High genetic diversity and differentiation of the Babesia ovis population in Turkey

Babesia ovis is a tick-transmitted protozoan haemoparasite causing ovine babesiosis in sheep and goats leading to considerable economic loss in Turkey and neighbouring countries. There are no vaccines available, therapeutic drugs leave toxic residues in meat and milk, and tick vector control entails environmental risks. A panel of eight mini- and micro-satellite marker loci was developed and applied to study genetic diversity and substructuring of B. ovis from western, central and eastern Turkey. A high genetic diversity (H_e  = 0.799) was found for the sample of overall B. ovis population (n = 107) analyzed. Principle component analysis (PCoA) revealed the existence of three parasite subpopulations: (a) a small subpopulation of isolates from Aydin, western Turkey; (b) a second cluster predominantly generated by isolates from western Turkey; and (c) a third cluster predominantly formed by isolates from central and eastern Turkey. Two B. ovis isolates from Israel included in the analysis clustered with isolates from central and eastern Turkey. This finding strongly suggests substructuring of a major Turkish population into western versus central-eastern subpopulations, while the additional smaller B. ovis population found in Aydin could have been introduced, more recently, to Turkey. STRUCTURE analysis suggests a limited exchange of parasite strains between the western and the central-eastern regions and vice versa, possibly due to limited trading of sheep. Importantly, evidence for recombinant genotypes was obtained in regionally interchanged parasite isolates. Important climatic differences between the western and the central/eastern region, with average yearly temperatures of 21°C versus 15°C, correspond with the identified geographical substructuring. We hypothesize that the different climatic conditions may result in variation in the activity of subpopulations of Rhipicephalus spp. tick vectors, which, in turn, could selectively maintain and transmit different parasite populations. These findings may have important implications for vaccine development and the spread of drug resistance.

Transcriptome and Proteome Response of Rhipicephalus annulatus Tick Vector to Babesia bigemina Infection

A system biology approach was used to gain insight into tick biology and interactions between vector and pathogen. Rhipicephalus annulatus is one of the main vectors of Babesia bigemina which has a massive impact on animal health. It is vital to obtain more information about this relationship, to better understand tick and pathogen biology, pathogen transmission dynamics, and new potential control approaches. In ticks, salivary glands (SGs) play a key role during pathogen infection and transmission. RNA sequencing obtained from uninfected and B. bigemina infected SGs obtained from fed female ticks resulted in 6823 and 6475 unigenes, respectively. From these, 360 unigenes were found to be differentially expressed (p < 0.05). Reversed phase liquid chromatography-mass spectrometry identified a total of 3679 tick proteins. Among them 406 were differently represented in response to Babesia infection. The omics data obtained suggested that Babesia infection lead to a reduction in the levels of mRNA and proteins (n = 237 transcripts, n = 212 proteins) when compared to uninfected controls. Integrated transcriptomics and proteomics datasets suggested a key role for stress response and apoptosis pathways in response to infection. Thus, six genes coding for GP80, death-associated protein kinase (DAPK-1), bax inhibitor-1 related (BI-1), heat shock protein (HSP), heat shock transcription factor (PHSTF), and queuine trna-ribosyltransferase (QtRibosyl) were selected and RNA interference (RNAi) performed. Gene silencing was obtained for all genes except phstf. Knockdown of gp80, dapk-1, and bi-1 led to a significant increase in Babesia infection levels while hsp and QtRibosyl knockdown resulted in a non-significant decrease of infection levels when compared to the respective controls. Gene knockdown did not affect tick survival, but engorged female weight and egg production were affected in the gp80, dapk-1, and QtRibosyl-silenced groups in comparison to controls. These results advanced our understanding of tick-Babesia molecular interactions, and suggested new tick antigens as putative targets for vaccination to control tick infestations and pathogen infection/transmission.

Exposure to Neospora spp. and Besnoitia spp. in wildlife from Israel

Neosporosis and besnoitiosis, caused by cyst-forming protozoa Neospora caninum and Besnoitia besnoiti, respectively, are parasitic infestations of livestock in Israel. These parasites cause significant economic losses in cattle due to reproductive and productive disorders. Both parasites have been detected in several wild ruminant species throughout other regions of the world, while the existence of a sylvatic life cycle in Israel remains uncertain. Thus, a wide panel of 871 sera from two wild carnivores and nine wild ruminant species were tested. All sera were first analysed by MAT for an initial screening and positive samples were confirmed a posteriori by Western blot. Additionally, a complementary IFAT was used for the detection of antibodies against N. caninum. Neospora antibodies were present in six out of the 11 species investigated, whereas Besnoitia antibodies were undetected. Golden jackal, red fox, addax, Arabian oryx, Persian fallow deer, mouflon, mountain gazelle, Nubian ibex, scimitar horned oryx and water buffalo were seropositive against N. caninum infection by IFAT and/or MAT. Moreover, the presence of Neospora spp.-specific antibodies was confirmed by Western blot in golden jackal (6/189; 3.2%), red fox (1/75; 1.3%), Persian fallow deer (13/232; 5.6%), mouflon (1/15; 16.7%), Nubian ibex (22/55; 40%) and water buffalo (12/18; 66.7%). Addax (1/49) and water buffalo (1/18) were MAT-seropositive against B. besnoiti but were seronegative by Western blot. Hence, Neospora sylvatic cycle is present in Israel and may cross over to a domestic life cycle. In contrast, wildlife species investigated are unlikely to present a risk of transmitting Besnoitia to livestock in Israel.

Besnoitia besnoiti lytic cycle in vitro and differences in invasion and intracellular proliferation among isolates

Background

Bovine besnoitiosis, caused by the protozoan Besnoitia besnoiti, reduces productivity and fertility of affected herds. Besnoitiosis continues to expand in Europe and no effective control tools are currently available. Experimental models are urgently needed. Herein, we describe for the first time the kinetics of standardised in vitro models for the B. besnoiti lytic cycle. This will aid to study the pathogenesis of the disease, in the screening for vaccine targets and drugs potentially useful for the treatment of besnoitiosis.

Methods

We compared invasion and proliferation of one B. tarandi (from Finland) and seven B. besnoiti isolates (Bb-Spain1, Bb-Spain2, Bb-Israel, Bb-Evora03, Bb-Ger1, Bb-France, Bb-Italy2) in MARC-145 cell culture. Host cell invasion was studied at 4, 6, 8 and 24 h post infection (hpi), and proliferation characteristics were compared at 24, 48, 72, 96, 120, and 144 hpi.

