Case presentation Case 16 Reporter: I2 林士傑 Date: 94/11/28

Chief complaint, present illness, & personal/past/family history A 17-year-old girl who had never traveled outside the United States, had recently spent the summer working as a waitress in Nantucket,Mass. On her return to her home in Washington, D.C., she developed a headache, fatigue, fever, shaking chills, joint and muscle aches, and other vague flu- like symptoms, which persisted for a month. She had been previously healthy,al-though she had had a splenectomy due to injuries suffered in a ski accident.

Physical examination headache,fatigue,fever,shaking chills joint and muscle aches, and other vague flu-like symptoms

Laboratory tests Blood count, and thick and thin blood smears. The thin smears, stained with Giemsa stain, →intraerythrocytic,pleomorphic, ringlike and crucifix-shaped structures, found peripherally in the pale red blood cells.

Fig.16.1

Babesiosis ( 巴貝氏原蟲病 ) Intraerythrocytic protozoan →malarialike illness

ETIOLOGY Babesia, B. microti &B. divergens are the most that cause human infections. Hosts→rodents,birds Reservoir→Ticks Vectors →Ixodid (hard-bodied) ticks Ixodes scapularis (I. dammini) I. ricinus,.

EPIDEMIOLOGY Ticks is prevalent: Nantucket Island of Massachusetts Block Island in Rhode Island Long Island,Shelter Island, Fire Island in New York focal areas in Connecticut, Wisconsin, Minnesota Between May~August In Nantucket → 60% of deer mice are infected with B. microti.

CLINICAL PRESENTATION Varies widely and resembles malaria or rickettsiosis Gradual onset of irregular fever, chills, sweating, muscle pain, and fatigue. Mild hepatosplenomegaly and mild hemolytic anemia progressing to jaundice, hemoglobinemia, and renal failure. The level of parasitemia may range from 1 to 50%.

DIAGNOSIS History:tick bites, febrile persons living in endemic areas Laboratory exam

Laboratory Findings Hemolytic anemia, normal to low leukocyte counts, abnormal liver function. Giemsa-stained blood smears :Ring forms & pleomorphic intraerythrocytic organisms on Unlike malaria, Babesia organisms do not produce pigment in RBC the absence of gametocytes and intracellular pigmentation help distinguish babesiosis from malaria. Indirect immunofluorescenceantibody test

Giemsa-stain For differentiate nuclear and/or cytoplasmic morphology of platelets, RBCs, WBCs, and parasites. In Wright- and Giemsa-stain:  the cytoplasm appears blue.  the nucleus is relatively large, eccentrically located, and red.  the distinct, rod-shaped, red-staining kinetoplast (a specialized mitochondrial structure) contains extranuclear DNA arranged as catenated minicircles and maxicircles

TREATMENT Intact spleen→self-limiting although symptoms may persist for months. Clindamycin(1.2 g Bid IV or 600 mg Tid po for 7~10 days) Quinine(650mgTid po for 7 days) Atovaquone(750mg po Bid for 7~10 days) Azithromycin(600 mg po Qd for 7~10 days) Severe infections (parasitemia/asplenic)→in addition to exchange transfusions Occasionally, pulmonary edema may develop after initiation of therapy.

Question 1 What is the probable diagnosis of this patient's infection? Name the protozoan blood parasite which is most likely to be responsible for this infection.

Answer 1 Dx→Babesiosis Protozoan → B. microti & B. divergens are the two that cause most human infections

Question 2 What are the ringlike and crucifix-shaped structures seen in the peripheral blood smear? Which aspect of the patient's history led to your conclusion about her diagnosis? Do you think that her history of having a splenectomy would have any relationship to her illness?

Answer 2 Ringlike&crucifix-shaped structures→merozoite Hints: 1.She had recently spent the summer working as a waitress in Nantucket,Mass. 2.She had had a splenectomy due to injuries suffered in a ski accident.

Question 3 Why is this infection common only in certain geographical areas?

Answer 3 Ticks is prevalent: Nantucket Island of Massachusetts Block Island in Rhode Island Long Island,Shelter Island, Fire Island in New York focal areas in Connecticut, Wisconsin, Minnesota Between May~August In Nantucket → 60% of deer mice are infected with B. microti.

Question 4 Which other infections are transmitted by the same vector?

Answer 4 Vector→Ticks ( 壁蝨 ) The tick of may simultaneously transmit 1.Borrelia burgdorferithe→Lyme disease 2.Ehrlichia (Anaplasma) species→ehrlichiosis (Rickettsia, Ehrlichia) =>Those coinfections may make clinical illness more severe and warrant special therapy.

Question 5 Describe the life cycle of this parasite.

Answer 5

Ticks ingest Babesia while feeding, and the parasite multiplies within the tick's gut wall. The organisms then spread to the salivary glands; their inoculation into a vertebrate host by a tick larva, nymph, or adult completes the cycle of transmission. Asexual reproduction of Babesia within RBCs1 produces two or four parasites RBCs

Question 6 In which other manner may this infection be transmitted?

Answer 6 Blood transfusion Acquired perinatally

Question 7 How do infections with this parasite in other geographical areas differ from the case described here?

Answer 7 The causative agent of babesiosis varies according to geographical region. Geographical region Northeastern United States California Washington Europe Protozoan Babesia microtiBabesia gibsoni Babesia divergens Vector Ixodes tick (transmits Lyme disease) unidentified Ixodes tick

Question 8 How may this infection be treated?

Answer 8 Intact spleen→self-limiting although symptoms may persist for months. Clindamycin(1.2 g Bid IV or 600 mg Tid po for 7~10 days) Quinine(650mgTid po for 7 days) Atovaquone(750mg po Bid for 7~10 days) Azithromycin(600 mg po Qd for 7~10 days) Severe infections (parasitemia/asplenic)→in addition to exchange transfusions Occasionally, pulmonary edema may develop after initiation of therapy.

References Harrison's Principles of Internal Medicine - 16th Ed. (2005) Infectious disease the clinican’s guide to diagnosis treatment and prevention 2005