Tuberculosis TB is unique among infections associated with HIV because it is transmissible to immunocompetent people via the respiratory route is easily treatable once identified may occur in earlystage HIV disease and is preventable with drug therapy. However multidrug resistance is a potentially serious problem. Even though its incidence has declined because of the use of directly observed therapy and other improved practices in Western countries this is not the case in developing countries where HIV is most prevalent. In earlystage HIV infection CD countcells per µL TB typically presents as a pulmonary disease. In advanced HIV infection TB often presents atypically with extrapulmonary systemic disease a common feature. Symptoms are usually constitutional and are not localized to one particular site often affecting bone marrow bone urinary and gastrointestinal tracts liver regional lymph nodes and the central nervous system.

Gastrointestinal infections

Esophagitis is an inflammation of the lining of the lower end of the esophagus gullet or swallowing tube leading to the stomach. In HIV infected individuals this is normally due to fungal candidiasis or viral herpes simplex or cytomegalovirus infections. In rare cases it could be due to mycobacteria.

Unexplained chronic diarrhea in HIV infection is due to many possible causes including common bacterial Salmonella Shigella Listeria or Campylobacter and parasitic infections and uncommon opportunistic infections such as cryptosporidiosis microsporidiosis Mycobacterium avium complex MAC and viruses astrovirus adenovirus rotavirus and cytomegalovirus the latter as a course of colitis. In some cases diarrhea may be a side effect of several drugs used to treat HIV or it may simply accompany HIV infection particularly during primary HIV infection. It may also be a side effect of antibiotics used to treat bacterial causes of diarrhea common for Clostridium difficile. In the later stages of HIV infection diarrhea is thought to be a reflection of changes in the way the intestinal tract absorbs nutrients and may be an important component of HIVrelated wasting.

Neurological and psychiatric involvement

HIV infection may lead to a variety of neuropsychiatric sequelae either by infection of the now susceptible nervous system by organisms or as a direct consequence of the illness itself.

Toxoplasmosis is a disease caused by the singlecelled parasite called Toxoplasma gondii it usually infects the brain causing toxoplasma encephalitis but it can infect and cause disease in the eyes and lungs. Cryptococcal meningitis is an infection of the meninx the membrane covering the brain and spinal cord by the fungus Cryptococcus neoformans. It can cause fevers headache fatigue nausea and vomiting. Patients may also develop seizures and confusion left untreated it can be lethal.

Progressive multifocal leukoencephalopathy PML is a demyelinating disease in which the gradual destruction of the myelin sheath covering the axons of nerve cells impairs the transmission of nerve impulses. It is caused by a virus called JC virus which occurs inof the population in latent form causing disease only when the immune system has been severely weakened as is the case for AIDS patients. It progresses rapidly usually causing death within months of diagnosis.