Results

In Besnoitia spp., the key parameters that determine the sequential adhesion-invasion, proliferation and egress steps are clearly distinct from those in the related apicomplexans Toxoplasma gondii and Neospora caninum. Besnoitia spp. host cell invasion is a rather slow process, since only 50 % of parasites were found intracellular after 3–6 h of exposure to host cells, and invasion still took place after 24 h. Invasion efficacy was significantly higher for Bb-France, Bb-Evora03 and Bb-Israel. In addition, the time span for endodyogeny to take place was as long as 18–35 h. Bb-Israel and B. tarandi isolates were most prolific, as determined by the tachyzoite yield at 72 hpi. The total tachyzoite yield could not be predicted neither by invasion-related parameters (velocity and half time invasion) nor by proliferation parameters (lag phase and doubling time (dT)). The lytic cycle of Besnoitia was asynchronous as evidenced by the presence of three different plaque-forming tachyzoite categories (lysis plaques, large and small parasitophorous vacuoles).

Conclusions

This study provides first insights into the lytic cycle of B. besnoiti isolates and a standardised in vitro model that allows screening of drug candidates for the treatment of besnoitiosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1405-9) contains supplementary material, which is available to authorized users.

Neospora caninum: Chronic and congenital infection in consecutive pregnancies of mice

Neospora caninum, the causative agent of bovine neosporosis is the major cause of abortion in cattle worldwide. The principal route of transmission is via in utero infection of the offspring. Congenitally-infected dams remain persistently infected for life and might undergo abortions in consecutive pregnancies. In the present study, the effect of N. caninum in chronic and congenital infection was examined. CD1 mice were infected intra-peritoneally with live tachyzoites of the NcIs491 isolate, while non-infected mice served as a control. There were no clinical signs of infection observed following inoculation, but high titers of specific anti- N. caninum antibodies were detected. A month after infection, when chronic-infection was established, mice were mated. Fertility, litter size and mortality rate were monitored within two generations of four consecutive pregnancies. During a nine months period of the study all females maintained high level of antibodies, while the non- infected control mice remained seronegative. There was no difference in the fertility rate of the dams, or in the litter size of infected and control mice. Mortality of offspring of the first and second generations of the infected dams was observed within the two first weeks of life. The vertical transmission was analyzed by PCR assay of offspring brains. PCR positive results were found in all 13 litters of the first generation tested during four consecutive pregnancies. The rate of vertical transmission slightly decreased in successive pregnancies being 74.2%, 59.5%, 48.1% and 40% for the first to fourth pregnancies respectively. In the second generation 21 out of 28 litters were found positive and the overall rate of vertical transmission was 28.5%. In chronically and congenitally infected dams N. caninum infection was maintained during all successive pregnancies for about 9 months. The results show that CD-1 outbred mice are a suitable model for studying chronic and congenital neosporosis.

Molecular detection of Babesia ovis in sheep and ticks using the gene encoding B. ovis surface protein D (BoSPD)

The gene encoding Babesia ovis surface protein D (BoSPD) was cloned from B. ovis cDNA library. This gene encodes a polypeptide chain of 155 amino acids, including a predicted 22 amino acid signal peptide. Sequence analysis of the BoSPD suggested that it is a surface protein with no known domains. BLAST analysis followed by multiple alignments showed four orthologs from other Apicomplexan species and suggested that BoSPD is specific for B. ovis. BoSPD-based PCR was then developed to specifically detect B. ovis in experimentally-infected sheep and Rhipicephalus bursa ticks, as well as in field samples. The PCR enabled detection of B. ovis at a calculated parasitemia of 0.0016% and was shown to be specific for B. ovis. Moreover, the BoSPD PCR allowed detection of prolonged subclinical infection in experimentally-infected lambs and in dissected organs of experimentally-infected ticks. Finally, the PCR was used to detect parasitemia in blood samples from naturally-infected sheep and in R. bursa ticks collected from sheep in an infected flock. These results suggest that the BoSPD gene sequence can be used as a specific and sensitive marker, allowing detection of subclinical parasitemia in sheep and in ticks. Based on its predicted properties, BoSPD may be considered as a candidate for anti-B. ovis vaccine development or a target for anti-B.ovis treatment.

First detection of Sarcoptes scabiei from domesticated pig (Sus scrofa) and genetic characterization of S. scabiei from pet, farm and wild hosts in Israel

In this report we describe for the first time the detection of Sarcoptes scabiei type suis mites on domestic pigs in Israel and examine its genetic variation compared with S. sabiei from other hosts. Microscopic examination of skin samples from S. scabiei-infested pigs (Sus scrofa domesticus) revealed all developmental stages of S. scabiei. To detect genetic differences between S. scabiei from different hosts, samples obtained from pig, rabbits (Orictolagus cuniculus), fox (Vulpes vulpes), jackal (Canis aureus) and hedgehog (Erinaceus concolor) were compared with GenBank-annotated sequences of three genetic markers. Segments from the following genes were examined: cytochrome C oxidase subunit 1 (COX1), glutathione-S-transferase 1 (GST1), and voltage-sensitive sodium channel (VSSC). COX1 analysis did not show correlation between host preference and genetic identity. However, GST1 and VSSC had a higher percentage of identical sites within S. scabiei type suis sequences, compared with samples from other hosts. Taking into account the limited numbers of GST1 and VSSC sequences available for comparison, this high similarity between sequences of geographically-distant, but host-related populations, may suggest that different host preference is at least partially correlated with genetic differences. This finding may help in future studies of the factors that drive host preferences in this parasite.

Transmission of Babesia ovis by different Rhipicephalus bursa developmental stages and infected blood injection

In this report, the transmission efficacy of Babesia ovis, the principal causative agent of ovine babesiosis, was studied by infestation of lambs with different Rhipicephalus bursa stages or by injection of infected blood. Infected blood injection induced acute babesiosis in splenectomized lambs, while only mild clinical signs were observed in intact animals. Both splenectomized and intact lambs developed high antibody titer, detectable for at least 180 days post infection. Infestation of splenectomized and intact lambs with infected tick larvae did not induce clinical babesiosis or specific serum response in any of the examined animals. Similarly, infestation of one splenectomized lamb with partially-fed infected R. bursa males did not induce any clinical response or seroconversion. Nymph infestation caused a mild clinical response followed by specific seroconversion, in one out of five lambs. All animals infested with infected unfed adults (males and females) showed mild-to-severe clinical signs 8 to 12 days post infestation. The acute phase was followed by a marked seroconversion. Our results indicate that the principal transmission of B. ovis is performed by adult R. bursa ticks, and that the host reaction can last as long as 6 months following the acute infection.

