Babesii microti: the Protozoan Plasmodium

Introduction

http://dpd.cdc.gov/dpdx/html/Frames/A-F/Babesiosis/body_Babesiosis_mic1.htm

Babesii microti are piroplasms (protozoan parasites) that present with malaria-like symptoms in humans.  Babesiosis is the disease process of the parasite in humans, and is commonly reported in the northeastern United States [2].  With the protozoan using erythrocytes as a platform for budding, symptoms such as fatigue, aches, and/or nausea and vomiting appear much like that of malaria.  Through a tick vector, infected humans are also introduced to Lyme disease and ehrlichiosis at the same time, creating difficulty for a proper diagnosis.

Description

Babesii is the genus name for this protozoan.  For human parasitism, microti is the genus of the parasite.  The symptoms presented in humans are similar to that of malaria (Plasmodium) [1], and is often misdiagnosed for this reason.  With a  one to four week incubation time inside humans, symptoms of other tick born diseases like Lyme disease may occur around the same time, further preventing a definite diagnosis.  Babesii microti attack red blood cells, reproduce through binary fission, and destroy the erythrocyte when reproduction is complete.  Weakness brought on by the destruction of red blood cells occurs.  Some individuals infected will have minor to no symptoms of infection.  High risk patients, such as those who are immunosuppressed, splenectomized, and/or elderly present with more symptoms.  In severe cases, patients are given an exchange transfusion [2]. 

Host's description

The white footed mouse, Peromyscus leucopus, is one of the two hosts of Babesii microti.  A common mouse, the white footed mouse is native to North America, and is found from Nova Scotia to Texas and even Mexico [4].  The deer tick, Ixodes scapularis, is the other host of Babesii microti, and is identified as the definitive host for this protozoan.  The deer tick is also known for carrying Lyme disease and human granulocytic ehrlichiosis.  Often times, humans who are infected with Babesii microti are also infected with Lyme disease and HEG [3].  This causes difficulty in diagnosing the infected patient who has symptoms that can only be explained as multiple infections.

Life cycle

http://www.dpd.cdc.gov/dpdx/images/ParasiteImages/A-F/Babesiosis/Babesia_LifeCycle.gif

Beginning with an infected tick, the sporozoites of Babesii microti enter the white-footed mouse.  In the blood stream, the sporophytes enter red blood cells and reproduce through budding.  This destroys the erythrocyte, and the protozoan's eventually differentiate into male and female gametes [1].  The mouse continues its life, and, when exposed to ticks that are not yet infected, the parasite travels into the tick as its definitive host.  Through contact in the mouse's bloodstream, the parasites will become sporozoites though the sporgonic cycle.  The cycle will continue in this manner.  However, humans can be infected through an infected tick feeding on the human.  For the parasite to enter the human through the tick vector, the tick has to be attached to the human for about twenty-four hours before the parasite is passed into the human [2].  Normally, this is a dead end for the parasite.  If the infected human were to donate blood and have this blood enter a non-infected human through a blood transfusion, the parasite may be passed on to a different individual.

Ecology

"Life Cycle of Babesia Microti." YouTube. URI's Center For Vector-Borne Disease, University of Rhode Island, 28 July 2009. Web. 20 Feb. 2012. <http://www.youtube.com/watch?v=JOakxoorjoQ>.

Documented cases of babesiosis occur mainly in the southern New England states near the coast.  Specifically, documented cases are commonly found in southern New York, Wisconsin, and Minnesota [3].  Ticks are born on the ground, usually in leaf litter.  With the white footed mouse also located close to the ground, ticks easily find the mammal and become infected with Babesii microti should the mouse be infected before this contact. 

Example of a shortened life cycle:

Babesii microti have a shorter life cycle than that of other parasites.  With a life cycle of two hosts, humans excluded, the protozoan's progeny is created more quickly than that of a parasite with three hosts or more.  The early maturation of Babesii microti in the white-footed mouse allows for sexual reproduction to occur in the deer tick, and have the sporozoites be transmitted to a mouse that is not infected. 

References

1)  "Babesiosis." DPDx Laboratory Identification of Parasites of Public Health Concern. CDC, 05 Dec. 2008. Web. 20 Feb. 2012. <http://www.dpd.cdc.gov/dpdx/HTML/Babesiosis.htm>.
2)  "Babesiosis." National Institute of Allergy and Infectious Diseases Home Page. NIH, 31 July 2008. Web. 20 Feb. 2012. <http://www.niaid.nih.gov/topics/babesiosis/Pages/default.aspx>.
3)  "Atovaquone and Azithromycin for the Treatment of Babesiosis".  Peter J. Krause, M.D., Timothy Lepore, M.D., Vijay K. Sikand, M.D., Joseph Gadbaw, Jr., M.D., Georgine Burke, Ph.D., Sam R. Telford, Sc.D., Peter Brassard, M.D., Diane Pearl, M.D., Jaber Azlanzadeh, Ph.D., Diane Christianson, R.N., Debra McGrath, R.N., and Andrew Spielman, Sc.D. N Engl J Med 2000; 343:1454-1458 November 16, 2000. http://www.nejm.org/doi/full/10.1056/NEJM200011163432004#t=articleBackground
4)  Linzey, A.V., Matson, J. & Timm, R. 2008. "Peromyscus leucopus". In: IUCN 2011. IUCN Red List of Threatened Species. Version 2011.2. <www.iucnredlist.org>. Downloaded on 20 February 2012.

Digital:
-http://www.dpd.cdc.gov/dpdx/images/ParasiteImages/A-F/Babesiosis/Babesia_LifeCycle.gif
-http://dpd.cdc.gov/dpdx/html/Frames/A-F/Babesiosis/body_Babesiosis_mic1.htm
-"Life Cycle of Babesia Microti." YouTube. URI's Center For Vector-Borne Disease, University of Rhode Island, 28 July 2009. Web. 20 Feb. 2012. <http://www.youtube.com/watch?v=JOakxoorjoQ>.