Part I. Introduction

In 1981, infections by the parasite Pneumocystis carinii in five previously healthy homosexual men led to the recognition of acquired immunodeficiency syndrome (AIDS) as a distinct clinical entity. Now AIDS, or human immunodeficiency virus (HIV) disease is a global health problem. Millions of people are infected and millions more severely immunocompromised, susceptible to many types of infection.

The purpose of this issue is to discuss eight parasitic infections that are commonly recognized in HIV disease in the United States: Strongyloides stercoralis, Entamoeba histolytica, Giardia lamblia, Cryptosporidium parvum, Isospora belli, the microsporidia, Toxoplasma gondii, and Pneumocystis carinii. Other parasites, some very unusual, may also be seen in the HIV positive host.

The collection, handling, and processing of specimens for parasite identification should follow standard laboratory procedures. The potential of infection when collecting stool, sputum, bronchial lavage and other specimens for parasite studies should be strongly emphasized to non-laboratory personnel, including other health-care workers, patients, and their families. These warnings would be especially important when organisms such as Strongyloides stercoralis or Cryptosporidium may be present
in the specimen..
 

Part II. The Immune Response

A. The immune response is a product of the combined activities of a variety of cells, tissues and organs.

Humoral immunity (immunoglobulin production) is mainly a result of the interaction of T helper cells (CD4+ cells), macrophages, and B cells. Cell mediated immunity involves T helper cells, macrophages, cytotoxic lymphocytes and other effector cells. T suppressor cells are important in regulating the immune response through the production of cytokines that have a suppressor effect on effector cells.

In HIV infections the immune response progressively decreases as CD4+ cells are destroyed following infection by the virus. The virus initially attaches to a membrane receptor, CD4. This is followed by entrance of the virus into the cell, replication, and finally, death of the infected cells. It should be noted that in additiion to T helper cells the virus can also infect a wide variety of other cells bearing the CD4 receptor, however, effects on these cells are not well understood.

Normal CD4 counts range from 430 to l,300 cells/mm3. Shortly after contact with the HIV virus, about l% of the CD4+ lymphocytes. When the number drops below 400/mm3, bacterial, viral, and fungal opportunistic infections develop. Pneumocystis carinni pneumonia (PCP), toxoplasmosis, and other serious parasitic infections occur mainly when the CD4 count fails below 200/mm3. The patient generally succumbs to overwhelming opportunistic infections when the count is below 50/mm3. (An earlier Learning Laboratorian issue discussed the CD4 count in the clinical interpretation of HIV disease {Kutt et al, l989].)

As HIV disease progresses, the frequency of opportunistic infections increases because of impaired immunity due to the loss of functioning T helper cells. Opportunistic infections can be atypical, more severe, and more difficult to treat than the corresponding disease in a non-HIV infected host. Symptoms of many opportunistic diseases can resemble those caused by a variety of other infectious and non-infectious conditions. The correct diagnosis of the opportunistic disease in the immunocompromised host, therefore, is critical to appropriate and timely therapy. This is especially true of parasitic infections.
Figure l illustrates the progression of immunodeficiency in HIV disease. The p24 antigen is a component of the viral capsid. It appears in the serum soon after infection (solid line) followed by antibodies to p24 (.....). Symptoms may not appear for many years (median of l0), but there are measurable low levels of viral antigen present during this time. The number of T helper lymphocytes steadily decreases, as the number and severity of clinical syndromes increases.

B. The immune response to parasites.

The immune response to parasites varies according to the type of parasite and partially to the site of infection. Extracellular parasites elicit mainly a humoral response (antibody formation) while intracellular parasites such as Toxoplasma gondii produce a cell mediated response involving macrophages and cytotoxic T cells. In addition, antibodies can enhance the killing function of macrophages against parasites through a process known as antibody-dependent cell-mediated cytotoxicity (ADCC). This may involve not only IgE but also IgE and eosinophils. Each of these different responses are mediated by the cytokines produced by CD4+ T lymphocytes. With the loss of these cells during the progress of infection there is generally reduced immune activity.