Propagation of the Israeli vaccine strain of Anaplasma centrale in tick cell lines

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First in vitro culture system for Anaplasma centrale.

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A. centrale infected and grew in two out of 32 tick cell lines tested.

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Potential for safer and more ethical bovine anaplasmosis vaccine.

Anaplasma centrale has been used in cattle as a live blood vaccine against the more pathogenic Anaplasma marginale for over 100 years. While A. marginale can be propagated in vitro in tick cell lines, facilitating studies on antigen production, immunisation and vector-pathogen interaction, to date there has been no in vitro culture system for A. centrale. In the present study, 25 cell lines derived from 13 ixodid tick species were inoculated with the Israeli vaccine strain of A. centrale and monitored for at least 12 weeks by microscopic examination of Giemsa-stained cytocentrifuge smears. Infection of 19 tick cell lines was subsequently attempted by transfer of cell-free supernate from vaccine-inoculated tick cells. In two separate experiments, rickettsial inclusions were detected in cultures of the Rhipicephalus appendiculatus cell line RAE25 28–32 days following inoculation with the vaccine. Presence of A. centrale in the RAE25 cells was confirmed by PCR assays targeting the 16S rRNA, groEL and msp4 genes; sequenced PCR products were 100% identical to published sequences of the respective genes in the Israeli vaccine strain of A. centrale. A. centrale was taken through three subcultures in RAE25 cells over a 30 week period. In a single experiment, the Dermacentor variabilis cell line DVE1 was also detectably infected with A. centrale 11 weeks after inoculation with the vaccine. Availability of an in vitro culture system for A. centrale in tick cells opens up the possibility of generating a safer and more ethical vaccine for bovine anaplasmosis.

Cross-protection between geographically distinct Anaplasma marginale isolates appears to be constrained by limited antibody responses

The rickettsia Anaplasma marginale causes the haemolytic disease bovine anaplasmosis, an economic problem in tropical and subtropical areas worldwide. The closely related but less pathogenic Anaplasma centrale is commonly used as a live vaccine to prevent anaplasmosis, but it can only be produced from infected blood. UFMG1 is a low pathogenic Brazilian strain of A. marginale, which has been shown to protect cattle against a high pathogenic Brazilian isolate. As UFMG1 can be grown in tick cells, the strain was proposed as a possible cell culture-derived vaccine. We have evaluated whether UFMG1 could protect cattle against a geographically distant heterologous strain, using A. centrale vaccination as a standard for comparison. Trial calves were infected with UFMG1, A. centrale or PBS. UFMG1-infected animals were more symptomatic than those infected with A. centrale, but none required treatment. All calves were then challenged with the Israeli A. marginale Gonen strain (one of the most prevalent strain in Israel). The A. centrale group had the mildest symptoms, while UFMG1 and control groups both had a more severe response. Nevertheless, the challenge did not cause life-threatening disease in any group. Animals infected with A. centrale had a significantly higher IgG response than UFMG1, when measured in an ELISA against initial bodies from their homologous strain or Gonen. The level of cross-reactivity of the response to initial infection correlated significantly with reduced symptoms after challenge. In conclusion, UFMG1 had limited effect in preventing disease by the geographically distant heterologous Gonen strain. While the low pathogenicity of the Gonen strain in this trial makes it impossible to conclusively state that UFMG1 would have given no protective effect against more serious disease, the comparatively low IgG response to UFMG1 suggests it would not have been as effective as A. centrale.

Cuticular fatty acid profile analysis of three Rhipicephalus tick species (Acari: Ixodidae)

Cuticular fatty acids (CFA) are important constituents of the arthropod exoskeleton, serving as structural and defense components, and participating in intra-species communication. Here we describe for the first time a comparative analysis of the CFA profiles of three tick species of the genus Rhipicephalus: R. annulatus, R. bursa and R. sanguineus. CFA profiles were determined for R. bursa and R. sanguineus grown both on rabbit or calf, and for R. annulatus grown on calf. CFA composition was compared for each species before and after ethanol treatment, for different hosts of each species, and between the different species. Our data suggest that adsorption of the host's fatty acids changes the apparent CFA composition. Ethanol treatment efficiently removed the unbound fatty acids from the ticks and revealed the actual composition. Comparison between ticks grown on rabbit versus calf showed significant difference in the relative abundance of fatty acids C14 and 9,12-C18:2 for R. bursa, and a difference in the relative abundance of C14 for R. sanguineus. Comparison of the CFA between the three species revealed significant differences in the abundance of fatty acids C16, 9,12-C18:2, 9-C18:1, C18 and C20. Our results show that while the host had a minor effect on CFA composition within each species, significant differences were observed in the CFA profiles of different species. We suggest that CFA profiles may be used to distinguish between related species. CFA analysis can also be used in studies of communication and defense mechanisms in ticks and other arthropods.

Artemisone inhibits in vitro and in vivo propagation of Babesia bovis and B. bigemina parasites

Artemisone was evaluated, in in vitro and in vivo, for control of bovine babesiosis caused by Babesia bigemina and Babesia bovis parasites. In vitro, artemisone reduced parasitemia in a dose-dependent manner: the inhibitory effects increased gradually, reaching a maximum inhibition of 99.6% and 86.4% for B. bigemina and B. bovis, respectively 72 h after initiation of treatment with initial parasitemia of 0.5%. In calves infected with either B. bigemina or B. bovis artemisone treatment was well tolerated and prevented development of acute babesiosis in all animals except for one B. bovis-infected calf. The treatment did not eliminate all blood parasites, and recovered animals carried a persistent low-level infection. Treatment with artemisone may be useful as an alternative drug for preventing the pathology that results from babesiosis, without interfering with acquired immune protection following recovery from an acute babesiosis infection or vaccination.

