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Journal of Virology, August 2008, p. 7741-7744, Vol. 82, No. 15
0022-538X/08/$08.00+0 doi:10.1128/JVI.00549-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
Interspecies Transmission of Simian Foamy Virus in a Natural Predator-Prey System 
Fabian H. Leendertz,1,2*
Florian Zirkel,1
Emmanuel Couacy-Hymann,3
Heinz Ellerbrok,1
Vladimir A. Morozov,4
Georg Pauli,1
Claudia Hedemann,1
Pierre Formenty,5
Siv Aina Jensen,1,6
Christophe Boesch,2 and
Sandra Junglen1,2
Robert Koch Institute, Nordufer 20, 13353 Berlin, Germany,1
Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany,2
Lanada/Lcpa, Bingerville, Côte d'Ivoire,3
Institute of Human Virology, University of Maryland, 725 W. Lombard Street, Baltimore, Maryland 21201,4
Ebola Taï Forest Project, World Health Organization, WHO Office, Abidjan, Côte d'Ivoire,5
Norwegian School of Veterinary Science, P.O. Box 8146 dep., N-0033 Oslo, Norway6
Received 12 March 2008/
Accepted 16 May 2008

ABSTRACT
Simian foamy viruses (SFV) are ancient retroviruses of primates
and have coevolved with their host species for as many as 30
million years. Although humans are not naturally infected with
foamy virus, infection is occasionally acquired through interspecies
transmission from nonhuman primates. We show that interspecies
transmissions occur in a natural hunter-prey system, i.e., between
wild chimpanzees and colobus monkeys, both of which harbor their
own species-specific strains of SFV. Chimpanzees infected with
chimpanzee SFV strains were shown to be coinfected with SFV
from colobus monkeys, indicating that apes are susceptible to
SFV superinfection, including highly divergent strains from
other primate species.

