Once HIV has had enough time to wear away at the immune system by steadily destroying the cells that once protected the body from invasion, symptoms of AIDS begin to appear. Indeed, the disease is officially defined by particularly low counts of CD4- expressing T-cells in a patient’s blood47. As a result of this decreased arsenal of immune cells, a plethora of normally harmless bacteria, fungi, and other microorganisms begin to invade the body. These infections, called opportunistic because they don’t infect individuals with healthy immune systems, require the “opportunity” offered when HIV destroys T cells to enter a human body. In this sense, HIV doesn’t actually kill a person; it merely opens the way for an army of other threats to colonize its immunodeficient victim including bacteria, fungi, other viruses, and parasites49.
Bacteria: A good example of an opportunistic bacterial infection is Pseudomonas aeruginosa, a microbe found throughout the natural world, including the human body. Normally harmless, the bacteria grows to unhealthy numbers in AIDS patients, causing pneumonia, ulcers, dermatitis (e.g. skin inflammation) and other reactions50. This diversity of symptoms is a reminder that each AIDS patient may have an entirely different reaction to the disease.
Fungal: The most common cause of fungal pneumonia among AIDS patients is Cryptococcus neoformans, a type of yeast that occurs naturally in soil samples and bird excrement51. It can also cause meningitis, as it has a tendency to colonize the central nervous system (CNS) in immunodepressed individuals such as AIDS patients.
Viral: Just because a patient has HIV doesn’t preclude infection with other viruses; in fact, it may actually make it easier for other viruses to invade, such as Cytomegalovirus (CMV), one of the major causes of mortality during the early US AIDS epidemic52. CMV causes a number of symptoms, from retinal lesions to CNS disorders53.
Parasites: Toxoplasma gondii is an example of a parasite that preys upon AIDS patients; it is normally encountered in uncooked meat or vegetables54. In AIDS patients, Toxoplasma colonization often causes sores in the brain, called lesions55. This condition, called toxoplasmic encephalitis, can produce neurological symptoms such as seizures and movement disorders, though it isn’t usually fatal56,57.
Comprehension Questions:
1. What does it mean to be “immunodeficient”?
2. How do pathogens that infect immunodeficient patients differ from regular pathogens?
