Invasive Burmese pythons alter host use and virus infection in the vector of a zoonotic virus

AbstractThe composition of wildlife communities can have strong effects on transmission of zoonotic vector-borne pathogens, with more diverse communities often supporting lower infection prevalence in vectors (dilution effect). The introduced Burmese python, Python bivittatus, is eliminating large and medium-sized mammals throughout southern Florida, USA, impacting local communities and the ecology of zoonotic pathogens. We investigated invasive predator-mediated impacts on ecology of Everglades virus (EVEV), a zoonotic pathogen endemic to Florida that circulates in mosquito-rodent cycle. Using binomial generalized linear mixed effects models of field data at areas of high and low python densities, we show that increasing diversity of dilution host (non-rodent mammals) is associated with decreasing blood meals on amplifying hosts (cotton rats), and that increasing cotton rat host use is associated with increasing EVEV infection in vector mosquitoes. The Burmese python has caused a dramatic decrease in mammal diversity in southern Florida, which has shifted vector host use towards EVEV amplifying hosts (rodents), resulting in an indirect increase in EVEV infection prevalence in vector mosquitoes, putatively elevating human transmission risk. Our results indicate that an invasive predator can impact wildlife communities in ways that indirectly affect human health, highlighting the need for conserving biological diversity and natural communities.

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Diversifying forest communities may change Lyme disease risk: extra dimension to the dilution effect in Europe

Parasitology ◽

10.1017/s0031182016000688 ◽

2016 ◽

Vol 143 (10) ◽

pp. 1310-1319 ◽

Cited By ~ 15

Author(s):

SANNE C. RUYTS ◽

EVY AMPOORTER ◽

ELENA C. COIPAN ◽

LANDER BAETEN ◽

DIETER HEYLEN ◽

...

Keyword(s):

North America ◽

Lyme Disease ◽

Borrelia Burgdorferi ◽

Disease Risk ◽

Severe Disease ◽

Dilution Effect ◽

Ixodid Ticks ◽

Infection Prevalence ◽

Host Diversity ◽

Pine Stands

SUMMARYLyme disease is caused by bacteria of theBorrelia burgdorferigenospecies complex and transmitted by Ixodid ticks. In North America only one pathogenic genospecies occurs, in Europe there are several. According to the dilution effect hypothesis (DEH), formulated in North America, nymphal infection prevalence (NIP) decreases with increasing host diversity since host species differ in transmission potential. We analysedBorreliainfection in nymphs from 94 forest stands in Belgium, which are part of a diversification gradient with a supposedly related increasing host diversity: from pine stands without to oak stands with a shrub layer. We expected changing tree species and forest structure to increase host diversity and decrease NIP. In contrast with the DEH, NIP did not differ between different forest types. Genospecies diversity however, and presumably also host diversity, was higher in oak than in pine stands. Infected nymphs tended to harbourBorrelia afzeliiinfection more often in pine stands whileBorrelia gariniiandBorrelia burgdorferiss. infection appeared to be more prevalent in oak stands. This has important health consequences, since the latter two cause more severe disease manifestations. We show that the DEH must be nuanced for Europe and should consider the response of multiple pathogenic genospecies.

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Topographic mapping of the interfaces between human and aquatic mosquito habitats to enable barrier targeting of interventions against malaria vectors

Royal Society Open Science ◽

10.1098/rsos.161055 ◽

2018 ◽

Vol 5 (5) ◽

pp. 161055

Author(s):

Victoria M. Mwakalinga ◽

Benn K. D. Sartorius ◽

Alex J. Limwagu ◽

Yeromin P. Mlacha ◽

Daniel F. Msellemu ◽

...

Keyword(s):

Epidemiological Survey ◽

Human Infection ◽

Transmission Risk ◽

Malaria Vectors ◽

Topographic Mapping ◽

Infection Prevalence ◽

Selective Targeting ◽

Water Accumulation ◽

Local Water ◽

Source Management

Geophysical topographic metrics of local water accumulation potential are freely available and have long been known as high-resolution predictors of where aquatic habitats for immature Anopheles mosquitoes are most abundant, resulting in elevated densities of adult malaria vectors and human infection burden. Using existing entomological and epidemiological survey data, here we illustrate how topography can also be used to map out the interfaces between wet, unoccupied valleys and dry, densely populated uplands, where malaria vector densities and infection risk are focally exacerbated. These topographically identifiable geophysical boundaries experience disproportionately high vector densities and malaria transmission risk, because this is where Anopheles mosquitoes first encounter humans when they search for blood after emerging or ovipositing in the valleys. Geophysical topographic indicators accounted for 67% of variance for vector density but for only 43% for infection prevalence, so they could enable very selective targeting of interventions against the former but not the latter (targeting ratios of 5.7 versus 1.5 to 1, respectively). So, in addition to being useful for targeting larval source management to wet valleys, geophysical topographic indicators may also be used to selectively target adult Anopheles mosquitoes with insecticidal residual sprays, fencing, vapour emanators or space sprays to barrier areas along their fringes.