Cytokines such as gamma interferon are involved in controlling multiplication of parasites. Macrophage killing function is stimulated, e.g. affecting both the intracellular Toxoplasma gondii and the extracellular Entamoeba histolytica.

Another T cell-dependent defense is walling off of the parasite through granuloma formation (Roitt et al, l993). Although this reaction isolates the parasite and its toxins from other host tissues, the accumulation of large areas of fibrosis can damage thfunction of the tissues and organs.

In addition to loss of immune activity in the host due to the HIV virus infection, parasites themselves have a number of mechanisms that enhance their survival. These factors may result in chronic infection even in otherwise healthy individuals. The mechanisms include antigen variations, intracellular and extracellular phases, and larval and adult forum with different surface antigens. The immune response must recognize different forms and variations in order to respond in an appropriate manner. Parasites also can produce factors that suppress the immune response, others can shed large amounts of soluble antigens that may neutralize the effect of the humoral response (Roitt et al, l993).

Additionally, there are side effects of the immune response to parasitic infection that can harm the host. Increased activity of macrophages and lymphocytes can cause enlargement and damage of the liver and spleen. Immune complexes can be deposited on cell membranes, leading to complement activation, thereby damaging and disrupting cellular function. The increase of IgE that occurs during worm infections causes release of mast-cell mediators, triggering allergic responses as severe as asthma and anaphylaxis. Autoantibodies may also be produced, damaging host tissue. Excessive release of cytokines may contribute to fever, diarrhea, and pulmonary problems. Non-specific immunosuppression can lead to secondary infections with bacteria and virus.

This brief overview of the immune response and parasitic infection has shown how the steady decrease in immune function due to HIV infection of T cells plus the destructive effects of the parasites themselves can lead to serious and often overwhelming parasitic infection in the HIV infected host.
 

Part III. Specific Parasites

Opportunistic infections by bacteria, fungi, and parasites often produce diseases with similar symptoms and therefore require careful differential diagnosis since treatment is usually different for each type of organism. Clinically significant gastrointestinal disease, for example, is present in up to 90% of HIV infected patients, and may be caused by Salmonella, Shigella, Campylobacter, the mycobacteria, Clostridium difficile, Candida, Histoplasma, Cytomegalovirus, Rotavirus, HIV enteropathy, Norwalk virus, as well as a number of parasites. Non-infectious causes can be lymphomas, Kaposi's sarcoma, and drug toxicity. A brief review of parasitic infections that are common in the HIV positive host is given in the following pages. The reader should refer to other resources for detailed instructions of identification procedures and diagnostic tests.

A. Strongyloides stercoralis

Strongyloides stercoralis is an intestinal roundworm of humans, found worldwide, that causes diarrhea and a wide range of other symptoms. As the organism goes through its migratory cycle in the normal host, symptoms may resemble those of bronchitis, pneumonia, and peptic ulcer disease as well as more typical intestinal infection. Asymptomatic infection can last 30 to 40 years. Strongyloidiasis can be a serious and life threatening disseminated disease in immunocompromised patients due to hyperinfection and massive tissue invasion by the parasite. The condition is further complicated by gram negative rod septicemia and meningitis. Strongyloides infection begins when filariform larvae penetrate the skin. The complicated life cycle includes filariform larvae in the lung phase, adults in the mucosa of the small bowel, and non-infectious rhabditiform larvae in the stool. In some cases (autoinfection) rhabditiform larvae in the intestines molt to infectious filariform larvae that penetrates the skin or mucosa and repeat the infectious cycle. Autoinfection progresses rapidly in the immunocompromised host, leading to
disseminated infection. The pulmonary barrier is penetrated by the larvae, which then enter the arterial circulation and disseminate to many organs (hyperinfection syndrome).

