Severe or fatal complications can occur at any time and are related to the obstruction of vessels in the internal

organs (liver, intestinal tract, adrenal glands, intravascular hemolysis/black water fever, and kidneys).

Blackwater fever is a complication of malaria that is a result of red blood cell lysis, releasing hemoglobin into

the bloodstream and urine, causing discoloration. The severity of the complications may not correlate with the

peripheral blood parasitemia, particularly in P. falciparum infections in a patient who has never been exposed

to malaria before (immunologically naïve).

Disseminated intravascular coagulation is a rare complication and is seen with a high parasitemia, pulmonary

edema, anemia, and cerebral and renal complications.

Vascular endothelial damage from endotoxins and bound parasitized blood cells may lead to clot formation in

small vessels. Cerebral malaria is more common in P. falciparum malaria, but can occur in the other species. If

the onset is gradual, the patient becomes disoriented or violent or may develop severe headaches and pass into

coma. However, some patients, including those with no prior symptoms, may suddenly become comatose.

Physical signs of central nervous system involvement vary, and there is no correlation between the severity of

the symptoms and the parasitemia.

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Extreme fevers, 41.7° C (107° F) or higher, may occur in an uncomplicated malaria attack or in cases of

cerebral malaria. Without vigorous therapy, the patient usually dies. Cerebral malaria is considered to be the

most serious complication and the major cause of death with P. falciparum; it occurs in up to 10% of all P.

falciparum patients admitted to the hospital and is responsible for 80% of fatal cases.

Plasmodium knowlesi

General Characteristics:

 P. knowlesi invades all ages of RBCs, and the number of infected cells can be significantly more than seen in

P. vivax, P. ovale, and P. malariae. P. knowlesi infection should be considered in patients with a travel history

to forested areas of Southeast Asia, especially if P. malariae is diagnosed, unusual forms are seen with

microscopy, or if a mixed infection with P. falciparum/P. malariae is diagnosed. Because the disease is

potentially fatal, proper identification to the species level is critical.

The early blood stages of P. knowlesi resemble those of P. falciparum, whereas the mature blood stages and

gametocytes resemble those of P. malariae.

Unfortunately, these infections are often misdiagnosed as the relatively benign P. malariae; however, infections

with P. knowlesi can be fatal. The RBCs are all sizes, there is no true stippling (fine, granular, blue stippling in

RBCs stained with Wright’s stain or red when using eosin hematoxylin as seen in Figure 21 (P. vivax photo,

third from the top), often there are multiple rings per RBC (there may be 2 to 3 rings), the rings ar delicate and

often have 2 to 3 dots of chromatin, band forms are typically seen with the developing trophozoites, and the

mature schizont contains 16 merozoites. The early stages mimic P. falciparum, whereas the later stages mimic

P. malariae. Because of different levels of parasitemia, low organism densities, and confusion among various

morphologic criteria for identification, detection of mixed infections can be quite difficult. Even if a mixed

infection is suspected, identification to the species level may not be possible using routine microscopy methods.

However, using polymerase chain reaction (PCR) methods, it is likely that higher detection and identification

rates of chronic and mixed malarial infections will be possible.

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Pathogenesis and Spectrum of Disease:

 Patients exhibit chills, minor headaches, and daily lowgrade fever. Patients who have been diagnosed with high numbers

of P. malariae organisms by microscopy should receive intensive management as appropriate for severe P. falciparum

malaria, assuming the infection is actually caused by P. knowlesi. Overall, these infections can beas severe as those caused

by P. falciparum, with fatal.

Laboratory diagnosis (ALL SPECIES):

 Examination of a single blood specimen is not sufficient to exclude the diagnosis of malaria, especially when the

patient has received partial prophylaxis or therapy and has a low number of organisms in the blood. Patients with a

relapse case or an early primary case may also have few organisms in the blood smear. Regardless of the presence or

absence of any fever periodicity, both thick (Figure 23) and thin blood films should be prepared immediately, and at

least 200 to 300 oil immersion fields should be examined on both films before a negative report is issued. If the

initial specimen is negative, additional blood specimens should be examined over a 36-hour time frame.

 Although Giemsa stain is recommended for all parasitic blood work, the organisms can also be seen with other

blood stains, such as Wright’s stain. Using any of the blood stains, the white blood cells (WBCs) serve as the builtin quality control; if the WBCs look good, any parasites present will also look good. compares the multinucleated

stages (schizont) of Plasmodium malariae and Plasmodium vivax. Fluorescent nucleic acid stains, such as acridine

orange, may also be used to identify organisms in infected RBCs. However, this may be more difficult to interpret

because of the presence of white blood cell nuclei or RBC Howell-Jolly bodies.

Figure 22 Plasmodium falciparum. A, Ring forms; B, oocyte; and C, sporozoites.

