apply it to datasets from Peru, Vietnam, and Cambodia.

Methods

Bayesian models were developed for estimating both the malaria prevalence using different diagnostic tests (microscopy, PCR & ELISA), without the need of a gold standard, and the tests' characteristics. Several sources of information, i.e. data, expert opinions and other sources of knowledge can be integrated into the model. This approach resulting in an optimal and harmonized estimate of malaria infection prevalence, with no conflict between the different sources of information, was tested on data from Peru, Vietnam and Cambodia.

Results

Malaria sero-prevalence was relatively low in all sites, with ELISA showing the highest estimates. The sensitivity of microscopy and ELISA were statistically lower in Vietnam than in the other sites. Similarly, the specificities of microscopy, ELISA and PCR were significantly lower in Vietnam than in the other sites. In Vietnam and Peru, microscopy was closer to the “true” estimate than the other 2 tests while as expected ELISA, with its lower specificity, usually overestimated the prevalence.

Conclusions

Bayesian methods are useful for analyzing prevalence results when no gold standard diagnostic test is available. Though some results are expected, e.g. PCR more sensitive than microscopy, a standardized and context-independent quantification of the diagnostic tests' characteristics (sensitivity and specificity) and the underlying malaria prevalence may be useful for comparing different sites. Indeed, the use of a single diagnostic technique could strongly bias the prevalence estimation. This limitation can be circumvented by using a Bayesian framework taking into account the imperfect characteristics of the currently available diagnostic tests. As discussed in the paper, this approach may further support global malaria burden estimation initiatives.

The sensitivity of PCR and serology in different Theileria parva epidemiological situations in Rwanda

Theileria parva is the causative agent of a lethal tick-borne disease of cattle occurring in eastern, central and southern Africa. Variations in the sensitivity of the serological and molecular tests with seasonal vector occurrence and discrepancies between low PCR prevalence and high T. parva vector density are a setback to estimate true prevalences. Therefore, the objectives of the present studies were to evaluate (1) the sensitivity of three serological tests (IFAT, ELISA and SELISA) and one molecular test (PCR) in the diagnosis of chronic T. parva infections in four different agro-ecological zones of Rwanda and (2) the effect of tick challenge and animal's age on the sensitivity of PCR. Blood samples from 635 bovines were collected in four agro-ecological zones of Rwanda. All sera were screened using the IFAT, ELISA, SELISA and PCR. The binary results of the four diagnostic tests were introduced separately for each agro-ecological zone in a Bayesian model to estimate the prevalence of T. parva infections and the sensitivity of the four diagnostic tests. All test specificities were set to 100%. The estimated T. parva prevalence was much higher (83-85%) than estimations based on single diagnostic tests. The estimated sensitivity of serological tests was relatively constant and ranged from 57 to 75% in the various areas. The sensitivity of PCR showed more pronounced variations, ranging from 66% in the low T. parva transmission (high land) zones compared to 24% in the highly vector infested (low land) zones. Calves and adult cattle (n=194) were also sampled in regularly and irregularly dipped herds in the low land region. The apparent T. parva prevalence detected by PCR was significantly higher in calves than in adult cattle and in herds regularly treated with acaricides, while no significant differences were found with IFAT. The conditional probability that a sample was positive at PCR while it was positive at IFAT was significantly lower in adults. The implication of these findings in the use of diagnostic assays for epidemiological studies is discussed.

Epidemiological studies on tick-borne diseases of cattle in Central Equatoria State, Southern Sudan

A herd-based study was carried out in Central Equatoria State, Southern Sudan, to study epidemiological aspects of tick-borne diseases. Six herds of cattle situated in three different locations were selected and investigated every 3 months during the year 2005. Blood smears for Giemsa staining and blood spots on filter paper for deoxyribonucleic acid extraction were collected from 600 apparently healthy indigenous cattle. A total of 69 (11.5%) samples showed the presence of piroplasms in Giemsa-stained blood smears, and polymerase chain reaction increased the detection limit to 297 (49.5%). Using reverse line blot, it was possible to detect and differentiate eight different piroplasms namely, Theileria parva (71.2%), Theileria mutans (73%), Theileria velifera (45.3%), Theileria taurotragi (2.7%), Theileria buffeli (0.5%), Theileria annulata (0.2%), Babesia bovis (1.7%), and Babesia bigemina (0.3%). Mixed infections were detected in 406 samples (67.7%) accounting for 17 different combinations. High infection of Theileria parva was reported among young calves compared to older cattle. The highest prevalence of Theileria parva was reported in the rainy season (October). The implications of these results on the epidemiology of tick-borne diseases are discussed with emphasis on East Coast fever.

Epidemiological studies on Theileriosis and the dynamics of Theileria parva infections in Rwanda

An epidemiological analysis based on three country wide surveys was carried out to determine the prevalence of infections with Theileria spp. in Rwanda. In the 1998 dry season, a total of 264 blood samples were submitted to Theileria spp. characterisation using the 18S species-specific PCR-RFLP assay. The same samples together with 634 samples (317 samples/season) collected during the 2002 dry season and the 2003 wet season were further analysed using the p104 Theileria parva specific PCR. The results from the 18S characterisation showed the presence of four Theileria spp., namely T. parva, T. mutans, T. taurotragi and T. velifera in the field. Half of the animals had multiple Theileria spp. infections. T. parva was the most prevalent and a high correlation (94%) was found between the prevalence results using the 18S and the p104 PCR assays. The prevalence of T. parva infections was stable over time and over season but decreased significantly from the high land to the low land areas. This unexpected trend cannot be explained alone by ecology or the dynamics of the tick population in the different zones, many other components such as breed type, tick control practices and grazing system are likely to play a role. Another important finding was the fact that young animals are infected early in life in all regions except in the high land zone indicating the existence of a particular epidemiological situation in this part of the country.

Estimating Disease Prevalence in a Bayesian Framework Using Probabilistic Constraints

Studies sometimes estimate the prevalence of a disease from the results of one or more diagnostic tests that are applied to individuals of unknown disease status. This approach invariably means that, in the absence of a gold standard and without external constraints, more parameters must be estimated than the data permit. Two assumptions are regularly made in the literature, namely that the test characteristics (sensitivity and specificity) are constant over populations and the tests are conditionally independent given the true disease status. These assumptions have been criticized recently as being unrealistic. Nevertheless, to estimate the prevalence, some restrictions on the parameter estimates need to be imposed. We consider 2 types of restrictions: deterministic and probabilistic restrictions, the latter arising in a Bayesian framework when expert knowledge is available. Furthermore, we consider 2 possible parameterizations allowing incorporation of these restrictions. The first is an extension of the approach of Gardner et al and Dendukuri and Joseph to more than 2 diagnostic tests and assuming conditional dependence. We argue that this system of equations is difficult to combine with expert opinions. The second approach, based on conditional probabilities, looks more promising, and we develop this approach in a Bayesian context. To evaluate the combination of data with the (deterministic and probabilistic) constraints, we apply the recently developed Deviance Information Criterion and effective number of parameters estimated (pD) together with an appropriate Bayesian P value. We illustrate our approach using data collected in a study on the prevalence of porcine cysticercosis with verification from external data.