Neospora caninum: in vivo and in vitro treatment with artemisone

Neosporosis caused by Neospora caninum has global economic, clinical, and epidemiological impacts, mainly in the cattle industry. Currently, there is no useful drug for treatment of neosporosis. This publication is the first to describe the significant benefits that artemisone has on Neospora infections both in vitro and in vivo. Artemisone is a new semi-synthetic 10-alkylamino artemisinin that is superior to other artemisinin derivatives in terms of its significantly higher antimalarial activity, its tolerance in vivo, lack of detectable neurotoxic potential, improved in vivo pharmacokinetics and metabolic stability. Low micromolar concentrations of artemisone inhibited in vitro Neospora development. Prophylactic and post-infection treatment profoundly reduced the number of infected cells and parasites per cell. In the in vivo gerbil model, a non-toxic dose prevented typical cerebral symptoms, in most animals. There were no signs of clinical symptoms and brain PCR was negative. Most treated gerbils produced high specific antibody titer and were protected against a challenge. Overall, artemisone could be considered as a future drug for neosporosis.

Concomitant infection of cattle with the vaccine strain Anaplasma marginale ss centrale and field strains of A. marginale

Bovine anaplasmosis, caused by Anaplasma marginale, the intraerythrocytic rickettsia, is controlled by vaccination with live Anaplasma marginale ss centrale (A. centrale), a subspecies of relatively low pathogenicity. We have experimentally demonstrated that an animal primarily infected with A. marginale, or with the related vaccine subspecies A. centrale can be infected with the heterologous subspecies, and carries both bacteria. The co-infection was detected in experimentally cross-infected calves for up to 3 months after the last inoculation with the heterologous subspecies. The occurrence of characteristic cyclic rickettsemia of A. centrale and A. marginale was observed by examination of Giemsa-stained blood smears, or by the presence of specific rickettsial DNA confirmed in PCR assays based on specific msp1a and msp4 for A. marginale, and on specifically designed msp3 and msp4 primers for A. centrale. Sequence analysis of msp4-specific fragments for each subspecies revealed the presence of dual infection in both calves on days 30 and 60 after cross-inoculation with the heterologous Anaplasma subspecies. The experimental cross-infection of calves clearly demonstrated that the concept of "infection exclusion" does not apply to Anaplasma infection in cattle; as there was no infection exclusion of A. marginale in A. centrale-infected cattle, and vice versa. The present results confirmed our previous findings that cattle grazing in an anaplasmosis-endemic field were subject to concomitant infection with both the vaccine A. centrale and the field A. marginale strains.

Isolation of Neospora caninum from dairy zero grazing cattle in Israel

First Israeli Neospora caninum isolates were obtained from brain tissues of aborted fetuses (NcIs491 and NcIs580) from dairy farms endemic for neosporosis and maintaining cattle on zero grazing. Tissues from different parts of the fetus brains were used to infect Vero cells. Tachyzoites of N. caninum were first observed in cultures from days 30 and 32 after infection. To confirm the identity of the isolated parasites, DNA extracts from brains and cultures were tested by PCR with specific primers based on the Nc5 gene. Specific fragments were amplified by PCR from infected cultures of both fetuses on day 25. Susceptible seronegative gerbils (Meriones tristrami) were inoculated intraperitoneally with 10(3) to 10(5) tenfold dilutions of subculture tachyzoites. The inoculated gerbils developed specific antibodies to N. caninum, with end-point serum dilution of 1:4096 in the IFA assay, whereas no neurological signs or deaths were seen during 4 months of observation.

Seroprevalence of Neospora spp. among asymptomatic horses, aborted mares and horses demonstrating neurological signs in Israel

Sera from 800 asymptomatic horses were examined for the presence of antibodies to Neospora caninum by immunofluorescence antibody test (IFAT). The presence of antibodies to N. caninum was also tested in sera from 52 mares that had aborted and 40 horses exhibiting neurological signs. A total of 95 (11.9%) of the 800 sera had antibodies for Neospora. Significantly higher seropositivity was obtained from horses that had neurological signs (21.2%) and from aborted mares (37.5%). There was significant linear-by-linear association between age and seropositivity. This is the first serologic survey for Neospora spp. antibodies performed on horses from the Middle East and the first to report significant difference in seropositivity between asymptomatic horses and horses exhibiting neurological signs.

Attenuated vaccines for tropical theileriosis, babesiosis and heartwater: the continuing necessity

Overwhelming evidence has accumulated of the effectiveness of immunization with live attenuated vaccines to control tick-borne diseases of livestock. Despite several disadvantages, vaccination with live attenuated organisms against tropical theileriosis, babesiosis and possibly heartwater constitutes one of the most cost-effective intervention strategies. Although great advances have been made through genomics and proteomics research, this has not yet translated into effective non-living vaccines. As a result, there is a continuing necessity to use available live vaccines in tick and tick-borne disease-control strategies adapted to conditions prevailing in many parts of the world.

Identification of midgut and salivary glands as specific and distinct barriers to efficient tick-borne transmission of Anaplasma marginale

Understanding the determinants of efficient tick-borne microbial transmission is needed to better predict the emergence of highly transmissible pathogen strains and disease outbreaks. Although the basic developmental cycle of Anaplasma and Ehrlichia spp. within the tick has been delineated, there are marked differences in the ability of specific strains to be efficiently tick transmitted. Using the highly transmissible St. Maries strain of Anaplasma marginale in Dermacentor andersoni as a positive control and two unrelated nontransmissible strains, we identified distinct barriers to efficient transmission within the tick. The Mississippi strain was unable to establish infection at the level of the midgut epithelium despite successful ingestion of infected blood following acquisition feeding on a bacteremic animal host. This inability to colonize the midgut epithelium prevented subsequent development within the salivary glands and transmission. In contrast, A. marginale subsp. centrale colonized the midgut and then the salivary glands, replicating to a titer indistinguishable from that of the highly transmissible St. Maries strain and at least 100 times greater than that previously associated with successful transmission. Nonetheless, A. marginale subsp. centrale was not transmitted, even when a large number of infected ticks was used for transmission feeding. These results establish that there are at least two specific barriers to efficient tick-borne transmission, the midgut and salivary glands, and highlight the complexity of the pathogen-tick interaction.

