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

South African Buffalo-Derived Theileria parva Is Distinct From Other Buffalo and Cattle-Derived T. parva

Theileria parva is a protozoan parasite transmitted by the brown-eared ticks, Rhipicephalus appendiculatus and Rhipicephalus zambeziensis. Buffaloes are the parasite's ancestral host, with cattle being the most recent host. The parasite has two transmission modes namely, cattle-cattle and buffalo-cattle transmission. Cattle-cattle T. parva transmission causes East Coast fever (ECF) and January disease syndromes. Buffalo to cattle transmission causes Corridor disease. Knowledge on the genetic diversity of South African T. parva populations will assist in determining its origin, evolution and identify any cattle-cattle transmitted strains. To achieve this, genomic DNA of blood and in vitro culture material infected with South African isolates (8160, 8301, 8200, 9620, 9656, 9679, Johnston, KNP2, HL3, KNP102, 9574, and 9581) were extracted and paired-end whole genome sequencing using Illumina HiSeq 2500 was performed. East and southern African sample data (Chitongo Z2, Katete B2, Kiambu Z464/C12, Mandali Z22H10, Entebbe, Nyakizu, Katumba, Buffalo LAWR, and Buffalo Z5E5) was also added for comparative purposes. Data was analyzed using BWA and SAMtools variant calling with the T. parva Muguga genome sequence used as a reference. Buffalo-derived strains had higher genetic diversity, with twice the number of variants compared to cattle-derived strains, confirming that buffaloes are ancestral reservoir hosts of T. parva. Host specific SNPs, however, could not be identified among the selected 74 gene sequences. Phylogenetically, strains tended to cluster by host with South African buffalo-derived strains clustering with buffalo-derived strains. Among the buffalo-derived strains, South African strains were genetically divergent from other buffalo-derived strains indicating possible geographic sub-structuring. Geographic sub- structuring was also observed within South Africa strains. The knowledge generated from this study indicates that to date, ECF is not circulating in buffalo from South Africa. It also shows that T. parva has historically been present in buffalo from South Africa before the introduction of ECF and was not introduced into buffalo during the ECF epidemic.

Bovine Organospecific Microvascular Endothelial Cell Lines as New and Relevant In Vitro Models to Study Viral Infections

Microvascular endothelial cells constitute potential targets for exogenous microorganisms, in particular for vector-borne pathogens. Their phenotypic and functional variations according to the organs they are coming from provide an explanation of the organ selectivity expressed in vivo by pathogens. In order to make available relevant tools for in vitro studies of infection mechanisms, our aim was to immortalize bovine organospecific endothelial cells but also to assess their permissivity to viral infection. Using transfection with SV40 large T antigen, six bovine microvascular endothelial cell lines from various organs and one macrovascular cell line from an umbilical cord were established. They display their own panel of endothelial progenitor/mature markers, as assessed by flow cytometry and RT-qPCR, as well as the typical angiogenesis capacity. Using both Bluetongue and foot-and-mouth disease viruses, we demonstrate that some cell lines are preferentially infected. In addition, they can be transfected and are able to express viral proteins such as BTV8-NS3. Such microvascular endothelial cell lines bring innovative tools for in vitro studies of infection by viruses or bacteria, allowing for the study of host-pathogen interaction mechanisms with the actual in vivo target cells. They are also suitable for applications linked to microvascularization, such as anti-angiogenic and anti-tumor research, growing fields in veterinary medicine.

Transcriptomic analysis of Ehrlichia ruminantium during the developmental stages in bovine and tick cell culture

The use of bioinformatics tools to search for possible vaccine candidates has been successful in recent years. In an attempt to search for additional vaccine candidates or improve the current heartwater vaccine design, a genome-wide transcriptional profile of E. ruminantium (Welgevonden strain) replicating in bovine endothelial cells (BA886) and Ixodes scapularis embryonic tick cells (IDE8) was performed. The RNA was collected from the infective extracellular form, the elementary bodies (EBs) and vegetative intracellular form, reticulate bodies (RBs) and was used for transcriptome sequencing. Several genes previously implicated with adhesion, attachment and pathogenicity were exclusively up-regulated in the EBs from bovine and tick cells. Similarly, genes involved in adaptation or survival of E. ruminantium in the host cells were up-regulated in the RBs from bovine cells. Thus, it was concluded that those genes expressed in the EBs might be important for infection of mammalian and tick host cells and these may be targets for both cell and humoral mediated immune responses. Alternatively, those exclusively expressed in the RBs may be important for survival in the host cells. Exported or secreted proteins exclusively expressed at this stage are ideal targets for the stimulation of cytotoxic T-lymphocyte (CTL) immune responses in the host.

In vitro culture of a novel genotype of Ehrlichia sp. from Brazil

Ehrlichiae are obligate intracytoplasmic Gram-negative, tick-borne bacteria belonging to the Anaplasmataceae family. Ehrlichioses are considered emerging diseases in both humans and animals. Several members of the genus Ehrlichia have been isolated and propagated in vitro. This study describes the continuous propagation of a Brazilian Ehrlichia sp. isolate in IDE8 tick cells, canine DH82 cells and bovine aorta cells. Initially, the organisms were isolated from the haemolymph of a Rhipicephalus (Boophilus) microplus tick into IDE8 cells. Infected IDE8 cells were brought from Brazil to Germany, where the organisms were continuously propagated in IDE8, DH82 and bovine aorta cells. Bovine aorta cells were infected and propagated for 3 months, corresponding to six subcultures, whereas the other two infected cell lines were kept for more than 1 year. During the cultivation period, 36 and 14 subcultures were carried out in IDE8 and DH82 cell cultures, respectively. Reinfection of IDE8 cells with organisms grown in DH82 cells was achieved. Sequence analysis made with a fragment of the 16S rRNA gene showed that this Ehrlicha sp. is closely related to Ehrlichia canis. However, the maximum likelihood phylogenetic tree shows that it falls in a separate phylogenetic clade from E. canis.

Natural history of Ehrlichia ruminantium

Ehrlichia ruminantium is an obligately intracellular proteobacterium which causes a disease known as heartwater or cowdriosis in some wild, and all domestic, ruminants. The organism is transmitted by ticks of the genus Amblyomma, and it is of serious economic importance wherever the natural vectors occur, an area which includes all of sub-Saharan Africa, and several islands in the Caribbean. The disease was first recognized in South Africa in the 19th century, where its tick-borne nature was determined in 1900, but the organism itself was not demonstrated until 1925, when it was recognized to be a rickettsia, initially named Rickettsia ruminantium. It was thus the first species of what are now known as Ehrlichia to be discovered, and most of the early work to elucidate the nature of the organisms, and its reservoirs and vectors, was performed in South Africa. The next milestone was the development, in 1945, of an infection and treatment regimen to immunize livestock, and this is still the only commercially available "vaccine" against the disease. Then in 1985, after fruitless attempts over many years, the organism was propagated reliably in tissue culture, opening the way for the first application of the newly developed techniques of molecular genetics. From 1990 onwards the pace of heartwater research accelerated rapidly, with notable advances in phylogeny, diagnosis, epidemiology, immunology, and vaccine development. The complete genome sequence was published in 2005, and during the last two years a new understanding has arisen of the remarkable genetic variability of the organism and new experimental vaccines have been developed. Despite all this the goal of producing an effective vaccine against the disease in the field still remains frustratingly just beyond reach. This article summarises our current understanding of the nature of E. ruminantium, at a time when the prospects for the development of an effective vaccine against the organism seem better than at any time since its discovery 83 years ago.

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.

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.