Disease and the dynamics of extinction

Invading infectious diseases can, in theory, lead to the extinction of host populations, particularly if reservoir species are present or if disease transmission is frequency-dependent. The number of historic or prehistoric extinctions that can unequivocally be attributed to infectious disease is relatively small, but gathering firm evidence in retrospect is extremely difficult. Amphibian chytridiomycosis and Tasmanian devil facial tumour disease (DFTD) are two very different infectious diseases that are currently threatening to cause extinctions in Australia. These provide an unusual opportunity to investigate the processes of disease-induced extinction and possible management strategies. Both diseases are apparently recent in origin. Tasmanian DFTD is entirely host-specific but potentially able to cause extinction because transmission depends weakly, if at all, on host density. Amphibian chytridiomycosis has a broad host range but is highly pathogenic only to some populations of some species. At present, both diseases can only be managed by attempting to isolate individuals or populations from disease. Management options to accelerate the process of evolution of host resistance or tolerance are being investigated in both cases. Anthropogenic changes including movement of diseases and hosts, habitat destruction and fragmentation and climate change are likely to increase emerging disease threats to biodiversity and it is critical to further develop strategies to manage these threats.

Download Full-text

Are any populations 'safe'? Unexpected reproductive decline in a population of Tasmanian devils free of devil facial tumour disease

Wildlife Research ◽

10.1071/wr16234 ◽

2018 ◽

Vol 45 (1) ◽

pp. 31 ◽

Cited By ~ 7

Author(s):

K. A. Farquharson ◽

R. M. Gooley ◽

S. Fox ◽

S. J. Huxtable ◽

K. Belov ◽

...

Keyword(s):

Conservation Management ◽

Southern Oscillation ◽

Demographic Data ◽

Management Strategies ◽

Natural Populations ◽

Significant Decline ◽

Tasmanian Devil ◽

Devil Facial Tumour Disease ◽

In The Wild ◽

Reproductive Rates

Context Conservation management relies on baseline demographic data of natural populations. For Tasmanian devils (Sarcophilus harrisii), threatened in the wild by two fatal and transmissible cancers (devil facial tumour disease DFTD: DFT1 and DFT2), understanding the characteristics of healthy populations is crucial for developing adaptive management strategies to bolster populations in the wild. Aims Our analysis aims to evaluate contemporary reproductive rates for wild, DFTD-free Tasmanian devil populations, and to provide a baseline with which to compare the outcome of current translocation activities. Methods We analysed 8 years of field-trapping data, including demographics and reproductive rates, across 2004–16, from the largest known DFTD-free remnant population at Woolnorth, Tasmania. Key results Surprisingly, we found a dramatic and statistically significant decline in female breeding rate when comparing data collected from 2004–2009 with data from 2014–2016. Unfortunately we do not have any data from the intermediate years. This decline in breeding rate was accompanied by a subtle but statistically significant decline in litter sizes. These changes were not associated with a change in body condition over the same period. Furthermore, we could not attribute the decline in breeding to a change in population size or sex ratio. Preliminary analysis suggested a possible association between annual breeding rate and coarse measures of environmental variation (Southern Oscillation Index), but any mechanistic associations are yet to be determined. Conclusions The decline in breeding rates was unexpected, so further monitoring and investigation into potential environmental and/or biological reasons for the decline in breeding rate are recommended before the arrival of DFTD at Woolnorth. Implications Our results provide valuable data to support the conservation management of Tasmanian devils in their native range. They also highlight the importance of continued monitoring of ‘safe’ populations, in the face of significant threats elsewhere.