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The influence of landscape and environmental factors on ranavirus epidemiology in amphibian assemblages

10.1101/167395 ◽

2017 ◽

Author(s):

Brian J. Tornabene ◽

Andrew R. Blaustein ◽

Cheryl J. Briggs ◽

Dana M. Calhoun ◽

Pieter T. J. Johnson ◽

...

Keyword(s):

Environmental Factors ◽

Host Species ◽

Dilution Effect ◽

Variance Partitioning ◽

Lower Probability ◽

Infection Prevalence ◽

Taxonomic Richness ◽

Amphibian Disease ◽

Competing Models ◽

Reservoir Hosts

ABSTRACTAimTo quantify the influence of a suite of landscape, abiotic, biotic, and host-level variables on ranavirus disease dynamics in amphibian assemblages at two biological levels (site and host-level).LocationWetlands within the East Bay region of California, USA.MethodsWe used competing models, multimodel inference, and variance partitioning to examine the influence of 16 landscape and environmental factors on patterns in site-level ranavirus presence and host-level ranavirus infection in 76 wetlands and 1,377 amphibian hosts representing five species.ResultsThe landscape factor explained more variation than any other factors in site-level ranavirus presence, but biotic and host-level factors explained more variation in host-level ranavirus infection. At both the site- and host-level, the probability of ranavirus presence correlated negatively with distance to nearest ranavirus-positive wetland. At the site-level, ranavirus presence was associated positively with taxonomic richness. However, infection prevalence within the amphibian population correlated negatively with vertebrate richness. Finally, amphibian host species differed in their likelihood of ranavirus infection: American Bullfrogs had the weakest association with infection while Western Toads had the strongest. After accounting for host species effects, hosts with greater snout-vent length had a lower probability of infection.Main conclusionsStrong spatial influences at both biological levels suggest that mobile taxa (e.g., adult amphibians, birds, reptiles) may facilitate the movement of ranavirus among hosts and across the landscape. Higher taxonomic richness at sites may provide more opportunities for colonization or the presence of reservoir hosts that may influence ranavirus presence. Higher host richness correlating with higher ranavirus infection is suggestive of a dilution effect that has been observed for other amphibian disease systems and warrants further investigation. Our study demonstrates that an array of landscape, environmental, and host-level factors were associated with ranavirus epidemiology and illustrates that their importance vary with biological level.

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Disruption of a host-parasite system following the introduction of an exotic host species

Parasitology ◽

10.1017/s0031182005007250 ◽

2005 ◽

Vol 130 (6) ◽

pp. 661-668 ◽

Cited By ~ 98

Author(s):

S. TELFER ◽

K. J. BOWN ◽

R. SEKULES ◽

M. BEGON ◽

T. HAYDEN ◽

...

Keyword(s):

Bank Vole ◽

Host Species ◽

Negative Relationship ◽

Dilution Effect ◽

Wood Mouse ◽

Clethrionomys Glareolus ◽

Infection Prevalence ◽

Wood Mice ◽

Effect Hypothesis ◽

Host Parasite

The potential of biological invasions to threaten native ecosystems is well recognized. Here we describe how an introduced species impacts on native host-parasite dynamics by acting as an alternative host. By sampling sites across an invasion front in Ireland, we quantified the influence of the introduced bank vole (Clethrionomys glareolus) on the epidemiology of infections caused by flea-transmitted haemoparasites of the genusBartonellain native wood mice (Apodemus sylvaticus).Bartonellainfections were detected on either side of the front but occurred exclusively in wood mice, despite being highly prevalent in both rodent species elsewhere in Europe. Bank vole introduction has, however, affected the wood mouse-Bartonellainteraction, with the infection prevalence of bothBartonella birtlesiiandBartonella tayloriideclining significantly with increasing bank vole density. Whilst flea prevalence in wood mice increases with wood mouse density in areas without bank voles, no such relationship is detected in invaded areas. The results are consistent with the dilution effect hypothesis. This predicts that for vector-transmitted parasites, the presence of less competent host species may reduce infection prevalence in the principal host. In addition we found a negative relationship betweenB. birtlesiiandB. tayloriiprevalences, indicating that these two microparasites may compete within hosts.

