Variation among Bm86 sequences in Rhipicephalus (Boophilus) microplus ticks collected from cattle across Thailand.

Anti-tick vaccines based on recombinant homologues Bm86 and Bm95 have become a more cost-effective and sustainable alternative to chemical pesticides commonly used to control the cattle tick, Rhipicephalus (Boophilus) microplus. However, Bm86 polymorphism among geographically separate ticks is reportedly associated with reduced effectiveness of these vaccines. The purpose of this study was to investigate the variation of Bm86 among cattle ticks collected from Northern, Northeastern, Central and Southern areas across Thailand. Bm86 cDNA and deduced amino acid sequences representing 29 female tick midgut samples were 95.6-97.0 and 91.5-93.5 % identical to the nucleotide and amino acid reference sequences, respectively, of the Australian Yeerongpilly vaccine strain. Multiple sequence analyses of these Bm86 variants indicated geographical relationships and polymorphism among Thai cattle ticks. Two larger groups of cattle tick strains were discernable based on this phylogenetic analysis of Bm86, a Thai group and a Latin American group. Thai female and male cattle ticks (50 pairs) were also subjected to detailed morphological characterization to confirm their identity. The majority of female ticks had morphological features consistent with those described for R. (B.) microplus, whereas, curiously, the majority of male ticks were more consistent with the recently re-instated R. (B.) australis. A number of these ticks had features consistent with both species. Further investigations are warranted to test the efficacies of rBm86-based vaccines to homologous and heterologous challenge infestations with Thai tick strains and for in-depth study of the phylogeny of Thai cattle ticks.

Molecular detection of divergent trypanosomes among rodents of Thailand.

Herpetosoma is a homogenous subgenus of several dozen named species that are often described as morphologically indistinguishable T. lewisi-like parasites. These trypanosomes normally infect rodents and utilize fleas as vectors. Although this trypanosome subgenus is considered non-pathogenic to normal hosts, some of them are on rare occasion reported in association with human disease. Recently, a T. lewisi-like infection was detected in a sick Thai infant, thus the objective of this study was to investigate the prevalence of T. lewisi infections among different rodents indigenous to Thailand in order to identify possible sources of human cases. Blood was collected from a total of 276 rodents trapped from urban and rural areas of three Thai provinces between 2006 and 2007. These samples were processed for DNA isolation and tested with a PCR assay universal for the genus Trypanosoma, followed by internal transcribed spacer 1 (ITS-1) sequence analysis to identify infections in positive samples. Herpetosoma known as T. lewisi-like trypanosomes were present among Rattus (14.3%) and Bandicota (18.0%) rodent species and salivarian trypanosomes closely related to T. evansi were detected in Leopoldamys (20%) and Rattus (2.0%) species. Herpetosoma were prevalent among rodents associated with both human and sylvatic habitats, while three of the four salivaria-positive rodents were from a forest biotope. A Herpetosoma ITS-1 sequence amplified from one of these samples was 97.9% identical to that reported for T. lewisi in an experimentally infected rat and 96.4% identical to the sequence amplified from blood from a Thai infant. Habitats where rodents were collected significantly affect rodent infection, at least for T. lewisi, suggesting that the degree of anthropization may influence the transmission of Trypanosoma spp. These results suggest that multiple Herpetosoma species or strains are enzootic to Thailand, and that Rattus and Bandicota species are possible sources of human exposure to these parasites.

Host surveys, ixodid tick biology and transmission scenarios as related to the tick-borne pathogen, Ehrlichia canis.

