Differentials
Lyme disease
SIGNS / SYMPTOMS
Lyme disease (Borrelia burgdorferi) is transmitted through the bite of the deer tick (Ixodes scapularis), the same vector as for Babesia microti.
Signs and symptoms may be similar.
Early Lyme disease may manifest with a characteristic 'bull's-eye' rash (erythema migrans). Erythema migrans is not seen in babesiosis.
INVESTIGATIONS
ELISA or immunofluorescence for Borrelia burgdorferi antibodies.
Diagnosis of Lyme disease does not exclude diagnosis of babesiosis, as co-infection can occur.
Human granulocytic anaplasmosis
SIGNS / SYMPTOMS
Caused by Anaplasma phagocytophilum.
Spreads through the bite of the Ixodes deer tick, the same vector as for Babesia microti and Lyme disease.
May present acutely, with fever, chills, and headache, as opposed to the more gradual onset of babesiosis. However, it may also present as a mild, self-limiting illness.
INVESTIGATIONS
Giemsa-stained thin blood smear may show the intra-granulocytic inclusions characteristic of human granulocytic anaplasmosis (HGA).
Acute and convalescent phase indirect fluorescent assay may reveal antibodies against A phagocytophilum.
Diagnosis of HGA does not exclude diagnosis of babesiosis, as co-infection can occur.
Rocky Mountain spotted fever
SIGNS / SYMPTOMS
Signs and symptoms may be similar.
Both are tick-borne infections, and both may cause fever, myalgias, thrombocytopenia, and anaemia.
Rocky Mountain spotted fever (RMSF) frequently presents with a maculopapular or petechial rash, whereas a rash is rare in babesiosis.
INVESTIGATIONS
Immunofluorescence or Luminex assay demonstrate RMSF antibodies (usually confirmed on convalescent serum).
Tularaemia
SIGNS / SYMPTOMS
Transmitted via ticks, flies, and other arthropod vectors.
Causes fever and anorexia similar to babesiosis. It can also cause septicaemia and death, even in people with intact immune systems.
Unlike babesiosis, it frequently causes suppurative lymphadenitis.
INVESTIGATIONS
Francisella tularensis can be isolated by blood culture with buffered charcoal and yeast extract or media supplemented with cysteine.
Malaria infection
SIGNS / SYMPTOMS
Signs and symptoms may be similar. However, geographic distribution of malaria and babesiosis is different, and the cyclic nature of malaria fever is absent in babesiosis.
If a patient has travelled to or resides in coastal areas of the northeastern US or the lakes region of the midwest, babesiosis is more likely. If the patient has travelled to sub-Saharan Africa or tropical regions, malaria is more likely.
INVESTIGATIONS
Giemsa- or Wright-stained thin blood smear: both Babesia microti and Plasmodium falciparum form multiple intra-erythrocytic rings, but P falciparum forms extra-erythrocytic gametocytes, whereas B microti does not. B microti may also form tetrads (Maltese cross) within RBCs.
Infectious mononucleosis
SIGNS / SYMPTOMS
Signs and symptoms may be similar, although splenomegaly is more prevalent.
Symptomatic infection often affects young, otherwise healthy people, whereas babesiosis is commonly symptomatic in older or immunocompromised people.
INVESTIGATIONS
FBC may reveal an atypical leukocytosis, as opposed to leukopenia observed with babesiosis.
Heterophile antibody test is positive for Epstein-Barr virus.
Cytomegalovirus infection
SIGNS / SYMPTOMS
Signs and symptoms may be similar.
Lymphadenopathy is commonly seen in cytomegalovirus (CMV) and not in babesiosis.
INVESTIGATIONS
FBC may reveal an atypical leukocytosis, whereas babesiosis may present with leukopenia.
Polymerase chain reaction of blood or body fluids for CMV DNA confirms infection.
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