Experimental transmission of Babesia microti by Rhipicephalus haemaphysaloides

Molecular detection of tick-borne piroplasmids in camel blood samples collected from Cairo and Giza governorates, Egypt

Piroplasmosis, a tick-borne disease affecting livestock, including camels, is caused by intracellular apicomplexan parasites belonging to the order Piroplasmida. Despite its importance, there's limited research on piroplasmosis among Egyptian camels. This study aimed to fill this gap by investigating tick-borne piroplasmids in camels from Cairo and Giza Governorates. Out of 181 blood samples collected between October 2021 and March 2022 from apparently healthy one-humped camels (Camelus dromedarius), PCR assays revealed a 41.4 % infection rate with various piroplasmids. Detected species included B. bovis (17.7 %), B. bigemina (12.2 %), B. caballi (8.3 %), B. naoakii (11.6 %), B. microti (1.7 %), T. equi (4.4 %), and Theileria spp. (28.7 %). Phylogenetic analysis revealed the first detection of T. equi genotype E in Egypt and identified a novel B. caballi genotype. Additionally, B. microti isolates were identified as the US-type. These findings shed lights on piroplasmosis among Egyptian camels, and provide valuable information for devising effective control strategies, especially B. microti, a pathogen with potential human health risks.

Haemaphysalis flava ticks as a competent vector of severe fever with thrombocytopenia syndrome virus

Severe fever with thrombocytopenia syndrome virus (SFTSV), a tick-borne Bunyavirus, causes an emerging hemorrhagic fever in humans with a high fatality in Asia. The tick vectors and hosts of SFTSV are not well studied. We evaluated SFTSV transmission in laboratory reared Haemaphysalis flava ticks. RT-PCR demonstrated that after acquisition feeding in SFTSV-infected rabbits, 10 % (4/40) engorged larvae, 25% (5/20) engorged nymphs, and 50% (5/10) engorged females of H. flava became SFTSV RNA positive; after engorged larvae and nymphs molted into nymphs and adults, respectively, 12.5% (3/24) newly molted nymphs and 20% (2/10) newly molted adults were SFTSV RNA positive. Among 30 engorged females that oviposited, 10% (3/30) clutches of eggs and 3.3% (1/30) colonies of larvae were RNA positive for SFTSV. RT-PCR also showed that 6 days after being infested with SFTSV-infected ticks, 100% (3/3) rabbits infested with larvae, 100% (2/2) rabbits infested with nymphs, and 100% (2/2) rabbits infested with adult ticks became SFTSV RNA positive. In conclusion, H. flava can acquire SFTSV from infected rabbits by feeding; there is transstadial and transovarial transmission of the virus and all three stages of H. flava can transmit SFTSV to rabbits by feeding. Thus, H. flava tick is an effective vector of SFTSV and may play a role in the transmission of SFTSV in wild animals and humans.

Infection rates, species diversity, and distribution of zoonotic Babesia parasites in ticks: a global systematic review and meta-analysis

Zoonotic Babesia species are emerging public health threats globally, and are the cause of a mild to severe malaria-like disease which may be life threatening in immunocompromised individuals. In this study, we determine the global infection rate, distribution, and the diversity of zoonotic Babesia species in tick vectors using a systematic review and meta-analysis. We used the random-effects model to pool data and determined quality of individual studies using the Joanna Briggs Institute critical appraisal instrument for prevalence studies, heterogeneity using Cochran's Q test, and across study bias using Egger's regression test. Herein, we reported a 2.16% (3915/175345, 95% CI: 1.76-2.66) global infection rate of zoonotic Babesia species (B. divergens, B. microti, and B. venatorum) in tick vectors across 36 countries and 4 continents. Sub-group infection rates ranged between 0.65% (95% CI: 0.09-4.49) and 3.70% (95% CI: 2.61-5.21). B. microti was the most prevalent (1.79%, 95% CI: 1.38-2.31) species reported in ticks, while Ixodes scapularis recorded the highest infection rate (3.92%, 95% CI: 2.55-5.99). Larvae 4.18% (95% CI: 2.15-7.97) and females 4.08% (95% CI: 2.56-6.43) were the tick stage and sex with the highest infection rates. The presence of B. divergens, B. microti, and B. venatorum in tick vectors as revealed by the present study suggests possible risk of transmission of these pathogens to humans, especially occupationally exposed population. The control of tick vectors through chemical and biological methods as well as the use of repellants and appropriate clothing by occupationally exposed population are suggested to curtail the epidemiologic, economic, and public health threats associated with this emerging public health crisis.

