Enzootic Babesia microti in Maine.

Area of Science:

• Parasitology
• Vector-borne diseases
• Mammalian ecology

Background:

• Human babesiosis is primarily associated with Babesia microti in the northeastern US, particularly in areas with deer ticks (Ixodes dammini).
• The presence of Babesia microti in rodents in other regions suggests a wider distribution, but zoonotic significance is linked to human-biting vectors.
• The role of Babesia microti in areas lacking Ixodes dammini requires investigation.

Purpose of the Study:

• To determine if Babesia microti is enzootic in regions of Maine where Ixodes dammini is absent but other ticks like Ixodes angustus or Ixodes muris are common.
• To investigate the presence and genetic diversity of Babesia microti in small mammals in tick-endemic areas without the primary human-biting vector.

Main Methods:

• Surveyed small mammals (chipmunks, voles, deer mice, shrews) from two sites in Maine.
• Detected Babesia microti infection using blood smears and polymerase chain reaction (PCR) targeting the 18S ribosomal DNA gene.
• Conducted phylogenetic analysis of the amplified Babesia microti DNA sequences.

Main Results:

• Three out of 43 small mammals (6.9%) tested positive for Babesia microti parasitemia.
• Phylogenetic analysis revealed the presence of two distinct forms of Babesia microti.
• The findings indicate Babesia microti can be enzootic in small mammal populations even in the absence of Ixodes dammini.

Conclusions:

• Babesia microti can exist in small mammal populations in areas where the primary vector, Ixodes dammini, is not present.
• The zoonotic risk of human babesiosis is strongly correlated with the presence of dense populations of the human-biting tick, Ixodes dammini.
• Understanding the enzootic cycle of Babesia microti is crucial for assessing and managing babesiosis risk in different geographical regions.