Theileria sergenti: experimental transmission by the long-nosed cattle louse, Linognathus vituli

Epidemiology and Transmission of Theileria orientalis in Australasia

Oriental theileriosis, a disease primarily impacting cattle is caused by an apicomplexan hemoprotozoan parasite, Theileria orientalis. It has now become established in the Australasia region. The organism was long considered a benign cause of persistent infections; however, an increase in clinical outbreaks since 2006 in the eastern Australian states and New Zealand was associated with the identification of the pathogenic Ikeda (Type 2) and Chitose (Type 1) genotypes. Unlike the pathogenic T. parva and T. annulate, which target leucocytes, clinical manifestation with T. orientalis is due to its effects on erythrocytes, with the infection sometimes designated as Theileria associated bovine anemia (TABA). In Australia and New Zealand, the tick Haemaphysalis longicornis is the principal vector, though other Haemaphysalis species are also likely vectors. The endemic status of infection with pathogenic genotypes in areas with low or absent tick populations is an apparent paradox that may be attributable to alternative modes of transmission, such as mechanical transmission by hematophagous insects (lice, mosquitoes, and biting flies), vertical transmission, and transmission via iatrogenic means. This review addresses the evidence for the different modes of transmission of T. orientalis with particular focus on the reported and potential vectors in Australasia.

A U.S. Isolate of Theileria orientalis Ikeda Is Not Transstadially Transmitted to Cattle by Rhipicephalus microplus

Theileria orientalis Ikeda has caused an epidemic of bovine anemia and abortion across several U.S. states. This apicomplexan hemoparasite is transmitted by Haemaphysalis longicornis ticks; however, it is unknown if other North American ticks are competent vectors. Since the disease movement is largely determined by the host tick range(s), the prediction of the T. orientalis spread among U.S. cattle populations requires determination of additional competent tick vectors. Although Rhipicephalus microplus has mostly been eradicated from the U.S., outbreaks in populations occur frequently, and the U.S. remains at risk for reintroduction. Since R. microplus is a vector of Theileria equi and T. orientalis DNA has been detected in R. microplus, the goal of this study was to determine whether R. microplus is a competent vector of T. orientalis. Larval R. microplus were applied to a splenectomized, T. orientalis Ikeda-infected calf for parasite acquisition, removed as molted adults, and applied to two T. orientalis naïve, splenectomized calves for transmission. After 60 days, the naïve calves remained negative for T. orientalis by PCR and cytology. Additionally, T. orientalis was not detected in the salivary glands or larval progeny of acquisition-fed adults. These data suggest that R. microplus is not a competent vector of the U.S. T. orientalis Ikeda isolate.

Approaches to Integrated Parasite Management (IPM) for Theileria orientalis with an Emphasis on Immunity

Integrated parasite management (IPM) for pests, pathogens and parasites involves reducing or breaking transmission to reduce the impact of infection or infestation. For Theileria orientalis, the critical impact of infection is the first wave of parasitaemia from the virulent genotypes, Ikeda and Chitose, associated with the sequelae from the development of anaemia. Therefore, current control measures for T. orientalis advocate excluding the movement of naïve stock from non-endemic regions into infected areas and controlling the tick Haemaphysalislongicornis, the final host. In Australia, treatment of established infection is limited to supportive therapy. To update and expand these options, this review examines progress towards prevention and therapy for T. orientalis, which are key elements for inclusion in IPM measures to control this parasite.

Detection and distribution of haematophagous flies and lice on cattle farms and potential role in the transmission of Theileria orientalis

