1. Introduction
Simian foamy virus (SFV) is a complex retrovirus classified within the
Simiispumavirus genus under the subfamily Spumaretrovirinae [
1,
2]. SFV was first described in 1954 [
3] and isolated in 1955 [
4] and, since then, numerous non-human primates have been described as hosts, including prosimians, Old World primates (OWP) [
5,
6,
7] and American primates (AP) [
8,
9,
10,
11]. Among AP, the first SFV was detected in 1973, in a culture of brain cells from
Ateles sp. [
12]. Nevertheless, it was only after 34 years that the first complete genome of this virus was obtained [
13,
14,
15]. AP are highly diverse, with approximately 187 species distributed within 23 genera under five families (Aotidae, Atelidae, Callitrichidae, Cebidae and Pitheciidae) according to molecular analyses [
16,
17]. Among AP, 41 species (~22%) have molecular evidence of SFV infection, however only five of them have complete viral genomes sequenced, a small number considering the wide diversity of AP. The available sequences include, in addition to the one that infects
Ateles sp. (SFVasp) [
10,
15], the SFV that infects
Callithrix jacchus (SFVcja) [
18],
Sapajus xanthosternos (SFVsxa) [
13],
Brachyteles arachnoides (SFVbar) [
14] and
Saimiri sciureus (SFVssc) [
18].
Little is known about the prevalence of SFV in AP. It is estimated that the average prevalence of SFV in captive AP is 23 - 61% [
8,
11,
12,
19,
20] and among the free-living AP is 16 - 29% [
8,
9,
20]. The scarce studies on natural SFV infections are a limiting factor in our understanding of the epidemiology of this virus [
10]. Furthermore, although there are few complete and partial SFV genomes from AP available in the literature, it is possible to observe through phylogenetic analyses that in general, as in OWP, SFV follows the co-speciation theory [
9,
11,
20]. AP arrived in the Americas approximately 40 million years ago [
21], diverging between 41.1 - 22.7 million years ago [
21]. As the AP speciation occurred recently and many of the existing species occupy the same environment and have similar habits, there is evidence of cross-species transmission events of SFV between AP species and genera [
7,
20,
22,
23].
Over 40% of AP species are endangered, including lion tamarins (genus
Leontopithecus) [
24]. The
Leontopithecus genus is composed of four species:
L. rosalia (golden-lion-tamarins),
L. chrysomelas (golden-faced-lion-tamarins),
L. chrysopygus (black-lion-tamarins) and
L. caissara (black-faced-lion-tamarins) [
25].
L. rosalia is endemic to the Atlantic Forest in Rio de Janeiro, Brazil [
26]. They are arboreal and territorial primates, living in small familiar groups. Classified as endangered by the International Union for Conservation of Nature in 2022 [
27], the non-governmental organization Associação Mico-Leão-Dourado (AMLD) has been working since 1992 on the conservation of this species in Rio de Janeiro [
28].
L. chrysomelas also inhabits the Atlantic Forest, being natural of the state of Bahia, Brazil. Despite that, some
L. chrysomelas have been found in the city of Niterói, Rio de Janeiro, Brazil, as a result of an introduction by a collector in the middle 90s [
29]. Therefore, these primates have been established in fragments of the Atlantic Forest in this city. Also considered endangered,
L. chrysomelas are monitored, captured, and transported for centers of preservation in their natural habitat in Bahia by institutions such as Centro de Primatologia do Rio de Janeiro (CPRJ), Fundação Pri-Matas, Instituto Chico Mendes de Conservação da Biodiversidade (ICMBio) and Instituto Estadual do Ambiente (Inea) [
29].
