Use of polymerase chain reaction for accurate follow-up of Loa loa experimental infection in Mandrillus sphinx

Mandrills (Mandrillus sphinx) experimentally infected with human Loa loa us ually remain microfilaremic for a long period of time. Nevertheless some co ntrol their microfilaremia while still harboring adults worms, and therefor e become occult-infected. A nested polymerase chain reaction (PCR) assay, t argeted on the repeat 3 region of the gene coding for the L. loa 15-kD prot ein (15r3-PCR), has been evaluated in mandrills infected with third-stage l arvae (L3) of L. loa. The results of this assay were negative during the pr epatency period (4 months after inoculation), but became positive when micr ofilariae appeared in the blood, and remained positive in all mandrills, ev en in those that became amicrofilaremic. These results show that the positi vity of the 15r3-PCR assay is linked to the appearance of microfilariae in peripheral blood and demonstrated that L. loa-specific DNA can be detected in blood from occult-infected mandrills.