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Prevalence of Trypanosoma cruzi and Leishmania chagasi infection and risk factors in a Colombian indigenous population

Revista do Instituto de Medicina Tropical de São Paulo ◽

10.1590/s0036-46651999000400005 ◽

1999 ◽

Vol 41 (4) ◽

pp. 229-234 ◽

Cited By ~ 9

Author(s):

Augusto CORREDOR ARJONA ◽

Carlos Arturo ALVAREZ MORENO ◽

Carlos Alberto AGUDELO ◽

Martha BUENO ◽

Myriam Consuelo LÓPEZ ◽

...

Keyword(s):

Trypanosoma Cruzi ◽

Skin Test ◽

Indigenous Population ◽

Transmission Risk ◽

Parasitic Infections ◽

Infection Prevalence ◽

Base Line ◽

Leishmania Chagasi ◽

Leishmanin Skin Test ◽

Improvement Programme

This study was carried out in order to obtain base-line data concerning the epidemiology of American Visceral Leishmaniasis and Chagas’ Disease in an indigenous population with whom the government is starting a dwelling improvement programme. Information was collected from 242 dwellings (1,440 people), by means of house to house interviews about socio-economic and environmental factors associated with Leishmania chagasi and Trypanosoma cruzi transmission risk. A leishmanin skin test was applied to 385 people and 454 blood samples were collected on filter paper in order to detect L. chagasi antibodies by ELISA and IFAT and T. cruzi antibodies by ELISA. T. cruzi seroprevalence was 8.7% by ELISA, L. chagasi was 4.6% and 5.1% by IFAT and ELISA, respectively. ELISA sensitivity and specificity for L. chagasi antibodies were 57% and 97.5% respectively, as compared to the IFAT. Leishmanin skin test positivity was 19%. L. chagasi infection prevalence, being defined as a positive result in the three-immunodiagnostic tests, was 17.1%. Additionally, 2.7% of the population studied was positive to both L. chagasi and T. cruzi, showing a possible cross-reaction. L. chagasi and T. cruzi seropositivity increased with age, while no association with gender was observed. Age (p<0.007), number of inhabitants (p<0.05), floor material (p<0.03) and recognition of vector (p<0.01) were associated with T. cruzi infection, whilst age ( p<0.007) and dwelling improvement (p<0.02) were associated with L. chagasi infection. It is necessary to evaluate the long-term impact of the dwelling improvement programme on these parasitic infections in this community.

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State of the States: Geographic Patterns of Diversity, Rarity, and Endemism

Precious Heritage ◽

10.1093/oso/9780195125191.003.0011 ◽

2000 ◽

Author(s):

Geoffrey A. Hammerson ◽

Larry E. Morse

Keyword(s):

Biological Diversity ◽

Dominant Role ◽

Fish Fauna ◽

The Future ◽

Ecological Patterns ◽

History Of ◽

Mammal Assemblages ◽

Southern Florida ◽

Alaskan Tundra ◽

Natural Boundaries

The natural geography of the 50 states varies tremendously, supporting an equally varied suite of wild species—from flocks of tropical birds in southern Florida to caribou migrations across the Alaskan tundra. The geography of risk, too, varies across the nation, reflecting the interaction between natural and human history. Similarly, present-day land and water uses will largely determine the future diversity and condition of the flora and fauna. We can learn much, though, from looking at the current condition of a state’s biota, since this both reflects the past and helps illuminate the future. A state’s ecological complexion and the evolutionary history of its biota are the primary determinants of its biological diversity. These environmental factors have encouraged spectacular diversification in many regions: for instance, the freshwater fish fauna in the Southeast, the magnificent conifers along the Pacific cordillera, and the small mammal assemblages of the arid Southwest. Conversely, geological events such as the expansion and contraction of the ice sheets have left other areas of the country with a more modest array of species. States, however, are artificial constructs laid out on the landscape’s natural ecological patterns. While some state lines follow natural boundaries, such as shorelines or major rivers, most cut across the land with no sensitivity to natural features or topography. Nonetheless, urban and rural dwellers alike identify with the major ecological regions within which they live, and this is often the source of considerable pride. Montana is “big sky country,” referring to the vast open plains that sweep up against the eastern phalanx of the Rocky Mountains. California’s moniker “the golden state” now refers more to its tawny hills of summer—unfortunately at present composed mostly of alien species—than to the nuggets first found at Sutter’s Creek. Maryland, home of the Chesapeake Bay, offers the tasty blue crab (Callinectes sapidus) as its unofficial invertebrate mascot. The list could go on, evidenced by the growing number of states that offer vanity license plates celebrating their natural environment. Natural features have always played a dominant role in determining patterns of settlement and land use.

