15.1E: Babesiosis

Learning Objectives

• Outline the life cycle of the Babesia microti parasite that causes babesiosis

Babesiosis is a malaria-like parasitic disease caused by Babesia. Babesia is a genus of protozoal piroplasms which are characterized by their ability to divide by binary fission. Also, protozoal piroplasms are sporozoan parasites, and so they possess both sexual and asexual phases. The piroplasm is categorized under Phylum Apicomplexa and specifically, Babesia, is a parasite transmitted via a tick vector. Many of the cases of Babesia infection are asymptomatic but can include mild fevers and diarrhea. The more severe cases are plagued with high fevers, shaking chills, and severe anemia, similar to symptoms seen in individuals infected with malaria. If the disease progresses without treatment and it is severe, the infected individual can suffer from organ failure and adult respiratory distress syndrome. Recently, there has been an increase in babesiosis diagnosis due to an increase in the number of individuals with immunodeficiencies coming into contact with ticks.

Figure: Babesia parasites: Other hemoprotozoan parasites such as these Babesia sp. resemble Plasmodium falciparum organisms. Though developmentally the Babesia spp. organisms resemble Plasmodium falciparum, these parasites present several distinguishing features: they vary more in shape and in size; and they do not produce pigment.

The life cycle of Babesia parasites is characterized by their ability to undergo reproduction in the erythrocytes. These parasites, within the red blood cells, form a distinctive structure called a “Maltese Cross” that is composed of four attached merozoites undergoing asexual budding. This asexual process results in hemolytic anemia. The Babesia microti life cycle includes two hosts, a rodent, primarily the white-footed mouse, and a tick.

During a blood meal, the tick introduces sporozoites into the mouse host. The sporozoites enter the erythrocytes and undergo asexual reproduction as previously mentioned. In the blood, the parasites will then differentiate into male and female gametes. The definitive host, the tick, will then ingest both types of gametes (upon another blood meal). The gametes will unite and undergo a sporogonic cycle resulting in sporozoite. The humans play a role in this cycle if they are bitten by an infected tick. The tick will introduce the sporozoites and the cycle will proceed. Diagnosis of babesiosis is performed using a Giemsa-test for parasitic identification. The “Maltese Cross” is observed on blood films and both serological testing for antibodies and PCR testing for Babesia from the peripheral blood is performed.

Figure: The life cycle of Babesia parasites: Babesia is capable of undergoing both sexual and asexual reproduction in its life cycle. Ticks transmit the human form of Babesiosis, so it often presents with other tick-borne illnesses such as Lyme disease.

Key Points

• Babesia, the parasite, is capable of undergoing both sexual and asexual reproduction in its life cycle.
• A majority of individuals infected with babesiosis are asymptomatic but severe cases display malaria-like symptoms which include high fevers, chills, shakes, and hemolytic anemia.
• A definitive characteristic of Babesia infection is the formation of a “Maltese Cross” structure within the erythrocytes that represents the asexual budding of four attached merozoites.

Key Terms

• piroplasms: a protozoan parasite of the phylum Apicomplexa.
• sporozoite: any of the minute active bodies into which a sporozoan divides just before it infects a new host cell
• hemolytic: producing hemolysis; destroying red blood cells