Clinical Manifestations and Pathogenic Mechanisms
Though Babesia can cause almost any problem, here are a few manifestations worth knowing.
After Babesia invades red blood cells, it destroys their structure and stops them from carrying oxygen properly. It also disrupts the body’s ability to make new blood cells.
Clinical presentations include:
- Hemolytic anemia
- Icterus (jaundice)
- Pyrexia (fever)
- Respiratory distress
- Splenic rupture and infarction
Emerging evidence also documents atypical immune responses including acute phase reactions and secondary hemophagocytic lymphohistiocytosis (sHLH) (Milanović et al., 2020; Mojtahed et al., 2020; Santos et al., 2020; Jacobs et al., 2025).
Blood Clots
Rodent models show that B. microti infection accelerates clotting and increases thrombotic risk. I am seeing far too many patients presenting with DVTs.
In pregnancy, Babesia has been shown to cause placental vascular damage through collagen deposition and red blood cell-to-vessel-wall adhesion (Jasik et al., 2024). This may undermine fetal health in many ways. It is never considered in cases of infertility or miscarriage.
Bovine Infections (B. bovis or B. bigemina)
- Cerebral hyperemia — a dangerous, abnormal increase in blood flow to the brain
- Inappetence — lowered appetite
- Lactation suppression — poor breast milk production
- Hemoglobinuria crisis — a sudden, severe episode where the immune system attacks red blood cells, causing hemolysis and releasing hemoglobin into the urine, resulting in dark-colored urine, severe fatigue, and shortness of breath. Treatment typically involves complement inhibitors.
Canine Infections
Beyond fever and reduced appetite, canine Babesia progresses to:
- Renal impairment
- Pancreatic inflammation
- Acute respiratory failure (“pulmonary shock”)
Persistent subclinical carriage — no symptoms, but still infectious — has been observed after treatment (Muench et al., 2023; Antognoni et al., 2025).
Multi-Organ Dysfunction
Various Babesia species further increase the risk of multi-organ dysfunction by activating the body’s clotting system and triggering harmful immune responses (Welzl et al., 2001; Okła et al., 2014; Preena et al., 2021).
Jia Z, Zhang Y, Zhao D, Wang H, Yu M, Liu Z, Zhang X, Cui J and Wang X (2025). Research progress on diagnostic techniques for different Babesia species in persistent infections. Front. Cell. Infect. Microbiol. 15:1575227. doi: 10.3389/fcimb.2025.1575227