Experimental Infection of Ticks: An Essential Tool for the Analysis of Babesia Species Biology and Transmission

Babesiosis is one of the most important tick-borne diseases in veterinary health, impacting mainly cattle, equidae, and canidae, and limiting the development of livestock industries worldwide. In humans, babesiosis is considered to be an emerging disease mostly due to Babesia divergens in Europe and Babesia microti in America. Despite this importance, our knowledge of Babesia sp. transmission by ticks is incomplete. The complexity of vectorial systems involving the vector, vertebrate host, and pathogen, as well as the complex feeding biology of ticks, may be part of the reason for the existing gaps in our knowledge. Indeed, this complexity renders the implementation of experimental systems that are as close as possible to natural conditions and allowing the study of tick-host-parasite interactions, quite difficult. However, it is unlikely that the development of more effective and sustainable control measures against babesiosis will emerge unless significant progress can be made in understanding this tripartite relationship. The various methods used to date to achieve tick transmission of Babesia spp. of medical and veterinary importance under experimental conditions are reviewed and discussed here.

Animal reservoirs of zoonotic Babesia species: A global systematic review and meta-analysis of their prevalence, distribution and species diversity

Zoonotic babesiosis caused by Babesia divergens, B. microti and B. venatorum is a vector-borne protozoan zoonosis of increasing public health importance worldwide. A complex system of animal reservoirs including a wide range of mammals and a limited number of birds play a central role in maintaining the infection. Governed by the PRISMA guidelines, we conducted a systematic review and meta-analysis to determine the global prevalence, distribution and the diversity of zoonotic Babesia species in animal reservoirs. We pooled data using the random-effects model and determined quality of individual studies, heterogeneity and across study bias using the Joanna Briggs Institute critical appraisal instrument for prevalence studies, Cochran's Q-test and Egger's regression test respectively. Seventy nine studies from 29 countries reported a total 9311 positive cases of zoonotic Babesia infections from 46,649 animal reservoirs, yielding an overall estimated prevalence of 12.45% (95% CI: 10.09-15.27). Continental prevalence ranged between 8.55 (95% CI: 1.90-31.11) in Africa and 27.81% (95% CI: 21.25-35.48) in North America. Estimated prevalence in relation to country income levels, methods of diagnosis, study periods, sample sizes and reservoir categories ranged between 4.97 (95% CI: 1.80-13.00) and 30.12% (95% CI: 22.49-39.04). B. divergens was the most prevalent (12.50%, 95% CI: 8.30-18.39) of the 3 species of zoonotic Babesia reported in animal reservoirs. Zoonotic Babesia infections are prevalent in animal reservoirs across the world with the highest prevalence in North America and domestic animals. B. microti had the widest geographic distribution. We recommend tick control as well as strategic and prophylactic treatment against these parasites in animal reservoirs to curtail the economic losses associated with zoonotic Babesia species and possible transmission to humans.

Detection of Multiple Intracellular Bacterial Pathogens in Haemaphysalis flava Ticks Collected from Hedgehogs in Central China

Tickborne intracellular bacterial pathogens including Anaplasma, Coxiella burnetti, Ehrlichia, and Rickettsia cause emerging infectious diseases worldwide. PCR was used to amplify the genes of these pathogens in Haemaphysalis flava ticks collected from hedgehogs in Central China. Among 125 samples including 20 egg batches, 24 engorged females, and 81 molted male and female adult ticks, the DNA sequences and phylogenetic analysis showed that the minimum infection rate of the ticks was 4% (5/125) for A. bovis, 3.2% (4/125) for C. burnetti, 9.6%, (12/125) for E. ewingii, and 5.6% for Rickettsia including R.japonica (3.2%, 4/125) and R. raoultii (2.4%, 3/125), respectively. The prevalence of these pathogens was significantly higher in dead engorged females (83.3%, 20/24) than in eggs (5%, 1/20) and molted ticks (8.6%, 7/81). Our study indicated that H. flava ticks could be infected with multiple species of tickborne pathogens including Anaplasma, C. burnetti, Ehrlichia, and Rickettsia in Central China, and the prevalence of these pathogens was reduced during transovarial and transstadial transmission in ticks, suggesting that ticks may not be real reservoirs but only vectors for these tickborne pathogens.

