Polyclonal antibody-based immunohistochemical detection of intraleukocytic Theileria parasites in roan and sable antelopes

Theileria parasites commonly infect African wild artiodactyls. In rare roan (Hippotragus equinus) and sable (H. niger) antelopes, Theileria sp. (sable)-associated calf mortalities constrain breeding programs. The pathogenicity of most leukocyte-transforming Theileria spp. originates in their invasion of and multiplication in various mononuclear leukocytes, the transformation of both infected and uninfected leukocytes, and their infiltration of multiple organs. Understanding the pathogenesis of theileriosis can be improved by the use of immunohistochemistry (IHC) to identify the localization of the parasites in tissue sections. Our aim was to develop a reproducible IHC assay to detect leukocyte-associated Theileria parasites in formalin-fixed, paraffin-embedded roan and sable tissues. Polyclonal antibodies were purified from the sera of 5 roans from an area endemic for Theileria sp. (sable) and tested for IHC reactivity in 55 infected and 39 control roan and sable antelopes, and for antigen and species cross-reactivity in an additional 58 cases. The 3 strongest antibodies consistently detected intraleukocytic theilerial antigens in known positive cases in roan and sable antelopes, and also detected other Theileria spp. in non-hippotraginid wild artiodactyl tissues. The antibodies did not cross-react with other apicomplexan protozoa, with the exception of Cryptosporidium. Given that PCR on its own cannot determine the significance of theilerial infection in wild ruminants, IHC is a useful laboratory test with which to confirm the diagnosis in these species.

Safety and efficacy of an attenuated heartwater (Ehrlichia ruminantium) vaccine administered by the intramuscular route in cattle, sheep and Angora goats

Heartwater is an economically important tick-borne disease of ruminants in Africa. The current commercial vaccine uses live Ehrlichia ruminantium from blood of infected sheep, requires antibiotic treatment during infection, needs to be administered intravenously and does not protect against all South African isolates. An attenuated tissue culture vaccine not requiring antibiotic treatment and effective against different field strains in small groups of goats and sheep was reported previously. The objective of the present study was to test safety and efficacy of this vaccine administered by intramuscular (i.m.) inoculation in larger groups of sheep, Angora goats and cattle. Animals were vaccinated via intravenous (i.v.) and i.m. routes and received E. ruminantium homologous challenge by feeding of infected ticks or by i.v. inoculation of infected blood. For vaccine titration in sheep and goats, the optimum safe and efficacious dose was determined using 2 ml equivalent of 10²-10⁵ culture-derived live elementary bodies (EBs). Similarly, the vaccine was titrated in cattle using 5 ml containing 10⁵-10⁷ EBs. Seventy percent of i.v. vaccinated and 9.7% of i.m. vaccinated Angora goats receiving 10⁵ EBs, developed severe reactions to vaccination and were treated. These treated animals and the remaining 90.3% of i.m.- vaccinated goats showed 100% protection against i.v. or tick challenge. Sheep and Angora goats vaccinated i.m. with 10⁴ EBs had no vaccination reactions and were fully protected against i.v. or tick challenge. Similarly, vaccinated cattle (dose 10⁶ EBs) did not react to vaccine inoculation and were fully protected against i.v. or tick homologous challenge. Control non-vaccinated animals reacted severely to challenge and required oxytetracycline treatment. This successfully demonstrated that Angora goats, sheep and cattle can be safely vaccinated with the attenuated E. ruminantium Welgevonden vaccine via the i.m. route, with no clinical reactions to vaccination and 100% protection against virulent i.v. and homologous tick challenge.