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Null expectations for disease dynamics in shrinking habitat: dilution or amplification?

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2016.0173 ◽

2017 ◽

Vol 372 (1722) ◽

pp. 20160173 ◽

Cited By ~ 22

Author(s):

Christina L. Faust ◽

Andrew P. Dobson ◽

Nicole Gottdenker ◽

Laura S. P. Bloomfield ◽

Hamish I. McCallum ◽

...

Keyword(s):

Infectious Disease ◽

Habitat Loss ◽

Disease Risk ◽

Dilution Effect ◽

Well Being ◽

Pathogen Transmission ◽

Policy Implications ◽

Infection Prevalence ◽

Density Dependent ◽

Host Competence

As biodiversity declines with anthropogenic land-use change, it is increasingly important to understand how changing biodiversity affects infectious disease risk. The dilution effect hypothesis, which points to decreases in biodiversity as critical to an increase in infection risk, has received considerable attention due to the allure of a win–win scenario for conservation and human well-being. Yet some empirical data suggest that the dilution effect is not a generalizable phenomenon. We explore the response of pathogen transmission dynamics to changes in biodiversity that are driven by habitat loss using an allometrically scaled multi-host model. With this model, we show that declining habitat, and thus declining biodiversity, can lead to either increasing or decreasing infectious-disease risk, measured as endemic prevalence. Whether larger habitats, and thus greater biodiversity, lead to a decrease (dilution effect) or increase (amplification effect) in infection prevalence depends upon the pathogen transmission mode and how host competence scales with body size. Dilution effects were detected for most frequency-transmitted pathogens and amplification effects were detected for density-dependent pathogens. Amplification effects were also observed over a particular range of habitat loss in frequency-dependent pathogens when we assumed that host competence was greatest in large-bodied species. By contrast, only amplification effects were observed for density-dependent pathogens; host competency only affected the magnitude of the effect. These models can be used to guide future empirical studies of biodiversity–disease relationships across gradients of habitat loss. The type of transmission, the relationship between host competence and community assembly, the identity of hosts contributing to transmission, and how transmission scales with area are essential factors to consider when elucidating the mechanisms driving disease risk in shrinking habitat. This article is part of the themed issue ‘Conservation, biodiversity and infectious disease: scientific evidence and policy implications'.

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Experimental Evidence for Opposing Effects of High Deer Density on Tick-Borne Pathogen Prevalence and Hazard

10.21203/rs.3.rs-586674/v1 ◽

2021 ◽

Author(s):

Sara Louise Gandy ◽

Elizabeth Kilbride ◽

Roman Biek ◽

Caroline Millins ◽

Lucy Gilbert

Keyword(s):

Lyme Disease ◽

Disease Risk ◽

Dilution Effect ◽

High Density ◽

Infection Prevalence ◽

Vegetation Height ◽

Deer Density ◽

Pathogen Prevalence ◽

Tick Reproduction ◽

The Impact

Abstract Background: Identifying the mechanisms driving disease risk is challenging for multi-host pathogens, such as Borrelia burgdorferi s.l., the tick-borne bacteria causing Lyme disease. Deer are tick reproduction hosts but do not transmit B. burgdorferi s.l., whereas rodents and birds are competent transmission hosts. Here, we use a long-term deer exclosure experiment to test three mechanisms for how high deer density might shape B. burgdorferi s.l. prevalence in ticks: increased prevalence due to higher larval tick densities facilitating high transmission on rodents (M1); alternatively, reduced B. burgdorferi s.l. prevalence because more larval ticks feed on deer rather than transmission-competent rodents (dilution effect) (M2), potentially due to ecological cascades, whereby higher deer grazing pressure lowers vegetation which decreases rodent abundance thus reducing transmission (M3).Methods: In a large enclosure where red deer stags were kept at high density (32.5 deer/km²), we used an experimental design consisting of eight plots of 0.23ha, four being fenced to simulate the absence of deer and four that were accessible to deer. In each plot we measured the density of questing nymphs and nymphal infection prevalence in spring, summer and autumn and quantified vegetation height and density, and small mammal abundance Results: Prevalence tended to be lower, though not conclusively so, in high deer density plots compared to exclosures (predicted prevalence of 1.0% vs 2.2%), suggesting that the dilution (M2) and cascade (M3) mechanisms might outweigh the increased opportunities for transmission (M1). Presence of deer at high density led to lower vegetation and fewer rodents, consistent with an ecological cascade. However, Lyme disease hazard (density of infected I. ricinus nymphs) was five times higher in high deer density plots due to tick density being 18 times higher.Conclusion: High densities of tick reproduction hosts such as deer can drive up vector-borne disease hazard, despite the potential to simultaneously reduce pathogen prevalence. This has implications for environmental pathogen management and for deer management, although the impact of intermediate deer densities now needs testing.