On the Northern Tablelands of New South Wales, Australia, endemic Theileria orientalis infection of cattle has been reported on farms where no ticks have been observed, raising the question of how Theileria is transmitted in these areas. To investigate the potential role of mechanical transmission by insects, the present study investigated the seasonal dynamics of biting fly species trapped between December 2017 and May 2019 on six cattle farms in the region where the presence of Theileria was confirmed. These flies, sucking lice collected from these farms and pools of Culicoides species affecting cattle also trapped in the region were subjected to qPCR detection of T. orientalis. Eleven species from eight genera of biting flies were collected using unbaited Nzi traps. Tabanid species were present in all farms, with Dasybasis oculata (43.6 %) and D. circumdata (27.6 %) being the most abundant and widespread species. The effect of season on the mean count per trapping event was statistically significant and highest in the summer months for Lilaea fuliginosa and D. oculata, and the autumn months for D. circumdata, with no seasonal effect on the abundance of the undescribed Dasybasis spp. No biting flies were trapped during the winter months. Sucking (Linognathus vituli and Haematopinus eurysternus) and biting (Bovicola bovis) cattle lice were also collected from all farms with the latter detected in only one farm. PCR screening for T. orientalis of trapped hematophagous insects resulted in parasite detection in the tabanid and Stomoxyini flies, biting midges and sucking lice with the highest proportion of positive samples for Haematopinus eurysternus (4/4 pools) and H. irritans exigua (6/15 individuals). The detection of the parasite in these potential vectors indicates a possible role in the mechanical transmission of T. orientalis and may partly explain the ubiquitous presence of Theileria in areas where ticks are absent.

A U.S. isolate of Theileria orientalis, Ikeda genotype, is transmitted to cattle by the invasive Asian longhorned tick, Haemaphysalis longicornis

Background

Theileria orientalis is a tick-borne hemoparasite that causes anemia, ill thrift, and death in cattle globally. The Ikeda strain of T.orientalis is more virulent than other strains, leading to severe clinical signs and death of up to 5% of affected animals. Within the Asia–Pacific region, where it affects 25% of Australian cattle, T.orientalis Ikeda has a significant economic impact on the cattle industry. In 2017, T.orientalis Ikeda was detected in a cattle herd in Albermarle County, Virginia, United States. Months earlier, the U.S. was alerted to the invasion of the Asian longhorned tick, Haemaphysalis longicornis, throughout the eastern U.S. Abundant H.longicornis ticks were identified on cattle in the T.orientalis-affected herd in VA, and a subset of ticks from the environment were PCR-positive for T.orientalis Ikeda. A strain of T.orientalis from a previous U.S. outbreak was not transmissible by H.longicornis; however, H.longicornis is the primary tick vector of T.orientalis Ikeda in other regions of the world. Thus, the objective of this study was to determine whether invasive H.longicornis ticks in the U.S. are competent vectors of T.orientalis Ikeda.

Methods

Nymphal H.longicornis ticks were fed on a splenectomized calf infected with the VA-U.S.-T.orientalis Ikeda strain. After molting, a subset of adult ticks from this cohort were dissected, and salivary glands assayed for T.orientalis Ikeda via qPCR. The remaining adult ticks from the group were allowed to feed on three calves. Calves were subsequently monitored for T.orientalis Ikeda infection via blood smear cytology and PCR.

Results

After acquisition feeding on a VA-U.S.-T.orientalis Ikeda-infected calf as nymphs, a subset of molted adult tick salivary glands tested positive by qPCR for T.orientalis Ikeda. Adult ticks from the same cohort successfully transmitted T.orientalis Ikeda to 3/3 naïve calves, each of which developed parasitemia reaching 0.4–0.9%.

Conclusions

Our findings demonstrate that U.S. H.longicornis ticks are competent vectors of the VA-U.S.-T.orientalis Ikeda strain. This data provides important information for the U.S. cattle industry regarding the potential spread of this parasite and the necessity of enhanced surveillance and control measures.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04659-9.

The role of sheep (Ovis aries) in maintaining Theileria orientalis Ikeda type infection

Theileria orientalis is a tick‒borne intracellular parasite of red blood cells that causes severe and mild infections in various ruminants worldwide. To date there have been 11 types identified within this species, of which 4 types are presently found in New Zealand cattle. Since 2012, New Zealand has suffered a substantial epidemic of infectious bovine anaemia in both dairy and beef cattle associated with the Ikeda type. The speed at which the disease spread through the North Island suggested that other species could have been involved in transmission. The aim of a series of related experiments was to test the null hypothesis that sheep cannot maintain T. orientalis Ikeda type infection or infect ticks that feed on them. Several studies were conducted over 2 years to address this hypothesis which together showed that sheep can have detectable levels of T. orientalis Ikeda type infection in both the acute and chronic phase and that Haemaphysalis longicornis larvae can become infected when feeding on sheep. No anaemia, weight loss or clinical disease was recorded in the sheep in the acute phase of infection. The levels of infection recorded in the sheep were much lower than those found in cattle, consistent with the sheep being asymptomatic carriers of T. orientalis Ikeda type infection.