Challenges in Tick-Borne Pathogen Detection: The Case for Babesia spp. Identification in the Tick Vector

The causative agents of Babesiosis are intraerythrocytic protozoa of the genus Babesia. Babesia parasites are present around the world, affecting several mammals including humans, pets and livestock, hence its medical and veterinary relevance. Babesia spp. detection in its invertebrate host is a main point in understanding the biology of the parasite to acquire more knowledge on the host–Babesia–vector interactions, as increasing knowledge of the Babesia lifecycle and babesiosis epidemiology can help prevent babesiosis outbreaks in susceptible mammals. The aim of the present review is to highlight the newest findings in this field, based on a bibliographic compilation of research studies recently carried out for the detection of the main Babesia species found in tick vectors affecting mammalian hosts, including the different tick stages such as adult ticks, larvae, nymphs and eggs, as well as the detection method implemented: microscopic tools for parasite identification and molecular tools for parasite DNA detection by conventional PCR, nested-PCR, PCR-RFLP, PCR-RLB hybridization, real time-PCR, LAMP and RAP assays. Although molecular identification of Babesia parasites has been achieved in several tick species and tissue samples, it is still necessary to carry out transmission experiments through biological models to confirm the vectorial capacity of various tick species.

A cysteine protease of Babesia microti and its interaction with tick cystatins

Babesiosis is a tick-borne protozoonosis caused by Babesia, which can cause fever, hemolytic anemia, hemoglobinuria, and even death. Babesia microti is a parasite found in rodents and can be pathogenic to humans. In this study, the full-length cDNA of a B. microti cysteine protease (BmCYP) was expressed and the recombinant rBmCYP protein analyzed and characterized. BmCYP is encoded by an ORF of 1.3 kb, with a predicted molecular weight of 50 kDa and a theoretical pI of 8.5. The amino acid sequence of BmCYP exhibits an identity of 32.9 to 35.2% with cysteine proteases of Babesia ovis, Babesia bovis, and Theileria, respectively. The results of the proteinase assays show that rBmCYP has cysteine protease enzymatic activity. In addition, we demonstrate that tick cystatins rRhcyst-1 and rRhcyst-2 were able to effectively inhibit the activity of rBmCYP; the inhibition rates were 57.2% and 30.9%, respectively. Tick cystatins Rhcyst-1 and Rhcyst-2 were differentially expressed in ticks that fed on Babesia-infected mice relative to non-infected control ticks. Our results suggest that BmCYP is a functional enzyme with cysteine protease enzymatic activity and may be involved in tick-B. microti interactions.

A family of serine protease inhibitors (serpins) and its expression profiles in the ovaries of Rhipicephalus haemaphysaloides

Serpins are evolutionarily conserved serine protease inhibitors found in many organisms. In arthropods, serpins are involved in feeding, development, oviposition, anti-coagulation and innate immune responses. We characterized of 11 serpins in the tick Rhipicephalus haemaphysaloides. These serpins have orthologous genes in other ticks, as indicated by phylogenetic analysis. Analysis of the reactive center loop and hinge regions of the protein sequences indicated that RHS7 encodes proteins that may lack proteinase inhibitor activity. All R. haemaphysaloides serpins had high amino acid sequence identities to Rhipicephalus microplus serpins. Tissue and temporal transcriptional profiling of eight R. haemaphysaloides serpins located in the ovaries demonstrated that they are transcribed during feeding and oviposition. These suggested their participation in the regulation of tick physiology. Immune serum from rabbits repeatedly infested with larvae, nymphs and adults of R. haemaphysaloides can recognize multiple recombinant serpins, respectively. After gene silencing, the blood feeding to repletion time was significantly longer and the 24 h attachment rate was significantly lower in the RHS3 and RHS7 knock down groups. The RHS9 and RHS11 silenced ticks had significant reduction in repletion time and egg-laying rate. Egg hatchability was significantly decreased in RHS4, RHS5 and RHS9 silenced ticks. All groups had significant reductions in engorged body weight. This study increases information on the serpins of R. haemaphysaloides and suggests that some RHSs are potential targets for development of tick vaccines.

