Frequent and recent human acquisition of simian foamy viruses through apes' bites in central Africa

Abstract

Human infection by simian foamy viruses (SFV) can be acquired by persons occupationally exposed to non-human primates (NHP) or in natural settings. This study aimed at getting better knowledge on SFV transmission dynamics, risk factors for such a zoonotic infection and, searching for intra-familial dissemination and the level of peripheral blood (pro)viral loads in infected individuals. We studied 1,321 people from the general adult population (mean age 49 yrs, 640 women and 681 men) and 198 individuals, mostly men, all of whom had encountered a NHP with a resulting bite or scratch. All of these, either Pygmies (436) or Bantus (1085) live in villages in South Cameroon. A specific SFV Western blot was used and two nested PCRs (polymerase, and LTR) were done on all the positive/borderline samples by serology. In the general population, 2/1,321 (0.2%) persons were found to be infected. In the second group, 37/198 (18.6%) persons were SFV positive. They were mostly infected by apes (37/39) FV (mainly gorilla). Infection by monkey FV was less frequent (2/39). The viral origin of the amplified sequences matched with the history reported by the hunters, most of which (83%) are aged 20 to 40 years and acquired the infection during the last twenty years. The (pro)viral load in 33 individuals infected by a gorilla FV was quite low (<1 to 145 copies per 10(5) cells) in the peripheral blood leucocytes. Of the 30 wives and 12 children from families of FV infected persons, only one woman was seropositive in WB without subsequent viral DNA amplification. We demonstrate a high level of recent transmission of SFVs to humans in natural settings specifically following severe gorilla bites during hunting activities. The virus was found to persist over several years, with low SFV loads in infected persons. Secondary transmission remains an open question.

Figure 1. Geographic distribution of the studied population.

Samples were collected systematically in the coloured areas without specific focus on a particular site. Native inhabitants of these areas include a great variety of ethnicities among which are the Banen, Yebekolo and Soo in the Centre (orange areas), the Bakola Pygmies, Mvae and Ngumba in purple colored area and finally the Baka Pygmies, the Bulu, Fang Badjoue and Zime tribes located in the blue coloured areas. The 198 individuals from the “contact group” are indicated by red (SFV-infected) and yellow (SFV non-infected) dots. The 2 SFV infected individuals from the “general population” are represented as black dots.

Figure 2. Serological and molecular results patterns for SFV detection.

A) Western blot results using purified classical chimpanzee antigen sero-positive samples (lanes 3, 4, 6, 10, 12). Sero-indeterminate (lanes 2, 7, 8, 14). Sero-negative samples (lanes 5, 9, 11, 13). Positive SFV control serum from a gorilla-infected human (lane 15), and a macaque (lane PC). B) Nested PCR detection of 465 bp Integrase sequences of SFV M = molecular weight marker. CN = Negative Control. HFV = Human foamy virus, positive control, H2O = Water.

Figure 3. SFV infected individuals harboring scars and lesions caused by NHP bites.

Scars from wounds by a small monkey in picture 1 (participant Bad50), chimpanzee in picture 2 (participant Bad327), gorilla in picture 3 (participant Bak56), picture 4 (participant Sabak36), picture 5 (Bad348), picture 6 (participant Bak132).

Figure 4. Distribution of tested and infected individuals from the “contact group”.

A) According to the age at contact with NHP B) According to the time of the contact with NHP.

Figure 5. Rooted phylogenetic tree generated with consensus sequences of 425 bp fragments of the SFV pol-In from apes-infected hunters and prototype old world non-human primates from the apes' clades.

The final consensus sequences from our study are highlighted in red (gorilla) and green (chimpanzee). Sequences are compared to known prototypes from different central African NHP species. Alignment was performed with Dambe version 4.5.68 and Clustal W. Phylogenetic analysis was performed with Paup, version 4.0b10 (Sinauer Associates, Sunderland, MA, USA) based on the Neighbour joining method applying the GTR model. Bootstrap analysis of 1000 replicates is indicated as numbers at nodes. Only values greater than 60% are shown. The scale of the tree is 0,1 nucleotide replacements per site. The tree is rooted on a divergent sequence from an Asian macaque. Species found in Cameroon are shown with asterisks. Sequences accession numbers are: JN049036 to JN049065 for gorilla sequences and JN049033 to JN049035 for Chimpanzee sequences.

Figure 6. Rooted phylogenetic tree generated with consensus sequences of 425 bp fragments of the SFV pol-In from monkeys-infected hunters and prototype old world non-human primates from the small monkeys' clades.

The final consensus sequences from our study are highlighted in blue (monkeys). Sequences are compared to known prototypes from different central African NHP species. Alignment was performed with the Dambe version 4.5.68 and Clustal W. Phylogenetic analysis was performed with Paup, version 4.0b10 (Sinauer Associates, Sunderland, MA, USA) based on the Neighbour joining method applying the GTR model. Bootstrap analysis of 1000 replicates is shown as numbers at nodes. Only values greater than 60% are shown. The scale of the tree is 0,1 nucleotides replacement per site. The tree is rooted on a divergent sequence from an Asian macaque. Species found in Cameroon are shown with asterisks. Sequences accession numbers are: JN049028 to JN049032.