Hyperinfection in the immunocompromised host can lead to septicemia and meningitis with enteric bacteria. The enteric bacteria are carried into the blood stream as the larvae migrate through the intestinal wall. Migrating larvae may also cause tissue and brain damage, and respiratory failure. A mortality rate approaching 50% is reported in immunocompromised patients with hyperinfection syndrome (Koneman et al, 1992).

Thiabendazole is the drug most commonly used. Ivermectin and albendazole have also been used experimentally and may be approved for use.

LABORATORY DIAGNOSIS

Laboratory diagnosis is based upon identification of the larval forms of the worm in the stool, duodenal drainage, and sputum. The form seen most often is the non-infectious rhabditiform larvae. In hyperinfection, infectious filariform larvae may be present in the stool and sputum. If stool specimens are negative, duodenal drainage should reveal the larvae, and possibly eggs and adults. The Entero-Test, consisting of weighted nylon string in a gelatin capsule, is used to sample the duodenal contents. One
end of the string is taped to the patient's face and the capsule is swallowed. The string is retrieved after 4 hours in the duodenum, and mucous is scraped off and examined. The mucous should be examined immediately by wet mount, or preserved in l0% formalin and PVA in case giardia is also present. Sputum specimens should not be concentrated, but examined in a manner similar to that used for the examination of duodenal contents.

Specimens should be examined immediately or preserved in formalin, since the larvae could molt or free living nematode contaminants (Rhabditis) could multiply, making identification more difficult. Hookworm larvae are very rare in stools, but when they are present they must be distinguished from Strongyloides larvae. Charcot-Leyden crystals, formed from disintegrated eosinophils, may also be present.

An eosinophil count should also be done, as eosinophil counts usually range from l0 to 50%. Declining or low eosinophil counts indicate a poor prognosis in strongyloidiasis (Howard et al, l994)

Safety measures are extremely important in handling all specimens. Filariform larvae, if present, could penetrate the skin of the laboratory worker and cause infection.

B. Entamoeba histolytica

Entamoeba histolytica is a protozoan parasite of humans found throughout the world, causing about 500,000 infections annually. Asymptomatic carriers are largely responsible for spread of infection through food or water contaminated by the cyst stage.

Ninety percent of infections are asymptomatic or very mild. In acute amebiasis, Entamoeba histolytica lyses the tissues of the colon and forms flask shaped ulcers. The patient may have few serious symptoms or develop severe bloody dysentery, leading to weight loss, fever, dehydration, and electrolyte imbalance. Chronic disease symptoms can be similar to those of ulcerative colitis, hepatic carcinoma, or diverticulitis. Extra-intestinal disease occurs when the organisms migrate through the intestinal mucosa into the blood or lymphatic system. The amoeba disseminate primarily to the liver, forming abscesses. Liver abscess leads to increased leukocyte count, abdominal pain, and fever. Liver function tests may remain normal, and jaundice is rare. The abscess may rupture into the pleural cavity, resulting lung infection characterized by chest pain, cough and fever. Migration of amoeba to the brain can cause focal amebic encephalitis. Dissemination of the amoeba in the immunocompromised host may
be enhanced if amebiasis is present but not diagnosed, and the patient may be treated with corticosteroids for inflammatory bowel disease. Amebiasis is treated by agents that affect the trophozoite (amoeboid) stage, and treatment depends upon the severity of the infection and its location. Large abscesses may have to be drained surgically for antibiotics to be effective. Metronidazole and iodoquin are two drugs that are commonly used in treatment, however metronidazole is not recommended for pregnant women.

LABORATORY DIAGNOSIS

Laboratory diagnosis is made by microscopic observation of the amoeba trophozoites and cysts in stool or tissue. An enzyme immunoassay to detect antigen in stool specimens is also available (Xia et al, l994) Indirect hemagglutination tests are positive in almost 87% to l00% of all liver abscesses and 85% to 95% of acute amoebic dysentery (Howard, l994). Serologic tests for antibody are unreliable in asymptomatic or non-invasive intestinal disease, or in immunocompromised patients who can no
longer mount an antibody response (Neva and Brown, l994). Where amebiasis is endemic, positive serology may indicate past infection rather than current infection.