The ehrlichioses have been subject to increasing interest from veterinary and public health perspectives, but experimental studies of these diseases and their etiologic agents can be challenging. Ehrlichia canis, the primary etiologic agent of canine monocytic ehrlichiosis, is relatively well characterized and offers unique advantages and opportunities to study interactions between a monocytotropic pathogen and both its vertebrate and invertebrate hosts. Historically, advances in tick-borne disease control strategies have typically followed explication of tick-pathogen-vertebrate interactions, thus it is reasonable to expect novel, more sustainable approaches to control of these diseases as the transmission of their associated infections are investigated at the molecular through ecological levels. Better understanding of the interactions between E. canis and its canine and tick hosts would also elucidate similar interactions for other Ehrlichia species as well as the potential roles of canine sentinels, reservoirs and models of tick-borne zoonoses. This article summarizes natural exposure studies and experimental investigations of E. canis in the context of what is understood about biological vectors of tick-borne Anaplasmataceae.

Cloning and expression of caprine interferon-gamma.

Caprine interferon-gamma (IFN-gamma) cDNA was cloned from mitogen stimulated peripheral blood mononuclear cell (PBMC) RNA utilizing the reverse transcription-polymerase chain reaction (RT-PCR). The cDNA open reading frame (ORF) is 498bp, encoding a putative 166 amino acid (aa) protein (19327Da). The predicted aa sequence homology of caprine IFN-gamma and the corresponding ovine, bovine and cervine cytokine is 98.8%, 95.2% and 92.8%, respectively. IFN-gamma cDNA was subcloned and expressed in two different plasmids under the control of either the human cytomegalovirus (CMV) immediate early promoter or the caprine arthritis-encephalitis virus long terminal repeat (CAEV LTR). Recombinant caprine IFN-gamma (rCaIFN-gamma) secreted by transfected COS-7 cells shared at least two antigenic epitopes with recombinant bovine IFN-gamma (rBoIFN-gamma) and exhibited biological activity in the vesicular stomatitis virus (VSV) cytopathic effect reduction assay. In-vivo expression of IFN-gamma cDNA promoted by the CAEV LTR was confirmed by the intramuscular (IM) injection of Balb/C mice with plasmid followed by Western blot analysis of mouse serum against purified rCaIFN-gamma produced in E. coli.

A novel 20-kilodalton protein conserved in Babesia bovis and B. bigemina stimulates memory CD4(+) T lymphocyte responses in B. bovis-immune cattle.

Acquired immunity against the hemoprotozoan parasite Babesia bovis is believed to depend on activation of antigen-specific CD4(+) T lymphocytes and IFN-gamma production. A strategy was employed to identify potentially protective antigens from B. bovis based on memory CD4(+) T lymphocyte recognition of fractionated merozoite proteins. Fractions of merozoites separated by continuous flow electrophoresis (CFE) that contained proteins of approximately 20 kDa were shown previously to stimulate memory CD4(+) lymphocyte responses in B. bovis-immune cattle with different MHC class II haplotypes. Expression library screening with rabbit antiserum raised against an immunostimulatory 20-kDa CFE fraction identified a 20-kDa protein (Bbo20) that contains a B lymphocyte epitope conserved in geographically distant B. bovis strains. An homologous 20-kDa protein that has 86.4% identity with Bbo20 and contains the conserved B cell epitope was identified in B. bigemina (Bbg20). Southern blot analysis indicated that both Babesia proteins are encoded by a single gene. Antibody against recombinant Bbo20 protein identified the antigen in CFE fractions shown previously to stimulate memory T lymphocyte responses in immune cattle. To verify Bbo20 as an immunostimulatory T lymphocyte antigen, CD4(+) T cell lines were propagated from B. bovis-immune cattle with merozoite antigen and shown to proliferate significantly against recombinant Bbo20 protein. Furthermore, Bbo20-specific CD4(+) T cell clones proliferated in response to several B. bovis strains and produced IFN-gamma. BLAST analysis revealed significant similarity of the Bbo20 and Bbg20 amino acid sequences with the hsp20/alpha-crystallin family.

Humoral immune response of dogs immunized with salivary gland, midgut, or repeated infestations with Rhipicephalus sanguineus.

