Babesiosis in asplenic hosts

Experimental transfusion-induced Babesia microti infection: dynamics of parasitemia and immune responses in a rhesus macaque model

BACKGROUND

Babesiosis is an emerging tick-borne infection in humans. The increasing numbers of reported cases of transfusion-associated babesiosis (TAB), primarily caused by Babesia microti, represents a concern for the safety of the US blood supply.

STUDY DESIGN AND METHODS

This study investigated kinetics of parasitemia and innate immune responses and dynamics of antibody responses during B. microti infection in rhesus macaques (RMs) using blood smears, quantitative polymerase chain reaction (qPCR), flow cytometry, and indirect fluorescent antibody testing. A total of six monkeys were transfused with either hamster or monkey-passaged B. microti-infected red blood cells (two and four monkeys, respectively) simulating TAB.

RESULTS

The prepatent period in monkeys inoculated with hamster-passaged B. microti was 35 days compared with 4 days in monkeys transfused with monkey-passaged B. microti; the latter monkeys also had markedly higher parasitemia levels. The duration of the window period from the first detected parasitemia by qPCR analysis to the first detected antibody response ranged from 10 to 17 days. Antibody responses fluctuated during the course of the infection. Innate responses assessed by the frequencies of monocytes and activated B cells correlated with the kinetics and magnitude of parasitemia. On Day 14, additional activation peaks were noted for CD14+CD16+ and CD14-CD16+ monocytes and for CD11c+ myeloid dendritic cells, but only in animals transfused with monkey-passaged B. microti. Parasitemia persisted in these immunocompetent animals, similar to human infection.

CONCLUSION

The results suggest that transfusion-associated transmission of B. microti leads to rapid onset of parasitemia (Day 4) in RMs, detectable antibody response 14 days later, and persistent parasitemia.

Infections of people with complement deficiencies and patients who have undergone splenectomy

The complement system comprises several fluid-phase and membrane-associated proteins. Under physiological conditions, activation of the fluid-phase components of complement is maintained under tight control and complement activation occurs primarily on surfaces recognized as "nonself" in an attempt to minimize damage to bystander host cells. Membrane complement components act to limit complement activation on host cells or to facilitate uptake of antigens or microbes "tagged" with complement fragments. While this review focuses on the role of complement in infectious diseases, work over the past couple of decades has defined several important functions of complement distinct from that of combating infections. Activation of complement in the fluid phase can occur through the classical, lectin, or alternative pathway. Deficiencies of components of the classical pathway lead to the development of autoimmune disorders and predispose individuals to recurrent respiratory infections and infections caused by encapsulated organisms, including Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae. While no individual with complete mannan-binding lectin (MBL) deficiency has been identified, low MBL levels have been linked to predisposition to, or severity of, several diseases. It appears that MBL may play an important role in children, who have a relatively immature adaptive immune response. C3 is the point at which all complement pathways converge, and complete deficiency of C3 invariably leads to severe infections, including those caused by meningococci and pneumococci. Deficiencies of the alternative and terminal complement pathways result in an almost exclusive predisposition to invasive meningococcal disease. The spleen plays an important role in antigen processing and the production of antibodies. Splenic macrophages are critical in clearing opsonized encapsulated bacteria (such as pneumococci, meningococci, and Escherichia coli) and intraerythrocytic parasites such as those causing malaria and babesiosis, which explains the fulminant nature of these infections in persons with anatomic or functional asplenia. Paramount to the management of patients with complement deficiencies and asplenia is educating patients about their predisposition to infection and the importance of preventive immunizations and seeking prompt medical attention.

Babesiosis in the immediate postoperative period after splenectomy for trauma

BACKGROUND

In an immunocompetent host, Babesia microti has not been reported as a cause of postoperative fever.

METHODS

Case report and literature review.

RESULTS

A 52-year-old woman living on Martha's Vineyard developed postoperative fever after splenectomy for trauma. The patient's mechanism of injury was a fall from a stationary bicycle. Intraoperatively, the patient was noted to have splenomegaly. Postoperatively, she developed fever and was found to have Babesia microti on blood smear with an otherwise negative fever evaluation. She was treated with atovaquone and azithromycin and made a full recovery.

CONCLUSIONS

For individuals who have lived or traveled in endemic areas, babesiosis should be considered as a possible cause of postoperative fever when other sources have been excluded. Patients undergoing splenectomy in an endemic area should be screened for babesiosis to prevent postoperative recrudescence of symptoms.

Fever of unknown origin (FUO) due to babesiosis in a immunocompetent host

Fevers of unknown origin (FUOs) are defined as prolonged fevers of 101 degrees F or greater lasting 3 or more weeks that remain undiagnosed after comprehensive inpatient/outpatient laboratory testing. Tick-borne infections are uncommon causes of FUOs. Any infectious disease accompanied by prolonged fevers can present as an FUO if the diagnosis is not suspected or if specific laboratory testing is not done to confirm the diagnosis. Babesiosis is transmitted by the Ixodes scapularis ticks endemic to areas in the northeastern United States. We present the case of a 73-year-old, non-human immunodeficiency virus, male from Long Island who presented with FUO for 6 weeks. As with malaria, there are usually few or no localizing signs in babesiosis. During the patient's hospitalization, babesiosis was suspected on the basis of nonspecific laboratory findings, that is, relative lymphopenia, thrombocytopenia, thrombocytopenia, and an elevated lactate dehydrogenase. When babesiosis was considered in the differential diagnosis, stained blood smears demonstrated the red blood cell inclusions of babesiosis. In the hospital, the patient developed noncardiac pulmonary edema, which rapidly resolved which has been described as a rare complication of babesiosis. He also had an elevated immunoglobulin-M Lyme titer indicating coinfection with Lyme disease. Although his hemolytic anemia persisted for weeks, he only had 3% parasitemia and intact splenic function. We believe this to be the first case of babesiosis presenting as an FUO in a normal host.