Up to six stool specimens, collected over a l5 day period, should be examined. If bloody mucous is present, it should be selected for examination. A direct saline mount done within 30 minutes of passage may show motile amoebas. Concentration and a permanent stained smear such as trichrome should always be done. Aspirates from sigmoidoscopy should be examined immediately for motiletrophozoites.

The amoeba form, or trophozoite, is seen more often in liquid stools. The trophozoite usually ranges from l5 to 30 microns in size, and may have ingested red blood cells within the cytoplasm. The cysts, l0 to 20 microns in diameter, are more often found in formed stool specimens and can have up to four nuclei. Charcot-Leyden crystals may be present in the specimen.

C. Giardia lamblia

Giardia lamblia is a flagellated protozoan parasite of humans and other mammals, and is generally more prevalent in children. It is common worldwide, and one of the most common parasitic diseases in the United States. Prevalence is increasing in the homosexual population due to anal and oral sexual practices, but the main route of transmission is through water or food that has been contaminated by fecal material. Outbreaks have been attributed to municipal water supplies as well as to water from
mountain streams. The disease does not seem to be any more severe in immunocompromised than in immunocompetent hosts. Giardia lamblia infects the duodenum. Infection ranges from asymptomatic to malabsorption syndrome, mucosal irritation, and increased mucous secretion. Patients may have pain, flatulence, bloating, and frothy, foul smelling stools. They may have non-bloody diarrhea with increased fat and mucous. Infection may involve the gall bladder, with resulting jaundice.

Quinacrime (Atabrine) or metronidazole is used for treatment.

LABORATORY DIAGNOSIS

Laboratory diagnosis is made by microscopic observation of Giardia trophozoites and cysts in stool or duodenal drainage. Enzyme immunoassays and fluorescent antibody assays that detect antigen in stool specimens are available and positive results indicate current infection (Garcia and Bruckner, l994). Presence of serum antibodies is not a good diagnostic aid because a positive result may indicate either past or present infection. Up to six stool specimens over a l5 day period may be necessary to
detect the parasite since Giardia adheres tightly to the duodenal mucosa, and tends to appear in "showers". Either the Entero-Test string capsule described for Strongyloides diagnosis, or biopsy may be necessary for detection of Giardia.

The trophozoite stage is described as having a "falling leaf" motility but this may be difficult to detect because of intestinal mucous. Using the trichrome stain the cysts are usually easy to see, however the trophozoites may be more difficult as they do not stain as readily. The pear shaped trophozoite ranges from l0 to 20 microns long and 5 to l5 micronswide. It contains two nuclei, and may be described as resembling a wide-eyed old man. On side view the trophozoite is spoon shaped. The cyst is egg shaped, 11 to l4 microns long by 7 to l0 microns wide. It contains four nuclei and a jumble of rod shaped bodies. Some cysts may be distorted; also the cytoplasm may pull away from the cyst wall leaving an empty space. The trophozoite is seen more often in liquid stools, the cyst in formed stools.

Part III Specific Parasites

D. Cryptosporidium parvum

Cryptosporidia are protozoa that infect the cells of the small bowel. They were first seen in veterinary medicine as a cause of diarrhea in calves. Today Cryptosporidiuym parvum is recognized as a worldwide cause of diarrhea in man, causing major outbreaks when water systems are contaminated, especially by animal wastes. High risk groups include workers and children in day care centers, animal handlers, and travelers, as well as the immunocompromised and malnourished.

The small bowel of humans and animals is the most common site of infection, but all areas of the gastrointestinal tract can become involved, including the esophagus, stomach, colon, and rectum, especially in the immunocompromised. Patients can have 5 to l0 watery (non-bloody), frothy, mucous-flecked stools a day, and in severe cases there may be a loss of up to l5 liters of fluid a day. There may also be nausea, fever, cramps, and loss of appetite. Severity of diarrhea is related to the number
of parasites infecting the host and the immune status of the host, particularly the number of CD4+ cells. The organism is capable of autoinfection, so the parasite burden can increase rapidly in the immunocompromised host..