The antibody (Ab) responses of dogs immunized with adult tick salivary gland (TSG), midgut (TMG), or repeated infestations of Rhipicephalus sanguineus were monitored to determine if there is an association between Ab production and R. sanguineus performance. Tick-naïve dogs were immunized with TSG or TMG and subjected to two challenge infestations. The control group was infested five times at 21-day intervals. The ELISA technique was used to measure Ab levels in sera from these dogs, which expressed different forms of resistance against R. sanguineus. In dogs immunized with TSG or TMG, similar Ab levels were detected against TMG, TSG, muscle, synganglion, and reproductive organs. However, these sera had different Ab levels against egg mass, unfed larvae, fed larvae, and nymph antigens. Ab levels to muscle, nerve, and reproductive antigens were lower than those observed when TMG or TSG antigens were used. Sera from dogs immunized with TMG or TSG responded to most tick stages or tissue antigens, whereas repeated infestation sera showed the lowest response among the three groups.

Development of a molecular probe to baboon interleukin-10 mRNA for in situ hybridization during experimental schistosomiasis.

A nucleic acid probe complementary to baboon interleukin 10 (IL-10) mRNA was developed for in situ hybridization. Highly conserved IL-10 protein sequences from several mammals were aligned to design oligonucleotide primers flanking a 270-bp sequence of the target cDNA. RNA was isolated from stimulated peripheral blood mononuclear cells (PBMC). IL-10 cDNA was reverse-transcribed from the total PBMC RNA and amplified with the polymerase chain reaction (PCR). Cloning and sequencing of the PCR product confirmed it to be of baboon IL-10 origin, with 97.8% identity to human and 100% identity to macaque mRNA sequences. The baboon IL-10 DNA probe hybridized in Southern blots to a 7.9-Kbp or 8.6-Kbp band after digestion of genomic baboon DNA with Bam H1 or Eco R1, respectively. Preliminary results with an antisense riboprobe derived from this sequence showed the presence of IL-10 mRNA in sections of granulomatous tissues.

Detection of Anaplasma marginale (Rickettsiales: Anaplasmataceae) in hemolymph of Dermacentor andersoni (Acari: Ixodidae) with the polymerase chain reaction.

The polymerase chain reaction (PCR) was used to detect Anaplasma marginale in hemolymph collected from live Dermacentor andersoni Stiles ticks. Hemolymph was collected from severed legs of male and female ticks exposed to A. marginale as either nymphs or adults. Heat treatment was found to be the optimum method of hemolymph preparation for PCR. Hemolymph samples were collected and pooled from adult ticks exposed as nymphs on days 0-10 of feeding on a susceptible calf. For male and female ticks exposed as adults, samples were collected as ticks fed 7 d on an infected calf, while being held 9 d between feedings, and during a second feeding of 10 d (or to repletion) when they transmitted the parasite. Hemolymph samples were collected from uninfected ticks at the same times to serve as controls. Anaplasma marginale DNA was amplified with primers BAP-2 (5'-GTATGGCACGTAGTCTTGGGATCA-3') and AL34S (5'-CAGCAGCAGCAAGACCTTCA-3'), which flank a 409-bp fragment of the A. marginale Florida isolate msp1 beta gene. Infected tick hemolymph was PCR-positive for A. marginale at all collection times, including unfed adults infected as nymphs and previously unexposed adults that fed on infected calves for only 1 d. The PCR-based assay of tick hemolymph proved to be a sensitive method for identification of infected ticks, potentially without killing them; it would be well suited for identification of laboratory- or field-infected ticks that could then be used for further studies. The primers used in this assay were also found specific when tested with species of 18 different genera, and universal for 7 A. marginale isolates from diverse geographical areas of the United States.

Detection of Anaplasma marginale (Rickettsiales: Anaplasmataceae) in secretagogue-induced oral secretions of Dermacentor andersoni (Acari: Ixodidae) with the polymerase chain reaction.

