scholarly journals Complexity and critical thresholds in the dynamics of visceral leishmaniasis

2020 ◽  
Vol 7 (12) ◽  
pp. 200904
Author(s):  
Shakir Bilal ◽  
Rocio Caja Rivera ◽  
Anuj Mubayi ◽  
Edwin Michael
Keyword(s):  
Visceral Leishmaniasis ◽  
Spatial Heterogeneity ◽  
Indian Subcontinent ◽  
Feeding Preference ◽  
Host Population ◽  
Human Infection ◽  
Stable Region ◽  
Human Populations ◽  
Vector Population ◽  
Host Competence

We study a general multi-host model of visceral leishmaniasis including both humans and animals, and where host and vector characteristics are captured via host competence along with vector biting preference. Additionally, the model accounts for spatial heterogeneity in human population and heterogeneity in biting behaviour of sandflies. We then use parameters for visceral leishmaniasis in the Indian subcontinent as an example and demonstrate that the model exhibits backward bifurcation, i.e. it has a human infection and a sandfly population threshold, characterized by a bi-stable region. These thresholds shift as a function of host competence, host population size, vector feeding preference, spatial heterogeneity, biting heterogeneity and control efforts. In particular, if control is applied through human treatment a new and lower human infection threshold is created, making elimination difficult to achieve, before eventually the human infection threshold no longer exists, making it impossible to control the disease by only reducing the infection levels below a certain threshold. A better strategy would be to reduce the human infection below a certain threshold potentially by early diagnosis, control animal population levels and keep the vector population under check. Spatial heterogeneity in human populations lowers the overall thresholds as a result of weak migration between patches.

scholarly journals Simulation of leaf curl disease dynamics in chili for strategic management options

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Buddhadeb Roy ◽  
Shailja Dubey ◽  
Amalendu Ghosh ◽  
Shalu Misra Shukla ◽  
Bikash Mandal ◽  
...  
Keyword(s):  
Disease Risk ◽  
Virus Transmission ◽  
Host Population ◽  
High Rate ◽  
Disease Dynamics ◽  
Model Framework ◽  
Management Options ◽  
Transmission Parameters ◽  
Vector Population ◽  
Leaf Curl

AbstractLeaf curl, a whitefly-borne begomovirus disease, is the cause of frequent epidemic in chili. In the present study, transmission parameters involved in tripartite interaction are estimated to simulate disease dynamics in a population dynamics model framework. Epidemic is characterized by a rapid conversion rate of healthy host population into infectious type. Infection rate as basic reproduction number, R0 = 13.54, has indicated a high rate of virus transmission. Equilibrium population of infectious host and viruliferous vector are observed to be sensitive to the immigration parameter. A small increase in immigration rate of viruliferous vector increased the population of both infectious host and viruliferous vector. Migrant viruliferous vectors, acquisition, and transmission rates as major parameters in the model indicate leaf curl epidemic is predominantly a vector -mediated process. Based on underlying principles of temperature influence on vector population abundance and transmission parameters, spatio-temporal pattern of disease risk predicted is noted to correspond with leaf curl distribution pattern in India. Temperature in the range of 15–35 °C plays an important role in epidemic as both vector population and virus transmission are influenced by temperature. Assessment of leaf curl dynamics would be a useful guide to crop planning and evolution of efficient management strategies.

scholarly journals Odour of domestic dogs infected with Leishmania infantum is attractive to female but not male sand flies: evidence for parasite manipulation

2020 ◽  
Author(s):  
Monica E. Staniek ◽  
James G.C. Hamilton
Keyword(s):  
Visceral Leishmaniasis ◽  
Leishmania Infantum ◽  
Feeding Activity ◽  
Blood Feeding ◽  
Human Infection ◽  
T Test ◽  
Domestic Dogs ◽  
Lutzomyia Longipalpis ◽  
Sand Flies ◽  
Paired T Test

