Vertical Transmission: A Vector-Independent Transmission Pathway of Babesia microti in the Natural Reservoir Host Peromyscus leucopus

Detection of a novel Babesia sp. in Amblyomma javanense, an ectoparasite of Sunda pangolins

BACKGROUND

Babesia is a protozoal, tick-borne parasite that can cause life-threatening disease in humans, wildlife and domestic animals worldwide. However, in Southeast Asia, little is known about the prevalence and diversity of Babesia species present in wildlife and the tick vectors responsible for its transmission. Recently, a novel Babesia species was reported in confiscated Sunda pangolins (Manis javanica) in Thailand. To investigate the presence of this parasite in Singapore, we conducted a molecular survey of Babesia spp. in free-roaming Sunda pangolins and their main ectoparasite, the Amblyomma javanense tick.

METHODS

Ticks and tissue samples were opportunistically collected from live and dead Sunda pangolins and screened using a PCR assay targeting the 18S rRNA gene of Babesia spp. DNA barcoding of the cytochrome oxidase subunit I (COI) mitochondrial gene was used to confirm the species of ticks that were Babesia positive.

RESULTS

A total of 296 ticks and 40 tissue samples were obtained from 21 Sunda pangolins throughout the 1-year study period. Babesia DNA was detected in five A. javanense ticks (minimum infection rate = 1.7%) and in nine different pangolins (52.9%) located across the country. Phylogenetic analysis revealed that the Babesia 18S sequences obtained from these samples grouped into a single monophyletic clade together with those derived from Sunda pangolins in Thailand and that this evolutionarily distinct species is basal to the Babesia sensu stricto clade, which encompasses a range of Babesia species that infect both domestic and wildlife vertebrate hosts.

CONCLUSIONS

This is the first report documenting the detection of a Babesia species in A. javanense ticks, the main ectoparasite of Sunda pangolins. While our results showed that A. javanense can carry this novel Babesia sp., additional confirmatory studies are required to demonstrate vector competency. Further studies are also necessary to investigate the role of other transmission pathways given the low infection rate of ticks in relation to the high infection rate of Sunda pangolins. Although it appears that this novel Babesia sp. is of little to no pathogenicity to Sunda pangolins, its potential to cause disease in other animals or humans cannot be ruled out.

Transfusion-transmitted Babesia spp.: a changing landscape of epidemiology, regulation, and risk mitigation

Babesia spp. are tick-borne parasites with a global distribution and diversity of vertebrate hosts. Over the next several decades, climate change is expected to impact humans, vectors, and vertebrate hosts and change the epidemiology of Babesia. Although humans are dead-end hosts for tick-transmitted Babesia, human-to-human transmission of Babesia spp. from transfusion of red blood cells and whole blood-derived platelet concentrates has been reported. In most patients, transfusion-transmitted Babesia (TTB) results in a moderate-to-severe illness. Currently, in North America, most cases of TTB have been described in the United States. TTB cases outside North America are rare, but case numbers may change over time with increased recognition of babesiosis and as the epidemiology of Babesia is impacted by climate change. Therefore, TTB is a concern of microbiologists working in blood operator settings, as well as in clinical settings where transfusion occurs. Microbiologists play an important role in deploying blood donor screening assays in Babesia endemic regions, identifying changing risks for Babesia in non-endemic areas, investigating recipients of blood products for TTB, and drafting TTB policies and guidelines. In this review, we provide an overview of the clinical presentation and epidemiology of TTB. We identify approaches and technologies to reduce the risk of collecting blood products from Babesia-infected donors and describe how investigations of TTB are undertaken. We also describe how microbiologists in Babesia non-endemic regions can assess for changing risks of TTB and decide when to focus on laboratory-test-based approaches or pathogen reduction to reduce TTB risk.

Serum metabolomic profiles in BALB/c mice induced by Babesia microti infection

Introduction

The protozoan parasite Babesia microti is the primary cause of human babesiosis. This parasite invades and multiplies inside red blood cells (RBCs), and infections differ significantly based on the age and immune competency of the host. The aim of this study was to investigate the use of serum metabolic profiling to identify systemic metabolic variations between B. microti-infected mice and noninfected controls.

Methods

A serum metabolomics analysis of BALB/c mice that had been intraperitoneally injected with 10⁷ B. microti-infected RBCs was performed. Serum samples from the early infected group (2 days postinfection), the acutely infected group (9 days postinfection), and the noninfected group were collected and evaluated using a liquid chromatography-mass spectrometry (LC-MS) platform. Principal component analysis (PCA), partial least squares discriminant analysis (PLS-DA), and orthogonal partial least squares discriminant analysis (OPLS-DA) identified metabolomic profiles that differentiated the B. microti-infected and noninfected groups.