First reports of indigenous lethal infection with Anaplasma marginale, Anaplasma bovis and Theileria orientalis in Croatian cattle

Anaplasmosis and theileriosis are important diseases with great economic impact that affect the cattle industry worldwide. In this study, we describe the first molecularly confirmed clinical cases of anaplasmosis caused by Anaplasma marginale and of a concurrent infection with A. bovis and Theileria orientalis in Croatian cattle. Clinical signs of A. marginale-infected cows included fever, lethargy, dark urine, as well as icteric and reddish mucous membranes. Postmortem examination revealed icterus, urinary bladder filled with dark urine and splenomegaly. A marginale was observed within erythrocytes on Giemsa-stained spleen imprints. Three affected cows were successfully treated with oxytetracycline, after which no new deaths occurred in the herd. Three cows in a different herd died suddenly and were found to be concurrently infected with A. bovis and T. orientalis. Postmortem examination revealed generalized icterus and urinary bladder filled with dark urine. These cases of A. marginale, A. bovis and T. orientalis infection show that bovine anaplasmosis and theileriosis are present within Croatian cattle and should be included in differential diagnostic protocols.

DNA of Theileria orientalis, T. equi and T. capreoli in stable flies (Stomoxys calcitrans)

Background

From a veterinary-medical point of view, the stable fly, Stomoxys calcitrans, is perhaps the economically most important blood-sucking muscoid fly species (Diptera: Muscidae), owing to its worldwide occurrence, frequently high local abundance, direct harm caused to livestock, pet animals and humans, as well as its vector role. Considering the latter in the context of protozoan parasites, the stable fly is a mechanical vector of trypanosomes and Besnoitia besnoiti. However, its role as a vector of piroplasms appears to be seldom studied, despite old data suggesting mechanical transmission of babesiae by dipteran flies.

Methods

In this study 395 stable flies (and one Haematobia stimulans) were collected at a cattle farm with known history of bovine theileriosis, and at further nine, randomly chosen locations in Hungary. These flies were separated according to sex (30 of them also cut into two parts: the head with mouthparts and the thorax-abdomen), followed by individual DNA extraction, then screening for piroplasms by PCR and sequencing.

Results

In stable flies, Theileria orientalis and T. capreoli were identified at the cattle farm and T. equi was identified in three other locations. At the cattle farm, significantly more male stable flies carried piroplasm DNA than females. There was no significant difference between the ratio of PCR-positive flies between the stable (void of cattle for at least two hours) and the pen on the pasture with cattle at the time of sampling. Among dissected flies (29 S. calcitrans and 1 H. stimulans), exclusively the thoracic-abdominal parts were PCR-positive, whereas the head and mouthparts remained negative.

Conclusions

Theileria DNA is detectable in stable flies, in the case of T. orientalis at least for two hours after blood-feeding, and in the case of T. capreoli also in the absence of infected hosts (i.e. roe deer). Male flies rather than females, and thoracic-abdominal (most likely crop) contents rather than mouthparts may pose a risk of mechanical transmission. These data suggest that it is worth to study further the vector role of stable flies in the epidemiology of theilerioses, in which not the immediate, but rather the delayed type transmission seems possible.