Inclusion of PD-L1 into a recombinant profilin antigen enhances immunity against Babesia microti in a murine model

Pathogens and cancer cells employ the programmed cell death-Ligand 1 (PD-L1)/ programmed cell death-1 (PD-1) signaling pathway to inhibit the immune response. Hence, blockade of PD-L1/PD-1 recognition through monoclonal antibodies enhances the immune response. Antibodies that block PD-L1 and PD-1 binding have been used for the prevention and therapy of human pathogenic diseases, but have not yet been evaluated for the treatment of infectious diseases of livestock. In the present study, a recombinant vaccine named PROF-PDL1E, was designed comprising the Babesia microti-derived vaccine candidate profilin and the host PD-L1 protein, and its effect on immunization against murine B. microti infection was evaluated. PD-L1-specific antibodies generated after vaccination blocked PD-L1 and PD-1 binding as shown by in vitro assays. PROF-PDL1E reduced the burden of B. microti in a mouse model and decreased PD-1 expression in T cells. Furthermore, no tissue damage could be observed after PROF-PDL1E vaccination as verified by hematoxylin and eosin tissue staining of essential organs. In conclusion, vaccines targeting immune checkpoints seem to be a promising strategy for anti-Babesia vaccine development.

Detection of novel piroplasmid species and Babesia microti and Theileria orientalis genotypes in hard ticks from Tengchong County, Southwest China

To reveal the genetic diversity of Babesia microti and Theileria orientalis in Southwest China, we conducted a molecular survey of piroplasms in hard ticks in a China-Myanmar border county. Host infesting and questing ticks were collected from Tengchong County in 2013 and 2014. Piroplasm infection in ticks was detected by PCR, and then, phylogenetic analysis was conducted to study the genetic diversity of the pathogens identified in ticks. All in all, six piroplasm species comprising of B. microti; B. orientalis; a novel Babesia species designated Babesia sp. Tengchong, China; T. orientalis; T. luwenshuni; and an as yet undescribed piroplasmid species referred to as Piroplasmid sp. Tengchong, China, have been identified after screening goat- and cattle-attached ticks. In addition, B. bigemina has been identified by screening questing ticks. Phylogenetic analysis based on the 18S rRNA and partial β-tubulin gene revealed two novel potentially zoonotic genotypes designated B. microti Tengchong-Type A and B. The T. orientalis genotypes identified in the present study represent the seven known genotypes 1-5, 7, and N3 as revealed by phylogenetic analysis of 18S rRNA and MPSP genes. Importantly, an additional genotype designated N4 has also been identified in this study, which brings the number of recognized T. orientalis genotypes to a total of twelve. Thus, besides the two novel species, Babesia sp. Tengchong, China, closely related to Babesia species isolated from yak and Piroplasmid sp. Tengchong, China, our study demonstrates that additional novel B. microti and T. orientalis genotypes exist in Southwest China.

Endosymbionts Alter Larva-to-Nymph Transstadial Transmission of Babesia microti in Rhipicephalus haemaphysaloides Ticks