Pulmonary complications of babesiosis: case report and literature review

Reported here is a rare case of babesiosis with pulmonary complications followed by a review of the literature. Babesiosis presents clinically as a malaria-like illness with fever, chills, headache, fatigue with lymphopenia, atypical lymphocytes, mildly or transiently elevated serum transaminases, thrombocytopenia, and increased lactate dehydrogenase (LDH) levels. The diagnosis of babesiosis is based on identification of Babesia spp. on a peripheral blood smear. Babesiosis is usually mild in normal hosts, but it may be severe or even fatal in asplenic patients. Pulmonary manifestations are rare in babesiosis, but non-cardiogenic pulmonary edema (NCPE) is the most frequent manifestation. NCPE in babesiosis does not appear to be related to the degree of parasitemia or splenic function and its onset may be early or late. NCPE usually resolves rapidly with supportive treatment; it is rarely fatal. Clinicians should suspect NCPE in patients with babesiosis who acutely develop shortness of breath and have chest radiograph findings compatible with acute pulmonary edema without cardiomegaly or pleural effusions.

Human malarial disease: a consequence of inflammatory cytokine release

Malaria causes an acute systemic human disease that bears many similarities, both clinically and mechanistically, to those caused by bacteria, rickettsia, and viruses. Over the past few decades, a literature has emerged that argues for most of the pathology seen in all of these infectious diseases being explained by activation of the inflammatory system, with the balance between the pro and anti-inflammatory cytokines being tipped towards the onset of systemic inflammation. Although not often expressed in energy terms, there is, when reduced to biochemical essentials, wide agreement that infection with falciparum malaria is often fatal because mitochondria are unable to generate enough ATP to maintain normal cellular function. Most, however, would contend that this largely occurs because sequestered parasitized red cells prevent sufficient oxygen getting to where it is needed. This review considers the evidence that an equally or more important way ATP deficiency arises in malaria, as well as these other infectious diseases, is an inability of mitochondria, through the effects of inflammatory cytokines on their function, to utilise available oxygen. This activity of these cytokines, plus their capacity to control the pathways through which oxygen supply to mitochondria are restricted (particularly through directing sequestration and driving anaemia), combine to make falciparum malaria primarily an inflammatory cytokine-driven disease.

Absence of erythrocyte sequestration in a case of babesiosis in a splenectomized human patient

Background

The importance of vascular occlusion in the pathogenesis of human haemoprotozoal disease is unresolved.

Methods

Giemsa-stained tissue sections from a human case of Babesia microti infection in a splenectomized patient with chronic lymphocytic leukaemia and colon cancer were examined to ascertain the distribution of parasitized erythrocytes within the vascular lumen.

Results

No evidence of sequestration was observed.

Conclusion

This first report on the vascular location of B. microti in human tissue suggests that severe multi-organ failure due to babesiosis is independent of sequestration of parasitized erythrocytes. A similar pathogenesis may also cause multi-organ failure in other intraerythrocytic protozoal infections, including falciparum malaria.

Babesiosis in humans: a treatment review

Human infections with Babesia species, in particular Babesia microti, are tick-borne illnesses that are being recognised with increased frequency. Coinfection with ehrlichiosis and Lyme disease is also being recognised as an important feature of these tick-borne illnesses. Despite the superficial resemblance of Babesia to malaria, these piroplasms do not respond to chloroquine or other similar drugs. However, the treatment of babesiosis using a clindamycin-quinine combination has been successful. Data in animal models and case-reports in humans have suggested that an atovaquone-azithromycin combination is also effective. This was confirmed in a recent prospective, open, randomised trial of clindamycin-quinine versus azithromycin-atovaquone. This paper reviews the literature on the treatment of human babesiosis and the animal models of these human pathogens.

Fulminant babesiosis treated with clindamycin, quinine, and whole-blood exchange transfusion

BACKGROUND

Babesiosis is an increasingly recognized parasitic infection with manifestations that range from a subclinical or mild flu-like illness to life-threatening disease. Risk factors that may be associated with a more severe clinical course include immunosuppression, splenectomy, and advanced age. The most effective chemotherapeutic regimen, clindamycin plus quinine, is sometimes ineffective in cases of severe disease.

CASE REPORT

A previously healthy, 58-year-old man was infected by Babesia microti, presumably through a tick bite. He developed fulminant disease characterized by severe hemolytic anemia, disseminated intravascular coagulation, acute renal failure, and respiratory failure. There was no history of splenectomy or immunodeficiency. He was given oral clindamycin (300 mg/4x/day) 2 days before admission. Oral quinine (650 mg/3x/day) was added upon hospitalization. There was no clinical improvement despite antibiotic therapy with clindamycin and quinine. On the second hospital day, a whole-blood exchange transfusion was performed to simultaneously lower the parasite load and replace the patient's plasma. With an automated blood cell separator, 87 percent of the patient's total blood volume was exchanged. As replacement fluid, 6.7 L of packed RBCs reconstituted with FFP (average Hct, 33%) was used. The patient's Hct increased from 26.9 percent before the exchange to 28.3 percent after the exchange. The percentage of parasitized RBCs decreased from 13.8 percent just before exchange to 4.2 percent immediately after exchange. There was rapid clinical improvement after the whole-blood exchange transfusion. The patient's subsequent clinical course was marked by a disappearance of the parasitemia and continued slow, general improvement. Therapy with clindamycin was continued for 14 days after the exchange transfusion and quinine for 17 days.

CONCLUSION

In cases of severe babesiosis, prompt institution of whole-blood exchange transfusion, in combination with appropriate antimicrobial therapy, can be life-saving.