Download Full-text

Disruption of Metapopulation Structure Reduces Tasmanian Devil Facial Tumour Disease Spread at the Expense of Abundance and Genetic Diversity

Pathogens ◽

10.3390/pathogens10121592 ◽

2021 ◽

Vol 10 (12) ◽

pp. 1592

Author(s):

Rowan Durrant ◽

Rodrigo Hamede ◽

Konstans Wells ◽

Miguel Lurgi

Keyword(s):

Genetic Diversity ◽

Disease Transmission ◽

Transmission Rate ◽

Extinction Risk ◽

Disease Prevalence ◽

Disease Spread ◽

Tasmanian Devil ◽

Local Populations ◽

Metapopulation Structure ◽

Devil Facial Tumour Disease

Metapopulation structure plays a fundamental role in the persistence of wildlife populations. It can also drive the spread of infectious diseases and transmissible cancers such as the Tasmanian devil facial tumour disease (DFTD). While disrupting this structure can reduce disease spread, it can also impair host resilience by disrupting gene flow and colonisation dynamics. Using an individual-based metapopulation model we investigated the synergistic effects of host dispersal, disease transmission rate and inter-individual contact distance for transmission, on the spread and persistence of DFTD from local to regional scales. Disease spread, and the ensuing population declines, are synergistically determined by individuals’ dispersal, disease transmission rate and within-population mixing. Transmission rates can be magnified by high dispersal and inter-individual transmission distance. The isolation of local populations effectively reduced metapopulation-level disease prevalence but caused severe declines in metapopulation size and genetic diversity. The relative position of managed (i.e., isolated) local populations had a significant effect on disease prevalence, highlighting the importance of considering metapopulation structure when implementing metapopulation-scale disease control measures. Our findings suggest that population isolation is not an ideal management method for preventing disease spread in species inhabiting already fragmented landscapes, where genetic diversity and extinction risk are already a concern.

Download Full-text

Reviewing the ecological evidence base for management of emerging tropical zoonoses: Kyasanur Forest Disease in India as a case study

PLoS Neglected Tropical Diseases ◽

10.1371/journal.pntd.0009243 ◽

2021 ◽

Vol 15 (4) ◽

pp. e0009243

Author(s):

Sarah J. Burthe ◽

Stefanie M. Schäfer ◽

Festus A. Asaaga ◽

Natrajan Balakrishnan ◽

Mohammed Mudasssar Chanda ◽

...

Keyword(s):

Disease Transmission ◽

Management Strategies ◽

Research Priorities ◽

Human Infection ◽

Pathogen Transmission ◽

Management Options ◽

Forest Disease ◽

Transmission Cycle ◽

Ecological Understanding ◽

Kyasanur Forest Disease

Zoonoses disproportionately affect tropical communities and are associated with human modification and use of ecosystems. Effective management is hampered by poor ecological understanding of disease transmission and often focuses on human vaccination or treatment. Better ecological understanding of multi-vector and multi-host transmission, social and environmental factors altering human exposure, might enable a broader suite of management options. Options may include “ecological interventions” that target vectors or hosts and require good knowledge of underlying transmission processes, which may be more effective, economical, and long lasting than conventional approaches. New frameworks identify the hierarchical series of barriers that a pathogen needs to overcome before human spillover occurs and demonstrate how ecological interventions may strengthen these barriers and complement human-focused disease control. We extend these frameworks for vector-borne zoonoses, focusing on Kyasanur Forest Disease Virus (KFDV), a tick-borne, neglected zoonosis affecting poor forest communities in India, involving complex communities of tick and host species. We identify the hierarchical barriers to pathogen transmission targeted by existing management. We show that existing interventions mainly focus on human barriers (via personal protection and vaccination) or at barriers relating to Kyasanur Forest Disease (KFD) vectors (tick control on cattle and at the sites of host (monkey) deaths). We review the validity of existing management guidance for KFD through literature review and interviews with disease managers. Efficacy of interventions was difficult to quantify due to poor empirical understanding of KFDV–vector–host ecology, particularly the role of cattle and monkeys in the disease transmission cycle. Cattle are hypothesised to amplify tick populations. Monkeys may act as sentinels of human infection or are hypothesised to act as amplifying hosts for KFDV, but the spatial scale of risk arising from ticks infected via monkeys versus small mammal reservoirs is unclear. We identified 19 urgent research priorities for refinement of current management strategies or development of ecological interventions targeting vectors and host barriers to prevent disease spillover in the future.