LIFE CYCLE OF HEPATOZOON CANIS (APICOMPLEXA: ADELEORINA: HEPATOZOIDAE) IN THE TICK RHIPICEPHALUS SANGUINEUS AND DOMESTIC DOG (CANIS FAMILIARIS)

The life cycle of the apicomplexan protozoon Hepatozoon canis in its natural hosts Rhipicephalus sanguineus (tick) and Canis familiaris (domestic dog) was studied in an experimental infection. Tick nymphs were fed on a naturally infected dog, or they were infected by percutaneous injection of blood. Dogs were inoculated by ingestion of adult ticks containing mature oocysts. Gamonts were in syzygy 24 hr after percutaneous injection of ticks. Early oocysts were detected 96 hr after nymph repletion, and mature oocysts in adult ticks were infective to dogs 40 days postmolt. Merogony was detected in dog bone marrow from 13 days postinoculation (PI) and included meronts containing 20-30 micromerozoites, and a second type with 2-4 macromerozoites. Monozoic cysts were observed in the spleen in conjunction with merogony. Gamontogony with infection of leukocytes by micromerozoites occurred from 26 days PI, and gamont parasitemia, which completed the life cycle, was detected 28 days PI. The length of the life cycle from nymphal attachment to parasitemia in dogs was 81 days. Increased body temperatures were evident from 16 to 27 days PI and paralleled the time of intensive bone marrow merogony. Skeletal pain and recumbency were manifested in 2 dogs. This study further elucidates the life cycle of H. canis and provides a sequential morphologic description of H. canis merogony, gamontogony, and sporogony.

Babesia bigemina: attenuation of an Uzbek isolate for immunization of cattle with live calf- or culture-derived parasites

The virulence of an Uzbek isolate of Babesia bigemina, obtained from infected Boophilus annulatus ticks from an endemic area in Uzbekistan, was attenuated for immunization of cattle with autochthonous calf- or culture-derived parasites in Uzbekistan. After four "slow passages" in vivo the virulence was reduced, as evidenced by the response of calves inoculated with an experimental live frozen vaccine produced from the following passage. The vaccine was safe and protective against homologous virulent challenge under laboratory conditions. The culture-derived experimental vaccine was produced from cultures initiated after 3 passages in vivo followed by 22 passages in vitro. The cultured parasites did not elicit any clinical sign, but inoculated calves seroconverted following vaccination and were protected against the virulent homologous challenge. Both calf- and culture-derived vaccines were safe for cattle grazing in an endemic area in Uzbekistan. Despite the high polymorphism of B. bigemina, as reported from various geographical regions, the Central Asian strain was attenuated similarly to those that form the basis of the existing live B. bigemina vaccines in other parts of the world.

Prevalence and Genetic Diversity of Anaplasma marginale Strains in Cattle in South Africa

Bovine anaplasmosis, caused by the tick-borne rickettsia Anaplasma marginale, is endemic in South Africa and results in considerable economic loss to the cattle industry. This study was designed to characterize strains of A. marginale at the molecular level from cattle raised in communal and commercial farms in the north-eastern and south-western regions of the Free State Province, South Africa, that varied in rainfall and vegetation. Seroprevalence to A. marginale was determined in 755 cattle by an Anaplasma spp. competitive enzyme-linked immunosorbent assay and ranged from 44% to 98% and was similar in both regions. While Anaplasma centrale was not targeted in this study, A. marginale infections were identified by species-specific msp1alpha polymerase chain reaction in 129 of 215 of the samples studied. Similar genetic diversity of A. marginale strains was found in both the north-eastern and south-western regions. The sequences of 29 A. marginalemsp1alpha amplicons from South African strains revealed considerable genetic diversity providing 14 new repeat sequences. However, 42% of MSP1a repeat sequences were not unique to this region. These results indicated the presence of common genotypes between South African, American and European strains of A. marginale. Cattle movement between different parts of South Africa was suggested by the presence of identical A. marginale MSP1a genotypes in north-eastern and south-western regions of the Free State Province. Control strategies for anaplasmosis in South Africa should therefore be designed to be protective against genetically heterogeneous strains of A. marginale.

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).

Isolation of Besnoitia besnoiti from infected cattle in Portugal

Besnoitia besnoiti, an obligate intracellular protozoan parasite belonging to the phylum apicomplexa, is the causative agent of bovine besnoitiosis. Besnoitiosis is responsible for significant losses in the cattle industry of Africa and Mediterranean countries due to the high morbidity rate, abortion and infertility in males. The acute stage of disease is associated with the proliferative forms (tachyzoites) and is characterized by fever, whimpery, general weakness and swelling of the superficial lymph nodes. During the following chronic stage, a huge number of cysts are formed mainly in the subcutaneous tissues. This process is non-reversible, and chronic besnoitiosis is characterized by hyper-sclerodermia, hyperkeratosis, alopecia and, in bulls, atrophy, sclerosis and focal necrosis that cause irreversible lesions in the testis. In this paper we report on the identification of large cysts in the skin of a cow and a bull in Portugal, which presented loss of hair and enlargement and pachydermis all over the body. The observation of a two-layered cyst wall within the host cell, the encapsulation of the host cell by a large outer cyst wall, and the subcutaneous localization of the cysts within the host, were characteristic for B. besnoiti. The parasites were isolated from the infected animals and successfully propagated in Vero cells without prior passages in laboratory animals. Morphological characterization of B. besnoiti tachyzoites and the amplification of the 149 bp segment from the internal transcribed spacer 1 (ITS1), aided with specific primers, confirmed the identification of B. besnoiti.

Emergence of distinct genotypes of Cryptosporidium parvum in structured host populations

Cryptosporidium parvum is an apicomplexan parasite that infects humans and ruminants. C. parvum isolated from cattle in northeastern Turkey and in Israel was genotyped using multiple polymorphic genetic markers, and the two populations were compared to assess the effect of cattle husbandry on the parasite's population structure. Dairy herds in Israel are permanently confined with essentially no opportunity for direct herd-to-herd transmission, whereas in Turkey there are more opportunities for transmission as animals range over wider areas and are frequently traded. A total of 76 C. parvum isolates from 16 locations in Israel and seven farms in the Kars region in northeastern Turkey were genotyped using 16 mini- and microsatellite markers. Significantly, in both countries distinct multilocus genotypes confined to individual farms were detected. The number of genotypes per farm was higher and mixed isolates were more frequent in Turkey than in Israel. As expected from the presence of distinct multilocus genotypes in individual herds, linkage disequilibrium among loci was detected in Israel. Together, these observations show that genetically distinct populations of C. parvum can emerge within a group of hosts in a relatively short time. This may explain the frequent detection of host-specific genotypes with unknown taxonomic status in surface water and the existence of geographically restricted C. hominis genotypes in humans.