Dissemination to bronchial epithelial cells can lead to respiratory infection characterized by an unremitting cough. Malnourished children as well as AIDS patients can develop respiratory disease along with diarrhea due to Cryptosporidium.

Gall bladder, biliary tract disease, and liver involvement is also possible. In gall bladder disease, cholecystectomy may be
necessary to prevent rupture and peritonitis.

Currently there is no effective treatment for cryptosporidiosis. Clinical remission seems to be related to the degree of
immunocompetence. Debilitated patients with disseminated infection usually die from overwhelming gastrointestinal disease.

LABORATORY DIAGNOSIS

The diagnostic and infective form of the parasite is the oocyst. Oocysts are round, 4 to 5 microns in diameter, and most often found in watery stools. Stool or sputum specimens should be placed in l0% formalin immediately upon collection. The stool or sputum specimen should be processed using a concentration or sedimentation procedure.

The most common test for identification is a modified acid fast stain of the formalin-ethyl acetate concentrated stool or sputum for the oocyst. Several specimens and at least five or six acid fast stains should be examined. Enzyme immunoassays and direct fluorescent assays increase sensitivity and specificity but are more expensive than the acid fast stain. They may be more useful when the parasite is present in small numbers, as when tracing the source of an outbreak.

Safety should be a primary concern both during collection, processing, and testing as the oocysts are infectious in unpreserved material.

E. Isospora belli

This protozoan parasite is more likely to be seen in patients from the Caribbean (Libman and Witzburg, l993).

Transmission is through contaminated food or water containing the oocytes, and there is some postulation that Isospora may also be sexually transmitted (Forthal and Guest, l984). Oocytes may survive in the environment for months if they are kept cool and moist.

Isospora belli infects the cells of the duodenum and jejunum of humans. Infection in the immunocompetent may be asymptomatic, mild, and transient. In AIDS patients it causes a syndrome similar to cryptosporidiosis, with up to l0 watery or soft, foamy and foul smelling stools per day. Malabsorption syndrome can also occur due to mucosal lesions and infiltration of mucosal tissue by eosinophils and other white blood cells. There may be pain and loss of appetite. In the immunocompromised patient, diarrhea can be profuse, leading to weakness, loss of appetite, and weight loss. The diarrhea may be prolonged and recur after treatment. This may be due to autoinfection of the organism.

Rest and bland diet may cure mild infections. In more severe cases, trimethoprim and sulfamethoxazole is usually effective. In AIDS patients relapse rates can be as high as 50% when antibiotic therapy is discontinued; therefore antibiotics must be administered for prolonged periods. Other drugs are effective also, including combinations of pyrimethamine and sulfadiazine.

LABORATORY DIAGNOSIS

The diagnostic and infective form of the parasite in the stool is the oocyst. The immature oocyst is most commonly seen, ellipsoidal, 20 to 30 microns long, containing a large round mass. The mature oocyst, containing two spherical sporocysts may also be seen, as well as Charcot-Leyden crystals.

Stool specimens should be preserved in l0% formalin, and concentrated. The organism may be observed on iodine stained wet mount. It is more easily seen on modified acid fast stained concentrated specimens, where the central mass of protoplasm and the sporocysts appear bright red.

F. Microsporidia

The microsporidia are obligate intracellular protozoa that are widely distributed in insects and other animals. The group is made up of several genera, Encephalitozoon, Nosema, Pleistophora, Enterocytozoon, Septata intestinalis, and Microsporidium. In AIDS patients the three reported most commonly are Enterocytozoon bieneusi, Encephalitozoon hellem, and Septata intestinalis. Spores, 2 to 7 microns in size, can be transmitted to other hosts through ingestion, inhalation, or direct inoculation.
Reports of infections are increasing, but the number of unrecognized cases is probably higher since the parasite is difficult to identify.