Download Full-text

Reducing the Extinction Risk of Populations Threatened by Infectious Diseases

Diversity ◽

10.3390/d13020063 ◽

2021 ◽

Vol 13 (2) ◽

pp. 63

Author(s):

Gael L. Glassock ◽

Catherine E. Grueber ◽

Katherine Belov ◽

Carolyn J. Hogg

Keyword(s):

Gene Flow ◽

Infectious Diseases ◽

Extinction Risk ◽

Population Decline ◽

Outbreeding Depression ◽

Tasmanian Devil ◽

Adaptive Potential ◽

Genetic Management ◽

Animal Populations ◽

Devil Facial Tumour Disease

Extinction risk is increasing for a range of species due to a variety of threats, including disease. Emerging infectious diseases can cause severe declines in wild animal populations, increasing population fragmentation and reducing gene flow. Small, isolated, host populations may lose adaptive potential and become more susceptible to extinction due to other threats. Management of the genetic consequences of disease-induced population decline is often necessary. Whilst disease threats need to be addressed, they can be difficult to mitigate. Actions implemented to conserve the Tasmanian devil (Sarcophilus harrisii), which has suffered decline to the deadly devil facial tumour disease (DFTD), exemplify how genetic management can be used to reduce extinction risk in populations threatened by disease. Supplementation is an emerging conservation technique that may benefit populations threatened by disease by enabling gene flow and conserving their adaptive potential through genetic restoration. Other candidate species may benefit from genetic management via supplementation but concerns regarding outbreeding depression may prevent widespread incorporation of this technique into wildlife disease management. However, existing knowledge can be used to identify populations that would benefit from supplementation where risk of outbreeding depression is low. For populations threatened by disease and, in situations where disease eradication is not an option, wildlife managers should consider genetic management to buffer the host species against inbreeding and loss of genetic diversity.

Download Full-text

Disruption of metapopulation structure effectively reduces Tasmanian devil facial tumour disease spread at the expense of abundance and genetic diversity

10.1101/2021.10.04.463046 ◽

2021 ◽

Author(s):

Rowan Durrant ◽

Rodrigo Hamede ◽

Konstans Wells ◽

Miguel Lurgi

Keyword(s):

Genetic Diversity ◽

Disease Transmission ◽

Transmission Rate ◽

Disease Spread ◽

Tasmanian Devil ◽

Population Mixing ◽

Metapopulation Structure ◽

High Dispersal ◽

Contact Distance ◽

Devil Facial Tumour Disease

Metapopulation structure (i.e. the spatial arrangement of local populations and corridors between them) plays a fundamental role in the persistence of wildlife populations, but can also drive the spread of infectious diseases. While the disruption of metapopulation connectivity can reduce disease spread, it can also impair host resilience by disrupting gene flow and colonisation dynamics. Thus, a pressing challenge for many wildlife populations is to elucidate whether the benefits of disease management methods that reduce metapopulation connectivity outweigh the associated risks. Directly transmissible cancers are clonal malignant cell lines capable to spread through host populations without immune recognition, when susceptible and infected hosts become in close contact. Using an individual-based metapopulation model we investigate the effects of the interplay between host dispersal, disease transmission rate and inter-individual contact distance for transmission (determining within-population mixing) on the spread and persistence of a transmissible cancer, Tasmanian devil facial tumour disease (DFTD), from local to regional scales. Further, we explore population isolation scenarios to devise management strategies to mitigate disease spread. Disease spread, and the ensuing population declines, are synergistically determined by individuals' dispersal, disease transmission rate and within-population mixing. Low to intermediate transmission rates can be magnified by high dispersal and inter-individual transmission distance. Once disease transmission rate is high, dispersal and inter-individual contact distance do not impact the outcome of the disease transmission dynamics. Isolation of local populations effectively reduced metapopulation-level disease prevalence but caused severe declines in metapopulation size and genetic diversity. The relative position of managed (i.e. isolated) populations within the metapopulation had a significant effect on disease prevalence, highlighting the importance of considering metapopulation structure when implementing metapopulation-scale disease control measures. Our findings suggests that population isolation is not an ideal management method for preventing disease spread in species inhabiting already fragmented landscapes, where genetic diversity and extinction risk are already a concern, such as the Tasmanian devil.

