Epidemiology of Concomitant Infection Due to Loa loa and Mansonella perstans in Gabon

Loa loa and Mansonella perstans are blood filarial parasites, endemic in the central and western African forest block, and transmitted by chrysops and culicoides flies, respectively. Loa loa is pathogenic and represents a major obstacle to the control of co-endemic filariae. Treatment of individuals with >8000 Loa loa microfilariae/ml can result in severe adverse reactions. M. perstans is prevalent in the tropics, with undefined clinical symptoms. We screened 4392 individuals for these infections in 212 Gabonese villages. The overall prevalence rates were 22.4% for Loa loa microfilariae, 10.2% for M. perstans, and 3.2% for mixed infection. These rates varied across the different ecosystems: forest, savannah, Lakeland, river (Ogouée), and equator. A correlation was found between the prevalence and intensity of microfilariae, while a negative relationship was found between clinical symptoms (pruritis, Calabar swelling) and the prevalence of Loa loa microfilaremia. This study confirms the spatial uniformity of the relationship between parasitological indices, and provides a map and baseline data for implementation of mass chemotherapy for these infections

Genetic immunisation by liver stage antigen 3 protects chimpanzees against malaria despite low immune responses.

BACKGROUND: The true interest of genetic immunisation might have been hastily underestimated based on overall immunogenicity data in humans and lack of parallelism with other, more classical immunisation methods. PRINCIPAL FINDINGS: Using malaria Liver Stage Antigen-3 (LSA-3), we report that genetic immunization induces in chimpanzees, the closest relative of humans, immune responses which are as scarce as those reported using other DNA vaccines in humans, but which nonetheless confer strong, sterile and reproducible protection. The pattern was consistent in 3/4 immunized apes against two high dose sporozoite challenges performed as late as 98 and 238 days post-immunization and by a heterologous strain. CONCLUSIONS: These results should, in our opinion, lead to a revisiting of the value of this unusual means of immunisation, using as a model a disease, malaria, in which virulent challenges of volunteers are ethically acceptable

Blood parasitaemia profiles in the chimpanzees after both sporozoite challenges.

<p>Names of control animals are italicized. Names of protected LSA-3 immunized chimpanzees are underlined. All results were confirmed by PCR and QBC analysis of the daily blood samples.</p

Interferon-gamma ELISpot assays.

<p>Bars correspond to the mean number of spot forming cells (SFC) per 10⁶ cells from triplicate wells, following stimulation by LSA-3 peptides (in gray), negative controls (open bars) or positive control PPD (in black) (see details in Mat. and Meth.). Results were considered as positive (dark gray) when SFC were both >20 and >the highest mean SFCs of negative controls plus two S.D. (not shown). Peptides that gave negative results in all assays are not reported here.</p

LSA-3 DNA immunization induces specific IFN-γ responses which are inhibited by an anti-MHC Class I blocking antibody.

<p>Chimpanzee's PBMC collected at week 30 were assayed for IFN-γ production in an ELISPOT assay with recombinant proteins GST-729 and GST-PC or peptide GP15, either in the absence (solid bars) or in the presence (open bars) of the HLA monomorphic monoclonal antibody W6/32 (Mat. and Meth.). Results are expressed as the mean number of IFN-γ SFCs per 1×10⁶ PBMC. The number of SFCs obtained with PBMC from the two negative control chimpanzees was not significant (not shown).</p