Prevalence and molecular detection of Babesia microti in rodents in Southeastern Shanxi, China.

Babesia is a tick-transmitted parasite that infects wild and domestic animals, causes babesiosis in humans, and is an increasing public health concern. Here, we investigated the prevalence and molecular characteristics of Babesia infections in the rodents in Southeastern Shanxi, China. Small rodents were captured, and the liver and spleen tissues were used for Babesia detection using traditional PCR and sequencing of the partial 18S rRNA gene. The analysis revealed that 27 of 252 small rodents were positive for Babesia, with an infection rate of 10.71%. The infection rates in different sexes and rodent tissues were not statistically different, but those in different rodent species, habitats, and sampling sites were statistically different. The highest risk of Babesia infection was observed in Niviventer confucianus captured from the forests in Huguan County. Forty-three sequences from 27 small rodents positive for Babesia infection were identified as Babesia microti, including 42 sequences from 26 N. confucianus, and one sequence from Apodemus agrarius. Phylogenetic analysis showed that all sequences were clustered together and had the closest genetic relationship with Babesia microti strains isolated from Rattus losea and N. confucianus in China, and belonged to the Kobe-type, which is pathogenic to humans. Compared to other Kobe-type strains based on the nearly complete 18S rRNA gene, the sequences obtained in this study showed the difference by 1-3 bp. Overall, a high prevalence of Babesia microti infection was observed in small rodents in Southeastern Shanxi, China, which could benefit us to take the implementation of relevant prevention and control measures in this area.

Identification of Babesia microti immunoreactive antigens by phage display cDNA screen.

Human babesiosis is a malaria-like illness caused by protozoan parasites of the genus Babesia. Babesia microti is responsible for most cases of human babesiosis in the United States, particularly in the Northeast and the Upper Midwest. Babesia microti is primarily transmitted to humans through the bite of infected deer ticks but also through the transfusion of blood components, particularly red blood cells. There is a high risk of severe and even fatal disease in immunocompromised patients. To date, serology testing relies on an indirect immunofluorescence assay that uses the whole Babesia microti antigen. Here, we report the construction of phage display cDNA libraries from Babesia microti-infected erythrocytes as well as human reticulocytes obtained from donors with hereditary hemochromatosis. Plasma samples were obtained from patients who were or had been infected with Babesia microti. The non-specific antibody reactivity of these plasma samples was minimized by pre-exposure to the human reticulocyte library. Using this novel experimental strategy, immunoreactive segments were identified in three Babesia microti antigens termed BmSA1 (also called BMN1-9; BmGPI12), BMN1-20 (BMN1-17; Bm32), and BM4.12 (N1-15). Moreover, our findings indicate that the major immunoreactive segment of BmSA1 does not overlap with the segment that mediates BmSA1 binding to mature erythrocytes. When used in combination, the three immunoreactive segments form the basis of a sensitive and comprehensive diagnostic immunoassay for human babesiosis, with implications for vaccine development.

Tafenoquine for Relapsing Babesiosis: A Case Series.

BACKGROUND: Relapsing babesiosis often occurs in highly immunocompromised patients and has been attributed to the acquisition of resistance against drugs commonly used for treatment such as atovaquone, azithromycin, and clindamycin. Tafenoquine, which is approved for malaria prophylaxis and presumptive antirelapse treatment of Plasmodium vivax malaria, has shown activity against Babesia microti in several animal models of acute infection and in a single human case of relapsing babesiosis. Here, we report 5 cases of relapsing babesiosis treated with tafenoquine, including the previous case, and begin to define the conditions for optimal use of tafenoquine in relapsing babesiosis. METHODS: A definitive diagnosis of babesiosis was made by microscopic examination of Giemsa-stained thin blood smears or a real-time polymerase chain reaction (PCR) that targets the parasite 18S rRNA gene. Clearance of B. microti infection was ascertained by use of blood smear and real-time PCR. RESULTS: Tafenoquine was initiated with a loading dose of 600 mg. A weekly maintenance dose consisted of 200 mg or 300 mg; the lower dose was associated with a delayed clearance of B. microti. In 2 cases, all antimicrobial agents but tafenoquine were discontinued prior to clearance of infection. In 2 other cases, clearance was achieved while tafenoquine was administered along with other antimicrobial agents. In 3 of these 4 cases, tafenoquine was used in combination with atovaquone-proguanil. Other agents included atovaquone, azithromycin, and/or clindamycin. In 1 case, tafenoquine was administered alone and failed to prevent relapse. CONCLUSIONS: Tafenoquine can be a useful adjunct for the treatment of highly immunocompromised patients experiencing relapsing babesiosis caused by B. microti.

