Serological Survey of Zoonotic Viruses in Invasive and Native Commensal Rodents in Senegal,West Africa

Abstract

Increasing studies on rodent-borne diseases still highlight the major role of rodents as reservoirs of numerous zoonoses of which the frequency is likely to increase worldwide as a result of accelerated anthropogenic changes, including biological invasions. Such a situation makes pathogen detection in rodent populations important, especially in the context of developing countries characterized by high infectious disease burden. Here, we used indirect fluorescent antibody tests to describe the circulation of potentially zoonotic viruses in both invasive (Mus musculus domesticus and Rattus rattus) and native (Mastomys erythroleucus and Mastomys natalensis) murine rodent populations in Senegal (West Africa). Of the 672 rodents tested, we reported 22 seropositive tests for Hantavirus, Orthopoxvirus, and Mammarenavirus genera, and no evidence of viral coinfection. This study is the first to report serological detection of Orthopoxvirus in rodents from Senegal, Mammarenavirus in R. rattus from Africa, and Hantavirus in M. m. domesticus and in M. erythroleucus. Further specific identification of the viral agents highlighted here is urgently needed for crucial public health concerns.

Background

At least 61% of human infectious diseases are caused by pathogens shared with wild or domestic animals (Taylor et al. 2001). Risks related to such zoonotic diseases are currently increasing worldwide because of accelerated anthropogenic changes that lead to dramatic modifications in the human–animal interfaces. Among these changes, biological invasions may favor the emergence of novel zoonotic agents in new areas or impact the epidemiology of local pathogens.

Rodents are major reservoirs of numerous zoonotic diseases caused by bacteria, protozoans, or viruses (Han et al. 2015). They are among the vertebrate species that have most benefitted from human movements to spread worldwide. The synanthropy of the more widely distributed rodent species will undoubtedly increase the opportunities for disease transmission to human populations.

Here, we report the circulation of viruses hosted by murine rodents commonly found in human dwellings in Senegal. In this country, the biological invasions of the house mouse, Mus musculus domesticus, and the black rat, Rattus rattus, and their consequences on native Mastomys species (Mastomys erythroleucus and Mastomys natalensis) have been well documented (Dalecky et al. 2015). We used serological assays to detect viral genera known to include zoonotic agents: Orthopoxvirus (family Poxviridae), Mammarenavirus (family Arenaviridae), and Hantavirus (family Bunyaviridae).

Methods

Rodent sampling was conducted during the dry season in 2013 and 2014. A total of 24 sites distributed along two invasion roads (one concerning the house mouse, the other the black rat) were surveyed from Western to Eastern Senegal (Table 1). We used the standardized live-trapping protocol and autopsy procedures described in Dalecky et al. (2015). Trapping campaigns within private properties were performed with prior agreement from local authorities. All animal-related procedures were carried out under our lab agreement for experiments on wild animals (n° 34-169-1), and followed the official guidelines of the American Society of Mammalogists (Sikes et al. 2011).

Table 1.

Results of Indirect Fluorescent Antibody Test per Rodent Species and Geographical Site (the Geographical Coordinates Are Provided)