Serum-free in vitro cultivation of Theileria annulata and Theileria parva schizont-infected lymphocytes

Theileriosis is a tick-borne disease caused by intracellular protozoa of the genus Theileria. The most important species in cattle are Theileria annulata and Theileria parva. Both species transform leucocyte host cells, resulting in their uncontrolled proliferation and immortalization. Vaccination with attenuated T. annulata-infected cell lines is currently the only practical means of inducing immunity in cattle. Culture media for Theileria spp. typically contain 10%-20% foetal bovine serum (FBS). The use of FBS is associated with several disadvantages, such as batch-to-batch variation, safety and ethical concerns. In this study, the suitability of serum-free media for the cultivation of Theileria-transformed cell lines was examined. Three commercial serum-free media (HL-1, ISF-1 and Hybridomed DIF 1000) were evaluated for their ability to support growth of the T. annulata A288 cell line. The generation doubling times were recorded for each medium and compared with those obtained with conventional FBS-containing RPMI-1640 medium. ISF-1 gave the shortest generation doubling time, averaging 35.4 ± 2.8 hr, significantly shorter than the 52.2 ± 14.9 hr recorded for the conventional medium (p = .0011). ISF-1 was subsequently tested with additional T. annulata strains. The doubling time of a Moroccan strain was significantly increased (65.4 ± 15.9 hr) compared with the control (47.7 ± 7.5 hr, p = .0004), whereas an Egyptian strain grew significantly faster in ISF-1 medium (43.4 ± 6.5 hr vs. 89.3 ± 24.8 hr, p = .0001). The latter strain also showed an improved generation doubling time of 73.7 ± 21.9 hr in an animal origin-free, serum-free, protein-free medium (PFHM II) compared with the control. Out of four South African T. parva strains and a Theileria strain isolated from roan antelope (Hippotragus equinus), only one T. parva strain could be propagated in ISF-1 medium. The use of serum-free medium may thus be suitable for some Theileria cell cultures and needs to be evaluated on a case-by-case basis. The relevance of Theileria cultivation in serum-free media for applications such as vaccine development requires further examination.

In vitro propagation and genome sequencing of three 'atypical' Ehrlichia ruminantium isolates

Three isolates of Ehrlichia ruminantium (Kümm 2, Omatjenne and Riverside), the causative agent of heartwater in domestic ruminants, were isolated in Ixodes scapularis (IDE8) tick cell cultures using the leukocyte fraction of infected sheep blood. All stocks were successfully propagated in IDE8 cells, whereas initiation attempts using endothelial cell cultures were unsuccessful. Therefore, the new technique should be included in any attempt to isolate field strains of E. ruminantium to enhance the probability of getting E. ruminantium isolates which might not be initiated in endothelial cells. Draft genome sequences of all three isolates were generated and compared with published genomes. The data confirmed previous phylogenetic studies that these three isolates are genetically very close to each other, but distinct from previously characterised E. ruminantium isolates. Genome comparisons indicated that the gene content and genomic synteny were highly conserved, with the exception of the membrane protein families. These findings expand our understanding of the genetic diversity of E. ruminantium and confirm the distinct phenotypic and genetic characteristics shared by these three isolates.

Investigations into the carrier-state of Theileria sp. (buffalo) in cattle

The Theileria are apicomplexan parasites transmitted by ticks to vertebrate hosts. Most Theileria species exhibit some form of host or vector specificity, since under endemic conditions only a limited number of tick species act as vectors and not all vertebrate hosts are able to maintain a persistent carrier state. Data for Theileria sp. (buffalo) suggest host specificity for African buffalo (Syncerus caffer). However, T. sp. (buffalo) infections in cattle co-grazing with African buffalo have been reported in Kenya and schizonts were cultured from these infected cattle, raising questions regarding host specificity. A Corridor disease outbreak in 2013 on a ranch in South Africa where cattle co-grazed with Theileria parva and T. sp. (buffalo) infected buffalo presented the opportunity to investigate the possible carrier-state of T. sp. (buffalo) in cattle using real-time PCR analysis. Almost all buffalo (n = 19, 95%) were infected with T. sp. (buffalo) and showed CP values (22-20) indicative of high parasitemia similar to that observed for buffalo in endemic areas. Conversely, only ~14-27% cattle (n = 69, 100, 96) were positive with CP values (31-40) suggesting low parasitemia and a carrier state epidemiology different from African buffalo. Long term monitoring of T. sp. (buffalo) positive cattle showed that most cattle lost their parasitemia or presented fluctuating parasitemia around the PCR assay detection limit. A single splenectomized animal showed a persistent carrier state. The general trends and epidemiology observed in cattle infected with T. sp. (buffalo) are similar to that seen for buffalo-adapted T. parva, for which a defined carrier state in cattle has not yet been proven. The study suggests that cattle may be infected by T. sp. (buffalo) but are not definitive hosts that play an important part in the epidemiology of this parasite.