Both species have ecological importance and are threatened by deforestation, habitat fragmentation, illegal traffic and diseases. They also face threats in competition for territory and resources or exposure to pathogens due to interaction with other primate species, like those from the
Callithrix genus [
30]. Although there are studies demonstrating the infection and prevalence of SFV in lion tamarins, they are limited to a few individuals and/or captive animals [
8,
11,
20,
31]. Herein, we describe for the first time the prevalence of SFV in free-living
L. rosalia and
L. chrysomelas.
4. Discussion
Despite APs being a highly diverse group with a wide geographic distribution in South and Central Americas [
51], data about the prevalence of viral agents, including SFV, remain scarce, especially in free-living populations. SFV are widely disseminated retroviral agents that coevolve with their primate hosts [
7] and their diagnosis and monitoring can serve as a biomarker of zoonotic transmission of the virus between different callitrichid species. This is the first study to show the prevalence of SFV in free-living populations of
L. chrysomelas and
L. rosalia. The SFV prevalence in both species are in agreement with those reported in previous studies, between 20 and 50% in free-living AP [
8,
11,
31]. We did observe a significant difference in the SFV proviral load (p = 0.005) between
L. chrysomelas (average SFV proviral load of 3.03 log per 10
6 cells) and
L. rosalia (3.27 log). Host immunogenetic diversity can act as a factor that impacts the viral burden in different individuals, with some managing to maintain low levels of proviral DNA and others failing to prevent viral replication and integration [
52]. The immune response to SFV is not yet well understood, however it is thought that IFN-γ production can play a role in SFV replication [
53]. In this sense, each individual could have different immune responses to SFV infections that lead to different proviral loads. Falcone
et al. argue that the distribution of infected cells in the oral mucosa might not be homogeneous [
54]. Thus, the mode of oral swabs collection may also impact the results of the proviral load detected in qPCR. In fact, Falcone
et al. found, through
in situ hybridization, that actively infected cells are distributed in small sparse foci [
54].
When comparing the prevalence of SFV infecting free-living
L. chrysomelas in this study with that of recently captured
L. chrysomelas [
11], the prevalence was similar, either in the comparison of individuals with up to six months of captivity (p = 0.72) or those that have been in captivity for more than six months (p = 0.13). In agreement to what has been found previously for OWP and AP, we did not find any significant difference between the SFV prevalence in males and females of both species, showing that sex is not a factor that impacts SFV transmission [
11,
31,
55].
Hood et al. [
52] showed that the SFV prevalence in animals tends to grow with advancing age in
Macaca fascicularis. As SFV promotes a chronic infection, implying that there is greater exposure to SFV as age advances [
20,
56], we sought to compare the SFV prevalence in juveniles, subadults and adults. The prevalence in juveniles was 29%, 22% in subadults and 42% in adults, and therefore there were no significant differences in SFV prevalence between the age groups.
In general, there was a high variability in SFV prevalence among the collection points sampled at AMLD (0 - 100%). The
L. rosalia population is distributed in 13 forest fragments, in an area of approximately 4,500 km
2 of lowland Atlantic coastal rainforest. Each fragment has limited or no forest connection with other fragments. These fragments are called management units (MUs). In 2019, AMLD had detected 24 social groups [
57]. The main factor responsible for habitat fragmentation is the presence of physical structures, such as roads, cars or traffic. This factor is known as the “barrier effect” and can cause restrictions on individual movement, ultimately resulting in losses in population size and persistence [
58]. The dispersion of
L. rosalia occurs more frequently from small and nearby fragments than from large, isolated forests. That being so, a fragmented landscape may lead to low dispersal rates [
59]. The population dynamics and viability is highly affected by dispersion [
60]. As some fragments inhabited by
L. rosalia are closer to roads than others, that may have impacted the number of collections [
58].
We attempted to correlate the geospatial arrangement of
L. rosalia with SFV prevalence, assuming that nearby groups would have similar prevalence, but due to the small sample size of each group, a robust statistical analysis was not possible to be conducted. With the provided data, we also observed the prevalence in each group within each of the AMLD animal collection points. Some points were better represented than others, as was the case at the Afetiva collection point (
Table 3). On the other hand, at other collection points, sampling probably did not represent the local population, such as at Sítio Quelinho and Andorinha points, with samples from a single group of two and four animals, respectively.
