Specific immunoglobulins are preparations that contain a high concentration of antibodies to particular viruses or bacteria or in the case of Anti-D, high concentration of antibodies to Rhesus Factor D (RhD). If they are given soon after exposure to the virus or bacterium concerned (e.g. soon after being bitten by a rabid animal), they will help to fight infection. This is particularly important in cases, where the affected person has not previously been vaccinated against the virus or bacterium. In such cases, it takes several days before the patient's own immune system produces effective antibodies; specific immunoglobulins can help provide protection (usually lasting a few weeks).