Results

Our results confirm that the serum metabolome is significantly influenced by acute B. microti infection and show that infection results in dysregulation of metabolic pathways and perturbation of metabolites. Acutely infected mice displayed perturbations in metabolites associated with taurine and hypotaurine metabolism, histidine metabolism, and arachidonic acid metabolism. Taurocholic acid, anserine, and arachidonic acid may be potential candidates as serological biomarkers for diagnosing B. microti infection at the acute stage. These metabolites could be further examined for their role in disease complexity.

Discussion

Our findings demonstrate that the acute stage of B. microti infection induces abnormalities in the metabolites present in mouse serum and provide new insight into the mechanisms involved in systemic metabolic changes that occur during B. microti infection.

What do we know about the microbiome of I. ricinus?

I. ricinus is an obligate hematophagous parasitic arthropod that is responsible for the transmission of a wide range of zoonotic pathogens including spirochetes of the genus Borrelia, Rickettsia spp., C. burnetii, Anaplasma phagocytophilum and Francisella tularensis, which are part the tick´s microbiome. Most of the studies focus on "pathogens" and only very few elucidate the role of "non-pathogenic" symbiotic microorganisms in I. ricinus. While most of the members of the microbiome are leading an intracellular lifestyle, they are able to complement tick´s nutrition and stress response having a great impact on tick´s survival and transmission of pathogens. The composition of the tick´s microbiome is not consistent and can be tied to the environment, tick species, developmental stage, or specific organ or tissue. Ovarian tissue harbors a stable microbiome consisting mainly but not exclusively of endosymbiotic bacteria, while the microbiome of the digestive system is rather unstable, and together with salivary glands, is mostly comprised of pathogens. The most prevalent endosymbionts found in ticks are Rickettsia spp., Ricketsiella spp., Coxiella-like and Francisella-like endosymbionts, Spiroplasma spp. and Candidatus Midichloria spp. Since microorganisms can modify ticks' behavior, such as mobility, feeding or saliva production, which results in increased survival rates, we aimed to elucidate the potential, tight relationship, and interaction between bacteria of the I. ricinus microbiome. Here we show that endosymbionts including Coxiella-like spp., can provide I. ricinus with different types of vitamin B (B2, B6, B7, B9) essential for eukaryotic organisms. Furthermore, we hypothesize that survival of Wolbachia spp., or the bacterial pathogen A. phagocytophilum can be supported by the tick itself since coinfection with symbiotic Spiroplasma ixodetis provides I. ricinus with complete metabolic pathway of folate biosynthesis necessary for DNA synthesis and cell division. Manipulation of tick´s endosymbiotic microbiome could present a perspective way of I. ricinus control and regulation of spread of emerging bacterial pathogens.

Human Babesiosis

Babesiosis is caused by intraerythrocytic parasites that are transmitted primarily by ticks, infrequently through blood transfusion, and rarely through transplacental transmission or organ transplantation. Human babesiosis is found throughout the world, but the incidence is highest in the Northeast and upper Midwestern United States. Babesiosis has clinical features that resemble malaria and can be fatal in immunocompromised and older patients. Diagnosis is confirmed by identification of Babesia parasites on blood smear or Babesia DNA with polymerase chain reaction. Standard treatment consists of atovaquone and azithromycin or clindamycin and quinine for 7 to 10 days.

Optimization of an Evaluation Method for Anti-Babesia microti Drug Efficacy

Babesiosis is an emerging zoonotic disease that is typically caused by Babesia microti infection. Clinical treatment of B. microti infection is challenging; hence, it is crucial to find new effective drugs. The current laboratory screening methods for anti-B. microti drugs are not optimized. We conducted drug-suppressive and drug-therapeutic tests to investigate whether use of an immunosuppressant and the target gene-based qPCR are helpful to reduce the number of animals affected and to improve parasite detection in an immunocompetent mouse model. These results were verified by subpassage test. In the drug-suppressive test, no B. microti were observed after immunosuppressant administration or in subpassage mice in the 100 mg/kg robenidine hydrochloride (ROBH) group. The opposite results were observed in the control, 50 mg/kg ROBH, atovaquone (ATO) + azithromycin (AZM), and proguanil hydrochloride (PGH) groups. Significant differences were observed in the EIR and target gene relative values (both P < 0.001) between the control group and any ROBH groups. In the drug-therapeutic test, recrudescence occurred in the 50 mg/kg ROBH, ATO+AZM, and control groups. This was not observed in the 100 mg/kg ROBH group after immunosuppressant administration. Similar findings were observed in the subpassage test. This suggests that a 4-day anti-B. microti drug-suppressive test can be used in preliminary drug screening. Potentially effective drugs can be verified by immunosuppressant test in subsequent drug-therapeutic tests. Thus, a laboratory evaluation method of anti-B. microti drug efficacy was optimized, which is highly accurate and requires a short drug screening time.