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Species diversity concurrently dilutes and amplifies transmission in a zoonotic host–pathogen system through competing mechanisms

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1807106115 ◽

2018 ◽

Vol 115 (31) ◽

pp. 7979-7984 ◽

Cited By ~ 31

Author(s):

Angela D. Luis ◽

Amy J. Kuenzi ◽

James N. Mills

Keyword(s):

Population Density ◽

Small Mammal ◽

Disease Ecology ◽

Transmission Rate ◽

Dilution Effect ◽

Reservoir Host ◽

Infection Prevalence ◽

Amplification Effect ◽

Host Pathogen ◽

Mammal Diversity

In this era of unprecedented biodiversity loss and increased zoonotic disease emergence, it is imperative to understand the effects of biodiversity on zoonotic pathogen dynamics in wildlife. Whether increasing biodiversity should lead to a decrease or increase in infection prevalence, termed the dilution and amplification effects, respectively, has been hotly debated in disease ecology. Sin Nombre hantavirus, which has an ∼35% mortality rate when it spills over into humans, occurs at a lower prevalence in the reservoir host, the North American deermouse, in areas with higher small mammal diversity—a dilution effect. However, the mechanism driving this relationship is not understood. Using a mechanistic mathematical model of infection dynamics and a unique long-term, high-resolution, multisite dataset, it appears that the observed dilution effect is a result of increasing small-mammal diversity leading to decreased deermouse population density and, subsequently, prevalence (a result of density-dependent transmission). However, once density is taken into account, there is an increase in the transmission rate at sites with higher diversity—a component amplification effect. Therefore, dilution and amplification are occurring at the same time in the same host–pathogen system; there is a component amplification effect (increase in transmission rate), but overall a net dilution because the effect of diversity on reservoir host population density is stronger. These results suggest we should focus on how biodiversity affects individual mechanisms that drive prevalence and their relative strengths if we want to make generalizable predictions across host–pathogen systems.

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Host Associations of Culex (Melanoconion) atratus (Diptera: Culicidae) and Culex (Melanoconion) pilosus from Florida, USA

Insects ◽

10.3390/insects10080239 ◽

2019 ◽

Vol 10 (8) ◽

pp. 239 ◽

Cited By ~ 1

Author(s):

Lawrence E. Reeves ◽

Isaiah Hoyer ◽

Carolina Acevedo ◽

Nathan D. Burkett-Cadena

Keyword(s):

Host Species ◽

The United States ◽

Host Use ◽

Use Patterns ◽

Mammalian Blood ◽

Southeastern Coastal Plain ◽

Southern Florida ◽

Invasive Exotic ◽

Blood Meals ◽

Host Associations

Characterizing the host-use patterns of mosquitoes is an essential component of understanding the transmission dynamics of mosquito-vectored pathogens. The host associations of two species of the medically important Culex subgenus Melanoconion, Culex atratus, and Culex pilosus are unknown or unclear, respectively. Both species have wide neotropical distributions. In the United States of America (USA), Culex pilosus occurs throughout the southeastern coastal plain, while Culex atratus is restricted to the southern Florida Peninsula. Using PCR-based blood meal analysis, we investigated the host associations of Culex atratus and Culex pilosus that were collected from Everglades National Park, Florida, USA We identified the host species of 208 Culex atratus and 168 Culex pilosus. Both species were narrowly associated with reptilian host species, particularly native and non-native lizards of the genus Anolis. Sampled Culex atratus exclusively fed on reptilian hosts, with >99% of blood meals derived from Anolis lizards. Culex pilosus fed predominantly from reptiles, but avian and mammalian blood meals were also detected. Of these, 92% of blood meals were derived from Anolis species. For both species, Anolis sagrei, an invasive exotic lizard in Florida, was the most frequently detected host species. These data indicate that Culex atratus and Culex pilosus are specialists of reptilian hosts, particularly Anolis lizards.

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