				Mastomys erythroleucus			Mastomys natalensis			Mus musculus domesticus			Rattus rattus
	Sites	Latitude (N)	Longitude (W)	N	n	S (%)	N	n	S (%)	N	n	S (%)	N	n	S (%)
Mouse invasion road	Aere Lao	16.40	−14.32	20	0	0	—	—	—	21	0	0	—	—	—
	Dagathie	15.62	−16.25	—	—	—	—	—	—	20	1 (H)	5	—	—	—
	Dendoudi	15.39	−13.53	22	—	0	—	—	—	18	0	0	—	—	—
	Doumnga Lao	16.33	−14.22	20	1 (M)	5	—	—	—	—	—	—	—	—	—
	Diomandiou walo	16.49	−15.00	14	0	0	—	—	—	—	—	—	—	—	—
	Dodel	16.48	−14.42	20	0	0	—	—	—	20	0	0	—	—	—
	Galoya	16.07	−13.85	14	1 (O)	7.1	—	—	—	21	0	0	—	—	—
	Lambango	15.46	−13.53	20	0	0	—	—	—	—	—	—	—	—	—
	Lougue	16.06	−13.91	21	1 (M)	4.8	—	—	—	22	1 (M)	4.5	—	—	—
	Mbakhana	16.08	−16.36	—	—	—	—	—	—	22	0	0	—	—	—
	Ndombo	16.43	−15.70	—	—	—	—	—	—	20	1 (H)	5	—	—	—
	Sare Maounde	15.98	−13.91	9	0	0	—	—	—	—	—	—	—	—	—
	Thilene	16.26	−16.18	—	—	—	—	—	—	20	0	0	—	—	—
Rat invasion road	Badi Nieriko	13.37	−13.37	13	1 (H)	7.7	—	—	—	—	—	—	24	1 (O); 2 (H)	4.1; 8.3
	Boutougoufara	13.39	−12.48	19	0	0	—	—	—	—	—	—	29	3 (O); 3 (M)	10.3; 10.3
	Bransan	13.26	−12.10	—	—	—	21	1 (M)	4.8	—	—	—	—	—	—
	Diakene—Wolof	12.45	−16.64	—	—	—	—	—	—	—	—	—	24	0	0
	Diattacounda	12.57	−15.68	—	—	—	—	—	—	—	—	—	28	1 (M)	3.6
	Kedougou	12.55	−12.17	—	—	—	21	0	0	—	—	—	22	0	0
	Mako	12.85	−12.35	—	—	—	26	0	0	—	—	—	—	—	—
	Marsassoum	12.83	−15.97	—	—	—	—	—	—	—	—	—	25	0	0
	Segou	12.41	−12.28	—	—	—	21	2 (M)	8.3	—	—	—	—	—	—
	Soutouta	13.80	−12.71	11	0	0	—	—	—	—	—	—	23	1 (M); 1 (H)	4.3; 4.3
	Tobor	12.66	−16.25	—	—	—	—	—	—	—	—	—	21	0	0

The letters in brackets indicate the viral genus serologically tested: (H) for Hantavirus, (M) for Mammarenavirus, and (O) for Orthopoxvirus.

N, number of rodents tested; n, number of seropositive rodents; S, seroprevalence (n/N) provided in percentage (%). “—” indicates that no rodent was trapped or tested.

Rodents were identified at the species level using morphology and genetics (from alcohol-preserved tissues deposited in the small mammal collection of the CBGP: ZFY2 gene-based RFLP for M. musculus subspecies; cytochrome b gene-based RFLP for Mastomys spp.; see references in Dalecky et al. 2015). Samples of cardiac blood were collected on 1 cm² spot on a large piece of Whatman blotting paper (Whatman International Ltd., Kent, England). Later, dried blood spot samples were eluted in 1.0 mL of phosphate-buffered saline and then tested with indirect fluorescent antibody tests (Kallio-Kokko et al. 2006) for detecting immunoglobulin G (IgG) specific or cross-reacting with cowpox virus (CPXV, orthopoxvirus), lymphocytic choriomeningitis virus (LCMV, mammarenavirus), and Dobrava-Belgrade virus (DOBV, hantavirus). Within each of the viral genera studied here, cross-reactivity between species is common. The positive controls were sera from antibody-positive humans for DOBV and CPXV, and a mouse monoclonal antibody for LCMV (Progen, Heidelberg). The secondary antibodies were anti-human (for DOBV and CPXV) and rabbit anti-mouse IgG fluorescein conjugates (DakoCytomation, Glostrup, Denmark) for LCMV.