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Serologic Methods:

 Several rapid malaria tests (RMTs) are now commercially available.

Molecular Diagnostics:

Other methods include direct detection of the five species by using a specific DNA probe after PCR amplification

of target DNA sequences.

Therapy:

Antimalarial drugs are classified according to the stage of malaria against which they are targeted. These drugs

are referred to as tissue schizonticides (which kill tissue schizonts), blood schizonticides (which kill blood

schizonts), gametocytocides (which kill gametocytes), and sporonticides (which prevent formation of sporozoites

within the mosquito). It is important for the clinician to know the species of Plasmodium involved in the

infection, the estimated parasitemia, and the geographic and patient travel history to assess the possibility of drug

resistance related to the organism and geographic area.

Babesia spp.:

 The genus Babesia includes approximately 100 species transmitted by ticks of the genus Ixodes. In addition to

humans, these blood parasites infect a variety of wild and domestic animals.

General characteristics:

 Organism Although the life cycle of Babesia spp. is similar to that of Plasmodium spp., no exoerythrocytic

stage has been described; also, sporozoites injected by the bite of an infected tick invade erythrocytes directly.

Once inside the erythrocytes, the trophozoites reproduce by binary fission rather than schizogony. Once the tick

begins to take a bloo meal; the sporozoites are injected into the host with the tick’s saliva.

Figure 23 A, Plasmodium malariae schizont. B, Plasmodium viax schizon

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The trophozoites of Babesia can mimic P. falciparum rings; however, there are differences that can help

differentiate the two organisms (Figure 24). Babesia trophozoites vary in size from 1 to 5 μm; the smallest are

smaller than P. falciparum rings. Also, ring forms outside of the RBCs and two to three rings per RBC are much

more common in Babesia. The ring forms of Babesia tend to be very pleomorphic and range in size, even within

a single RBC. The diagnostic tetrads, the Maltese Cross, though not seen in every specimen or species, may be

present (see Figure 24).

Pathogenesis and spectrum of disease:

 Babesiosis is clinically similar to malaria, and symptoms include high fever, myalgias, malaise, fatigue,

hepatosplenomegaly, and anemia.

Laboratory diagnosis:

 Examination of thick and thin stained blood films is the most direct approach t diagnosis.

Molecular Diagnostics:

Although rare, molecular methods such as PCR are available in some laboratories.

Therapy:

Mild cases caused by B. microti usually resolve spontaneously, and in more serious cases, treatment with

clindamycin and quinine or atovaquone and azithromycin is used.

Prevention:

 Personal protective measures, such as long pants, longsleeved shirts, and insect repellant, may reduce the riskof

infection when outdoors in endemic areas for the tick vectors.

Figure 24 Babesia in red blood cells.

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Trypanosoma spp.:

 Trypanosoma spp. are hemoflagellate protozoa that live in the blood and tissue of the human host ( Figures 25).

African trypanosomiasis:

The primary area of endemic infection with T. brucei gambiense (West African trypanosomiasis) coincides with

the vector tsetse fly belt through the heart of Africa, where 300,000 to 500,000 people may be infected in Western

and Central Africa. T. brucei rhodesiense (which causes Rhodesian trypanosomiasis or East African sleeping

sickness) is more limited in distribution than T. brucei gambiense, being found only in central East Africa, where

the disease has been responsible for some of the most serious obstacles to economic and social development of

Africa. Within this area, the tsetse flies prefer animal blood, which therefore limits the raising of livestock. The

infection in humans has a greater morbidity and mortality than does T. brucei gambiense infection, and game

animals, such as the bushbuck, and cattle are natural reservoir hosts.

A unique feature of African trypanosomes is their ability to change the antigenic surface coat of the outer

membrane of the trypomastigote, helping to evade the host immune response. The trypomastigote surface is

Figure 25Trypanosoma cruzi trypomastigote

Figure 26 A, Trypanosoma cruzi in blood film (1600×). B, Trypanosoma cruzi parasites in cardiac muscle (2500×).

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covered with a dense coat of variant surface glycoprotein (VSG). There are approximately 100 to 1000 genes in

the genome, responsible for encoding as many as 1000 different VSGs. More than 100 serotypes have been

detected in a single infection. It is postulated that the trypomastigote changes its antigenic coat about every 5 to 7

days (antigenic variation). This change is responsible for successive waves of parasitemia every 7 to 14 days and

allows the parasite to evade the host humoral immune response.

Each time the antigenic coat changes, the host does not recognize the organism and must mount a new

immunologic response. The sustained high immunoglobulin M (IgM) levels are a result of the parasite producing

variable antigen types, and in an immunocompetent host, the absence of elevated IgM levels in serum rules out

trypanosomiasis.