Maternally inherited endosymbionts inhabit a variety of arthropods. Some of them can protect the arthropod host against a wide range of pathogens. However, very little is known about the association between endosymbionts and pathogen susceptibility in ticks. The present study investigated the effect of endosymbionts on larva-to-nymph transstadial transmission of Babesia microti by Rhipicephalus haemaphysaloides ticks. Engorged female ticks were injected with PBS, ciprofloxacin or kanamycin. The offspring larvae were used to infest B. microti-positive mice. Prevalence of B. microti among the nymphs in different treatment groups and its association with endosymbiont density in the larvae were analyzed. The results showed that the prevalence of B. microti in the kanamycin-treated group (63.9%, 95% confidence interval (CI): 52.8–75.0%) was higher than that in the PBS (23.6%, 95% CI: 13.8–33.4%) or ciprofloxacin-treated (25.0%, 95% CI: 15.0–35.0%) groups. This increased prevalence was associated with reduced density of Coxiella-like endosymbiont but was not related to the density of Rickettsia-like endosymbiont. No direct evidence has previously been reported about the impact of Coxiella-like endosymbiont on pathogen susceptibility in ticks. This study reveals that endosymbionts are potentially important defensive symbionts of R. haemaphysaloides which may influence the colonization or susceptibility of B. microti in the tick host.

Tissue Localization and Variation of Major Symbionts in Haemaphysalis longicornis, Rhipicephalus haemaphysaloides, and Dermacentor silvarum in China

Ticks are important disease vectors, as they transmit a variety of human and animal pathogens worldwide. Symbionts that coevolved with ticks confer crucial benefits to their host in nutrition metabolism, fecundity, and vector competence. Although over 100 tick species have been identified in China, general information on tick symbiosis is limited. Here, we visualized the tissue distribution of Coxiella sp. and Rickettsia sp. in lab-reared Haemaphysalis longicornis and Rhipicephalus haemaphysaloides by fluorescent in situ hybridization. We found that Coxiella sp. colonized exclusively the Malpighian tubules and ovaries of H. longicornis, while Rickettsia sp. additionally colonized the midgut of R. haemaphysaloides We also investigated the population structure of microbiota in Dermacentor silvarum ticks collected from Inner Mongolia, China, and found that Coxiella, Rickettsia, and Pseudomonas are the three dominant genera. No significant difference in microbiota composition was found between male and female D. silvarum ticks. We again analyzed the tissue localization of Coxiella sp. and Rickettsia sp. and found that they displayed tissue tropisms similar to those in R. haemaphysaloides, except that Rickettsia sp. colonized the nuclei of spermatids instead of ovaries in D. silvarum Altogether, our results suggest that Coxiella sp. and Rickettsia sp. are the main symbionts in the three ticks and reside primarily in midgut, Malpighian tubules, and reproductive tissues, but their tissue distribution varies in association with species and sexes.IMPORTANCE Tick-borne diseases constitute a major public health burden, as they are increasing in frequency and severity worldwide. The presence of symbionts helps ticks to metabolize nutrients, promotes fecundity, and influences pathogen infections. Increasing numbers of tick-borne pathogens have been identified in China; however, knowledge of native ticks, especially tick symbiosis, is limited. In this study, we analyze the distribution of Coxiella sp. and Rickettsia sp. in tissues of laboratory-reared Haemaphysalis longicornis and Rhipicephalus haemaphysaloides and field-collected Dermacentor silvarum We found that the localization patterns of Coxiella sp. in three Chinese tick species were similar to those of other tick species. We also found a previously undefined intracellular localization of Rickettsia sp. in tick midgut and spermatids. In addition, we demonstrate that tissue tropisms of symbionts vary between species and sexes. Our findings provide new insights into the tissue localization of symbionts in native Chinese ticks and pave the way for further understanding of their functional capabilities and symbiotic interactions with ticks.

Effects of antibiotic treatment on the fecundity of Rhipicephalus haemaphysaloides ticks

BACKGROUND

Endosymbiotic bacteria inhabit a variety of arthropods including ticks and may have multiple effects on the host's survival, reproduction or pathogen acquisition and transmission. Rhipicephalus haemaphysaloides is one of the most widely distributed tick species in China. The symbiotic bacteria composition and their impacts to R. haemaphysaloides ticks have not been studied. The present study investigated the composition of microbial community in R. haemaphysaloides ticks and then assessed the effects of endosymbionts on the host's fecundity by antibiotic treatment experiments.

METHODS

The microbial population of female and male R. haemaphysaloides ticks was analyzed using Illumina Miseq sequencing of 16S rRNA gene. Thirty engorged female ticks were then randomly divided into five groups and injected with ampicillin, ciprofloxacin, kanamycin, tetracycline, or phosphate-buffered solution (PBS), respectively. Effects of antibiotic treatments on maternal oviposition, egg hatching and density of endosymbionts were evaluated.

