Page 86 - AIDSBK23C

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CHAPTER 3 - OPPORTUNISTIC INFECTIONS IN AIDS

The various infectious agents that are defined by the Centers for Disease Control (CDC)
as diagnostic of AIDS when present in persons infected with HIV can produce a host of clinical
and pathologic conditions. There may be regional, racial, age, or gender-associated variations in
the incidences of opportunistic infections seen with AIDS. Table 5 depicts organ or organ
system distribution of AIDS-defining diseases in a large metropolitan public hospital autopsy
series. Table 6 indicates the extent of dissemination for those diseases. Table 7 outlines the
various treatment modalities.[396]

PNEUMOCYSTIS JIROVECI (CARINII) INFECTIONS

Prior to the AIDS epidemic, Pneumocystis jiroveci, formerly called P carinii, was known
primarily as an opportunistic pathogen of severely debilitated or immunocompromised persons,
including patients on chemotherapy, renal transplant recipients, patients with congenital immune
deficiencies, and nutritionally deprived infants. Though still infecting these groups, P jiroveci
(carinii) today is most often seen in association with AIDS. Infection with P jiroveci (carinii) is
acquired via the respiratory tract and is primarily manifested as a severe pneumonia, called
Pneumocystis jiroveci (carinii) pneumonia (PCP). P jiroveci (carinii) was originally classified
as a protozoan, but now grouped with fungi based on genetic analysis. It is spread via an
airborne route from person to person. Asymptomatic colonization may occur in
immunocompetent hosts.[397]
This organism is widely distributed, with variants in many mammalian hosts, but
Pneumocystis historically has complicated the course of AIDS more often in North America and
Europe than in Africa and Asia. However, the numbers of cases of PCP in developed nations are
dropping due to prophylaxis, while cases in developing nations are increasing, particularly in
conjunction with concomitant Mycobacterium tuberculosis infection.[398]
Serologic evidence suggests that most humans have become exposed to P jiroveci
(carinii) by age 2. However, there are no defined clinical syndromes for P jiroveci (carinii)
infection in immunocompetent persons. Molecular typing has identified over 50 different
variants of P jiroveci (carinii). Most of the variations occur in the internal transcribed spacer
(ITS) regions 1 and 2 of the nuclear rRNA operon. Analysis of these genotypes reveals that
patients may become reinfected with new genotypes, or that a different genotype of the organism
may be detected during a single episode of pneumonia. However, the clinical severity of
infection is not affected by genotype.[399] Immunocompromised persons who develop PCP
probably have reinfection rather than reactivation of prior infection.[400]
P jiroveci (carinii) is a one-celled organism with a life cycle similar to that of protozoa
such as Toxoplasma gondii. Ultrastructurally, P jiroveci (carinii) organisms lack a complex
organelle system but contain intracystic bodies, which is typical of protozoa. However, both
argyrophilia of the P jiroveci (carinii) cyst walls as well as ribosomal RNA sequence studies
suggest that P jiroveci (carinii) is a fungal organism most closely related to Saccharomyces.
There is not as yet a routine culture method available for this organism outside of research
laboratories. Serologic testing is not often useful, for most people have some detectable
antibodies. Diagnosis is routinely made histopathologically by obtaining tissue or cytologic
specimens from the lung.[401,402]