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

Abstract

Abstract. Mandrills (Mandrillus sphinx) experimentally infected with human Loa loa usually remain microfilaremic for a long period of time. Nevertheless some control their microfilaremia while still harboring adults worms, and therefore become occult-infected. A nested polymerase chain reaction (PCR) assay, targeted on the repeat 3 region of the gene coding for the L. loa 15-kD protein (15r3-PCR), has been evaluated in mandrills infected with third-stage larvae (L3) of L. loa. The results of this assay were negative during the prepatency period (4 months after inoculation), but became positive when microfilariae appeared in the blood, and remained positive in all mandrills, even in those that became amicrofilaremic. These results show that the positivity 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.Loa loa is a filarial parasite transmitted by tabanid flies that is limited to the rain forest of central and west Africa. 1 This parasite has been estimated to cause chronic infection in as many as 13 million people. The disease is usually characterized by localized angioedema, arthralgia, or ocular problems caused by subconjunctival migration of the adult worms. In exceptional cases, serious sequelae such as endomyocardial fibrosis, 2 renal and pulmonary complications, 3,4 and encephalitis after administration of diethylcarbamazine 5,6 have been reported.In endemic areas, 20-30% of residents are microfilaremic, 7,8 and about twice as many are occult infected, harboring adult worms without showing microfilaremia. 9,10 Microscopy is universally used for both collection of epidemiologic data and medical diagnosis of loiasis, but this method is unable to detect occult infection. Various antibody-based assays have been used to measure host antibodies in L. loa-exposed or -infected individuals, 11 but these assays are not able to distinguish between past and current infection, nor can they be used to assess the efficacy of chemotherapeutic agents. 12 Currently, to overcome these problems, polymerase chain reaction (PCR) assays have been developed to detect several filarial species in blood from infected individuals: Brugia malayi, 13 Wuchereria bancrofti, [14][15][16] and L. loa. 17,18Research on the L. loa parasite has been hampered by the lack of a suitable animal model. However, since 1990 it has been shown that the mandrill (Mandrillus sphinx) can be experimentally infected with human L. loa. 19 Moreover, the evolution of infection is closely related to that seen in humans after long-term follow-up. 20 The aim of the present study was to investigate the ability to detect and to followup the evolution of human L. loa experimental infection in mandrills using a PCR assay. MATERIALS AND METHODS Animals.Twelve 2-5-year-old M. sphinx housed at the CIRMF Primate Center were screened for the presence of microfilariae in blood by leukoconcentration and by PCR. Eight had negative results b...

Loiasis

“…The specificity and sensitivity of this method are 100% and 95%, respectively. This molecular assay gives negative results during prepatency, however, and the DNA detected may be derived from just dead or dying mff (Touré et al, 1999b).…”

Analysis of Alternatively Spliced Domains in Multimodular Gene Products - The Extracellular Matrix Glycoprotein Tenascin C

“…(Touré et al 1999b). L.15r3-PCR also detects simian occult L. loa and could be used to identify infected animals before their inclusion in preclinical trials.…”