Lassa serology in natural populations of rodents and horizontal transmission

Lassa virus causes hemorrhagic fever in West Africa. Previously, we demonstrated by PCR screening that only the multimammate mouse, Mastomys natalensis, hosts Lassa virus in Guinea. In the present study, we used the same specimen collection from 17 villages in Coastal, Upper, and Forest Guinea to investigate the Lassa virus serology in the rodent population. The aim was to determine the dynamics of antibody development in M. natalensis and to detect potential spillover infections in other rodent species. Immunoglobulin G (IgG) antibody screening was performed using the indirect immunofluorescence assay with the Guinean Lassa virus strain Bantou 289 as antigen. The overall seroprevalence was 8% (129/1551) with the following rodents testing positive: 109 M. natalensis, seven Mastomys erythroleucus, four Lemniscomys striatus, four Praomys daltoni, three Mus minutoides, and two Praomys rostratus. Nearly all of them (122/129) originated from Bantou, Tanganya, and Gbetaya, where Lassa virus is highly endemic in M. natalensis. The antibody seroprevalence in M. natalensis from this high-endemic area (27%; 108/396) depended on the village, habitat, host age, and host abundance. A main positive factor was age; the maximum seroprevalence reached 50% in older animals. Our data fit with a model implicating that most M. natalensis rodents become horizontally infected, clear the virus within a period significantly shorter than their life span, and develop antibodies. In addition, the detection of antibodies in other species trapped in the habitats of M. natalensis suggests spillover infections.

Determining Ancestry between Rodent- and Human-Derived Virus Sequences in Endemic Foci: Towards a More Integral Molecular Epidemiology of Lassa Fever within West Africa

Lassa fever is a viral hemorrhagic illness responsible for thousands of human deaths in West Africa yearly. Rodents are known as natural reservoirs of the causative Lassa mammarenavirus (LASV) while humans are regarded as incidental, spill-over hosts. Analysis of genetic sequences continues to add to our understanding of the evolutionary history, emergence patterns, and the epidemiology of LASV. Hitherto, the source of data in such investigations has mainly comprised human clinical samples. Presently, a rise in the quantity of virus strains accessed through ecological studies over the last 15 years now allows us to explore how LASV sequences obtained from rodents might affect phylogenetic patterns. In this study, we phylogenetically compared LASV sequences obtained from both rodents and humans across West Africa, including those from two localities highly endemic for the disease: Ekpoma in Nigeria and Kenema in Sierra Leone. We performed a time-calibrated phylogeny, using a Bayesian analysis on 198 taxa, including 102 sequences from rodents and 96 from humans. Contrary to expectation, our results show that LASV strains detected in humans within these localities, even those sampled recently, are consistently ancient to those circulating in rodents in the same area. We discuss the possibilities connected to this preliminary outcome. We also propose modalities to guide more comprehensive comparisons of human and rodent data in LASV molecular epidemiological studies.

Bacterial lipid modification enhances immunoprophylaxis of filarial abundant larval transcript-2 protein in Mastomys model

As in many other parasitic diseases, efficacious vaccine for lymphatic filariasis has been elusive for want of new approaches leaving billions of people either debilitated or at risk. With multiple B- and T-cell epitopes, the abundant larval transcript-2 (ALT-2) of the filarial worm, Brugia malayi, has been shown to be a promising immunoprophylactic target. To enhance its efficacy, it was lipid modified using our recently developed protein engineering tool, which then offered 30% more immunoprotection (49 vs. 79%) in Mastomys coucha model. Sustained high levels of IFN-γ (about 100 times) and high antibody titres (10-fold) elicited by lipid-modified ALT-2, as compared to the native form, indicated the maintenance of Th1/Th2 balance that is impaired in filariasis. Thus, this study provides the basis for developing efficacious vaccines for filariasis and other parasitic diseases by exploiting bacterial lipid modification.

Comparative Genomic Characterization of the Multimammate Mouse Mastomys coucha

Mastomys are the most widespread African rodent and carriers of various diseases such as the plague or Lassa virus. In addition, mastomys have rapidly gained a large number of mammary glands. Here, we generated a genome, variome, and transcriptomes for Mastomys coucha. As mastomys diverged at similar times from mouse and rat, we demonstrate their utility as a comparative genomic tool for these commonly used animal models. Furthermore, we identified over 500 mastomys accelerated regions, often residing near important mammary developmental genes or within their exons leading to protein sequence changes. Functional characterization of a noncoding mastomys accelerated region, located in the HoxD locus, showed enhancer activity in mouse developing mammary glands. Combined, our results provide genomic resources for mastomys and highlight their potential both as a comparative genomic tool and for the identification of mammary gland number determining factors.

Host competence of African rodents Arvicanthis neumanni, A. niloticus and Mastomys natalensis for Leishmania major

Cutaneous leishmaniasis caused by Leishmania major is a typical zoonosis circulating in rodents. In Sub-Saharan Africa the reservoirs remain to be identified, although L. major has been detected in several rodent species including members of the genera Arvicanthis and Mastomys. However, differentiation of true reservoir hosts from incidental hosts requires in-depth studies both in the field and in the laboratory, with the best method for testing the infectiousness of hosts to biting vectors being xenodiagnosis. Here we studied experimental infections of three L. major strains in Arvicanthis neumanni, A. niloticus and Mastomys natalensis; the infections were initiated either with sand fly-derived or with culture-derived Leishmania promastigotes. Inoculated rodents were monitored for several months and tested by xenodiagnoses for their infectiousness to Phlebotomus duboscqi, the natural vector of L. major in Sub-Saharan Africa. The distribution and load of parasites were determined post mortem using qPCR from the blood, skin and viscera samples. The attractiveness of Arvicanthis and Mastomys to P. duboscqi was tested by pair-wise comparisons. Three L. major strains used significantly differed in infectivity: the Middle Eastern strain infected a low proportion of rodents, while two Sub-Saharan isolates (LV109, LV110) infected a high percentage of animals and LV110 also produced higher parasite loads in all host species. All three rodent species maintained parasites of the LV109 strain for 20-25 weeks and were able to infect P. duboscqi without apparent health complications: infected animals showed only temporary swellings or changes of pigmentation at the site of inoculation. However, the higher infection rates, more generalized distribution of parasites and longer infectiousness period to sand flies in M. natalensis suggest that this species plays the more important reservoir role in the life cycle of L. major in Sub-Saharan Africa. Arvicanthis species may serve as potential reservoirs in seasons/periods of low abundance of Mastomys.