RESULTS

Illumina Miseq sequencing showed that Coxiella and Rickettsia were the predominant bacterial genera inhabiting R. haemaphysaloides ticks. Antibiotic treatment experiments found that kanamycin reduced the density of Coxiella-like endosymbiont (Coxiella-LE hereafter) in eggs, ciprofloxacin reduced the density of Rickettsia-like endosymbiont (Rickettsia-LE), and tetracycline had effect on both endosymbionts, while ampicillin affected neither. Meanwhile hatching rates of eggs were observed to decrease greatly in the kanamycin or tetracycline-treated group but maintained in the ampicillin or ciprofloxacin-treated group. Furthermore, the reduced hatching rates were found to be associated with density of Coxiella-LE in eggs.

CONCLUSIONS

The findings indicate that Coxiella-LE is essential for the reproduction of R. haemaphysaloides ticks, and that kanamycin can be used to study the role of Coxiella-LE on ticks.

Prevalence and diversity of piroplasms and ticks in young raccoons and an association of Babesia sensu stricto infections with splenomegaly

Piroplasms are intraerythrocytic parasites that are often transmitted by ixodid ticks, but vertical transmission is an alternative route for some species. In the USA, raccoons (Procyon lotor) are hosts for two known species, a Babesia microti-like sp. and Babesia lotori (in Babesia sensu stricto group). To better understand the natural history of Babesia in raccoons, we tested young raccoons from Minnesota and Colorado for Babesia spp., examined them for ticks, and assessing for splenomegaly as a sign of clinical disease. Raccoons from both states were infected with B. microti-like sp. and Babesia sensu stricto spp. Infections of B. microti-like were common, even in 1-week-old raccoons, suggesting vertical transmission. Babesia sensu stricto infections were more common in older raccoons. Raccoons infected with Babesia sensu stricto had significantly higher spleen:body weight ratios compared with uninfected or B. microti-like sp.-infected raccoons. Ticks were only found on raccoons from Minnesota. The most common and abundant tick was Ixodes texanus but Ixodes scapularis and Dermacentor variabilis were also found on raccoons. We report piroplasm infections and infestations with several tick species in very young raccoons. Young raccoons infected with Babesia sensu stricto spp. had higher spleen:body weight ratios, suggesting a disease risk.

Molecular evidence for the transovarial passage of Babesia gibsoni in Haemaphysalis hystricis (Acari: Ixodidae) ticks from Taiwan: a novel vector for canine babesiosis

BACKGROUND

Babesia gibsoni is the predominant tick-borne protozoan blood parasite affecting dogs throughout the Oriental region. Babesia gibsoni is transmitted by Haemaphysalis longicornis, whereas a similar role has been suggested for Rhipicephalus sanguineus. Haemaphysalis longicornis does not occur in Taiwan, but R. sanguineus is widely distributed on dogs. However, clinical cases of babesiosis are mainly restricted to the northern part of the island. The discrepancy between tick distribution and clinical cases stimulated us to investigate the tick species distribution on dogs in northern Taiwan, with the aim to identify the local vector for canine babesiosis.

METHODS

Ticks were collected from stray dogs or free ranging pet dogs in northern Taiwan between 2015 and 2017 and, after identification, were tested for the presence of tick-borne Babesia parasites using PCR and reverse line blot (RLB) hybridisation. Moreover, engorged ticks collected from the dogs were incubated at 28 °C to allow them to oviposit. Their subsequent larval progeny was also examined by PCR/RLB.

RESULTS

A total of 1085 ticks collected from 144 stray dogs at different residential areas consisted of 5 different species: H. hystricis (n = 435), R. sanguineus (n = 582), R. haemaphysaloides (n = 43), Amblyomma testudinarium (n = 14) and Ixodes ovatus (n = 11) were identified. Babesia gibsoni DNA was detected in H. hystricis females (10.3%), males (7.0%) and in 2.6% of the nymphs. One R. sanguineus female and one A. testudinarium female tick also carried B. gibsoni DNA. DNA of B. gibsoni was demonstrated in 11 out of 68 (16.2%) batches of larval ticks derived from engorged H. hystricus ticks only. Babesia vogeli DNA was detected only in R. sanguineus females (2.6%) and males (2.4%). DNA of B. vogeli was detected in 13 out of 95 (13.7%) batches of larval ticks derived from engorged R.sanguineus females.