L-cysteine replaces microaerophilous culture conditions for the in vitro initiation of Theileria equi

Fifty-one blood samples of carrier horses from Theileria equi-endemic localities in South Africa were used for two different methods of in vitro culture initiation of T. equi parasites. Cultures were initiated either in a oxygen-reduced gas mixture or in a 5% CO2-in-air atmosphere in combination with L-cysteine-supplemented culture medium. Out of the 51 blood samples, 43 and 42 cultures, respectively, became culture positive. A possible explanation for this observation is proposed.

In vitro isolation of Ehrlichia ruminantium from ovine blood into Ixodes scapularis (IDE8) cell cultures

Four stocks of Ehrlichia ruminantium (Welgevonden, Ball3, Nonile and Blaauwkrans), the causative agent of heartwater in domestic ruminants, were isolated into Ixodes scapularis (IDE8) tick cells using the leukocyte fraction of the blood of infected sheep. Organisms of two of the E. ruminantium stocks (Welgevonden and Blaauwkrans) propagated in IDE8 cells were also successfully used to infect bovine endothelial cells. All stocks were successfully propagated in IDE8 cells using Dulbecco's modified Eagle's medium nutrient mixture Ham F-12 containing 10% foetal bovine serum (FBS). The technique should be included in any attempt to isolate uncharacterized E. ruminantium stocks.

In vitro cultivation of a south African isolate of an Anaplasma sp. in tick cell cultures

This paper describes the first successful in vitro cultivation of a South African isolate of an Anaplasma sp., initially thought to be Anaplasma marginale, in the continuous tick cell line IDE8. Blood from a bovine naturally infected with A. marginale kept on the farm Kaalplaas (28 degrees 08' E, 25 degrees 38' S) was collected, frozen, thawed and used as inoculum on confluent IDE8 cell cultures. Twenty days after culture initiation small intracellular colonies were detected in a Cytospin smear prepared from culture supernatant. Cultures were passaged on Day 34. Attempts to infect IRE/CTVM18 cell cultures with the Kaalplaas isolate derived from IDE8 cultures failed, whereas a reference stock of A. marginale from Israel infected IRE/CTVM18 tick cell cultures. Attempts to infect various mammalian cell lines (BA 886, SBE 189, Vero, L 929, MDBK) and bovine erythrocytes, kept under various atmospheric conditions, with tick cell-derived Anaplasma sp. or the Israeli strain of A. marginale failed. Molecular characterization revealed that the blood inoculum used to initiate the culture contained both A. marginale and Anaplasma sp. (Omatienne) whereas the organisms from established cultures were only Anaplasma sp. (Omatjenne).

Ehrlichia ruminantium variants which do not cause heartwater found in South Africa

