Final answer:
IgM antibodies to T. gondii in an adult indicate a current or recent infection because they are the first antibodies produced in response to an infection. IgG antibodies signal a later stage or past exposure. A follow-up serum test can confirm ongoing infections.
Step-by-step explanation:
IgM antibodies to T. gondii in an adult are an indicator of current or recent infection. IgM antibodies are the first to be produced in response to an initial exposure to an antigen. They suggest that the patient's immune system is actively responding to a recent infection by T. gondii. The presence of these antibodies does not indicate chronic infection, past infection, or antibodies transmitted from another person.
It is important to note that IgG antibodies would indicate a later stage of infection or past exposure as they are produced after class switching during the immune response. If there is concern about whether the infection is active, a second serum sample can be taken two weeks later; a four-fold increase in neutralizing titer would suggest a new or ongoing infection.