TEXT
Simian foamy viruses (SFV) and their nonhuman primate hosts
demonstrate coevolution (
20). Despite the fact that SFV strains
have been described for most Old World primate species, no human-specific
foamy virus has yet been identified (
16). However, zoonotic
transmissions of SFV from various nonhuman primates to zookeepers
and central African hunters or others having close contact with
nonhuman primates are known to occur (
5,
8-
10,
21,
22). Such
viruses have sequences that show a close relationship to SFV
sequences from several nonhuman primate species (Fig.
1). Until
now, it has been unclear whether such interspecies transmission
can also take place when the hunter is naturally infected with
its own species-specific SFV. Wild chimpanzees that regularly
hunt and consume western red colobus monkeys (
4) provide such
a situation.
Wild chimpanzees (
Pan troglodytes verus) and western red colobus
monkeys (
Piliocolobus badius) sharing a rainforest habitat,
the Taï National Park, Côte d'Ivoire, were tested
for SFV infection. The chimpanzees have been under human observation
for more than 25 years and are known individually as a result
of a project focusing on wild chimpanzee behavior. Tissue samples
were obtained from 14 chimpanzees that had died of anthrax,
respiratory disease, or other causes (
12,
14,
15). Samples of
blood, collected in EDTA, from nine red colobus monkeys were
obtained under anesthesia, and organ samples were collected
from the remains of a further two that had been killed and eaten
by chimpanzees (
15). All represented adult animals.
Using the SFV primers for the integrase gene (19), previous analyses revealed that 12 of the 14 chimpanzees harbored SFV strains (SFVcpz) corresponding to strains described for the chimpanzee subspecies Pan troglodytes verus (details will be published elsewhere). Also 11 red colobus monkeys were tested positive for SFV using the same primers and standard conditions (96°C for 5 min; 40 cycles 96°C for 1 min, 56°C [first PCR] or 60°C [nested PCR] for 30 s, 72°C for 1 min; and a final elongation step at 72°C for 10 min). PCR products were purified using the QIAquick PCR purification kit (Qiagen) and sequenced directly in both directions without interim cloning.
Phylogenetic analysis using the neighbor joining method (BioEdit, PHYLIP 3.572 package) of these 389-bp sequences was performed (18). Bootstrap resampling with 1,000 replicates was employed to place approximate confidence limits on individual branches. The tree revealed a species-specific SFV lineage (SFVwrc) unique to red colobus monkeys. Based on sequences derived from SFVwrc, species-specific primers were designed for a first-round PCR (SFVwrc 1s, 5' CATACAATTACCACTCCAAGCCT; SFVwrc 2as, 5' CAGACAAATCCAGTCATACCATC; 473 bp). Consecutively, two seminested PCRs combining primer SFVwrc 1s with SFVwrc 3s (5' CTCAGTACTGGTGGCCAAATCTTAGA; 220 bp) and SFVwrc 2as with SFVwrc 4as (5' CCAGTCATACCATCGACTACTACAAGG; 423 bp) were performed. SFV sequences were amplified from spleen DNA of 2 of the 14 wild chimpanzees by using the SFVwrc-specific primers. All PCR products were sequenced, aligned, and compared to the public database using BLAST NCBI (Table 1). High similarity of the sequences derived from the chimpanzees using the SFVwrc primers and the colobus monkey sequences was seen (similarity of 98 to 99%). In contrast, the SFV chimpanzee sequences derived through PCRs using the generic SFV primers were only distantly related (78 to 81%), pointing to a double infection with two different SFV isolates.
Sequences were aligned using BioEdit, and phylogenetic analyses
using the neighbor joining method as well as the maximum likelihood
algorithms (PHYLIP 3.572 package; data not shown) revealed two
well-separated clusters of colobus and chimpanzee SFV strains.
Sequences obtained from chimpanzee samples using SFV
wrc-specific
primers showed that 2 of the 14 chimpanzees already infected
with SFV
cpz were simultaneously infected with SFV
wrc (Fig.
1).
Two chimpanzees were SFV
cpz negative; however, these were infants,
and it has been shown that seroconversion usually occurs when
primates get older (
3,
11). These two chimpanzees were also
negative for SFV
wrc. It should be noted that chimpanzee and
colobus samples were collected at different times on different
occasions and handled separately at all times and that extensive
precautions were taken to avoid cross-contamination during DNA
preparation and PCR analysis.
The two dually infected chimpanzees harbored unique SFVwrc strains, indicating the introduction of SFVwrc on independent occasions, rather than onward transmission of SFVwrc among chimpanzees. Several studies have shown that exposure to saliva is a predominant route of SFV transmission (6, 7, 10, 21). It is thus likely that the two chimpanzees acquired SFVwrc in the context of predation, as especially the males are frequent hunters and may be bitten by their prey. In addition, male chimpanzees consume significantly more monkey meat than females and chew entire bones, a habit that may cause lesions in the oral cavity (4). The two SFVwrc-positive chimpanzees were both males, known to hunt frequently. We had previously demonstrated infection of these chimpanzees with another retrovirus, the simian T-cell leukemia virus type 1 (STLV-1), as a result of red colobus monkey consumption. However, in that study no preexisting infection with a chimpanzee-specific STLV was found (13). Noninvasive methods, such as those described by others (15a), will allow specific and more-extensive molecular epidemiological screenings of entire chimpanzee populations for SFVcpz and for strains specific to other primate species. Others have, for example, shown the presence of one Cercopithecus SFV among 177 SFV-positive chimpanzee fecal samples (15a). However, generic integrase primers were used for this study. The use of species-specific foamy virus primers would most likely reveal a higher prevalence of SFV from other monkey species in the predator chimpanzee. Such screenings will provide further insight into interspecies SFV transmission and will help to identify risk factors associated with SFV transmission, such as hunting frequency and feeding strategies documented in the behavior studies. Our results demonstrate that, in addition to the presence of a species-specific SFV in a given host, transmission of other SFV from other species can occur in a natural primate predator-prey system, resulting in infections with divergent SFV isolates.
Moreover, prior infection with SFVcpz does not seem to exclude infection with other SFV strains, a finding that may have important implications for foamy viruses as vaccine vectors (2). Coinfection has the potential to generate recombinants if the coinfecting viruses replicate in the same cell, possibly resulting in new pathological properties of viruses, as has been shown for simian immunodeficiency virus (1). Further studies are needed to specifically test for strain recombination and the existence of recombinant SFV lineages in wild chimpanzees. At this point, the phylogeny of the chimpanzee SFVcpz strains described here clearly supports the cospeciation hypothesis suggested by others (20).
The high prevalence of SFVcpz may be explained by intense social interactions, such as biting, whereas the low prevalence of SFVwrc in the chimpanzees suggests that SFVwrc is not or is rarely transmitted between the chimpanzees. This points to a dead-end infection of the superinfecting strain, as observed (albeit with a limited number of cases) in humans infected with SFV strains from nonhuman primates (5, 17, 21). Again, noninvasive methods will help address these issues, using wild chimpanzees as a model to investigate the fate of species-specific and new SFV in a host.
Nucleotide sequence accession numbers.
New sequences of integrase-encoding regions of SFV strains were deposited in GenBank under accession numbers EU545383 to EU545395.

ACKNOWLEDGMENTS
We thank the Ivorian authorities for their long-term support,
in particular the Ministry of the Environment and Forests, as
well as the Ministry of Research, the directorship of the Taï
National Park, and the Swiss Research Centre in Abidjan.
We thank Steven Norley and Beatrice Hahn for helpful discussions and copy editing and Julia Tesch and Angelina Kus for technical support with sequencing.

FOOTNOTES
* Corresponding author. Mailing address: NG2, Emerging Zoonoses, Robert Koch Institute, Nordufer 20, 13353 Berlin, Germany. Phone: 493045472592. Fax: 493045472181. E-mail:
LeendertzF{at}rki.de 
Published ahead of print on 28 May 2008. 

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Journal of Virology, August 2008, p. 7741-7744, Vol. 82, No. 15
0022-538X/08/$08.00+0 doi:10.1128/JVI.00549-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
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