TOPICS

HOT TOPICS IN EIA RESEARCH

Persistent Infection

One of the hallmarks of infections with EIAV and other lentiviruses is the persistence of the agent in the host for life, despite what appear to be potent immune responses to infection. Even in horses that are infected and without any outward signs of disease the virus genetic material is carried in tissue reservoirs. Some inapparent carriers of EIAV break with clinical disease with high levels of EIAV free in the blood when the immune responses that help keep the virus levels low in the blood are relaxed/inhibited by stress/drug treatment.

Figure 1
The figure shows fever responses (pink line; anything above the dotted line is a "fever") and platelet counts (yellow line) over time with 4 ponies and 2 donkeys infected with the same dose and strain of virus.

Figure 2: Cartoon demonstrating what can be seen following a 10 day treatment with a commonly used corticosteroid. For purposes of control of the infection, we make the assumption that all infected equids have the potential demonstrated here.

One way the virus evades host immune responses and persists is based on the high mutation rate in EIAV and other lentiviruses. The genes that code for the surface unit proteins contain what are called variable and hypervariable regions. The consequences of mutations in these regions are an array of constantly changing antigens displayed on the surface, giving the strain with the novel antigens a chance to replicate to high levels until specific immune responses against these new antigens are produced. The analogy we often use is a variety of constantly changing colors on the flags adorning the virus particle.

Updated on: February 17, 2010