Download Full-text

Saving the Tasmanian Devil

10.1071/9781486307197 ◽

2019 ◽

Cited By ~ 4

Keyword(s):

Genetic Research ◽

Habitat Destruction ◽

Tasmanian Devil ◽

Australian Government ◽

Management Actions ◽

Vehicle Collision ◽

Devil Facial Tumour Disease ◽

Research Findings ◽

Climate Events ◽

Insight Into

The Tasmanian devil is threatened by Devil Facial Tumour Disease (DFTD), a transmissible form of cancer that has reduced the population by over 80%. Persecution, extreme climate events, vehicle collision and habitat destruction also put pressure on this endangered species. The recovery effort to save the Tasmanian devil commenced over 15 years ago as a collaborative initiative between the Tasmanian government, the Australian government, the Zoo and Aquarium Association Australasia, and many research institutions. Saving the Tasmanian Devil documents the journey taken by partner organisations in discovering what DFTD is, the effect it has on wild devil populations, and the outcomes achieved through research and management actions. Chapters describe all aspects of devil conservation, including the captive devil populations, applied pathology, immunology and genetic research findings, adaptive management, and the importance of advocacy and partnerships. This book will provide management practitioners and conservation scientists with insight into the complexities of undertaking a program of this scale, and will also be of value to researchers, students and others interested in conservation.

Download Full-text

Integrative molecular phylogeography in the context of infectious diseases on the human-animal interface

Parasitology ◽

10.1017/s0031182012001102 ◽

2012 ◽

Vol 139 (14) ◽

pp. 1939-1951 ◽

Cited By ~ 9

Author(s):

REBECCA R. GRAY ◽

MARCO SALEMI

Keyword(s):

Infectious Diseases ◽

Disease Transmission ◽

Habitat Destruction ◽

Food Sources ◽

Animal Origin ◽

Effective Control ◽

Past Century ◽

Long Distance ◽

Live Animal ◽

Molecular Phylogeography

SUMMARYThe rate of new emerging infectious diseases entering the human population has increased over the past century, with pathogens originating from animals or from products of animal origin accounting for the vast majority. Primary risk factors for the emergence and spread of emerging zoonoses include expansion and intensification of animal agriculture and long-distance live animal transport, live animal markets, bushmeat consumption and habitat destruction. Developing effective control strategies is contingent upon the ability to test causative hypotheses of disease transmission within a statistical framework. Broadly speaking, molecular phylogeography offers a framework in which specific hypotheses regarding pathogen gene flow and dispersal within an ecological context can be compared. A number of different methods has been developed for this application. Here, our intent is firstly to discuss the application of a wide variety of statistically based methods (including Bayesian reconstruction, network parsimony analysis and regression) to specific viruses (influenza, salmon anaemia virus, foot and mouth disease and Rift Valley Fever) that have been associated with animal farming/movements; and secondly to place them in the larger framework of the threat of potential zoonotic events as well as the economic and biosecurity implications of pathogen outbreaks among our animal food sources.

Download Full-text

Perbedaan Metode Three Compartement Sink dengan Air Panas dan Larutan Klorin terhadap Angka Kuman Alat Makan di RSU Queen Latifa

JURNAL NUTRISIA ◽

10.29238/jnutri.v19i2.27 ◽

2017 ◽

Vol 19 (2) ◽

pp. 126-130

Author(s):

Rifatun Hasanah ◽

Setyowati Setyowati ◽

Noor Tifauzah

Keyword(s):