In 1994 a batch of apparently healthy goats was selected for intended export to the USA from a heartwater-free and vector tick-free region of South Africa. The animals were tested serologically for heartwater, using either or both an IFA and an ELISA test, and 52% were found to be serologically positive. A PCR assay based on Ehrlichia ruminantium 16S gene sequences gave positive results for 54% of the animals, suggesting that apparently non-pathogenic E. ruminantium variants existed in this heartwater-free area. To identify and characterise the agents responsible for the positive serological and PCR results, ticks and animal blood samples were collected from two of the three farms involved in the original survey during two successive seasons of expected peak tick activity. Ticks were kept alive for a minimum of 3 weeks to allow digestion of any blood meal before being processed. Over the two seasons, 28% of the livestock and 15% of the ticks sampled were found to be carrying E. ruminantium. E. ruminantium 16S and pCS20 sequences were detected in all of the four tick species collected from the livestock (Rhipicephalus evertsi evertsi, Rhipicephalus evertsi mimeticus, Hyalomma truncatum, Hyalomma marginatum rufipes), suggesting that some of the species may act as vectors. Animals generally carried multiple E. ruminantium 16S genotypes, whereas ticks rarely carried more than one. Infection levels in both animals and ticks were too low to generate a marked response when a blood stabilate was sub-passaged in a clean sheep, preventing the subsequent establishment of any of the organisms in culture.

An attenuated Ehrlichia ruminantium (Welgevonden stock) vaccine protects small ruminants against virulent heartwater challenge

Heartwater is a tick-borne disease of ruminants caused by the intracellular rickettsia Ehrlichia ruminantium. The only commercially available immunization procedure involves infecting animals with cryopreserved sheep blood containing virulent E. ruminantium organisms, followed by treatment with tetracyclines when fever develops. The virulent Welgevonden stock of E. ruminantium was attenuated by continuous propagation of the organisms in a canine macrophage-monocyte cell line (DH82), followed by re-adaptation to grow in a bovine endothelial cell line (BA 886). The material used for the present experiments consisted of the attenuated stock between passages 43 and 64 after re-adaptation. When inoculated into sheep or goats the attenuated organisms did not produce disease, and the only symptom observed was a rise in body temperature in most, but not all, animals. All sheep injected with 2 ml of culture suspension were subsequently found to be fully protected against a lethal needle challenge with the virulent homologous stock or with one of four different heterologous stocks (Ball 3, Gardel, Mara 87/7, Blaauwkrans). Titrations of elementary body suspensions showed that 2ml of a 1:10,000 dilution of culture suspension injected into sheep or goats was still sufficient to trigger an immune response which resisted a lethal needle challenge with the virulent Welgevonden stock. Adult Amblyomma hebraeum ticks, fed as nymphs on sheep immunized with DH82-derived organisms of passage 111, were able to transmit the attenuated stock to a naive sheep, which was found to be protected against a subsequent lethal homologous needle challenge.

Characterization of the pCS20 region of different Ehrlichia ruminantium isolates

Heartwater is a serious tick-borne disease of ruminants caused by the rickettsial organism Ehrlichia (Cowdria) ruminantium. A diagnostic test, targeting the pCS20 genomic region and using PCR amplification and probe hybridization, detects E. ruminantium infection in ticks and animals. However, only the pCS20 sequence of the Crystal Springs E. ruminantium isolate is available and the existence of sequence variation amongst different E. ruminantium isolates has not been determined. Primers were designed from the published pCS20 sequence to obtain sequences of the pCS20 region of various E. ruminantium isolates. These primers were unable to amplify the pCS20 region from genomic Welgevonden DNA and genome walking was used to characterize the pCS20 region. This technique showed that the published pCS20 sequence is from a chimeric clone. Sequences of the pCS20 region of 14 different E. ruminantium isolates were determined after amplification with newly designed primers. Sequencing data indicated that West African E. ruminantium isolates are highly conserved, whereas more variation occurs amongst the southern African isolates. These results facilitated the design of a short pCS20 probe and a large PCR target that improved the sensitivity of the E. ruminantium detection assay.

In vitro infection by Ehrlichia ruminantium of baby hamster kidney (BHK), Chinese hamster ovary (CHO-K1) and Madin Darby bovine kidney (MDBK) cells

The Welgevonden stock of Ehrlichia ruminantium, aetiological agent of heartwater, was propagated in baby hamster kidney (BHK) cells, Chinese hamster ovary (CHO-K1) cells and Madin Darby bovine kidney (MDBK) cells. The cultures required supplementation of the medium with cycloheximide for reliable growth of E. ruminantium. Growth of the Welgevonden stock in BHK and CHO-K1 cells could lead to the development of suspension cultures suitable for the mass production of E. ruminantium for an inactivated elementary body vaccine.

