A Maximum Entropy Species Distribution Model to Estimate the Distribution of Bushpigs on Madagascar and Its Implications for African Swine Fever

Bushpigs (Potamochoerus larvatus) play a major role in the socio-ecosystem of Madagascar, particularly in rural areas. They are largely hunted by rural populations as a major source of income and protein. They can also represent a potential source of pathogens for domestic animals and people. For example, it is hypothesized that bushpigs might compromise African swine fever (ASF) eradication programs by sporadically transmitting the virus to domestic pigs. However, available knowledge on the distribution of bushpigs in Madagascar is limited. In this study, we estimated the distribution of bushpigs on Madagascar using a species distribution model (SDM). We retrieved 206 sightings of bushpigs in Madagascar during 1990–2016 and predicted the distribution by using 37 climatic, geographic, and agricultural/human variables related to the presence of bushpigs and running a presence-background maximum entropy SDM. Our model identified three main areas with a high suitability for bushpigs: in the north, central-western, and east of the island (AUC = 0.84). The main contributors to the model were the vegetation index (51.3%), percentage of land covered by trees (17.6%), and annual averaged monthly precipitation (12.6%). In addition, we identified areas in central Madagascar with a high density of domestic pigs and a high suitability score for bushpigs. These results may help to identify bushpig areas at the interface with domestic pigs to assess the risk of pathogen transmission and to design ecological assessments, wildlife management studies, or targeted surveillance and research studies related to many bushpig-borne pathogens, such as ASF, which is an endemic problem in the country, as well as zoonotic diseases such as cysticercosis and hepatitis E. Our approach could also be extrapolated to other species of wild swine in other countries.

Bushpig (Potamochoerus larvatus) Hunting in Rural Areas of Madagascar and Its Health and Socioeconomic Implications

Bushmeat consumption and trade plays a relevant role in many tropical countries as a source of protein and income for rural populations. In Madagascar, rural populations depend heavily on natural resources and wildlife as source of income and protein. The bushpig (Potamochoerus larvatus) is the largest mammal available in the island and regularly hunted. However, little is known about the importance and characteristics of this activity and its implication as a potential source of pathogens for both humans and domestic animals. A cross-sectional study was conducted in 2014–2015 in five different regions of rural Madagascar suspected to have significant bushpig populations to (i) quantify and characterize the importance of bushpig hunting, (ii) assess the socioeconomic impact of bushpig trade, (iii) evaluate the potential pathogen transmission between bushpigs, domestic pigs and humans. A total of 77 hunters, 10 butchers and 95 pig farmers were individually interviewed. Hunting seasonality and the perception of local hunters with regards to the dynamics of bushpig populations in the last decade differed between the tropical dry and tropical sub-arid climatic zones. The top reason for hunting bushpigs was crop protection but personal consumption and selling of meat were also common. Hunting efficacy was largely dependent on the technique used. Snares and traps, the most widely used techniques, allowed the majority of hunters to catch from one to 10 bushpigs per year. Limited commercial bushpig trade was observed with only 0.8 bushpig sold in average per year and per hunter, representing a 16 USD income. The average price per kilo sold was USD 0.8 and the average profit received by each butcher/collector after the sale of a carcass was USD 11.9. No perception of disease risks nor precautions were taken to prevent potential pathogen transmission from bushpig to humans or pigs. Most of the hunters (68%) indicated that they had never seen a diseased bushpig. Bushpig hunting in our study areas in Madagascar was basically a small-scale subsistence hunting, very different from commercial bushmeat hunting described in areas of Central Africa or the Amazon Basin. More research is needed to verify the sustainability of bushpig hunting and its potential role in terms of reducing pressure on other endemic wildlife species and transmitting pathogens to humans and pigs.

Estimation of the Lethality Rate, Recovery Rate, and Case Fatality Ratio of Classical Swine Fever in Japanese Wild Boar: An Analysis of the Epidemics From September 2018 to March 2019

Understanding the morbidity and lethality of diseases is necessary to evaluate the effectiveness of countermeasure against the epidemics (e.g., vaccination). To estimate them, detailed data on host population dynamics are required; however, estimating the population size for wildlife is often difficult. We aimed to elucidate the morbidity and lethality of classical swine fever (CSF) currently highly prevalent in the wild boar population in Japan. To this end, we estimated lethality rate, recovery rate, and case fatality ratio (CFR) of CSF without detailed data on the population estimates of wild boar. A mathematical model was constructed to describe the CSF dynamics and population dynamics of wild boar. We fitted the model to the (i) results of the reverse transcription polymerase chain reaction (RT-PCR) test for the CSFV gene and the (ii) results of the enzyme-linked immunosorbent assay (ELISA) test for the antibody against CSFV in sampled wild boar. In the 280 wild boar sampled from September 2018 to March 2019 in the major CSF-affected area in Japan, the lethality rate and recovery rate of CSF per week were estimated as 0.165 (95% confidence interval: 0.081–0.250) and 0.004 (0–0.009), respectively. While the estimate of lethality rate of CSF was similar with the estimates in previous studies, the recovery rate was lower than those reported previously. CFR was estimated as 0.959 (0.904–0.981) using our estimate of recovery rate. This study is the first to estimate lethality rate of CSF from the dynamics of CSF epidemics in the wild boar population. Since the value of CFR is sensitive to the value of recovery rate, the accuracy in the estimate of recovery rate is a key for the accurate estimation of CFR. A long-term transmission experiment of moderately virulent strains may lead to more accurate estimation of the recovery rate and CFR of CSF.