A longitudinal study of the effect of Theileria orientalis Ikeda type infection on three New Zealand dairy farms naturally infected at pasture

The aims of this study were to monitor the change in Theileria orientalis Ikeda type infection intensity, haematocrit, milk production and reproduction on three New Zealand spring calving dairy herds, over the 2014-2015 milking season. Three spring calving dairy farms, A, B and C, from high risk (endemically stable), low risk (endemically unstable), and zero risk (disease-free) tick areas respectively were followed through the 2014-2015 milking season. On Farms, A and B, 100 cows were randomly selected at the first visit, and the same cows blood sampled every month thereafter, whilst on Farm C, the whole herd was blood sampled bimonthly (140 cows). Blood samples were tested for haematocrit, by centrifugation, and Ikeda infection intensity, using qPCR. Animals that were Ikeda type PCR positive at the first sampling were described as prevalence cases and cows that were negative at the first sampling and became PCR positive during the sampling period were described as incidence cases. Production and reproduction data were accessed through LIC MINDA® and milk production data was standardised to energy corrected milk (ECM). In addition, the effect of buparvaquone (BPQ) treatment on milk production was estimated on Farm B. The prevalence of infection at the first sampling was 100 % on Farm A, 57 % on Farm B and 26 % on Farm C. The incidence risk of infection over the sampling period on Farms B and C was 25 % and 2 % and the incident rate was 0.026 and 0.002 cases per cow-month respectively. The average infection intensity for prevalence cases on all farms was low throughout the milking season, <7000 Ikeda organisms/μL however, cases of anaemia still occurred. There was no direct effect of infection intensity on milk production or from being a prevalence case compared to an uninfected cow on milk production, across all farms. However, on Farm B there was a loss of 266 kg (95 % CI 82 ̶ 450) ECM (∼20 kg milk solids) for incidence cases and a loss of 458 kg (95 % CI 211 ̶ 710) of ECM for buparvaquone treated cows, compared to uninfected cows. No significant effect of Ikeda infection on reproduction could be shown for Farms B and C, reproductive data for Farm A was not available. The effect of T. orientalis Ikeda type infection on production and reproduction appears to be minimal once animals have passed through the acute phase of infection and reached the chronic, asymptomatic carrier phase of infection.

Evaluation of the natural vertical transmission of Theileria orientalis

Bovine theileriosis, caused by Theileria orientalis, is endemic from East Asia to Oceania. Even though the disease is mainly transmitted by Haemaphysalis ticks, the T. orientalis parasite can also be transmitted vertically. To develop proper control measures, the frequency of each transmission route must be elucidated. However, the frequency of vertical transmission, including transplacental transmission, of T. orientalis in naturally infected cattle is still controversial. This study aimed to clarify the frequency of the vertical transmission of T. orientalis in naturally infected cattle. Blood samples were collected from 204 T. orientalis-infected dams and their 211 newborn calves (including 7 sets of twins) within the first 24 h as well as 30 days after birth. Furthermore, 31 and 24 calves born to T. orientalis-infected and uninfected dams, respectively, were continuously surveyed for infection until 5 months of age. A total of 5 (2.4%) dams were diagnosed with mild anemia, whereas most of the dams were asymptomatic based on hematological examination and clinical signs. PCR analysis was performed on whole blood to determine the presence of T. orientalis in calves, and no calves were PCR positive 0 and 30 days after birth. However, 9.6% and 0% of the calves born to T. orientalis-infected and uninfected dams, respectively, tested positive at 3 and 5 months of age. The sampled calves were fed in-house, and the survey was conducted during the cold season; thus, horizontal transmission through blood-sucking insects rarely occurred. Therefore, the vertical transmission of T. orientalis took as long as 3 months to become detectable by PCR and occurred in approximately 10% of field cattle.

Prevalence studies for Theileria orientalis conducted during the early stages of the 2012 New Zealand epidemic of Theileria associated bovine anaemia