For phylogenetic analysis, a conventional PCR of the
pol region was carried out and 8% (4 out of 45) of the positive samples for SFV were amplified. SUch limited PCR amplification success may be indicative of a great genetic variability of SFV strains circulating among this group of animals. The pol PCR was developed with the few available sequences of SFV infecting the primate families Cebidae and Callitrichidae, which included SFV from
Sapajus,
Callithrix, and
Leontopithecus [
11]. In this sense, the primers used may not comprise the diversity of SFV present in these families of primates, being a major limitation for the study of molecular characterization by conventional methods. As new strains of SFV are sequenced, especially through massive sequencing techniques, an improvement in molecular techniques for detecting this virus is warranted.
The only SFV sequence of
L. rosalia obtained formed a monophyletic clade with a previous SFVlro sequence from a captive
L. rosalia specimen from the Rio de Janeiro Primate Center obtained in the study by Muniz and collaborators [
20]. However, there was no grouping with any clade of the SFVlchrysom lineages, which would be expected by the co-divergence hypothesis. The identification of two circulating strains in
L. chrysomelas was observed in [
11], in which viral strains SFVlcm-1 and SFVlcm-2 were identified. In agreement with what was found in Muniz
et al. [
8], we also observe two circulating SFV strains in the
Sapajus genus. One hypothesis is that the co-speciation process between SFV and AP might still be in progress. On the other hand, the SFVs infecting the
Leontopithecus genus do not group in the same clade, and one alternative explanation would be that ongoing zoonotic transmission events occurred that resulted in multiple SFV strains coevolving with their primate hosts in
Leontopithecus. That could explain the fact that we observe monophyletic clades of SFV within the primates families Cebidae and Callitrichidae, but the SFV infecting the same families do not cluster together.
The same phenomenon may take place in
L. rosalia, and it is possible that we have sequenced only one of the SFV strains infecting that species. A more recent cross species SFV transmission event from
Sapajus to
L. rosalia may not be discarded, but only could have occurred in captivity, since the
Sapajus apella is not autochthonous of the state of Rio de Janeiro [
61]. This could explain the grouping between the sequences of SFVlro and SFV from
S. apella seen herein, since some
L. rosalia specimens have been reintroduced into the wild or are descendants of reintroduced animals. Thus, the animals may have had direct or indirect contact with
Sapajus during their time in captivity, although it is not common for animals of different species to be housed in the same enclosure. Those hypotheses could be better investigated through the use of molecular dating techniques. However, since the sequence generated is short (213 bp) compared to the
pol gene (approximately 3,440 bp), testing such hypotheses is not currently permitted. The same event of SFVlro clustering with SFVsxa was observed in captive
L. rosalia in [
20], and the hypothesis of two independent cross-species SFV transmission events is debated, with a possible ancient host-switching. The sequencing of larger regions of
pol and/or other viral genes from the wide range of SFVs infecting AP will allow more robust phylogenetic analyses, bringing a better resolution and understanding onto the evolution of SFV in AP.
The SFV infecting Pitheciidae form a monophyletic clade with the previous Cebidae family classification [
8] and, with the recently division in the Cebidae family in Cebidae, Callitrichidae and Aotidae, multiple strains are noted infecting the three families, similar to what occurs with papillomavirus [
62]. Although the SFV infecting the Pitheciidae family do not form a monophyletic clade in our analysis, they grouped together in other studies by our group [
8,
20]. The SFV of the Atelidae family is the only one within the AP to exhibit a unique clade. We observe monophyletic clades with multiple SFV strains, except for
Sapajus xanthosternos. Several strains do not form single monophyletic clades, but rather multiple strains circulating between
Sapajus and
Leontopithecus in a virus complex for which we do not have representative viruses sequenced. Besides the short fragment used for phylogenetic and timescale analysis, the dating matches the dates of separation of the of the Old World primates and New World primates, with the split between catarrhines and platyrrhines occurring between 41.1 and 36.7 My [
21], with the crown Platyrrhini diverging in 26.5-22.7 Mya [
21]. The most recent common ancestor (MRCA) of Pitheciidae diversified approximately in 18.08 Mya [
63], the MRCA of Atelidae radiated at 15.29 My [
63] and the MRCA of Cebidae diverged in 20.86 My. The diversification between
Leontopithecus–
Callimico and
Callithrix is estimated to have occurred at 10–11 Mya [
64].
