Causative agent of canine heartworm (Dirofilaria immitis) detected in wild lemurs

Effects of land use, habitat characteristics, and small mammal community composition on Leptospira prevalence in northeast Madagascar

Human activities can increase or decrease risks of acquiring a zoonotic disease, notably by affecting the composition and abundance of hosts. This study investigated the links between land use and infectious disease risk in northeast Madagascar, where human subsistence activities and population growth are encroaching on native habitats and the associated biota. We collected new data on pathogenic Leptospira, which are bacteria maintained in small mammal reservoirs. Transmission can occur through close contact, but most frequently through indirect contact with water contaminated by the urine of infected hosts. The probability of infection and prevalence was compared across a gradient of natural moist evergreen forest, nearby forest fragments, flooded rice and other types of agricultural fields, and in homes in a rural village. Using these data, we tested specific hypotheses for how land use alters ecological communities and influences disease transmission. The relative abundance and proportion of exotic species was highest in the anthropogenic habitats, while the relative abundance of native species was highest in the forested habitats. Prevalence of Leptospira was significantly higher in introduced compared to endemic species. Lastly, the probability of infection with Leptospira was highest in introduced small mammal species, and lower in forest fragments compared to other habitat types. Our results highlight how human land use affects the small mammal community composition and in turn disease dynamics. Introduced species likely transmit Leptospira to native species where they co-occur, and may displace the Leptospira species naturally occurring in Madagascar. The frequent spatial overlap of people and introduced species likely also has consequences for public health.

Many neglected tropical diseases have reservoirs in wildlife. The effects of human activities on wildlife include changes in species abundance, community composition, and the transmission dynamics of parasites. Introduced species, especially black rats (Rattus rattus) are known to transmit zoonotic diseases among wildlife species and people. Leptospira, a water-borne bacterium that infects wildlife and people, is an important pathogen in the tropics, and in Madagascar, multiple strains and hosts have been identified. We tested how land use gradients in a forest-frontier agricultural system affect the composition of small mammal communities, and in turn the prevalence of Leptospira. We investigated 11 species of small mammals, including native rodents and tenrecs, as well as introduced rodents and shrews, in old growth forest, forest fragments, agricultural fields, and in a village. Leptospira prevalence and infection risk were highest in introduced species compared to native species and lower in forest fragments. The results highlight how the introduction of non-native species affects the variation in disease prevalence in small mammals, with potential consequences for spill-over to people.

The Progressive Spread of the Vascular Wilt Like Pathogen of Calophyllum Detected in Ranomafana National Park, Madagascar

Pathogens are threatening crops worldwide, but little attention has been given to the threat to tree species in undisturbed rainforest. This communication reports the first case of a tree die off caused by a "wilt" in Madagascar. In 2016 while monitoring monthly tree phenology of Ranomafana National Park (RNP), the Centre ValBio research station observed that many Calophyllum adult trees had brown wilted leaves. There are three species of Calophyllum in this rainforest, C. paniculatum, C. drouhardii, and C. milvum, and all three have contracted this pathogen. Our goal was to document the spead of this suspected wilt in Calophyllum trees and determine if site, elevation and DBH had an influence on tree mortality. In 2019 we conducted an inventory of all Calophyllum trees in RNP and 42% of the observed trees were dead. The species with the highest mortality was C. paniculatum, with 53% of trees dead, followed by C. milvum with 18%, and C. drouhardii with only 2% of surveyed trees dead. Bark beetle traces were observed in all dead Calophyllum trees. Tree death caused by this suspected fungal pathogen has spread across a major river in the area and has been found at mid and high elevations. Our results show that C. paniculatum trees with a larger DBH have a higher mortality risk. Our report highlights the importance of fighting invasive pathogens that threaten protected ecosystems.