Since 1982 there have been two epidemics of bovine anaemia associated with Theileria orientalis infection (TABA) in New Zealand. The latest and more serious epidemic started in 2012 and is associated with the T. orientalis (Ikeda) type. In 2013 the Ministry for Primary Industries (MPI) carried out several epidemiological investigations on the TABA epidemic, which included a series of on-farm herd prevalence studies. The aims of this paper are to present and summarise the results of these herd prevalence studies. The data were collected from March 2013 to September 2013 and comprised 26 farms. For 21/26 of these farms, a T. orientalis (Ikeda) positive index case of TABA precipitated the follow-up herd prevalence study. Each herd prevalence study involved a random sample of 10 cows for haematocrit, for piroplasm counts (number of Theileria infected RBCs per 1000 RBCs) and for PCR molecular diagnosis. Animals were diagnosed anaemic if the haematocrit ≤0.24. The results showed that for the index cases, the average haematocrit = 0.10 L/L and the average piroplasm count = 10.9 Theileria infected RBCs per 1000 RBCs, and for the herd prevalence studies the average haematocrit = 0.26 and the average piroplasm count = 6.9. The average herd prevalence of T. orientalis (Ikeda) PCR positive cattle and of anaemic cattle was 87% and 26% respectively. For dairy herds (n = 7 herds) it took, on average, 80 days for the within herd prevalence of anaemia to return to zero after the initial diagnosis. In conclusion the prevalence studies showed that infection rates and anaemia rates were already high in herds when the index case of TABA was observed. At the time, these prevalence studies significantly added to our understanding of the epidemiology of the evolving T. orientalis (Ikeda) epidemic and furthermore met the New Zealand MPI objective of being rapid and applied, fit for purpose and completed at a relatively low cost.

The effect of month, farm type and latitude on the level of anaemia associated with Theileria orientalis Ikeda type infection in New Zealand cattle naturally infected at pasture

Commencing in 2012, an epidemic of infectious bovine anaemia associated with Theileria orientalis Ikeda type has been present in New Zealand. The aims of this study were to analyse the temporal and spatial effects of T. orientalis Ikeda type infection on the sample submission rates and haematocrits of infected cattle over the first two years of the New Zealand epidemic. The data were collected from 30/08/2012 to 28/11/2014 and included all samples that met the case definition for Theileria associated bovine anaemia (TABA) and tested positive for T. orientalis Ikeda type by PCR. The sample submission rates by month and farm type were highly seasonal with dairy farm submissions peaking in September a month before beef farm submissions peaked. A second lesser peak of dairy farm submissions in April was absent for beef farms. A mixed effects model was fitted to the data and showed a significant interaction between farm production type (dairy or beef) and month of sampling (p=0.006) and between latitude and month of sampling (p=0.024). The estimated haematocrit, adjusted for month and latitude, for dairy cattle=0.125 (95%CI 0.121-0.129) and for beef cattle=0.151 (95% CI 0.138-0.165), p<0.0001. This research shows that infected beef animals tend to be less severely affected than dairy animals and that the month of sampling and latitude of the sampled farm have significant and interacting effects on the level of anaemia associated with T. orientalis Ikeda type infection.

Using a rule-based envelope model to predict the expansion of habitat suitability within New Zealand for the tick Haemaphysalis longicornis, with future projections based on two climate change scenarios

Haemaphysalis longicornis is the only species of tick present in New Zealand which infests livestock and is also the only competent vector for Theileria orientalis. Since 2012, New Zealand has suffered from an epidemic of infectious bovine anaemia associated with T. orientalis, an obligate intracellular protozoan parasite of cattle and buffaloes. The aim of this study was to predict the spatial distribution of habitat suitability of New Zealand for the tick H. longicornis using a simple rule-based climate envelope model, to validate the model against published data and use the validated model to project an expansion in habitat suitability for H. longicornis under two alternative climate change scenarios for the periods 2046-2065 and 2081-2100, relative to the climate of 1981-2010. A rule-based climate envelope model was developed based on the environmental requirements for off-host tick survival. The resulting model was validated against a maximum entropy environmental niche model of environmental suitability for T. orientalis transmission and against a H. longicornis occurrence map. Validation was completed using the I-similarity statistic and by linear regression. The H. longicornis climate envelope model predicted that 75% of cattle farms in the North Island, 3% of cattle farms in the South Island and 54% of cattle farms in New Zealand overall have habitats potentially suitable for the establishment of H. longicornis. The validation methods showed an acceptable level of agreement between the envelope model and published data. Both of the climate change scenarios, for each of the time periods, projected only slight to moderate increases in the average farm habitat suitability scores for all the South Island regions. However, only for the West Coast, Marlborough, Tasman, and Nelson regions did these increases in environmental suitability translate into an increased proportion of cattle farms with low or high H. longicornis habitat suitability. These results will have important implications for the geographical progression of Theileria-associated bovine anaemia (TABA) in New Zealand and will also be of interest to Haemaphysalis longicornis researchers in Australia, Japan, Korea and New Zealand.