The polymerase chain reaction (PCR) was used to detect Anaplasma marginale in secretagogue-induced oral secretions of male and female Dermacentor andersoni Stiles exposed as nymphs or adults by feeding on infected calves. A 409-bp DNA fragment derived from the A. marginale (Florida isolate) msp1 beta gene was amplified with oligonucleotide primers BAP-2 (5'-GTATGGCACGTAGTCTTGGGATCA-3') and AL34S (5'-CAGCAGCAGCAAGACCTTCA-3'). The target DNA was amplified in oral secretions of female ticks exposed to A. marginale as adults and stimulated to secrete by injection of dopamine. Conversely, A. marginale was detected in saliva from prefed female ticks exposed as nymphs only after stimulation with a combination of dopamine, gamma-aminobutyric acid, pilocarpine, and theophylline. Saliva from ticks exposed as nymphs and stimulated with ergot alkaloids did not contain the A. marginale target DNA. Saliva collected after 11 d of feeding from dopamine-stimulated male ticks contained A. marginale DNA. The results indicate that A. marginale is present in tick saliva and suggest that the parasite can be transmitted to cattle via saliva of feeding ixodid ticks. The variable appearance of A. marginale in saliva, regardless of the method used to induce salivation, suggests that transmission of A. marginale may be affected by the physiological state of the tick.

Performance of female Rhipicephalus sanguineus (Acari: Ixodidae) fed on dogs exposed to multiple infestations or immunization with tick salivary gland or midgut tissues.

This investigation compared the effects of repeated infestations to immunization of dogs with tick salivary gland or midgut extracts on the feeding and fecundity performances of female Rhipicephalus sanguineus (Latrielle). In each immunized group, three tick-naive dogs were immunized three times with tick salivary gland or midgut extracts, and twice challenged at 21-d intervals by allowing 80 female and 40 male adult ticks to feed on each host. The repeated infestation group of three naive dogs was infested five times at 21-d intervals by the same numbers of ticks. The repeated infestation group showed a trend of reduced tick performance after the third infestation, but some of the tick performance parameters had recovered by the fifth infestation. Tick attachment was reduced by immunization with either tick salivary gland or midgut extract. Immunization with tick salivary gland extract had the greatest impact on the feeding period and engorgement weight of the female ticks. Immunization with tick midgut extract resulted in the greatest reduction of tick fecundity parameters, which included preoviposition, oviposition, and egg-incubation periods in addition to reduced egg production and egg viability. These results confirm that dogs can become resistant to R. sanguineus, and demonstrate that immunization with tick salivary gland or midgut extract has different effects on tick feeding and fecundity.

Epidemiology of Sarcocystis neurona infections in domestic cats (Felis domesticus) and its association with equine protozoal myeloencephalitis (EPM) case farms and feral cats from a mobile spay and neuter clinic.

Equine protozoal myeloencephalitis (EPM) is a serious neurologic disease in the horse most commonly caused by Sarcocystis neurona. The domestic cat (Felis domesticus) is an intermediate host for S. neurona. In the present study, nine farms, known to have prior clinically diagnosed cases of EPM and a resident cat population were identified and sampled accordingly. In addition to the farm cats sampled, samples were also collected from a mobile spay and neuter clinic. Overall, serum samples were collected in 2001 from 310 cats, with samples including barn, feral and inside/outside cats. Of these 310 samples, 35 were from nine horse farms. Horse serum samples were also collected and traps were set for opossums at each of the farms. The S. neurona direct agglutination test (SAT) was used for both the horse and cat serum samples (1:25 dilution). Fourteen of 35 (40%) cats sampled from horse farms had circulating S. neurona agglutinating antibodies. Twenty-seven of the 275 (10%) cats from the spay/neuter clinic also had detectable S. neurona antibodies. Overall, 115 of 123 (93%) horses tested positive for anti-S. neurona antibodies, with each farm having greater than a 75% exposure rate among sampled horses. Twenty-one opossums were trapped on seven of the nine farms. Eleven opossums had Sarcocystis sp. sporocysts, six of them were identified as S. neurona sporocysts based on bioassays in gamma-interferon gene knockout mice with each opossum representing a different farm. Demonstration of S. neurona agglutinating antibodies in domestic and feral cats corroborates previous research demonstrating feral cats to be naturally infected, and also suggests that cats can be frequently infected with S. neurona and serve as one of several natural intermediate hosts for S. neurona.