CONCLUSIONS

Babesia gibsoni DNA was detected in the larval progeny of H. hystricis ticks only, whereas B. vogeli was restricted to the larvae of R. sanguineus. This provides evidence for transovarial passage of B. gibsoni in H. hystricis and evidence that this tick does act as the local vector for this parasite on dogs in northern Taiwan where most cases of babesiosis are reported. The vectorial capacity of R. sanguineus for babesiosis is probably restricted to the transmission of B. vogeli only.

Evaluation on Infectivity of Babesia microti to Domestic Animals and Ticks Outside the Ixodes Genus

Babesiosis caused by Babesia microti parasite is an emerging tick borne zoonotic disease that was confirmed recently in China. To understand the epidemiology characteristics of this emerging disease, infectivity of B. microti to domestic animals and ticks outside the genus Ixodes was evaluated in this study. Different domestic animals, chick, pig, goat, dog and the reference host rat were experimentally inoculated with B. microti-infected erythrocytes and the parasite infection was monitored daily by blood smear observation, real-time PCR detection, nested-PCR and special antibody responses during 55 days period. The results showed that rats infected with B. microti showed a typical sustained infection with strongly antibody responses; however, both goats and dogs infected with B. microti only showed transient antibody responses and the parasite was not found by blood smear observation or PCR; neither the parasite nor the special antibodies were detected in experimental chicks and pigs. On the other hand, the present study also experimentally investigated the infectivity of B. microti to Rhipicephalus haemaphysaloides, Haemaphysalis longicornis, and Hyalomma asiaticum three species of ticks outside the genus Ixodes and the transmission experiment of B. microti between H. longicornis ticks and mice. Results showed that B. microti can be detected in the nymph and adult of these species after molting from engorged tick fed on infected mice, but the parasite was not detected in larvae hatching from eggs of engorged female tick fed on the infected mice. Transmission of B. microti to mice by infected H. longicornis nymphs was confirmed. These results indicated that these domestic animals do not have reservoir competence for B. microti, however, three species of ticks out of the genus Ixodes, common in China were successfully infected by B. microti, with H. longicornis showing the potential of transmitting the parasite to the vertebrate host.

The immunomodulatory protein RH36 is relating to blood-feeding success and oviposition in hard ticks

An immunomodulatory protein designated RH36 was identified in the tick Rhipicephalus haemaphysaloides. The cDNA sequence of RH36 has 844bp and encodes a deduced protein with a predicted molecular weight of 24kDa. Bioinformatics analysis indicated that RH36 presented a degree of similarity of 34.36% with the immunomodulatory protein p36 from the tick Dermacentor andersoni. The recombinant RH36 (rRH36) expressed in Sf9 insect cells suppressed the T-lymphocyte mitogen-driven in vitro proliferation of splenocytes and the expression of several cytokines such as IL-2, IL-12, and TNF-α. Furthermore, the proliferation of splenocytes isolated from rRH36-inoculated mice was significantly lower than that in control mice, suggesting that rRH36 could directly suppress immune responses in vivo. In addition, microarray analysis of splenocytes indicated that the expression of several immunomodulatory genes was downregulated by rRH36. The silencing of the RH36 gene by RNAi led to a 37.5% decrease in the tick attachment rate 24h after placement into the rabbit ears, whereas vaccination with RH36 caused a 53.06% decrease in the tick engorgement rate. Unexpectedly, RNAi induced a significant decrease in the oviposition rate, ovary weight at day 12 after engorgement, and egg-hatching rate. The effects of RH36 on blood feeding and oviposition were further confirmed by vaccination tests using the recombinant protein. These results indicate that RH36 is a novel member of immunosuppressant proteins and affects tick blood feeding and oviposition.