Transplacental transmission of Theileria orientalis occurs at a low rate in field-affected cattle: infection in utero does not appear to be a major cause of abortion

Background

Bovine theileriosis, caused by the haemoprotozoan Theileria orientalis, is an emerging disease in East Asia and Australasia. Previous studies have demonstrated transplacental transmission of various Theileria spp. but molecular confirmation of transplacental transmission of T. orientalis has never been confirmed in the field. In this study, cow-calf (< 48 h old) pairs were sampled across 3 herds; opportunistic samples from aborted foetuses or stillborn calves were also examined. Molecular (multiplex qPCR) and serological (ELISA) methods were used to determine infection prevalence and the presence of anti-Theileria antibodies in each herd. In addition, pregnant heifers and foetal calves were sampled at abattoir and tested for the presence of T. orientalis by qPCR.

Results

The qPCR results indicated that, even though there was a high prevalence of T. orientalis infection in cows, the rate of transplacental transmission to their calves was low, with only one newborn calf from one herd and one foetus from the abattoir testing positive for T. orientalis DNA. Five aborted foetuses and stillborn calves, 3 of which were derived from a herd experiencing a high number of clinical theileriosis cases at the time of sampling, all tested negative for T. orientalis by qPCR. This suggests that in utero infection of calves with T. orientalis may not be a major driver of abortions during theileriosis outbreaks. Temporal monitoring of 20 calves born to T. orientalis-positive mothers indicated that T. orientalis was detectable in most calves between 10 and 27 days post-partum, consistent with prior field studies on adult cattle introduced to Theileria-affected herds. There was a positive correlation between the ELISA ratio of newborn calves and their mothers within 48 h of calving; however, maternal antibodies were only detectable in some calves and only for 4–4.5 weeks post-partum. All calves displayed high parasite loads peaking at 4–8 weeks post-partum, with only some calves subsequently mounting a detectable adaptive antibody response.

Conclusions

These findings indicate transplacental transmission of T. orientalis appears to play only a minor role in persistence of T. orientalis infection in the field; however calves are highly susceptible to developing high level T. orientalis infections at 4–8 weeks of age regardless of whether maternal antibodies are present post-partum.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2166-9) contains supplementary material, which is available to authorized users.

Predicting the potential environmental suitability for Theileria orientalis transmission in New Zealand cattle using maximum entropy niche modelling

The tick-borne haemoparasite Theileria orientalis is the most important infectious cause of anaemia in New Zealand cattle. Since 2012 a previously unrecorded type, T. orientalis type 2 (Ikeda), has been associated with disease outbreaks of anaemia, lethargy, jaundice and deaths on over 1000 New Zealand cattle farms, with most of the affected farms found in the upper North Island. The aim of this study was to model the relative environmental suitability for T. orientalis transmission throughout New Zealand, to predict the proportion of cattle farms potentially suitable for active T. orientalis infection by region, island and the whole of New Zealand and to estimate the average relative environmental suitability per farm by region, island and the whole of New Zealand. The relative environmental suitability for T. orientalis transmission was estimated using the Maxent (maximum entropy) modelling program. The Maxent model predicted that 99% of North Island cattle farms (n=36,257), 64% South Island cattle farms (n=15,542) and 89% of New Zealand cattle farms overall (n=51,799) could potentially be suitable for T. orientalis transmission. The average relative environmental suitability of T. orientalis transmission at the farm level was 0.34 in the North Island, 0.02 in the South Island and 0.24 overall. The study showed that the potential spatial distribution of T. orientalis environmental suitability was much greater than presumed in the early part of the Theileria associated bovine anaemia (TABA) epidemic. Maximum entropy offers a computer efficient method of modelling the probability of habitat suitability for an arthropod vectored disease. This model could help estimate the boundaries of the endemically stable and endemically unstable areas for T. orientalis transmission within New Zealand and be of considerable value in informing practitioner and farmer biosecurity decisions in these respective areas.