General Characteristics:

Trypanosomal forms are ingested by the tsetse fly (Glossina spp.) when a blood meal is taken. The organisms

multiply in the lumen of the midgut and hindgut of the fly. After approximately 2 weeks, the organisms migrate

back to salivary glands where the organisms attach to the epithelial cells of the salivary ducts and then transform to

their epimastigote forms. Multiplication continues within the salivary gland, and metacyclic (infective) forms

develop from the epimastigotes in 2 to 5 days.

While feeding, the fly introduces the metacyclic trypanosomal forms into the next victim in saliva injected into the

puncture wound. The entire developmental cycle in the fly takes about 3 weeks, and once infected, the tsetse fly

remains infected for life.

In fresh blood, the trypanosomes move rapidly among the red blood cells. An undulating membrane and flagellum

may be seen with slower moving organisms. The trypomastigote forms are 14 to 33 μm long and 1.5 to 3.5 μm

wide , With a blood stain, the granular cytoplasm stains pale blue. The centrally located nucleus stains reddish. At

the posterior end of the organism is the kinetoplast, which also stains reddish, and the remaining intracytoplasmic

flagellum (axoneme), which may not be noticeable. The flagellum arises from the kinetoplast, as does the

undulating membrane.

The flagellum runs along the edge of the undulating membrane until the undulating membrane merges with the

trypanosome body at the anterior end of the organism. At this point, the flagellum becomes free to extend beyond

the body.

Pathogenesis and Spectrum of Disease:

 Trypanosoma brucei gambiense. African trypanosomiasis caused by T. brucei gambiense (West African sleeping

sickness) has a long, mild, chronic course that ends in death with central nervous system (CNS) involvement after

several years’ duration. This is unlike the disease caused by T. brucei rhodesiense (East African sleeping

sickness), which has a short course and ends fatally within 1 year. After the host has been bitten by an infected

tsetse fly, a nodule or chancre at the site may develop after a few days. Usually, this primary lesion will resolve

spontaneously within 1 to 2 weeks, and is rarely seen in patients living in an endemic area. Trypomastigotes may

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be detected in fluid aspirated from the ulcer. The trypomastigotes enter the bloodstream, causing a low-grade

parasitemia that may continue for months with the patient remaining asymptomatic. This is considered stage I

disease, where the patient can have systemic trypanosomiasis without CNS involvement. During this time,

theparasites may be difficult to detect, even by thick blood film examinations. The infection may self-cure during

this period without development of symptoms or lymph node invasion. Symptoms may occur months to years after

infection. When the lymph nodes are invaded, the first symptoms appear and include remittent, irregular fevers

with night sweats. Headaches, malaise, and anorexia may also be present. The febrile periods of up to 1 week

alternate with afebrile periods of variable duration. Many trypomastigotes may be found in the circulating blood

during fevers, but few are seen during afebrile periods. Lymphadenopathy is a consistent feature of Gambian

trypanosomiasis, and the enlarged lymph nodes are soft and painless. In addition to lymph node involvement, the

spleen and liver become enlarged. With Gambian trypanosomiasis, the blood lymphatic stage may last for years

before the sleeping sickness syndrome occurs. When the organisms finally invade the CNS, the sleeping sickness

stage of the infection is initiated (stage II disease). Behavioral and personality changes are seen during CNS

invasion. This stage of the disease is characterized by steady progressive meningoencephalitis, apathy, confusion,

fatigue, loss of coordination, and somnolence (state of drowsiness). In the terminal phase of the disease, the patient

becomes emaciated and progresses to profound coma and death, usually from secondary infection. Thus, the

typical signs of true sleeping sickness are seen in patients with Gambian disease.

Trypanosoma brucei rhodesiense. T. brucei rhodesiense produces a more rapid, fulminating disease than does T.

brucei gambiense. Fever, severe headaches, irritability, extreme fatigue, swollen lymph nodes, and aching muscles

and joints are typical symptoms. Progressive confusion, personality changes, slurred speech, seizures, and difficulty in

walking and talking occur as the organisms invade the CNS. The early stages of the infection are like those of T.

brucei gambiense infections. However, CNS invasion occurs early, the disease progresses more rapidly, and death

may occur before there is extensive CNS involvement. The incubation period is short, often within 1 to 4 weeks,

with trypomastigotes being more numerous and appearing earlier in the blood. Lymph node involvement is less

pronounced. Febrile episodes are more frequent, and the patients are more anemic and more likely to develop

myocarditis or jaundice. Some patients may develop persistent tachycardia, and death may result from arrhythmia and

congestive heart failure. Myocarditis may develop in patients with Gambian trypanosomiasisbut is more common and

severe with the Rhodesian form.

Laboratory Diagnosis (All Species):

Routine Methods. Blood can be collected from either finger stick or venipuncture (use EDTA anticoagulant).