Suidae and Tayassuidae

The Suidae and Tayassuidae live on all continents except Antarctica. True wild boars were indigenous to Europe and Asia and are the ancestors to the domestic pig; with whom they share the same scientific name Sus scrofa. Wild boars have been introduced to the Americas and many islands. Because of the close genetic relationship, in many areas they have interbred with domestic pigs and formed considerable populations of feral suids that represent wild boar and feral pig crosses. Wild suid populations are relatively hardy and most disease research has been focused on their potential as a reservoir for diseases of concern for commercial pig production. The Togian Island babirusa, pygmy hog, Visayan warty pig, Javan warty pig, and Chacoan peccary are endangered. For all species, hunting, habitat loss, and hybridization are important threats to conservation.

Classical swine fever in pigs: recent developments and future perspectives

Classical swine fever (CSF) is one of the most devastating epizootic diseases of pigs, causing high morbidity and mortality worldwide. The diversity of clinical signs and similarity in disease manifestations to other diseases make CSF difficult to diagnose with certainty. The disease is further complicated by the presence of a number of different strains belonging to three phylogenetic groups. Advanced diagnostic techniques allow detection of antigens or antibodies in clinical samples, leading to implementation of proper and effective control programs. Polymerase chain reaction (PCR)-based methods, including portable real-time PCR, provide diagnosis in a few hours with precision and accuracy, even at the point of care. The disease is controlled by following a stamping out policy in countries where vaccination is not practiced, whereas immunization with live attenuated vaccines containing the 'C' strain is effectively used to control the disease in endemic countries. To overcome the problem of differentiation of infected from vaccinated animals, different types of marker vaccines, with variable degrees of efficacy, along with companion diagnostic assays have been developed and may be useful in controlling and even eradicating the disease in the foreseeable future. The present review aims to provide an overview and status of CSF as a whole with special reference to swine husbandry in India.

History of ‘swine fever’ in Southern Africa

The histories of the two swine fevers in southern Africa differ widely. Classical swine fever (hog cholera) has been known in the northern hemisphere since 1830 and it is probable that early cases of ‘swine fever’ in European settlers’ pigs in southern Africa were accepted to be that disease. It was only in 1921 that the first description of African swine fever as an entity different from classical swine fever was published after the disease had been studied in settlers’ pigs in Kenya. Shortly after that, reports of African swine fever in settlers’ pigs emerged from South Africa and Angola. In South Africa, the report related to pigs in the north-eastern part of the country. Previously (in 1905 or earlier) a disease assumed to be classical swine fever caused high mortality among pigs in the Western Cape and was only eradicated in 1918. African swine fever was found over the following years to be endemic in most southern African countries. Classical swine fever, however, apart from an introduction with subsequent endemic establishment in Madagascar and a number of introductions into Mauritius, the last one in 2000, had apparently remained absent from the region until it was diagnosed in the Western and subsequently the Eastern Cape of South Africa in 2005. It was eradicated by 2007. The history of these diseases in the southern African region demonstrates their importance and their potential for spread over long distances, emphasising the need for improved management of both diseases wherever they occur.

The challenges of classical swine fever control: modified live and E2 subunit vaccines

Classical swine fever (CSF) is an economically important, highly contagious disease of swine worldwide. CSF is caused by classical swine fever virus (CSFV), and domestic pigs and wild boars are its only natural hosts. The two main strategies used to control CSF epidemic are systematic prophylactic vaccination and a non-vaccination stamping-out policy. This review compares the protective efficacy of the routinely used modified live vaccine (MLV) and E2 subunit vaccines and summarizes the factors that influence the efficacy of the vaccines and the challenges that both vaccines face to CSF control. Although MLV provide earlier and more complete protection than E2 subunit vaccines, it has the drawback of not allowing differentiation between infected and vaccinated animals (DIVA). The marker vaccine of E2 protein with companion discriminatory test to detect antibodies against E(rns) allows DIVA and is a promising strategy for future control and eradication of CSF. Maternal derived antibody (MDA) is the critical factor in impairing the efficacy of both MLV and E2 subunit vaccines, so the well-designed vaccination programs of sows and piglets should be considered together. Because of the antigen variation among various genotypes of CSFV, antibodies raised by either MLV or subunit vaccine neutralize genotypically homologous strains better than heterologous ones. However, although this is not a major concern for MLV as the induced immune responses can protect pigs against the challenge of various genotypes of CSFVs, it is critical for E2 subunit vaccines. It is thus necessary to evaluate whether the E2 subunit vaccine can completely protect against the current prevalent strains in the field. An ideal new generation of vaccine should be able to maintain the high protective efficiency of MLV and overcome the problem of antigenic variations while allowing for DIVA.