Mechanical transfer of Theileria orientalis: possible roles of biting arthropods, colostrum and husbandry practices in disease transmission

Background

The intracellular protozoal parasite Theileria orientalis has rapidly spread across South-eastern Australia, substantially impacting local cattle industries since 2006. Haemaphysalis longicornis appears to be a biological vector in the endemic regions. Mechanical transfer of blood by biting arthropods, in colostrum or iatrogenic transmission though husbandry procedures is another possible mode of transmission. This study assesses the risk of these mechanical modes of transmission.

Methods

Blood was collected from a T. orientalis Ikeda positive Angus steer, and was inoculated into the jugular vein of 9 calves in 3 treatment groups, each with 3 animals. Calves in Group 1 received 10 ml of cryopreserved blood, while those in Groups 2 and 3 received 1 ml (fresh blood) and 0.1 ml (cryopreserved), respectively. An additional three animals remained as negative controls and the donor calf was also followed as a positive control. Blood was collected over 3 months, and analysed via qPCR for the presence of the parasite. Samples of the sucking louse Linognathus vituli were collected opportunistically from calves 5 months after inoculation and tested for T. orientalis. For the colostral transmission study, 30 samples of blood and colostrum were collected from cows at calving in an endemic herd. These samples along with blood from their calves were tested by qPCR for T. orientalis and for antibodies to the major piroplasm surface protein (MPSP).

Results

Eight of the nine inoculated calves became positive for T. orientalis. The prepatent period of these infections was inversely correlated with inoculation dose. All negative control calves remained negative and the positive control calf remained positive.

Samples of L. vituli tested positive for T. orientalis Ikeda, while some samples of colostrum were also shown to be qPCR and anti-MPSP positive. All calves in the colostral study tested qPCR negative although one was antibody-positive.

Conclusions

T. orientalis is capable of being mechanically transferred by intravenous inoculation with small volumes of blood and is detectable up to 5 months post-infection. Animals infected by this means may play a significant role in the transmission of the disease by acting as asymptomatic carriers. Other modes of blood transfer, including biting arthropods and colostral transfer are also possible modes of disease transmission.

An observational study of the vertical transmission of Theileria orientalis (Ikeda) in a New Zealand pastoral dairy herd

Although only recently recognised, Theileria orientalis (Ikeda) is now the most important infectious cause of anaemia in New Zealand cattle. The aim of this study was to test if vertical transmission of T. orientalis (Ikeda) from dam to calf across the placenta occurs in naturally infected New Zealand dairy cattle and to also test whether the infection status of the dam at calving affects the future susceptibility of its offspring to T. orientalis (Ikeda) infection. Dairy cows (n=97) and their calves were sampled at calving; and the calves again at 4 months of age. All samples were measured for haematocrit and screened for T. orientalis genotypes using a multiplex Buffeli, Chitose and Ikeda specific TaqMan assay. Ikeda positive samples were further tested by singleplex PCR in triplicate to calculate the Ikeda infection intensity as genomes/μl of blood from each infected animal. No T. orientalis (Ikeda) infected calves were born to either T. orientalis (Ikeda) infected or uninfected dams. There were 56/97 dams positive for T. orientalis (Ikeda) infection at calving and 79/90 calves positive for T. orientalis (Ikeda) infection at 4 months of age but no effect on calf susceptibility of dam infection status at calving. There was a significant negative effect of infection intensity on haematocrit after controlling for whether the infected animal was a dam or a 4 month old calf. Vertical trans-uterine transmission of T. orientalis (Ikeda) infection is unlikely in chronically infected dairy cows and thus not a factor in the epidemiology of T. orientalis (Ikeda) infection.