The prevalence of Dirofilaria immitis and D. repens in the Old World

Dirofilaria immitis and D. repens are endemic throughout Europe and southern eastern regions of Asia and reported with increasing frequency in Africa. Nevertheless, the increased awareness of veterinary practitioners, even in countries where the prevalence is low, has led to a decrease D. immitis prevalence in dogs, especially in previously endemic/hyper-endemic areas. Prevalence has significantly increased, however, in areas where heartworm has apparently spread more recently, such as Central and North Eastern Europe. Furthermore, autochthonous cases have been observed in Siberia. Low seroprevalence has been reported in Croatia, while in Romania it has reached 14%. In Greece, the prevalence ranges between 0.7% and 25% whilst in Turkey is 0-18%. Data for canine dirofilariosis in Africa is scarce, and most are case reports. Overall, the dominant species is Achanthocheilonema dracunculoides, although both D. immitis and D. repens have been reported from some countries. In the Far East, the prevalence ranges from 2% to 15% in northeastern of China. In Hong Kong a novel species has been found in dogs and humans (Candidatus Dirofilaria hongkongensis). In India, the prevalence ranges from 4.7%-29.5% in Northeastern states. The main factors that have influenced the spreading of Dirofilaria infections are the climate changes and the introduction of new, invasive, competent mosquito species such as Aedes albopictus and Ae. koreicus. Other factors include relocation and insufficient prevention in dogs, manly in the new areas of colonization. Feline heartworm infection has been diagnosed in every European country when diagnosed either by the Knott test or by serology for circulating antibodies and antigens of the parasite. However, prevalence is much lower than in dogs. In spite of the continuing spreading of heartworm infection, D. repens is the main concern in Europe, mostly for physicians, while the infection is nearly always asymptomatic in dogs. The infection is spreading from Portugal to the Southeastern regions of Finland and Siberia, and in some areas its prevalence overlaps that of D. immitis. Many reasons make more difficult the control of D. repens than D. immitis: the frequent lack of clinical symptoms of suspicion, the specific diagnosis being possible only by blood examination and the inefficacy of some macrocyclic lactones.

Differences in infection patterns of vector-borne blood-stage parasites of sympatric Malagasy primate species (Microcebus murinus, M. ravelobensis)

The dynamic relationship of vector-borne parasites, arthropod vectors and their hosts is prone to change under the influence of climate change, global integration, shifting demographics and deforestation. It is therefore essential to better understand parasitism in wildlife populations, including parasites transmitted by blood-feeding vectors, and explore host range and heterogeneity of parasitic infections. We investigated Giemsa stained blood smears of two sympatric Malagasy primate species (Microcebus murinus: 184 samples from 69 individuals and M. ravelobensis: 264 samples from 91 individuals) for blood-stage parasites and tested for a potential influence of host species, sex, body mass and sampling month on blood-stage parasite prevalence and infection intensity. No protozoan parasites were detected in either host species. A host-specific difference was observed in filarial nematode infections, with higher risk of infection in M. murinus (prevalence 30.43%), than in M. ravelobensis (prevalence 6.59%), which may be explained by differences in host behavior and/or immune competence, linked to the period of host-parasite coevolution. Neither sex nor sampling month influenced infection prevalence or intensity significantly. We did not observe a negative effect of microfilarial infections on host fitness when taking body mass as a proxy. Our results support the hypothesis of a long-term evolutionary adaptation of hosts and parasites, leading to persistent infection with low morbidity. Morphological and molecular analyses indicate the finding of a new species, “Lemurfilaria lemuris”. Genetic analysis furthermore showed >99% sequence identity with microfilariae described from a sympatric, larger-bodied lemur species of a different genus, suggesting low host-specificity of the detected filariae and pathogen transmission across genus boundaries. Findings contribute to a more comprehensive picture of vector-borne diseases of Malagasy lemurs.

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Small Malagasy primate species are hosts of the newly described Lemurfilaria lemuris.

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Risk of microfilarial infection and infection intensity differed between host species.

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This could be linked to differences in host socioecology and/or phylogeography.

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No influence of microfilarial infection on host body mass was observed.

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>99% sequence identity of filariae from lemur hosts of different genera.