The blood brain barrier is the brain's traffic cop, usually preventing parasites from entering the brain and taking up residence. Sometimes, though, parasites bypass this barrier. Once inside, parasites find an oasis--the brain provides an ideal environment for parasites to live and grow. Taenia solium (the pork tapeworm that causes cysticercosis), Naegleria fowleri (freshwater amoeba that causes primary amoebic meningo-cephalitis) and Toxoplasma gondii (microscopic protozoa that causes toxoplasmosis) are all parasites that can infect the brain. The most common cause of brain parasites in the United States is the pork tapeworm.
According to the Centers for Disease Control and Prevention (CDC), headaches are one of the first symptoms a person infected with one of these organisms will experience. Such headaches can be accompanied by a sensitivity to light or blurred vision. This symptom is common in all types of parasitic brain infection.
As the infection grows and begins to affect more brain tissue, the patient might experience general confusion, according to the Mayo Clinic. Such confusion might be exhibited as memory difficulties, disorientation, inattention to people and surroundings and an inability to make decisions. Both Naegleria and pork tapeworm infections cause confusion, as stated by the Mayo Clinic and Discovery.com.
Fever develops as the body's response to infection, activating the immune system. This fever may or may not help fight parasitic infection. According to Healthmad.com, some brain parasites, such as the amoeba that causes Naegleria infection, can shed portions of itself to act as a decoy against the immune system. Fever will still occur, but the immune system will "chase" the decoy, enabling the infection to progress.
Nausea, possibly triggered by the presence of parasites in particular parts of the brain, is experienced with parasitic infection. The California Institute of Technology (Cal Tech) states that when larvae attach to brain-fluid cavities, nausea can result. With pork tapeworm infection, nausea could be linked to a secondary parasitic infection in the gastrointestinal tract.
As a Naegleria infection advances, seizures can occur, according to the CDC. Cal Tech researchers, in describing pork tapeworm infection, state that seizures are caused by larvae attaching to brain tissue.
Change in Specific Brain Function
Depending on the portion of the brain that is infected, the patient might experience other specific symptoms, such as a loss of balance, paranoia or hallucinations.
According to the CDC, as a Naegleria infection progresses, the patient can develop hydrocephalus, which is fluid build-up in the brain.