Low seroprevalence of antibodies to Neospora caninum in wild canids in Israel

The role of domestic dogs in the epidemiology of Neospora caninum as well as the relationship between N. caninum infection of farm dogs and cattle were demonstrated, however, evidence is scarce regarding the role of wild canids in domestic animal neosporosis. The present study was undertaken to evaluate the role of wild canids in the epidemiology of bovine neosporosis in Israel by analyzing the prevalence of antibodies to N. caninum in wild canids. Sera samples were collected from 114 free ranging wild golden jackals (Canis aureus), 24 red foxes (Vulpes vulpes) and nine wolves (Canis lupus), which were collected in Israel during the years 1999-2004. Of a total of 147 wild canids tested antibodies to N. caninum were only found in two golden jackals with IFAT titers of 1:50, and in one red fox and one wolf with IFAT titer of 1:400. The low seroprevalence found in this study (2.7%) indicated that wild canids probably do not have an important role in the epidemiology of N. caninum in Israel. However, since the diet of different species of wild canids and even diverse populations of the same canid species vary, it is possible that other results might be obtained from specific wild canids populations, which scavenge in the vicinity of infected bovines.

Molecular and serological detection of A. centrale- and A. marginale-infected cattle grazing within an endemic area

A reverse line blot hybridization (RLB) one-stage nested PCR (nPCR) for Anaplasma centrale and a nested PCR for Anaplasma marginale were used to detect infected cattle grazing within an endemic region in Israel. A novel set of PCR primers and oligonucleotide probes based on a 16S ribosomal RNA gene was designed for RLB detection of both Anaplasma species, and the performance of the molecular assays compared. The immunofluorescent antibody test (IFA) was used to detect antibodies to both Anaplasma species, whereas, a highly sensitive and specific competitive enzyme-linked immunosorbent assay (cELISA) was used to detect antibodies in A. centrale-vaccinated cattle. The RLB and the nested PCR procedures showed bacteremia with sensitivity of 50 infected erythrocytes per milliliter. Up to 93% of the A. centrale vaccinates carried specific antibodies that were detected by cELISA, and up to 71% of the vaccinated cattle were found to be naturally infected with A. marginale according to the PCR and the RLB assays. Nevertheless, no severe outbreaks of A. marginale infection occurred among vaccinated herds in this endemic region. It appears that both, molecular tools and serology are useful for evaluation of the vaccine efficacy. In the light of wide natural field infection with A. marginale, strong recommendations to continue the A. centrale vaccination program regime will continue until a new generation of non-blood-based vaccine will be developed.

Genetic diversity of anaplasma species major surface proteins and implications for anaplasmosis serodiagnosis and vaccine development

The genus Anaplasma (Rickettsiales: Anaplasmataceae) includes several pathogens of veterinary and human medical importance. An understanding of the diversity of Anaplasma major surface proteins (MSPs), including those MSPs that modulate infection, development of persistent infections, and transmission of pathogens by ticks, is derived in part, by characterization and phylogenetic analyses of geographic strains. Information concerning the genetic diversity of Anaplasma spp. MSPs will likely influence the development of serodiagnostic assays and vaccine strategies for the control of anaplasmosis.

Vaccination of older Bos taurus bulls against bovine babesiosis

Two separate groups of Bos taurus bulls, one of 106 and the second of 27 animals, imported to Israel from areas free of Babesia bovis and Babesia bigemina, were vaccinated against babesiosis with a bivalent live attenuated vaccine. In light of the fact that routine vaccination is recommended at the weaning age, these bulls--of highly susceptible breeds--were kept under close surveillance to prevent losses that might be caused by severe clinical reactions to their vaccination at the age of 16-18 months. Seven days after vaccination, about one-third of the 106 bulls in the first group developed clinical signs of B. bigemina infection, which peaked at day 9, and then diminished from day 11, when the patent period known for B. bovis infection was observed. Because of the severe clinical responses a total of 36% of the bulls required babesicidal treatment. Despite the treatment Babesia were not sterilized: 33 and 68% of the animals remained PCR positive for B. bigemina and B. bovis, respectively. To mitigate the severe responses to vaccination, the 27 bulls of the second group were vaccinated in two-steps: they were inoculated initially with avirulent culture-derived parasites and then vaccinated with the conventional donor-derived vaccine a month later. None of the bulls in the latter group developed clinical babesiosis, all were serologically positive to B. bigemina, and 67% showed seroconversion to B. bovis. In light of the experience described here, it is suggested that sensitive older cattle be vaccinated against babesiosis by priming them with avirulent in vitro-cultured parasites and then inoculating them with the conventional donor-derived vaccines.

Ultrastructure of Besnoitia besnoiti tissue cysts and bradyzoites

Besnoitia besnoiti is an economically important tissue cyst-forming apicomplexan of cattle in Africa and Israel. Tissue cysts and bradyzoites of B. besnoiti from the skin of a naturally infected bull were studied by transmission electron microscopy. Tissue cysts enclosed host cell and bradyzoites. Bradyzoites were 6-7.5 x 1.9-2.3 microm in size and contained organelles found in coccidian merozoites including numerous micronemes, rhoptries, amylopectin granules, and a posteriorly located nucleus. Enigmatic bodies, characteristically found in Besnoitia sp. bradyzoites, were not observed. Therefore, enigmatic bodies should be removed as a generic character of the bradyzoites of Besnoitia species.

An enzyme-linked immunosorbent assay for antibodies to Hepatozoon canis

Canine hepatozoonosis is a tick-borne protozoal disease caused in the Old World and South America by Hepatozoon canis. An enzyme-linked immunosorbent assay (ELISA) using purified H. canis gamont antigen was applied for the detection of antibodies reactive with H. canis. Evaluation of the ELISA with sera from naturally infected parasitemic dogs indicated that it was sensitive (86%), specific (97%), and comparable to the indirect fluorescent antibody test (IFAT) for the detection of H. canis antibodies. A variable degree of serologic cross-reactivity was found between sera from H. americanum-infected dogs and the H. canis antigen. Dogs experimentally infected with H. canis seroconverted 1-4 weeks post-infection (PI). Antibody levels peaked at 7-9 weeks PI and gradually declined thereafter remaining above the cut-off value until the conclusion of the study 7 months PI. The ELISA will be valuable for serological evaluation of dogs suspected of exposure to H. canis and for epidemiological studies.