Utilization of stress in the development of an equine model for equine protozoal myeloencephalitis.

Neurologic disease in horses caused by Sarcocystis neurona is difficult to diagnose, treat, or prevent, due to the lack of knowledge about the pathogenesis of the disease. This in turn is confounded by the lack of a reliable equine model of equine protozoal myeloencephalitis (EPM). Epidemiologic studies have implicated stress as a risk factor for this disease, thus, the role of transport stress was evaluated for incorporation into an equine model for EPM. Sporocysts from feral opossums were bioassayed in interferon-gamma gene knockout (KO) mice to determine minimum number of viable S. neurona sporocysts in the inoculum. A minimum of 80,000 viable S. neurona sporocysts were fed to each of the nine horses. A total of 12 S. neurona antibody negative horses were divided into four groups (1-4). Three horses (group 1) were fed sporocysts on the day of arrival at the study site, three horses were fed sporocysts 14 days after acclimatization (group 2), three horses were given sporocysts and dexamethasone 14 days after acclimatization (group 3) and three horses were controls (group 4). All horses fed sporocysts in the study developed antibodies to S. neurona in serum and cerebrospinal fluid (CSF) and developed clinical signs of neurologic disease. The most severe clinical signs were in horses in group 1 subjected to transport stress. The least severe neurologic signs were in horses treated with dexamethasone (group 3). Clinical signs improved in four horses from two treatment groups by the time of euthanasia (group 1, day 44; group 3, day 47). Post-mortem examinations, and tissues that were collected for light microscopy, immunohistochemistry, tissue cultures, and bioassay in KO mice, revealed no direct evidence of S. neurona infection. However, there were lesions compatible with S. neurona infection in horses. The results of this investigation suggest that stress can play a role in the pathogenesis of EPM. There is also evidence to suggest that horses in nature may clear the organism routinely, which may explain the relatively high number of normal horses with CSF antibodies to S. neurona compared to the prevalence of EPM.

Sarcocystis neurona infections in raccoons (Procyon lotor): evidence for natural infection with sarcocysts, transmission of infection to opossums (Didelphis virginiana), and experimental induction of neurologic disease in raccoons.

Equine protozoal myeloencephalitis (EPM) is a serious neurologic disease of horses in the Americas and Sarcocystis neurona is the most common etiologic agent. The distribution of S. neurona infections follows the geographical distributions of its definitive hosts, opossums (Didelphis virginiana, Didelphis albiventris). Recently, cats and skunks were reported as experimental and armadillos as natural intermediate hosts of S. neurona. In the present report, raccoons (Procyon lotor) were identified as a natural intermediate host of S. neurona. Two laboratory-raised opossums were found to shed S. neurona-like sporocysts after ingesting tongues of naturally-infected raccoons. Interferon-gamma gene knockout (KO) mice fed raccoon-opossum-derived sporocysts developed neurologic signs. S. neurona was identified immunohistochemically in tissues of KO mice fed sporocysts and the parasite was isolated in cell cultures inoculated with infected KO mouse tissues. The DNA obtained from the tongue of a naturally-infected raccoon, brains of KO mice that had neurological signs, and from the organisms recovered in cell cultures inoculated with brains of neurologic KO mice, corresponded to that of S. neurona. Two raccoons fed mature S. neurona sarcocysts did not shed sporocysts in their feces, indicating raccoons are not likely to be its definitive host. Two raccoons fed sporocysts from opossum feces developed clinical illness and S. neurona-associated encephalomyelitis was found in raccoons killed 14 and 22 days after feeding sporocysts; schizonts and merozoites were seen in encephalitic lesions.