AbstractGlobally visceral leishmaniasis (VL) causes thousands of human deaths every year. In South America, the etiologic agent, Leishmania infantum, is transmitted from an infected canine reservoir to human hosts by the blood-feeding activity of the sand fly vector, predominantly, Lutzomyia longipalpis. Previous evidence from model rodent systems have suggested that the odour of infected hosts is altered by the parasite making them more attractive to the vector leading to an increased biting rate and improved transmission prospects for the pathogen. However, the effect of Le. infantum infection on the attractiveness of naturally infected dogs which are integral to human infection, has not been assessed.Hair collected from infected and uninfected dogs residing in a VL endemic city in Brazil. was entrained to collect the volatile chemical odours present in the headspace. Female and male Lu. longipalpis sand flies were offered a choice of infected or uninfected odour in a series of behavioural experiments. Control experiments established that female and male Lu. longipalpis were equally attracted to uninfected dog odour, female Lu. longipalpis were significantly more attracted to infected dog odour than uninfected dog odour in all 15 experimental replicates (average 45.7±0.87 females attracted to infected odour; 23.9±0.82 to uninfected odour; paired T-test, P=0.000). Male Lu. longipalpis did not significantly prefer either infected or uninfected odour (average 36.1±0.4 males to infected odour; 35.7±0.6 to uninfected odour; paired T-test, P=0.722). A significantly greater proportion of females chose the infected dog odour compared to the males (paired T-test, P=0.000).The results show that dogs infected with Le. infantum are significantly more attractive to blood-feeding female than male sand flies. This is strong evidence for parasite manipulation of the host odour in a natural transmission system and indicates that infected dogs may have a disproportionate significance in maintaining infection in canine and human infection.Author SummaryVisceral leishmaniasis (VL) is a disease caused by the Protist parasite Leishmania infantum. In Brazil and other South and Central American countries, the parasite is transmitted by the blood-feeding activity of infected female Lutzomyia longipalpis sand flies. The disease leads to thousands of human cases and deaths every year. Domestic dogs are the reservoir of infection for humans therefore understanding the effect of infection on dogs is important in developing an understanding of the epidemiology of the disease. Although previous studies on rodent models of Le. infantum infection have shown that infected Golden Hamsters are more attractive to Lu. longipalpis the attractiveness of naturally infected dogs to the insect vector has not been previously been investigated. In this study we showed that the odour of infected dogs is significantly more attractive to female sand flies which can transmit the pathogen than to male sand flies which do not. This clear-cut difference in attraction of female and males suggests that the females are preferentially attracted by parasite infected hosts and may lead to enhanced infection and transmission opportunities for the parasite.

scholarly journals The role of livestock movements in the spread of Rift Valley fever virus in animals and humans in Mayotte, 2018–19

2021 ◽  
Vol 15 (3) ◽  
pp. e0009202
Author(s):  
Younjung Kim ◽  
Raphaëlle Métras ◽  
Laure Dommergues ◽  
Chouanibou Youssouffi ◽  
Soihibou Combo ◽  
...  
Keyword(s):  
Rift Valley ◽  
Rift Valley Fever ◽  
Rift Valley Fever Virus ◽  
Human Infection ◽  
Temporal Sequence ◽  
Spatial Proximity ◽  
Human Populations ◽  
Public Health Importance ◽  
Valley Fever ◽  
Livestock Density

Rift Valley fever (RVF) is a vector-borne viral disease of major animal and public health importance. In 2018–19, it caused an epidemic in both livestock and human populations of the island of Mayotte. Using Bayesian modelling approaches, we assessed the spatio-temporal pattern of RVF virus (RVFV) infection in livestock and human populations across the island, and factors shaping it. First, we assessed if (i) livestock movements, (ii) spatial proximity from communes with infected animals, and (iii) livestock density were associated with the temporal sequence of RVFV introduction into Mayotte communes’ livestock populations. Second, we assessed whether the rate of human infection was associated with (a) spatial proximity from and (b) livestock density of communes with infected animals. Our analyses showed that the temporal sequence of RVFV introduction into communes’ livestock populations was associated with livestock movements and spatial proximity from communes with infected animals, with livestock movements being associated with the best model fit. Moreover, the pattern of human cases was associated with their spatial proximity from communes with infected animals, with the risk of human infection sharply increasing if livestock in the same or close communes were infected. This study highlights the importance of understanding livestock movement networks in informing the design of risk-based RVF surveillance programs.

Population dynamics of two species of intestinal helminth in oystercatchers (Haematopus ostralegus)

1995 ◽  
Vol 73 (2) ◽  
pp. 296-308 ◽  
Author(s):  
C. P. Goater ◽  
J. D. Goss-Custard ◽  
C. R. Kennedy
Keyword(s):  
Paratenic Host ◽  
Feeding Preference ◽  
Host Population ◽  
Intestinal Helminth ◽  
Host Feeding ◽  
Intestinal Helminths ◽  
Host Age ◽  
Intermediate Hosts ◽  
Second Intermediate Host ◽  
Haematopus Ostralegus

The cestode Micrasomacanthus rectacantha and the trematode Psilostomum brevicolle are the two most common intestinal helminths of oystercatchers, Haematopus ostralegus, on the Exe estuary, England. Each was present in 57 of 60 birds, in numbers ranging from 1 to 9833 and from 1 to 182, respectively. Cockles (Cerastoderma edule) were used as paratenic host by M. rectacantha and as second intermediate host by P. brevicolle. Over 90% of the transmission of M. rectacantha from intermediate hosts occurred in winter, between cockles and juvenile birds. Exposure to M. rectacantha was highest in cockles from muddy sites, where up to 80% of older cockles were infected with 1–14 larvae. Exposure to P. brevicolle was similarly high at one sandy site. Juveniles also made up > 90% of the birds present on the estuary in summer, when significantly more worms were gravid. Estimates based on the numbers of uterine eggs per individual P. brevicolle showed that 8 % of the total Exe population of oystercatchers (ca. 200) contributed 51% of the eggs to the estuary. The results implicate host age, host feeding preference, and host population structure as important factors determining variation in helminth abundance in birds.