Microsporidia infects the enterocyte of the small bowel, causing diarrhea. Spores released from the host cell pass in the stool, or may directly reinfect the enterocyte. In the normal host the intestinal disease is mild, short, and self limiting. The most common disease in the immunocompromised host is severe enteritis with chronic watery diarrhea (four to eight non bloody stools per day), fever, nausea, anorexia and weight loss. Microsporidia in some patients may spread from the intestines
throughout the body. They have been found in the kidney, gall bladder, heart, muscle, diaphragm, liver, lungs, sinus, nasal epithelium, and eyes (Garcia and Bruckner, l993; Neva and Brown, l994). Other symptoms can include myositis and muscle degeneration, hepatitis, convulsion, vomiting, headache, fever, and unconsciousness.

Treatment results have been variable with a number of antibiotics and agents, such as metronidazole, sulfasalazine and lomotil. Disease can reactivate since organisms persist in the tissues.

LABORATORY DIAGNOSIS

Electron microscopy of biopsy specimens is the standard for identification of microsporidia, but may not be sensitive enough to detect small numbers of organisms. The organism has been stained with modified trichrome for stool and sputum, Giemsa for touch preparations of tissue, or acid fast stains for plastic-embedded tissue (Garcia and Bruckner, l994). The spore should be l to l.5 microns long, with a pink to red wall. It contains a polar tube which may appear as an interior stripe or the interior may be
clear. Bacteria, yeast, and debris can be confused with microsporidia, and positive controls must be stained and examined with the specimen stains, and these may be difficult to obtain.

AIDS patients with microsporidium infections generally have a CD4 count below 200 cells/mm3 and often below l00 cells/mm3. Specific, reliable serological tests to indicate infection have not been developed. The organisms are common in nature and a positive serological test may not indicate disease even in an immunocompetent host.

G. Toxoplasma gondii

Toxoplasma are tissue protozoa that can infect tissues of a wide variety of vertebrate animals, including humans. The organism exists as cysts (bradyzoites) in muscle and brain and as intracellular trophozoites (tachyzoites).

Transmission occurs through ingestion of raw meat or cat feces containing infective stages of the parasite. Infection in immunocompetent individuals is generally asymptomatic or mild, but congenital infection may have devastating consequences to the fetus and newborn. In the immunocompromised, the nervous system is most often involved. Toxoplasmosis is the moscommon cause of opportunistic infection in the brain in HIV positive patients. Toxoplasma is also the second most common cause of retinitis in the HIV infected host, second only to cytomegalovirus.

Intracellular tachyzoites multiply and lyse the cells, creating continually expanding lesions. In the immunocompetent hose, the parasite then forms cysts, halting the spread. Also in the immunocompromised host, the organism can spread to other organs and tissues through the bloodstream or lymphatics. Existing cysts can become reactivated.

The mild form of the disease resembles mononucleosis, with lymphadenopathy, muscle pain, and fever. Skin rash, high fever and chills, myocarditis, hepatitis, pneumonia, retinitis, and central nervous system (CNS) involvement can result from disseminated infection. Central nervous system infections result in encephalopathy, meningoencephalitis, cerebral mass lesions, altered mental state, motor impairment, seizures, abnormal reflexes, and other signs of neurologic damage.

Low doses trimethoprim with sulfamethoxazole as prophylaxis or treatment can protect against toxoplasmosis as well as Pneumocystis carinii pneumonia. Once infected, another choice of treatment is pyrimethamine and sulfadiazine. Lifelong suppressive therapy is also required, as the drugs inhibit folate metabolism and do not kill the parasite.

LABORATORY DIAGNOSIS

Serology is commonly used to indicate infection with Toxoplasma. Indirect fluorescent antibody (IFA) tests and various types of ELISA tests are used for detection of IgG and IgM antibody. Rising IgG titers and specific IgM titers of l:64 (IFA) or l:256 (ELISA) indicate probable infection in the immunocompetent host. Antibody levels peak early in infection, and a single high
serum titer of l:l000 or more may indicate a possible diagnosis. Serology may be difficult to interpret in HIV positive patients since antibody levels may be suppressed.