Completion of the life cycle of Sarcocystis neurona.

Sarcocystis neurona is the most important cause of a neurologic disease in horses, equine protozoal myeloencephalitis (EPM). The complete life cycle of S. neurona, including the description of sarcocysts and intermediate hosts, has not been completed until now. Opossums (Didelphis spp.) are definitive hosts, and horses and other mammals are aberrant hosts. In the present study, laboratory-raised domestic cats (Felis domesticus) were fed sporocysts from the intestine of a naturally infected opossum (Didelphis virginiana). Microscopic sarcocysts, with a maximum size of 700 x 50 microm, developed in the muscles of the cats. The DNA of bradyzoites released from sarcocysts was confirmed as S. neurona. Laboratory-raised opossums (D. virginiana) fed cat muscles containing the sarcocysts shed sporocysts in their feces. The sporocysts were approximately 10(-12) x 6.5-8.0 microm in size. Gamma interferon knockout mice fed sporocysts from experimentally infected opossums developed clinical sarcocystosis, and S. neurona was identified in their tissues using S. neurona-specific polyclonal rabbit serum. Two seronegative ponies fed sporocysts from an experimentally-infected opossum developed S. neurona-specific antibodies within 14 days.

Intermediate site of development of Anaplasma marginale in feeding adult Dermacentor andersoni ticks that were infected as nymphs.

The development of Anaplasma marginale in midgut epithelial cells was studied in feeding, transmitting adult Dermacentor andersoni ticks. Laboratory-reared ticks experimentally infected as nymphs were allowed to feed from 1 to 9 days on susceptible calves. Gut tissues from ticks were collected on each day they fed (total, 9 days) and were processed for light and transmission electron microscopy. Colonies of A marginale were abundant during the first 6 days of feeding, after which numbers decreased. Colonies were adherent to the basement membrane of gut cells early during feeding, with resultant flattening of the colonies. Colonies also were seen in muscle cells on the hemocoel side of the basement membrane. Morphologic features of A marginale within muscle cells varied and were similar to those observed in gut cells. In addition, however, a large reticulated form in the colonies was observed in muscle cells and appeared to give rise to small particles by budding. Development of A marginale in muscle cells appears to represent an intermediate site of development between those in gut and in salivary glands.

Transstadial and attempted transovarial transmission of Anaplasma marginale by Dermacentor variabilis.

Transstadial and transovarial transmission of Anaplasma marginale by Dermacentor variabilis were attempted with with ticks exposed to the organism once by feeding as larvae or nymphs, and twice by feeding as larvae and nymphs. Typical colonies of A marginale were in gut tissues of adults that were infected as larvae, larvae and nymphs, and as nymphs; repeated exposure of ticks did not appear to result in an increase in the number of colonies in the gut of subsequently molted adults nor did it affect severity of the clinical disease that developed in cattle they fed on. In contrast, colonies of A marginale were not found in the midgut epithelium of unfed nymphs exposed as larvae, even though companion nymphs transmitted the parasite, causing severe clinical anaplasmosis in susceptible calves. The organism was not transmitted transovarially by F1 larvae or nymphs from the groups exposed as parent larvae, nymphs, larvae and nymphs, and as adults. Some of the calves fed on by F1 progeny had a few erythrocytic marginale bodies that looked suspiciously like A marginale, as well as postchallenge exposure prepatent periods that were longer than other calves in the transovarial transmission study. Sera from these calves were tested for antibody to A marginale, using a highly sensitive immunoblot technique. Antibodies were not detected in any of the sera.

Humoral immune response of dairy cattle immunized with rBm95 (KU-VAC1) derived from Thai Rhipicephalus microplus.