Author Contributions
Conceptualization, A.F.A.S., M.D., M.A.S.; methodology, D.L.G., T.S.M., M.A.C.C., C.F.A.S., T.M.F., M.D.H., B.C.A., F.L.S., S.S.F., S.B.M., A.P., C. R.R.; validation, C.F.A.S., T.M.F., M.D.H., B.C.A., F.L.S., S.S.F., S.B.M., A.P., C.R.R.; formal analysis, D.L.G., T.S.M., M.A.C.C., A.F.A.S., M.D.; investigation, D.L.G., T.S.M., M.A.C.C.; resources, A.F.A.S., M.D., M.A.S; data curation, D.L.G., T.S.M., M.A.C.C., T.M.F., M.D.H., B.C.A., F.L.S., S.S.F., S.B.M., A.P., C. R.R.; writing—original draft preparation, D.L.G., T.S.M., A.F.A.S., M.D.; writing—review and editing, D.L.G., T.S.M., T.M.F., A.P., C. R.R., M.A.S., M.D., A.F.A.S.; supervision, M.D., A.F.A.S.; project administration, M.D., A.F.A.S.; funding acquisition, A.F.A.S... All authors have read and agreed to the published version of the manuscript.
Figure 1.
Prevalence of SFV infection. 1A. Prevalence according to Leontopithecus species. Of the 102 L. rosalia, 34 (33%) were infected. Of the 48 L. chrysomelas, 11 (23%) were infected. The green bars represent SFV-positive individuals, while blue represents SFV-negative specimens. No significant difference was observed (p = 0.500). 1B. Prevalence according to sex in L. rosalia and in L. chrysomelas. The dark pink bars represent SFV-positive females, while light pink bars represent SFV-negative females. The dark blue bars represent SFV-positive males, while light blue bars represent the SFV-negative males. No significant difference was observed (p = 0.180). 1C. Prevalence according to the age group in L. rosalia. The green bars represent SFV-positive individuals, while blue bars represent SFV-negative individuals. SFV prevalence was split into juveniles (4 to 9 months), subadults (9 to 12 months) and adults (over 12 months). No statistically significant difference was observed between the comparison of the age classes. In all three panels, the number of individuals is found within the bars.
Figure 1.
Prevalence of SFV infection. 1A. Prevalence according to Leontopithecus species. Of the 102 L. rosalia, 34 (33%) were infected. Of the 48 L. chrysomelas, 11 (23%) were infected. The green bars represent SFV-positive individuals, while blue represents SFV-negative specimens. No significant difference was observed (p = 0.500). 1B. Prevalence according to sex in L. rosalia and in L. chrysomelas. The dark pink bars represent SFV-positive females, while light pink bars represent SFV-negative females. The dark blue bars represent SFV-positive males, while light blue bars represent the SFV-negative males. No significant difference was observed (p = 0.180). 1C. Prevalence according to the age group in L. rosalia. The green bars represent SFV-positive individuals, while blue bars represent SFV-negative individuals. SFV prevalence was split into juveniles (4 to 9 months), subadults (9 to 12 months) and adults (over 12 months). No statistically significant difference was observed between the comparison of the age classes. In all three panels, the number of individuals is found within the bars.

Figure 2.
Geographic distribution of the groups sampled in the AMLD in the state of Rio de Janeiro (RJ), in the municipalities of Silva Jardim and Rio Bonito. In (A) the state of RJ is highlighted on the map of Brazil. In (B), the collection points of AMLD in the state of RJ are highlighted. In (C), we highlight the municipalities where the collections were carried out, with Silva Jardim being the most representative, with 10 collection points, and Rio Bonito with only one. Each color represents a different collection point, as can be seen in the image. SFV prevalence in each of the collection points can be seen in the legend.