Challenges in the Diagnosis of Visceral Leishmaniasis on the Indian Subcontinent

2016 ◽  
pp. 125-134
Author(s):  
Suman Rijal ◽  
François Chappuis ◽  
Jorge Alvar ◽  
Marleen Boelaert
Keyword(s):  
Visceral Leishmaniasis ◽  
Indian Subcontinent

scholarly journals Towards elimination of visceral leishmaniasis in the Indian subcontinent—Translating research to practice to public health

2017 ◽  
Vol 11 (10) ◽  
pp. e0005889 ◽  
Author(s):  
Siddhivinayak Hirve ◽  
Axel Kroeger ◽  
Greg Matlashewski ◽  
Dinesh Mondal ◽  
Megha Raj Banjara ◽  
...  
Keyword(s):  
Public Health ◽  
Visceral Leishmaniasis ◽  
Indian Subcontinent ◽  
Research To Practice

scholarly journals Policy Recommendations From Transmission Modeling for the Elimination of Visceral Leishmaniasis in the Indian Subcontinent

2018 ◽  
Vol 66 (suppl_4) ◽  
pp. S301-S308 ◽  
Author(s):  
Epke A Le Rutte ◽  
Lloyd A C Chapman ◽  
Luc E Coffeng ◽  
José A Ruiz-Postigo ◽  
Piero L Olliaro ◽  
...  
Keyword(s):  
Visceral Leishmaniasis ◽  
Indian Subcontinent ◽  
Policy Recommendations ◽  
Transmission Modeling

scholarly journals Genetically and Antigenically Divergent Influenza A(H9N2) Viruses Exhibit Differential Replication and Transmission Phenotypes in Mammalian Models

2020 ◽  
Vol 94 (17) ◽  
Author(s):  
Jessica A. Belser ◽  
Xiangjie Sun ◽  
Nicole Brock ◽  
Claudia Pappas ◽  
Joanna A. Pulit-Penaloza ◽  
...  
Keyword(s):  
Influenza A ◽  
Human Infection ◽  
Influenza Viruses ◽  
Human Populations ◽  
Human Respiratory Tract ◽  
Live Bird Markets ◽  
Human Infections ◽  
Live Bird

ABSTRACT Low-pathogenicity avian influenza A(H9N2) viruses, enzootic in poultry populations in Asia, are associated with fewer confirmed human infections but higher rates of seropositivity compared to A(H5) or A(H7) subtype viruses. Cocirculation of A(H5) and A(H7) viruses leads to the generation of reassortant viruses bearing A(H9N2) internal genes with markers of mammalian adaptation, warranting continued surveillance in both avian and human populations. Here, we describe active surveillance efforts in live poultry markets in Vietnam in 2018 and compare representative viruses to G1 and Y280 lineage viruses that have infected humans. Receptor binding properties, pH thresholds for HA activation, in vitro replication in human respiratory tract cells, and in vivo mammalian pathogenicity and transmissibility were investigated. While A(H9N2) viruses from both poultry and humans exhibited features associated with mammalian adaptation, one human isolate from 2018, A/Anhui-Lujiang/39/2018, exhibited increased capacity for replication and transmission, demonstrating the pandemic potential of A(H9N2) viruses. IMPORTANCE A(H9N2) influenza viruses are widespread in poultry in many parts of the world and for over 20 years have sporadically jumped species barriers to cause human infection. As these viruses continue to diversify genetically and antigenically, it is critical to closely monitor viruses responsible for human infections, to ascertain if A(H9N2) viruses are acquiring properties that make them better suited to infect and spread among humans. In this study, we describe an active poultry surveillance system established in Vietnam to identify the scope of influenza viruses present in live bird markets and the threat they pose to human health. Assessment of a recent A(H9N2) virus isolated from an individual in China in 2018 is also reported, and it was found to exhibit properties of adaptation to humans and, importantly, it shows similarities to strains isolated from the live bird markets of Vietnam.

scholarly journals Genomes of Leishmania parasites directly sequenced from patients with visceral leishmaniasis in the Indian subcontinent

2019 ◽  
Vol 13 (12) ◽  
pp. e0007900 ◽  
Author(s):  
Malgorzata A. Domagalska ◽  
Hideo Imamura ◽  
Mandy Sanders ◽  
Frederik Van den Broeck ◽  
Narayan Raj Bhattarai ◽  
...  
Keyword(s):  
Visceral Leishmaniasis ◽  
Indian Subcontinent ◽  
Leishmania Parasites
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