Molecular conservation of MSP4 and MSP5 in Anaplasma marginale and A. centrale vaccine strain

Anaplasma centrale msp4 and msp5 genes were cloned and sequenced, and the recombinant proteins were expressed. The identity between Anaplasma marginale and A. centrale MSP4 was 83% in the nucleotide sequences and 91.7% in the encoded protein sequences. A. centrale msp5 nucleotide sequences shared 86.8% identity with A. marginale msp5, and there was 92.9% homology between A. centrale and A. marginale encoded amino acids of the MSP5 protein. Southern blots hybridized with probes derived from the msp4 and msp5 central regions indicate that msp4 and msp5 of A. centrale are encoded by single copy genes. Recombinant MSP4 and MSP5 fusion proteins reacted with anti-A. marginale monoclonal antibodies ANAR76A1 and ANAF16C, respectively, demonstrating the conservation of conformation-sensitive B-cell epitopes between A. centrale and A. marginale. These data demonstrate the structural and antigenic conservation of MSP4 and MSP5 in A. centrale and A. marginale. This conservation is consistent with the cross-protective immunity between A. marginale and A. centrale and supports the development of improved vaccines based upon common outer membrane proteins.

Infection with a proposed new subspecies of Babesia canis, Babesia canis subsp. presentii, in domestic cats

Parasitemia with a large Babesia species was identified in two domestic cats from Israel. One cat, also coinfected with feline immunodeficiency virus and "Candidatus Mycoplasma haemominutum," had profound icterus and anemia which resolved after therapy, whereas a second cat was an asymptomatic carrier. Amplification and sequencing of the 18S rRNA gene, followed by phylogenetic analyses, indicated that infection was caused by Babesia canis. However, the sequences of the internal transcribed and 5.8S rRNA regions of the ribosomal operon used for subspeciation of B. canis were markedly different from the recognized subspecies of B. canis, which include B. canis vogeli, B. canis canis, and B. canis rossi. Based on phylogenetic comparisons of the 18S rRNA gene, 5.8S, and internal transcribed spacer sequences of the isolates from the cats and on the smaller sizes of the merozoite and trophozoite stages of this parasite, which distinguish it from the subspecies of B. canis present in dogs, we propose to identify the novel feline genotype of B. canis described in the present study as a new subspecies, B. canis subsp. presentii.

Proteolytic enzyme activity and attenuation of virulence in Theileria annulata schizont-infected cells

A field isolate of Theileria annulata (Uzbek strain) was obtained from calves infected by Hyalomma anatolicum ticks collected from an endemic region in Uzbekistan. Schizont-infected bovine cells that had been established and propagated in cell culture were examined for attenuation both in vivo, by inoculating cells from various passages into calves, and in vitro for metalloproteinase activity. During serial subcultivation a gradual reduction in virulence and in enzyme activity in cells infected with the Uzbek strain were observed. Complete attenuation of the Uzbek isolate was obtained at about passage 80, and only traces of proteolysis were detected in gelatin substrate gels. In contrast, there was no direct correlation between virulence and enzyme levels in an Israeli strain. While schizonts of the Israeli strain were completely attenuated at passage 80, proteolysis in the substrate gels was detected up to passage 197. Solid immunity was observed in calves immunized with attenuated T. annulata schizonts of the Uzbek strain upon challenge with the homologous H. excavatum sporozoites. For a strain to be used for vaccine production, it appears that animal inoculation still remains the most reliable method to assess the degree of attenuation and protection.

Monozoic cysts of Hepatozoon canis

Small monozoic cysts found in the spleen of dogs infected with Hepatozoon canis are described from naturally and experimentally infected dogs. These forms of H. canis resemble cysts formed by other Hepatozoon species that infect frogs, lizards, and grey squirrels as intermediate hosts. The H. canis cyst stage differs in size and morphology from the large cysts of H. americanum, the second Hepatozoon species known to infect dogs.

Phylogenetic analysis of the erythrocytic Anaplasma species based on 16S rDNA and GroEL (HSP60) sequences of A. marginale, A. centrale, and A. ovis and the specific detection of A. centrale vaccine strain

Phenotypic criteria for the identification of erythrocytic ruminant Anaplasma species has relied on subjective identification methods such as host pathogenicity (virulence for cattle or sheep) and/or the location of Anaplasma inclusion bodies within the host's red cells. Sequence comparisons of new and available GenBank Accessions were investigated to elucidate the relationships among these closely related Anaplasma species. Twenty-one 16S rDNA and GroEL (HSP60) sequences from 13 Anaplasma marginale (South Africa, Namibia, Zimbabwe, Israel, USA, Australia and Uruguay), three A. centrale (South Africa and Japan), two A. ovis (USA and South Africa), and two unknown Anaplasma species isolated from wild ruminants (South Africa), were compared. 16S rDNA maximum-likelihood and distance trees separated all A. marginale (and the two wild ruminant isolates) from the two South African A. centrale (including original vaccine strain, Theiler, 1911). The Japanese A. centrale (Aomori) demonstrated the lowest sequence identity to the remaining erythrocytic Anaplasma species. A. ovis inter-species relationships could not be resolved through the 16S rDNA analyses, whereas strong bootstrap branch support is demonstrated in the GroEL distance tree using A. ovis OVI strain. All erythrocytic Anaplasma species and isolates were confirmed to belong to the same cluster showing strong branch support to Anaplasma (Ehrlichia) phagocytophilum with Ehrlichia (Cowdria) ruminantium and Rickettsia rickettsii serving as appropriate out-groups. Based on groEL sequences, a specific PCR method was developed which amplified A. centrale vaccine (Theiler, 1911) specifically. This study confirms the suitability of 16S rDNA sequences to define genera and demonstrates the usefulness of GroEL sequences for defining species of erythrocytic Anaplasma.