Figure 2.
Geographic distribution of the groups sampled in the AMLD in the state of Rio de Janeiro (RJ), in the municipalities of Silva Jardim and Rio Bonito. In (A) the state of RJ is highlighted on the map of Brazil. In (B), the collection points of AMLD in the state of RJ are highlighted. In (C), we highlight the municipalities where the collections were carried out, with Silva Jardim being the most representative, with 10 collection points, and Rio Bonito with only one. Each color represents a different collection point, as can be seen in the image. SFV prevalence in each of the collection points can be seen in the legend.
Figure 3.
SFV proviral load among the animals studied. (A) SFV proviral load according to species. L. rosalia is represented in green and L. chrysomelas in blue; p-value = 0.0051. (B) SFV proviral load according to sex. L. rosalia is represented in light green and L. chrysomelas in dark green. No statistically significant difference was observed according to the sex in L. rosalia (p = 0.2266) nor in L. chrysomelas (p = 0.5809). (C) SFV proviral load according to age group in L.rosalia. No significant differences were observed between age groups.
Figure 3.
SFV proviral load among the animals studied. (A) SFV proviral load according to species. L. rosalia is represented in green and L. chrysomelas in blue; p-value = 0.0051. (B) SFV proviral load according to sex. L. rosalia is represented in light green and L. chrysomelas in dark green. No statistically significant difference was observed according to the sex in L. rosalia (p = 0.2266) nor in L. chrysomelas (p = 0.5809). (C) SFV proviral load according to age group in L.rosalia. No significant differences were observed between age groups.
Figure 4.
Phylogenetic tree inferred using maximum likelihood analysis with a fragment of SFV viral polymerase (213-bp). The new sequence generated in the current study is marked with a golden star. The host species within the Callitrichidae and the Cebidae families are listed. The node labels are colored according to the host family used in the dataset. The node labels colored in black represent support for SH-aLRT and bootstrap equal to or greater than 75%. When only SH-aLRT is superior to the cutoff, the label is represented in gray, while only UFBoot node labels are represented by white squares. When both parameters are lower than 75%, no label is depicted. Purple rectangles represent the calibration points used to further explore the timescale of the phylogeny.
Figure 4.
Phylogenetic tree inferred using maximum likelihood analysis with a fragment of SFV viral polymerase (213-bp). The new sequence generated in the current study is marked with a golden star. The host species within the Callitrichidae and the Cebidae families are listed. The node labels are colored according to the host family used in the dataset. The node labels colored in black represent support for SH-aLRT and bootstrap equal to or greater than 75%. When only SH-aLRT is superior to the cutoff, the label is represented in gray, while only UFBoot node labels are represented by white squares. When both parameters are lower than 75%, no label is depicted. Purple rectangles represent the calibration points used to further explore the timescale of the phylogeny.
Figure 5.
Timescale phylogenetic tree generated by RelTime-ML. Estimated host divergence dates were used to calibrate internal nodes of the viral tree. The node labels are colored according to the host family used in the dataset. The sequence generated in the current study is marked with a golden star. The x-axis summarizes geological time scale of the timetree: Oligocene (Ol), Miocene (Mio), Plioceno (Pli) and Pleistocene (Ple).
Figure 5.
Timescale phylogenetic tree generated by RelTime-ML. Estimated host divergence dates were used to calibrate internal nodes of the viral tree. The node labels are colored according to the host family used in the dataset. The sequence generated in the current study is marked with a golden star. The x-axis summarizes geological time scale of the timetree: Oligocene (Ol), Miocene (Mio), Plioceno (Pli) and Pleistocene (Ple).
Table 1.
Demographic data of Leontopithecus population.
Table 1.
Demographic data of Leontopithecus population.
Individuals |
L. rosalia |
L. chrysomelas |
All individuals |
102 |
48 |
Males |
54 (53%) |
29 (60%) |
Females |
48 (7%) |
19 (40%) |
Adults |
48 (47%) |
N/A* |
Subadults |
23 (23%) |
N/A |
Juveniles |
31 (30%) |
N/A |
Median weight (grams) |
521 (259 - 754) g |
N/A |
Average knee-heel distance |
83 (65 -97) cm |
N/A |
Median collection per site |
5 (2-26) |
N/A |
Table 2.