The presence of crescent shaped tachyzoites, 4 to 8 microns long, in tissue or spinal fluid is a significant finding microscopically.
Demonstration of the parasite on Wright or Giemsa stain of lung biopsy material is required for diagnosis of pulmonary disease.
The organism may be observed in histologic preparations of tissue or cultured in tissue culture or mice. They have been
detected by immunofluorescence within 2 days of inoculation into MRC-5 cells.

In the immunocompetent host, positive histology or culture may not be diagnostic for the disease because the cysts can be present without active infection. In the immunocompromised host with clinical symptoms, observation or isolation of the parasite along with interpretation of serologic results can be an important aid in diagnosis.

H. Pneumocystis carinii

Pneumocystis infects the alveolar spaces of the lungs in a wide variety of mammals, including humans. It has been classified as a protozoan, but recent studies indicate that it may be more closely related to the fungi.

In the immunocompetent host there is usually an asymptomatic or mild infection. Symptoms include shortness of breath, non-productive cough, and low grade fever. In immunocompromised patients onset is generally rapid, but AIDS patients may have an incubation period lasting up to a year, with weight loss, diarrhea, non-productive cough, and low grade fever. Pneumocystis is the major cause of pneumonia (PCP) in HIV infected patients (over 80%). As the disease progresses, cyanosis can develop and progress to asphyxiation and death. Extra-pulmonary infections may result following damage to the endothelial tissues, especially by methods used to aerosolize pentamidine. Choroiditis may be an earlyindication of disseminated disease.

In AIDS patients, combined trimethoprim and sulfamethoxazole is given when the CD4+ cell count drops below 200/mm2, and is the treatment of choice following infection. A more toxic drug, pentamidine isethionate can be given intramuscularly, intravenously, or as an aerosol. Oxygen and assisted ventilation may also be necessary.

LABORATORY DIAGNOSIS

Diagnosis is based on observation of the organism in lung tissue or secretions. Specimens include lung biopsy, broncho-alveolar lavage, and brush biopsy using bronchoscopy. Sputum is generally not recommended, but may be positive in AIDS patients since they usually have abundant organisms present.

A variety of stains may be used to visualize the organism. Silver stains and toluidine O can be used to stain the cysts. With silver stains, the organism appears as a brown, often crumpled disk about 5 microns in diameter. Toluidine O stains the cyst wall and trophozoites blue. Giemsa will stain the trophozoites only, as pink dots within a clear space, but is more difficult to read and interpret than the silver stain. Monoclonal antibody with immunofluorescence has been reported to improve detection of the parasite (Garcia and Bruckner, l993) . Serologic tests are not reliable for diagnosis.
 

Part IV. Conclusion

Parasitic infections that cause relatively mild diseases in the normal host can cause severe, recurrent, and life threatening infections in the immunocompromised host. Many of the parasitic diseases prevalent in HIV infected patients can have unusual manifestations and cause a wide range of non-specific symptoms; therefore, physicians may have difficulty making a clinical diagnosis. Treatment is challenging for a variety of reasons, primarily because of the lack of host immune function. With impaired antibody production, serologic tests for identification become unreliable. Other laboratory tests, therefore, are
important aids to diagnosis, not only in the detection and identification of the parasite, but also the determination of the immune status of the host.

This issue has discussed eight parasites that are frequently seen in HIV-infected and other immunocompromised patients. Table I gives an overview of the diseases and laboratory tests for each. The reader should note that opportunistic parasitic disease is not limited to these organisms. Others such as Acanthamoeba, Blastocystis, Anisakis, and Taenia are examples of parasites that the laboratorian may find associated with disease in the immunocompromised. As medical treatments and diagnostic methods become more sophisticated, more patients will be effectively treated, but there may be increasing numbers of opportunistic infections that will require the expertise of laboratory personnel. All levels of laboratory personnel should be aware of these diseases and should be trained to expect the unexpected.

Medical College of Georgia - 1993

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