Immunity against Boophilus annulatus induced by the Bm86 (Tick-GARD) vaccine

Friesian cattle were immunized with two inoculations of anti-tick Bm86 (Tick-GARD) vaccine and were challenged 30 or 90 d later with Boophilus annulatus larvae derived from 1.2 g of eggs. No nymphs or adult ticks were found on the immunized cattle during four weeks after challenge. Repeated infestations (2 to 4) with larvae on three other calves during a period of 160 and 390 d after the immunization did not result in development of nymphal and adult stages. In control, non-immunized cattle infested with corresponding batches of larvae 1380 to 4653 replete adult female ticks were collected. Larvae issued from Babesia bovis-infected female ticks transmitted the infection to Bm86-immunized cattle, but the progeny of B. bigemina-infected females did not. Since B. bigemina is transmitted exclusively by nymphal stages of Bo. annulatus these results support the observation that immunity induced by Bm86 affects the larval stage of this tick.

Expression of Anaplasma marginale major surface protein 2 operon-associated proteins during mammalian and arthropod infection

The antigenically variant major surface protein 2 (MSP2) of Anaplasma marginale is expressed from a 3.5-kb operon that contains, in a 5'-to-3' direction, four open reading frames, opag3, opag2, opag1, and msp2. This operon structure was shown to be conserved among genotypically and phenotypically distinct A. marginale, A. ovis, and A. centrale strains. The individual OpAG amino acid sequences are highly conserved among A. marginale strains, with identities ranging from 95 to 99%. OpAG2 and OpAG3 were expressed by all examined A. marginale strains during the acute rickettsemia in the mammalian host and, like MSP2, localize to the bacterial surface. OpAG2 and OpAG3 were also expressed in an infected Ixodes scapularis tick cell line. In contrast, the same A. marginale strains expressed only OpAG2 in two different Dermacentor spp. during transmission feeding. OpAG1 expression was not detected in the infected mammalian host, the infected tick cell line, or within infected Dermacentor ticks. The differential expression of outer membrane proteins from within an operon is a novel finding in tick-transmitted bacteria, and the regulation of expression may be broadly applicable to understanding how the pathogen adapts to the mammalian host-tick vector transition.

Pan-Mediterranean comparison for the molecular detection of Theileria annulata

Seven laboratories decided to compare their molecular diagnostic techniques to identify Mediterranean theileriosis caused by Theileria annulata. Each laboratory used either PCR or PCR and reverse line blot hybridization (RLB) to identify T. annulata. Five laboratories sent their own samples to laboratory 4 to be recoded and passed on to at least two other laboratories. A total of 120 blood samples were analyzed during this study, generating 540 results. Laboratory 1 sent only T. annulata-infected samples (positive control batch), and all the laboratories testing this batch found 100% infection. Laboratory 2 sent only negative samples from a Mediterranean area where T. annulata was unknown, and two laboratories out of three found a few positive samples in these negative samples. For the remaining samples, detection performance was variable. Agreement between laboratories ranged from 21.4 to 91.3%. The overall mismatch between laboratories was around 30% by whatever technique used. This paper describes the methodological parameters that could explain the variation of results.

Babesia bovis and B. bigemina: Persistence of infection in friesian cows following vaccination with live antibabesial vaccines

The persistence of Babesia bovis and B. bigemina infection in Friesian cows, following vaccination with attenuated live vaccines, was assessed by subinoculation of blood into splenectomized calves. Subinoculation tests showed that B. bigemina persisted in two out of 20 cows vaccinated 10 and 46 months previously, and that B. bovis persisted in 11 out of 22 cows vaccinated 10 to 47 months previously. Antibody was detected in five B. bigemina - and 15B. bovis -vaccinated cows. Parasites of both species persisted among the serologically negative cows, whereas blood obtained from serologically positive cows failed to transmit infection. It is concluded that in the absence of reinfection Friesian cattle may spontaneously eliminate B. bigemina and B. bovis infection after various periods following vaccination.

Detection of the Anaplasma centralevaccine strain and specific differentiation from Anaplasma marginale in vaccinated and infected cattle

Bovine anaplasmosis caused by the intraerythrocytic rickettsia Anaplasma marginale is the most prevalent tick-borne disease of cattle worldwide. The most efficient method to control anaplasmosis is by vaccination using live Anaplasma centrale, a closely related species or subspecies of low pathogenicity that is capable of inducing significant protection against the more virulent A. marginale. In the present study, we applied PCR assays to detect and discriminate field infection with A. marginale from A. centrale persistently infected vaccinates. Direct and one-stage nested PCR were based on A. centrale mbp58 specific sequence, with the assay sensitivity level of 0.00001% for nested PCR performed in a single amplification step. Size polymorphism in the A. marginale msp1 alpha gene among strains was used to design a PCR capable of discriminating between the Israel T and NT strains of A. marginale and the encoded MSP1a size polymorphism was confirmed by immunoprecipitation. The detection of A. centrale in 72% of vaccinated field-grazing cattle clearly indicated that the majority of vaccinated cattle remain carriers. A. marginalewas detected in 64% of these vaccinated cattle, demonstrating that, as expected, natural transmission occurs within the endemic region. The lack of severe A. marginaleoutbreaks in this region, despite ongoing transmission, is consistent with protection being provided by widespread vaccination with A. centrale.

Immunological relationship between Neospora caninum and Besnoitia besnoiti

Neospora caninum is a coccidian parasite identified as a major cause of abortion in cattle. A combined infection of N. caninum with another taxonomically related parasite of cattle, Besnoitia besnoiti can occur in geographical areas endemic for both species. Both infections are routinely diagnosed serologically, and incorrect diagnosis could occur if immunological cross-reactivity exists between the two parasites. To investigate the possible degree of cross-reactivity, we compared results obtained with two serological techniques, immunofluorescent antibody test (IFA), and Western blot analysis on known positive and negative sera. The test sera were derived from naturally infected cattle and from experimentally infected Mongolian gerbils. In IFA of bovine sera, no cross-reactvity was detected at the commonly used serum dilution cutoffs of 1:200 for N. caninum and 1:256 for B. besnoiti. However, at 1:64 dilution of both cattle and gerbil sera, anti-N. caninum sera reacted with B. besnoiti antigen in some individual samples. Anti-B. besnoiti serum did not react with N. caninum antigen at any dilution. This low level one directional cross-reactivity was confirmed by Western blot analysis. B. besnoiti antigen showed two immunoreactive bands when probed with anti-N. caninum serum, while no bands appeared when N. caninum antigen was probed with B. besnoiti antiserum. Immunization and challenge experiments in the highly susceptible Mongolian gerbil (Meriones unguiculatus) showed essentially no cross-protection between N. caninum and B. besnoiti.