Transmission risk evaluation of transfusion blood containing low-density Babesia microti.

Background: Babesia is a unique apicomplexan parasite that specifically invades and proliferates in red blood cells and can be transmitted via blood transfusion, resulting in transfusion-transmitted babesiosis. However, detecting Babesia in blood before transfusion has not received enough attention, and the risk of transfusing blood containing a low density of Babesia microti (B. microti) is unclear, possibly threatening public health and wellness. Purpose: This study aimed to determine the lower detection limit of B. microti in blood and to evaluate the transmission risk of blood transfusion containing low-density B. microti. Methods: Infected BALB/c mouse models were established by transfusing infected whole blood with different infection rates and densities of B. microti. Microscopic examination, nested Polymerase Chain Reaction (nested PCR), and an enzyme-linked immunosorbent assay (ELISA) were used to evaluate the infection status of the mouse models. Meanwhile, the nested PCR detection limit of B. microti was obtained using pure B. microti DNA samples with serial concentrations and whole blood samples with different densities of B. microti-infected red blood cells. Thereafter, whole mouse blood with a B. microti density lower than that of the nested PCR detection limit and human blood samples infected with B. microti were transfused into healthy mice to assess the transmission risk in mouse models. The infection status of these mice was evaluated through microscopic examination, nested PCR tests, and ELISA. Results: The mice inoculated with different densities of B. microti reached the peak infection rate on different days. Overall, the higher the blood B. microti density was, the earlier the peak infection rate was reached. The levels of specific antibodies against B. microti in the blood of the infected mice increased sharply during the first 30 days of infection, reaching a peak level at 60 days post-infection, and maintaining a high level thereafter. The nested PCR detection limits of B. microti DNA and parasite density were 3 fg and 5.48 parasites/µL, respectively. The whole blood containing an extremely low density of B. microti and human blood samples infected with B. microti could infect mice, confirming the transmission risk of transfusing blood with low-density B. microti. Conclusion: Whole blood containing extremely low density of B. microti poses a high transmission risk when transfused between mice and mice or human and mice, suggesting that Babesia detection should be considered by governments, hospitals, and disease prevention and control centers as a mandatory test before blood donation or transfusion.

The Occurrence and Diversity of Tick-Borne Pathogens in Small Mammals from Serbia.

Background: Despite abundance of small mammals in Serbia, there is no information on their role in the epidemiology of tick-borne diseases (TBDs). This retrospective study aimed to identify different tick-borne pathogens (TBPs) in small mammals in Serbia collected during 2011. Materials and Methods: A total of 179 small mammals were collected from seven different localities in Serbia. The five localities belong to the capital city of Serbia-Belgrade: recreational areas-Ada Ciganlija, Titov gaj, and Kosutnjak as well as mountainous suburban areas used for hiking-Avala and Kosmaj. The locality Veliko Gradiste is a tourist place in northeastern Serbia, whereas the locality Milosev Do is a remote area in western Serbia with minor human impact on the environment. Results: The results of the presented retrospective study are the first findings of Rickettsia helvetica, Rickettsia monacensis, Neoehrlichia mikurensis, Borrelia afzelii, Borrelia miyamotoi, Babesia microti, Hepatozoon canis, and Coxiella burnetii in small mammals in Serbia. The presence of R. helvetica was confirmed in two Apodemus flavicollis, the presence of one of the following pathogens, R. monacensis, B. afzelii, H. canis, Ba. microti, and N. mikurensis was confirmed in one A. flavicollis each, whereas the presence of B. miyamotoi was confirmed in one Apodemus agrarius. Coinfection with B. afzelii and Ba. microti was confirmed in one A. flavicollis. DNA of C. burnetii was detected in 3 of 18 pools. Conclusions: The results confirm that detected pathogens circulate in the sylvatic cycle in Serbia and point to small mammals as potential reservoir hosts for the detected TBPs. Further large-scale studies on contemporary samples are needed to clarify the exact role of particular small mammal species in the epidemiology of TBDs caused by the detected pathogens.