Infectious Diseases ◽

Confidence Level ◽

Disease Transmission ◽

T Test ◽

Hot Water ◽

Independent Test ◽

The Difference ◽

Hospital Use

Background:One of the efforts in preventing congenital food disease is by washing the cutlery perfectly. The cutlery used by patients with infectious diseases should be noted more, because it has a risk in disease transmission through cutlery. The process of washing the cutlery for infected patients in Queen Latifa Hospital use three compartement sink method with hot water, while the three compartement sink method with clorine solvent has never been tested. Purpose: Research was to determine the difference in the number of germs in the tool was washed using three compartement sink method with hot water and with clorine solvent. Method:Types of research is experiment with rancangan percobaan acak kelompok (RAK). The object of this research is 4 plates and 4 bowls. The number of experimental units in this research were 2 treatments x 2 cutlery x 2 checks x 2 reapetitions = 16 experimental units. The analysis used independent t-test with 95% confidence level. Result :The average number of germs in the cutlery washed using the three compartment sink method with hot water was 1 x 101 cfu / cm2, whereas with chlorine solvent is 0.2 cfu / cm2. Independent test t-test shows p = 0.049 which means the hypothesis is accepted. onclusion : There are differences in the number of germs in the washing cutlery using the three compartment sink method with hot water and with chlorine solvent. Keywords: number of germs, cutlery, three compartment sink

Download Full-text

Perbedaan Metode Three Compartement Sink dengan Air Panas dan Larutan Klorin terhadap Angka Kuman Alat Makan di RSU Queen Latifa

JURNAL NUTRISIA ◽

10.29238/jnutri.v19i2.262 ◽

2017 ◽

Vol 19 (2) ◽

pp. 126

Author(s):

Rifatun Hasanah ◽

Setyowati Setyowati ◽

Noor Tifauzah

Keyword(s):

Infectious Diseases ◽

Confidence Level ◽

Disease Transmission ◽

T Test ◽

Hot Water ◽

Independent Test ◽

The Difference ◽

Hospital Use

Background:One of the efforts in preventing congenital food disease is by washing the cutlery perfectly. The cutlery used by patients with infectious diseases should be noted more, because it has a risk in disease transmission through cutlery. The process of washing the cutlery for infected patients in Queen Latifa Hospital use three compartement sink method with hot water, while the three compartement sink method with clorine solvent has never been tested. Purpose: Research was to determine the difference in the number of germs in the tool was washed using three compartement sink method with hot water and with clorine solvent. Method:Types of research is experiment with rancangan percobaan acak kelompok (RAK). The object of this research is 4 plates and 4 bowls. The number of experimental units in this research were 2 treatments x 2 cutlery x 2 checks x 2 reapetitions = 16 experimental units. The analysis used independent t-test with 95% confidence level. Result :The average number of germs in the cutlery washed using the three compartment sink method with hot water was 1 x 101 cfu / cm2, whereas with chlorine solvent is 0.2 cfu / cm2. Independent test t-test shows p = 0.049 which means the hypothesis is accepted. Conclusion : There are differences in the number of germs in the washing cutlery using the three compartment sink method with hot water and with chlorine solvent.

Download Full-text

Spatial-temporal transmission dynamics and control of infectious diseases: Ebola virus disease (EVD) as a case study

10.1093/oso/9780198789833.003.0004 ◽

2018 ◽

Author(s):

Cécile Viboud ◽

Hélène Broutin ◽

Gerardo Chowell

Keyword(s):

Infectious Diseases ◽

Disease Transmission ◽

Ebola Virus ◽

Temporal Dynamics ◽

Virus Disease ◽

Spatial Dynamics ◽

Childhood Diseases ◽

Middle Income ◽

Theoretical Concepts ◽

Dynamics And Control

Disentangling the spatial-temporal dynamics of infectious disease transmission is important to address issues of disease persistence, epidemic growth and optimal control. In this chapter, we review key concepts relating to the spatial-temporal dynamics of infectious diseases in meta-populations, whereby geographically separate subpopulations are connected by migration or mobility rates. We review the dynamics of colonization, persistence and extinction of emerging and recurrent pathogens in meta-populations; the role of demographic and environmental factors; and geographic heterogeneity in epidemic growth rate. We illustrate theoretical concepts by reviewing the spatial dynamics of childhood diseases and other acute infections in low- and middle-income countries, and provide a detailed description of the spatial-temporal dynamics of the 2014–16 Ebola epidemic in West Africa. We further discuss how increased availability of empirical data and recent methodological developments provide a deeper mechanistic understanding of transmission processes in space and time, and make recommendations for future work.

Download Full-text