Multiple thick and thin blood films should be made for examination, and multiple blood examinations should be

done before trypanosomiasis is ruled out. Parasites will be found in large numbers in the blood during the febrile

period and in small numbers when the patient is afebrile. In addition to thin and thick blood films, a buffy coat

concentration method is recommended to detect the parasites. Parasites can be detected on thin blood films with a

detection limit at approximately 1 parasite/200 microscopic fields (high dry power magnification, ×400) and thick

blood smears when the numbers are greater than 2000/mL, and when they are greater than 100/mL with hematocrit

capillary tube concentration.

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Antigen Detection. A simple and rapid test, the card

indirect agglutination trypanosomiasis test (TrypTect CIATT), is available, primarily in areas of endemic

infection, for the detection of circulating antigens in persons with African trypanosomiasis. The sensitivity of the

test (95.8% for T. brucei gambiense and 97.7% for T. brucei rhodesiense) is significantly higher than those for

lymph node puncture, micro hematocrit centrifugation, and cerebrospinal fluid examination (CSF) after single and

double centrifugation. Its specificity is excellent, and it has a high positive predictive value.

Antibody Detection. Serologic techniques that have been widely used for epidemiologic screening include

indirect fluorescent antibody assays (enzyme-linked immunosorbent assay [ELISA]), the indirect

hemagglutination test, and the card agglutination trypanosomiasis test. A major problem in endemic areas is that

individuals have elevated antibody levels attributable to exposure to animal trypanosomes that are noninfectious to

humans.

Serumand CSF IgM concentrations are of diagnostic value. However, CSF antibody titers should be interpreted

with caution because of the lack of reference values and the possibility that the CSF will contain serum as the

result of a traumatic tap.

Molecular Diagnostics:

Referral laboratories have used molecular methods to detect infections and differentiate species, but these

methods are not routinely used in the field.

Therapy:

All drugs used in the therapy of African trypanosomiasis are toxic and require prolonged administration.

Treatment should be started as soon as possible, and the antiparasitic drug selected depends on whether the CNS

is infected.

American trypanosomiasis:

 American trypanosomiasis (Chagas’ disease) is a zoonosis occurring throughout the American continent and

involves reduviid bugs/kissing bugs (vectors) living in close association with human reservoirs (dogs, cats,

armadillos, opossums, raccoons, and rodents). Transmission to humans depends on the defecation habits of the

insect vector.

humans vary with the geographic area. A very serious problem is disease acquisition through blood transfusion

and organ transplantation. A large number of patients with positive serologic results can remain asymptomatic.

Patients can present with either acute or chronic disease.

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Trypanosoma cruzi:

General Characteristics:

 Trypomastigotes are ingested by the bug as it obtains a blood meal. The trypomastigotes transform into

epimastigotes that multiply in the posterior portion of the bug’s midgut. After 8 to 10 days, trypomastigotes

develop from the epimastigotes. Humans contract Chagas’ disease when the bug defecates while taking a blood

meal and the parasites in the feces are rubbed or scratched into the bite wound or onto mucosal surfaces.

In humans, T. cruzi is found in two forms: amastigotes and trypomastigotes ,The trypomastigote form is present in

the blood and infects the host cells. The amastigote form multiplies within the cell, eventually destroying the cell,

and both amastigotes and trypomastigotes are released into the blood.

 The trypomastigote is approximately 20 μm long, and it usually assumes a C or U shape in stained blood films.

Trypomastigotes occur in the blood in two forms: a long slender form and a short stubby one. The nucleus is

situated in the center of the body, with a large oval kinetoplast located at the posterior extremity. A flagellum

arises from the kinetoplast and extends along the outer edge of an undulating membrane until it reaches the

anterior end of the body, where it projects as a free flagellum. When the trypomastigotes are stained with any of

the blood stains, the cytoplasm stains blue and the nucleus, kinetoplast, and flagellum stain red or violet.

When the trypomastigote penetrates a cell, it loses its flagellum and undulating membrane and divides by binary

fission to form an amastigote .

The amastigote continues to divide and eventually fills and destroys the infected cell. Both amastigote and

trypomastigote forms are released from the cell. The amastigote is indistinguishable from those found in

leishmanial infections. It is 2 to 6 μm in diameter and contains a large nucleus and rod-shaped kinetoplast that

stains red or violet with blood stains. The cytoplasm stains blue. Only the trypomastigotes are found free in the

peripheral blood.

Pathogenesis and Spectrum of Disease:

The clinical stages associated with Chagas’ disease are categorized as acute, indeterminate, and chronic. The acute

stage represents the initial encounter of the patient with the parasite, whereas the chronic phase is the result of late

sequelae. In children under the age of 5, the disease is seen in its acute form, whereas in older children and adults,

the disease is milder and is commonly diagnosed in the subacute or chronic form. The incubation period in

humans is about 7 to 14 days but is somewhat longer in some patients.