In vitro infection of nonendothelial cells by Ehrlichia ruminantium

The Welgevonden stock of Ehrlichia ruminantium was propagated in eight nonendothelial cell cultures derived from different animal species, both ruminants and nonruminants. The origins of the cells were: bovine fetal testis (BFT), cat ovary (COC), donkey fibroblasts (DFC), sheep fibroblasts (E(2)), horse testis (HTC), lamb fetal testis (LFT), mouse connective tissue (L), and African green monkey kidney (Vero). Four cell culture types (BFT, E(2), LFT and Vero) required supplementation of the medium with cycloheximide for suitable growth of E. ruminantium, whereas the other four (COC, DFC, HTC, and L) did not. Three other stocks of E. ruminantium, Senegal, Ball 3, and Gardel, were also propagated, either in LFT cultures only or in both E(2) and LFT cell cultures. The Welgevonden stock was successfully initiated using E(2) and LFT cell cultures.

Amino acid content of cell cultures infected with Cowdria ruminantium propagated in a protein-free medium

The in vitro culture of Cowdria ruminantium, the causative agent of heartwater in domestic ruminants, was first achieved in 1985. Culture media were usually supplemented with serum and tryptose phosphate broth, both undefined components, contributing to great variability. Recently, we reported about the propagation of stocks of C. ruminantium in a protein-free culture medium referred to as SFMC-23, which is chemically fully defined. To clarify whether the amino acid composition in SFMC-23 is adequate for the in vitro propagation of Cowdria, the Welgevonden stock was propagated in SFMC-23 medium. After a 3-day culture period, samples were taken from uninfected and infected bovine endothelial cell cultures. They were analyzed for free amino acids by the Pico Taq reversed-phase HPLC precolumn derivatization method. Eighteen different amino acids were examined. A considerable decrease in concentration was observed with proline (29%) and glutamine (62%). Further dramatic changes were observed with amino acids which accumulated in the culture medium: aspartic acid, serine, asparagine, tryptophane, glycine, and alanine. The concentration of alanine increased by approximately 660%. The concentrations of all other amino acids analyzed remained within a 25% range, either increasing or decreasing. These results suggest that only glutamine may run short during in vitro cultivation. It seems more likely that accumulation of various amino acids may impact negatively on long-term Cowdria propagation.

The Kümm isolate of Ehrlichia ruminantium: in vitro isolation, propagation and characterization

An effective culture system for Ehrlichia (Cowdria) ruminantium comb. nov. was first established in 1985 and many stocks were subsequently isolated and propagated in vitro. A notable exception, however, was the Kümm isolate that resisted all attempts at in vitro culture until the successful experiment described here. In one experiment white blood cells were harvested from heparinized blood derived from a sheep infected with the Kümm isolate. The cells were added to DH 82 cells and incubated at 37 degrees C. The high metabolic activity of the DH 82 cells necessitated that cell growth be retarded by the addition of cycloheximide. Colonies were first detected 19 days after culture initiation and, once the cultures were established, they could be passaged every 3 days. Bovine and sheep endothelial cells were readily infected with culture supernatant obtained from the infected DH 82 cells. In a further experiment another sheep was infected, using a higher dose of the same batch of Kümm stabilate, and we attempted to infect several different cell lines: these were DH 82 cells, bovine aorta (BA 886) cells, sheep brain endothelial (SBE 189) cells and sheep fibroblastoid cells (E2). Ten days after culture initiation only the E2 cells had become positive for E. ruminantium. Culture supernatant from the first cultured isolate (Kümm-1) was less virulent for mice than that of the second cultured isolate (Kümm-2) which killed all mice. Upon molecular characterization with E. ruminantium 16S probes we found that Kümm-1 hybridized with a Senegal 16S genotype probe, whereas Kümm-2 hybridized only with an Omatjenne 16S genotype probe. The original stabilate used to infect the sheep hybridized with both probes. These results clearly indicate that two different stocks had been isolated in culture.