The Global Emergence of Human Babesiosis

Babesiosis is an emerging tick-borne disease caused by intraerythrocytic protozoa that are primarily transmitted by hard-bodied (ixodid) ticks and rarely through blood transfusion, perinatally, and organ transplantation. More than 100 Babesia species infect a wide spectrum of wild and domestic animals worldwide and six have been identified as human pathogens. Babesia microti is the predominant species that infects humans, is found throughout the world, and causes endemic disease in the United States and China. Babesia venatorum and Babesia crassa-like agent also cause endemic disease in China. Babesia divergens is the predominant species in Europe where fulminant cases have been reported sporadically. The number of B. microti infections has been increasing globally in recent decades. In the United States, more than 2000 cases are reported each year, although the actual number is thought to be much higher. In this review of the epidemiology of human babesiosis, we discuss epidemiologic tools used to monitor disease location and frequency; demographics and modes of transmission; the location of human babesiosis; the causative Babesia species in the Americas, Europe, Asia, Africa, and Australia; the primary clinical characteristics associated with each of these infections; and the increasing global health burden of this disease.

Babesia microti Immunoreactive Rhoptry-Associated Protein-1 Paralogs Are Ancestral Members of the Piroplasmid-Confined RAP-1 Family

Babesia, Cytauxzoon and Theileria are tick-borne apicomplexan parasites of the order Piroplasmida, responsible for diseases in humans and animals. Members of the piroplasmid rhoptry-associated protein-1 (pRAP-1) family have a signature cysteine-rich domain and are important for parasite development. We propose that the closely linked B. microti genes annotated as BMR1_03g00947 and BMR1_03g00960 encode two paralogue pRAP-1-like proteins named BmIPA48 and Bm960. The two genes are tandemly arranged head to tail, highly expressed in blood stage parasites, syntenic to rap-1 genes of other piroplasmids, and share large portions of an almost identical ~225 bp sequence located in their 5' putative regulatory regions. BmIPA48 and Bm960 proteins contain a N-terminal signal peptide, share very low sequence identity (<13%) with pRAP-1 from other species, and harbor one or more transmembrane domains. Diversification of the piroplasmid-confined prap-1 family is characterized by amplification of genes, protein domains, and a high sequence polymorphism. This suggests a functional involvement of pRAP-1 at the parasite-host interface, possibly in parasite adhesion, attachment, and/or evasion of the host immune defenses. Both BmIPA48 and Bm960 are recognized by antibodies in sera from humans infected with B. microti and might be promising candidates for developing novel serodiagnosis and vaccines.

Impact of Babesia microti infection on the initiation and course of pregnancy in BALB/c mice

Background

Protozoa in the genus Babesia are transmitted to humans through tick bites and cause babesiosis, a malaria-like illness. Vertical transmission of Babesia spp. has been reported in mammals; however, the exact timing and mechanisms involved are not currently known. The aims of this study were to evaluate the success of vertical transmission of B. microti in female mice infected before pregnancy (mated during the acute or chronic phases of Babesia infection) and that of pregnant mice infected during early and advanced pregnancy; to evaluate the possible influence of pregnancy on the course of parasite infections (parasitaemia); and to assess pathological changes induced by parasitic infection.

Methods

The first set of experiments involved two groups of female mice infected with B. microti before mating, and inseminated on the 7th day and after the 40th day post infection. A second set of experiments involved female mice infected with B. microti during pregnancy, on the 4th and 12th days of pregnancy. Blood smears and PCR targeting the 559 bp 18S rRNA gene fragment were used for the detection of B. microti. Pathology was assessed histologically.

Results

Successful development of pregnancy was recorded only in females mated during the chronic phase of infection. The success of vertical transmission of B. microti in this group was 63%. No evidence of pregnancy was found in females mated during the acute phase of infection or on the 4th day of pregnancy. In the group infected on the 12th day of pregnancy, numerous complications including loss of pregnancy and stillbirths were recorded. During the acute phase of infection, parasitaemia was lower in pregnant females in comparison to infected, non-pregnant control females.

Conclusions

Acute B. microti infection prevents the initiation of pregnancy and embryonic development if it occurs during the first trimester, and causes severe complications in foetal BALB/c mice in the second and third trimesters of pregnancy. Chronic B. microti infection has no detrimental impact on the initiation and development of pregnancy, but results in congenital infection of the offspring. Further study is required to determine the extent to which maternal anti-babesial immune responses contribute to compromise pregnancy in the murine model of congenital Babesia infection.