Theileria orientalis: a review

Theileria orientalis (also known historically as T. sergenti and T. buffeli) is responsible for benign or non-transforming theileriosis, and exerts its major effect through erythrocyte destruction. The life cycle of T. orientalis is essentially similar to that of other Theileria species, except that the schizonts do not induce transformation and fatal lymphoproliferation. The pathogenesis of anaemia as a result of infection is not clearly established and may be multifaceted. Clinical signs of weakness, reluctance to walk and abortion are early but non-specific indications of disease, particularly if accompanied by a history of cattle being moved. Physical examination may reveal pallor (pale eyes, vaginal mucosa), pyrexia, and elevated heart and respiratory rates. T. orientalis is an economically important parasite of cattle in New Zealand, Australia and Japan, especially where naïve animals are introduced into an endemic area or in animals under stress. Increased awareness of the risks posed by the parasite is required to enable management practices to be implemented to minimise its impact.

Detection of Theileria orientalis genotypes in Haemaphysalis longicornis ticks from southern Australia

Background

Theileria are blood-borne intracellular protozoal parasites belonging to the phylum Apicomplexa. Previously considered a benign parasite in Australia, outbreaks of clinical disease resulting from Theileria orientalis genotypes have been reported in Australia since 2006. Since this time, outbreaks have become widespread in south-eastern Australia, resulting in significant adverse impacts on local dairy and beef industries. This paper provides the first investigation into the possible biological and mechanical vectors involved in the rapid spread of the parasite.

Methods

To identify possible vectors for disease, ticks, biting flies and mosquitoes were collected within active outbreak regions of Gippsland, Victoria. Ticks were collected from cattle and wildlife, and mosquitoes and biting flies were collected in traps in close proximity to outbreak herds. Ticks were identified via DNA barcoding of the mitochondrial cytochrome oxidase I gene. Barcoded ticks were pooled according to species or phylogenetic group and tested for the presence of T. orientalis and the genotypes Ikeda, Chitose and Buffeli using real-time PCR.

Results

DNA barcoding and phylogenetic analysis identified ticks from the following species: Haemaphysalis longicornis, Ixodes holocyclus, Ixodes cornuatus, Ixodes hirsti, and Bothriocroton concolor. Additional Haemaphysalis, Ixodes and Bothriocroton spp. were also identified. Of the ticks investigated, only H. longicornis ticks from cattle carried theilerial DNA, with the genotypes Ikeda, Chitose and Buffeli represented. Mosquitoes collected in close proximity to outbreak herds included; Aedes camptorhynchus, Aedes notoscriptus, Coquillettidia linealis, Culex australicus, and Culex molestus. Low levels of T. orientalis Buffeli genotype were detected in some mosquitoes. The haematophagous flies tested negative.

Conclusions

This is the first demonstration of a potential vector for T. orientalis in the current Australasian disease outbreak.

Population dynamics of Theileria sergenti in persistently infected cattle and vector ticks analysed by a polymerase chain reaction

Theileria sergenti Shintoku stock consists of 2 parasite populations bearing 2 allelic forms of p33/32, an immunodominant piroplasm surface protein. Parasite population changes during parasite passages among cattle and tick vectors, and during persistent infection in individual calves were analysed by using allele-specific polymerase chain reaction (PCR). The parasite DNAs were prepared from piroplasms from calves which had been infected with Shintoku stock by inoculation of sporozoite stabilates or parasitized erythrocytes, and from sporozoite stabilates which had been prepared from Shintoku stock-infected ticks. Changes in a dominant parasite population were demonstrated during transmission from calves to vector ticks and from infected ticks to calves. Parasite population changes were also apparent during persistent infection in cattle over several months, and this change is thought to occur under host immune pressure. The results of this study indicate that expression of diverse forms of p33/32 may play a role in parasite persistence within mammalian hosts and its transmission from tick vector.

International collaborative research: significance of tick-borne hemoparasitic diseases to world animal health

A general review is given of the tick-borne hemoparasitic diseases of greatest economic importance in ruminants, babesiosis, anaplasmosis, theileriosis and cowdriosis, each caused by one or more species of hemoparasites. Most affected are cattle and small ruminants, buffalo are more resistant and little is known regarding camels. The situation varies from one continent or region to another. Innate and breed susceptibility to these diseases are of tremendous importance. Disease in the field cannot be considered separated from the whole complex of tick-borne diseases and from the ticks themselves, particularly if the aim is to attain endemic stability. International coordination is needed now that research funds are scarce. An appendix contains tables with hemoparasites of various domestic animals and notes with background details.