Continuous in vitro propagation of Cowdria ruminantium (Welgevonden stock) in a canine macrophage-monocyte cell line

The Welgevonden stock of Cowdria ruminantium, aetiologic agent of heartwater, was continuously propagated in DH82 cells, a continuous canine macrophage-monocyte cell line. Cultures of DH82 cells were readily infected provided that the culture medium was supplemented with cycloheximide. Cultures were split at regular 3-day intervals and infection rates ranged between 60% and 95%. Cultures were continuously propagated through more than 125 passages over a period of more than one year.

A chemically defined medium for the growth of Cowdria ruminantium

Chemically defined media, termed SFMC-23 and SFMC-36, were devised for the in vitro culture of Cowdria ruminantium, the causative agent of heartwater in domestic ruminants. Both media were based on Dulbecco's modified Eagle's medium nutrient mixture Ham F-12 (DME/F-12) containing various supplements. Medium SFMC-23 and SFMC-36 supported the long-term growth of the Welgevonden stock of C. ruminantium for a total of 55 and 28 passages, respectively, with regular passage intervals of 3 days. Using SFMC-23, split ratios varied from 5-10, depending on which host cell line was used. Other stocks of C. ruminantium (Sankat, Blaauwkrantz, Senegal) were successfully propagated for a test period of ten passages.

Serum-free media for the in vitro cultivation of Cowdria ruminantium

The in vitro culture of Cowdria ruminantium, the causative agent of heartwater in domestic ruminants, was first achieved in 1985; since then, most groups working with this culture system have used media which were supplemented with serum and, in addition, most of them contained tryptose phosphate broth. These undefined products vary from batch to batch and often fail to support the growth of C. ruminantium. We are therefore working towards the development of a completely chemically defined medium for Cowdria culture. We attempted the propagation of the Welgevonden stock of C. ruminantium in bovine endothelial cell cultures in a variety of serum-free culture media. Four synthetic media gave unsatisfactory results, these were: SFRE-199, Iscove's modified Dulbecco's medium, Dulbecco's modified Eagle's medium, and Leibovitz L-15. These media were all supplemented with a proprietary solution A (components solution A of the HL-1 medium kit, containing transferrin, testosterone, sodium selenite, ethanolamine, saturated and unsaturated fatty acids, and stabilizing proteins). Three other serum-free media did support the growth of C. ruminantium: a modified HL-1 medium, Dulbecco's modified Eagle's medium nutrient mixture Ham F-12 (DME/F-12), and RPMI 1640. The chemical composition of DME/F-12 and RPMI 1640 are published, but not that of the HL-1 medium. Each of these media was supplemented with proprietary solution A. Various supplements were investigated as alternative to the incompletely specified solution A; bovine lipoproteins and bovine transferrin were identified as essential supplements which effectively replaced compound solution A. C. ruminantium was propagated in the three growth-supportive media for at least 10 passages.

In vitro isolation and cultivation of Cowdria ruminantium under serum-free culture conditions

Three stocks of Cowdria ruminantium, the causative agent of heartwater in domestic ruminants, were propagated in bovine endothelial cells in a serum-free culture medium. The Vosloo, Welgevonden and Senegal stocks were propagated for a period of more than 203, 134, and 43 days, respectively. Two of the C ruminantium stocks (Vosloo and Senegal) were also successfully initiated under serum-free culture conditions. The serum-free medium consisted of a modified HL-1 medium. The Senegal stock was successfully propagated in Dulbecco's modified Eagle's medium nutrient mixture Ham F-12 containing 10 per cent fetal bovine serum.