Circulation of Lassa virus across the endemic Edo-Ondo axis, Nigeria, with cross-species transmission between multimammate mice

We phylogenetically compared sequences of the zoonotic Lassa virus (LASV) obtained from Mastomys rodents in seven localities across the highly endemic Edo and Ondo States within Nigeria. Sequencing 1641 nt from the S segment of the virus genome, we resolved clades within lineage II that were either limited to Ebudin and Okhuesan in Edo state (2g-beta) or along Owo-Okeluse-Ifon in Ondo state (2g-gamma). We also found clades within Ekpoma, a relatively large cosmopolitan town in Edo state, that extended into other localities within Edo (2g-alpha) and Ondo (2g-delta). LASV variants from M. natalensis within Ebudin and Ekpoma in Edo State (dated approximately 1961) were more ancient compared to those from Ondo state (approximately 1977), suggesting a broadly east-west virus migration across south-western Nigeria; a pattern not always consistent with LASV sequences derived from humans in the same localities. Additionally, in Ebudin and Ekpoma, LASV sequences between M. natalensis and M. erythroleucus were interspersed on the phylogenetic tree, but those from M. erythroleucus were estimated to emerge more recently (approximately 2005). Overall, our results show that LASV amplification in certain localities (reaching a prevalence as high as 76% in Okeluse), anthropogenically-aided spread of rodent-borne variants amidst the larger towns (involving communal accommodation such as student hostels), and virus-exchange between syntopic M. natalensis and M. erythroleucus rodents (as the latter, a savanna species, encroaches southward into the degraded forest) pose perpetual zoonotic hazard across the Edo-Ondo Lassa fever belt, threatening to accelerate the dissemination of the virus into non endemic areas.

Understanding the transmission pathways of Lassa fever: A mathematical modeling approach

The spread of Lassa fever infection is increasing in West Africa over the last decade. The impact of this can better be understood when considering the various possible transmission routes. We designed a mathematical model for the epidemiology of Lassa Fever using a system of nonlinear ordinary differential equations to determine the effect of transmission pathways toward the infection progression in humans and rodents including those usually neglected such as the environmental surface and aerosol routes. We analyzed the model and carried out numerical simulations to determine the impact of each transmission routes. Our results showed that the burden of Lassa fever infection is increased when all the transmission routes are incorporated and most single transmission routes are less harmful, but when in combination with other transmission routes, they increase the Lassa fever burden. It is therefore important to consider multiple transmission routes to better estimate the Lassa fever burden optimally and in turn determine control strategies targeted at the transmission pathways.

A mouse in the spotlight: Response capacity to artificial light at night in a rodent pest species, the southern multimammate mouse (Mastomys coucha)

Multimammate mice are prolific breeders, can cause significant agricultural damage, and are reservoir hosts for a number of pathogens. They are nocturnal and given their success in urbanised rural environments, we were interested in how they would respond to increasingly bright anthropogenic spaces. We evaluated the locomotor activity of southern multimammate mice (Mastomys coucha), under four treatments: in an outdoor enclosure with natural light and temperature fluctuations, in a laboratory under a standard light regime, and two artificial light at night (ALAN) regimes (2 Lux) of varying proximity. The study animals remained nocturnal for the duration of the experiments. They were more active under the laboratory conditions with lower day-time light levels compared to the outdoor treatment but reduced their activity under ALAN. When the night light originated remotely, activity levels decreased by more than 50%, whereas under direct ALAN from above the cages, there was a 75% decrease in activity. The onset of activity was later during the two LAN treatments. We concluded that Mastomys coucha is strongly averse to light and show severe behavioural and circadian responses to light at night. We predict that it is unlikely that Mastomys will flourish in cities, but that they could thrive in and around dark urbanised refugia.

The first cases of Lassa fever in Ghana

Lassa fever is a zoonotic disease endemic in West Africa but with no previous case reported in Ghana. We describe the first two laboratory confirmed cases of Lassa fever from the Ashanti Region of Ghana detected in October and December, 2011.

Construction and expression of vectors encoding biologically active rodent gonadotropins

The gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), are important hormones in vertebrate reproduction. The isolation of gonadotropins from the pituitary gland is sub-optimal, as the cross-contamination of one hormone with another is common and often results in the variation in the measured activity of LH and FSH. The production of recombinant hormones is, therefore, a viable approach to solve this problem. This study aimed to express recombinant rat, mouse, and mastomys FSH and LH in Chinese hamster ovary (CHO) cells. Their common α-subunits along with their hormone-specific β-subunits were encoded in a single mammalian expression vector. FSH from all three species was expressed, whereas expression was achieved only for the mouse LH. Immunohistochemistry for rat alpha subunit of glycoprotein hormone (αGSU) and LHβ and FSHβ subunits confirmed the production of the dimeric hormone in CHO cells. The recombinant rodent gonadotropins were confirmed to be biologically active; estradiol production was increased by recombinant FSH in granulosa cells, while recombinant LH increased testosterone production in Leydig cells.