Rhipicephalus (Boophilus) microplus is an important cause of economic losses in Thailand through direct effects of feeding on cattle and pathogen transmission. Current tick control methods rely on expensive chemical acaricides that result in environmental contamination, residues in food animal products and acaricide-resistant ticks. Anti-tick vaccines based on concealed antigens have shown promising results in the control of cattle tick. Thus, recombinant Bm95 (rBm95) from Thai R. microplus (KU-VAC1) was cloned and expressed to test as an anti-tick vaccine in Thailand. The objective of this study was to compare antibody responses induced by KU-VAC1 to that obtained after vaccination with Gavac that is based on the Bm86 homologue. Four groups of six cattle each were immunized with KU-VAC1, Gavac, adjuvant or phosphate-buffered saline, and boosted three times at 21-day intervals. Enzyme-linked-immunosorbent serologic assay were used to measure the humoral antibody responses specific to Thai rBm95. Cattle immunized with either KU-VAC1 or Gavac showed significantly greater antibody production than the controls. Antibody titres were detected after the first immunization and peaked after the seventh week. These results indicated that KU-VAC1 and Gavac are similarly immunogenic, and that further studies are warranted to compare performance parameters of ticks fed on immunized cattle.

Immunization of rabbits with recombinant serine protease inhibitor reduces the performance of adult female Rhipicephalus microplus.

Molecules secreted from the tick salivary gland modulate the vertebrate host immune response, thus representing potential targets for novel tick control measures. Tick salivary gland serine protease inhibitor (Serpin) is one such molecule that may facilitate tick feeding, blood meal digestion and pathogen transmission. The objective of this study was to determine the immunogenicity and protection of recombinant Rhipicephalus (Boophilus) microplus salivary gland Serpin (rSerpin) in rabbits. Rabbits were injected with rSerpin, adjuvant or phosphate-buffered saline (PBS) alone, and challenge infested with 500 R. microplus larvae that were allowed to continuously feed and moult through the adult stage. All immunized rabbits generated antibodies to rSerpin in the second week after immunization. Ticks fed on immunized rabbits resulted in 83% reduction in adult engorgement and 34% reduction in egg mass weight compared with the PBS control. These results indicated that this tick Serpin is immunogenic to rabbits, and suggested that this vaccine candidate antigen can confer protective immunity against cattle ticks in this experimental model.

Pathologic evidence of ehrlichiosis in calves inoculated with Ehrlichia chaffeensis.

An immunocompetent animal disease model based on infection with Ehrlichia chaffeensis would facilitate research toward understanding mechanisms responsible for the broad range of clinical signs associated with human monocytic ehrlichiosis (HME). The adaptability of this model for the experimental feeding of tick species and stages and for testing therapies comparable to those for human diseases are additional advantages of large animal models. Herein, we summarize pathology reports for calves that developed fatal disease after experimental inoculation with E. chaffeensis. Elevated liver enzyme levels and lung pathology among these calves corroborated earlier reports of severe HME. Thus, an experimental disease model based on infection of outbred immunocompetent hosts with E. chaffeensis could be within our grasp for the first time.

Antibiotic clearance of Ehrlichia canis from dogs infected by intravenous inoculation of carrier blood.

Ehrlichia canis is the etiologic agent of canine monocytic ehrlichiosis (CME) and is a useful model for zoonotic tick-borne pathogens, many of which infect dogs. The purpose of this study was to evaluate rifampin and doxycycline regimens for clearance of E. canis infections in addition to alleviation of CME. Beagles were infected with E. canis by intravenous inoculation with carrier blood and treated with either rifampin or doxycycline after the acute phase of CME. Improved hematological values demonstrated that both treatments effectively relieved signs of the disease. Peripheral blood from all dogs became PCR negative after antibiotic treatment, suggesting that these infections were eliminated and that rifampin is an effective alternative chemotherapeutic agent for treatment of CME.