The area of the bird sampled is also an important consideration. The pharynx (throat) is best sampled early in the course of infection, since it is positive early and remains positive for a long time. The cloaca and feces tend to become positive later in infection. When possible, it is best to sample several sites.
Antibody Detection is a serologic test that may be used for Psittacosis. This test requires that the bird is able to mount an adequate immune response. IgM is an antibody that is manufactured early in the course of infection.
The EBA or Elementary Body Agglutination test measures IgM and therefore will be positive early in infection.
IgG is an antibody produced later in infection and may be elevated for a long period of time after infection and subsequent treatment. DCF or Direct Compliment Fixation detects IgG. A single positive IgG means the bird has responded to an infection in its immunilogical detectable past. IgG will decline over time. Some birds – such as the smaller psittacines – will not mount positive DCF titers. Additionally, DCF will be negative in the early stages of infection.
Therefore, a negative DCF does not mean no infection.
An active infection is demonstrated by a four-fold or greater increase in paired antibody titers taken 2 weeks apart or positive antigen assays.
A new test that has become available is the PCR – Polymerase Chain Reaction. This is a DNA amplification technique. It is extremely sensitive as well as specific and rapid. It will detect small numbers of EB’s (chlamydial organisms).
Advantages of the PCR are that it is very sensitive and specific and will detect both viable (living) and nonviable chlamydiae.
A positive PCR in asymptomatic bird means exposure. Although very sensitive, it is unable to distinguish between exposure, a carrier state, and an active infection.
Swabs taken from the cloaca and fecal samples may be evaluated for the presence of chlamydial organisms. The biggest problem with looking for shedding of the organism is that it may be shed intermittently. Thus a false negative will be the result if no chlamydiae are present in the sample evaluated.
In summary, the greatest accuracy can be achieved when the appropriate test is run at the appropriate time.
As a screen – an EBA (IgM) and PCR (using blood, choanal and cloacal swabs) may be done. If the bird is clinically ill, a PCR or Quick View Elisa (another test) may be done. Accuracy can be increased when more than one type of test is done.
The next article will discuss treatment of Psittacosis (Parrot Fever).