SFV prevalence and proviral load according to age group in Leontopithecus rosalia.
Table 2.
SFV prevalence and proviral load according to age group in Leontopithecus rosalia.
Collection point |
Animals sampled |
Juveniles |
Subadults |
Adults |
Prevalence (%) |
Average proviral load* |
Afetiva Farm |
26 |
12 |
9 |
5 |
19 |
03.04 |
Tamarins Farm |
5 |
0 |
2 |
3 |
40 |
3.81 |
Igarapé |
12 |
3 |
3 |
6 |
50 |
3.30 |
Nova esperança |
19 |
4 |
4 |
11 |
21 |
3.14 |
Rio Vermelho |
9 |
4 |
0 |
5 |
22 |
2.74 |
Ribeirão |
2 |
0 |
0 |
2 |
0 |
N/A |
Santa Helena |
13 |
1 |
4 |
8 |
35 |
3.73 |
Santa Helena I |
4 |
1 |
1 |
2 |
50 |
4.56 |
Sítio Quelinho |
2 |
1 |
0 |
1 |
100 |
3.91 |
Tertúlio |
2 |
1 |
0 |
1 |
50 |
3.93 |
Monte Moriá |
5 |
4 |
0 |
1 |
40 |
3.63 |
Andorinha |
3 |
0 |
0 |
3 |
100 |
4.22 |
Table 3.
SFV prevalence and proviral load according to location of collection in Leontopithecus rosalia.
Table 3.
SFV prevalence and proviral load according to location of collection in Leontopithecus rosalia.
Collection point |
Group |
Animals |
Prevalence (%) |
#break#Average proviral load*
|
Afetiva |
Afetiva 1 |
2 |
50%% |
2.05 |
Afetiva |
Afetiva 2/ AF2 |
12 |
25% |
2.19 |
Afetiva |
Afetiva 3/ AF3 |
2 |
0% |
N/A* |
Afetiva |
UR |
4 |
0% |
N/A |
Afetiva |
FP |
5 |
20% |
2.33 |
Afetiva |
FP3 |
1 |
0% |
N/A |
Andorinha |
CH2 |
3 |
100% |
4.22 |
Tamarins Farm |
Sidney 3 |
1 |
100% |
3.49 |
Tamarins Farm |
TM2 |
4 |
25,00% |
4.12 |
Igarapé |
IG |
8 |
62% |
2.81 |
Igarapé |
ph2 |
4 |
25% |
1.88 |
Moriá Mount |
Ronaldo Machado (RM) |
2 |
40% |
6.63 |
Nova Esperança |
GM2 |
3 |
0% |
N/A |
Nova Esperança |
GM3 |
7 |
29% |
3.02 |
Nova Esperança |
GM4 |
2 |
100% |
3.05 |
Nova Esperança |
GM5 |
4 |
0% |
N/A |
Nova Esperança |
GM7 |
3 |
0% |
N/A |
Rio vermelho |
M6 |
1 |
100% |
2.51 |
Rio vermelho |
Mistura fina |
3 |
0% |
N/A |
Rio vermelho |
RV |
4 |
25% |
2.96 |
Rio vermelho |
RT |
1 |
0% |
N/A |
Ribeirão |
ZN |
2 |
0% |
N/A |
Santa Helena |
FN |
2 |
100% |
2.65 |
Santa Helena |
JA |
5 |
20% |
4.34 |
Santa Helena |
JN |
2 |
100% |
4.30 |
Santa Helena |
JR |
4 |
0% |
N/A |
Santa Helena 1 |
SH |
1 |
0% |
N/A |
Santa Helena 1 |
SS2 |
3 |
67% |
4.56 |
Sítio Quelinho |
q1 |
2 |
100% |
3.91 |
Tertulio |
JD |
2 |
50% |
3.93 |