Plasmodium determination

Dibakou, Serge Ely, Souza, Alain, Boundenga, Larson, Givalois, Laurent, Mercier-Delarue, Séverine, Simon, François, Prugnolle, Franck, Huchard, Elise & Charpentier, Marie Je., 2020, Ecological, parasitological and individual determinants of plasma neopterin levels in a natural mandrill population, International Journal for Parasitology: Parasites and Wildlife 11, pp. 198-206 : 200-201

2.6. Plasmodium determination

We evaluated the impact of Plasmodium parasitaemia on neopterin concentrations and performed qPCRs designed to amplify two different fragments located in the cytochrome b gene, one specific of P. mandrilli (106bp) and the other of P. gonderi (188bp), as previously described ( Charpentier et al., 2019). In the studied mandrills, average prevalences were 33.0–41.1% (female-male, resp.) for P. mandrilli and 37.6–43.9% (female-male, resp.) for P. gonderi (and see: Charpentier et al., 2019). In our sample, parasitaemia ranged from 1 to 1,267,280 copies in females per μl of blood (median: 0; mean ± SD: 61 ± 216 after excluding one outlier - i.e.> 130,000 copies) and 1–273,424 copies in males (median: 0; mean ± SD: 540 ± 3182 after excluding two outliers) for P. mandrilli and from 1 to 2,551,395 copies in females (median: 0; mean ± SD: 1296 ± 8247 after excluding one outlier) and from 1 to 100,182 copies in males (median: 0; mean ± SD: 1614 ± 10,154) for P. gonderi . Both parasitaemia were uncorrelated in the three data sets (Pearson correlations: all individuals r = −0.007, P = 0.92; adult females: r = −0.015, P = 0.90; adult males: r = −0.068, P = 0.73).

2.7. SIV status

Like in HIV-infected human populations, the diagnosis of the SIV status is a combination of serological and molecular assays in the initial phase of the infection. We first screened sera samples for specific antibodies to SIVmnd-1 and SIVmnd-2 as previously reported (Souquière et al., 2001). Briefly, we determined the antibody reactivity against the SIV V3 loop Env protein by a specific SIVmnd peptide-based immunoassay. This initial screening is highly sensitive and primary infection can therefore be detected as early as 2–3 days following infection. Positive samples were then tested by PCR to quantify viral load and pol sequenced for phylogenetic analyses to differentiate between the two SIV types (Souquière et al., 2001). The combination between immunoassays and quantitative PCR allowed to identify the early stages of a primary infection characterized by the presence of viruses in large quantities and the absence (or very low quantities) of antibodies. The late stages of a primary infection (1–6 months following infection) were then inferred from Western Blot profiles. They are characterized by the absence (or low quantity) of viruses with the persistence of a particular pattern of reactivity against viral proteins (no reactivity against viral enzymes) in Western Blot. Primo-infection is followed by a chronic phase, also determined by Western Blot, associated to a slight decrease in CD4 + T cells count, and a lower proportion of naïve CD8 + T cells (Pandrea et al., 2003; Souquière et al., 2014) .

In the study population, 13 males (aged 8.9–20.4) and 2 females (aged 10.6–19.5) were positive to SIV infection. We considered two stages of SIV infection because each of them represents an important phase of the virus cycle: primo-infection (high viremia) and chronic infection (Onanga et al., 2006, 2002).