Results and Discussion

From a total of 672 rodents tested, 22 were seropositive (Table 1). Five rodents were seropositive for orthopoxviruses and corresponded to four R. rattus and a single M. erythroleucus. Eleven rodents were seropositive for mammarenaviruses and belonged to the four species analyzed in this study. Six rodents were seropositive for hantaviruses and belonged to M. erythroleucus, M. m. domesticus, and R. rattus. Most rodents were seronegative and no rodent individual was seropositive for more than one virus genus. Serological analyses did not allow the identification of viruses at a finer specific level because of the cross-reactivity within the virus genera studied here. Besides, no appropriate sample with regard to organs collected or storage conditions was available for performing molecular assays that would enable to specify virus taxonomy.

Rodent serological studies dedicated to the viral genera targeted here remain scarce in Senegal. To our knowledge, this work is the first to provide serological evidence of orthopoxviruses in rodents from Senegal, and in M. erythroleucus from Africa. Orthopoxvirus antibodies may indicate infection with Monkeypox virus or Taterapox virus that have previously been isolated from West African rodents (Falendysz et al. 2015 and references therein). The latter belonged to other species than those studied here. We cannot, however, exclude that other Orthopoxvirus species circulate in African rodents. They could have been brought by R. rattus for which serological evidence of orthopoxviruses was found in central Africa (Salzer et al. 2013).

Mammarenavirus antibodies were already reported in M. m. domesticus and Mastomys sp. in Senegal (Saluzzo et al. 1988). Conversely, it is the first time that Mammarenavirus antibodies are reported in R. rattus in Africa. Here, Mammarenavirus antibodies detected may be those targeting virus species from Old World complex (involving LCMV, Mopeia, Lassa, Gairo, and Morogoro viruses) usually associated with murine rodents in Africa. Among these virus species, only Lassa was found to infect Mastomys species in West Africa (Olayemi et al. 2016). Current knowledge suggest that M. m. domesticus might carry LCMV of which it is known to be the natural reservoir host worldwide, including Africa.

Finally, Hantavirus antibodies were already found in R. rattus in Senegal (Witkowski et al. 2014), but this is the first serological evidence for Hantavirus infection in M. m. domesticus and M. erythroleucus in Africa. The detection of antibodies against hantaviruses in M. m. domesticus and M. erythroleucus is surprising, and deserves particular attention considering the fact that these species were not yet known as Hantavirus reservoir hosts. Hantavirus seropositivity in R. rattus may indicate infection with indigenous African hantaviruses recently identified (Witkowski et al. 2014) or more probably with hantaviruses brought by R. rattus from other continents (Kruger et al. 2015).

In conclusion, this study provides serological evidence of Hantavirus, Mammarenavirus, and Orthopoxvirus circulating in commensal rodents in Senegal. In the future, collecting appropriate samples for specific molecular screening would be of great help to identify these viruses at the species levels and thus to ascertain their geographic origin (exotic or endemic). Such research will provide important information for public and veterinary health surveillance as well as the development of prevention strategies.

Footnotes

Acknowledgments

We thank Ambroise Dalecky, Khalilou Bâ, Mamadou Kane, Aliou Sow, Philippe Gauthier, Youssou Niang, and Mamoudou Diallo for their participation in the field sampling in Senegal. We also thank Laurent Granjon and Jean-Marc Duplantier for their precious help and advice during this work. We are particularly indebted to all the people in Senegal who allowed us to carry out rodent trapping in their homes. We acknowledge the ANR ENEMI project (ANR-11-JSV7-0006) for funding and the French Embassy in Senegal for PhD scholarships.

Authors' Contributions

C.A.D. wrote the first draft of the article. N.C. and C.B. designed the rodent sampling. C.A.D., N.C., and C.B. managed and performed the extensive field work. H.H. and T.S. performed the serological analyses. N.C., H.H., T.S., and C.B. critically revised the article and gave final approval of the version to be submitted.

Author Disclosure Statement

No competing financial interests exist.

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