Holly Gaff's research while affiliated with University of KwaZulu-Natal and other places
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Publications (46)
There is a vast amount of geo-referenced data in many fields of study including ecological studies. Geo-referencing is usually by point referencing; that is, latitudes and longitudes or by areal referencing, which includes districts, counties, states, provinces and other administrative units. The availability of large geo-referenced datasets for mo...
Purpose: Orofacial manifestations of Lyme disease can affect head and neck anatomical structures that are frequently examined by dental professionals. The purpose of this systematic review was to examine the literature for types and frequencies of orofacial manifestations documented in populations in the United States (US) with Lyme disease.Methods...
The rising prevalence of tick-borne diseases in humans in recent decades has called attention to the need for more information on geographic risk for public health planning. Species distribution models (SDMs) are an increasingly utilized method of constructing potential geographic ranges. There are many knowledge gaps in our understanding of risk o...
Tick-borne diseases are a growing problem in many parts of the world, and their surveillance and control touches on challenging issues in medical entomology, agricultural health, veterinary medicine, and biosecurity. Spatial approaches can be used to synthesize the data generated by integrative One Health surveillance systems, and help stakeholders...
The Gulf Coast tick, Amblyomma maculatum, is undergoing a northward expansion along the United States East Coast, most recently establishing populations in Virginia, Maryland, and Delaware. This expansion has human health implications, as A. maculatum is the primary natural vector of the bacterium Rickettsia parkeri, which causes a spotted fever-ty...
Vector borne diseases (VBDs) are often seen by the highly developed nations of the world as an issue of poor tropical countries. While framing the problem this way—through the paradigm of a poverty-trap—may leverage aid and motivate political will toward disease control, it misses a wide range of socio-political contexts both driving, and driven by...
The American dog tick, Dermacentor variabilis (Say) (Acari: Ixodidae), is a vector for several human disease-causing pathogens such as tularemia, Rocky Mountain spotted fever, and the understudied spotted fever group rickettsiae (SFGR) infection caused by Rickettsia montanensis. It is important for public health planning and intervention to underst...
Mark-recapture techniques have been widely used and specialized to study organisms throughout the field of biology. To mark-recapture ticks (Ixodida), we have created a simple method to mark ticks using nail polish applied with an insect pin secured in a pencil that allows for a variety of questions to be answered. For measuring tick control effica...
The American dog tick, Dermacentor variabilis (Say), is a vector for several human disease causing pathogens such as tularemia, Rocky Mountain spotted fever, and the understudied spotted fever group rickettsiae (SFGR) infection caused by Rickettsia montanensis . It is important for public health planning and intervention to understand the distribut...
The key to the conservation of harvested species is the maintenance of reproductive success. Yet for many marine species large, old individuals are targeted despite their disproportionate contribution to reproduction. We hypothesized that a combination of no-take marine protected areas (MPAs) and harvest slot limits (maximum and minimum size limits...
The rising prevalence of tick-borne diseases in humans in recent decades has called attention to the need for more information on geographic risk for public health planning. Species distribution models (SDMs) are an increasingly utilized method of constructing potential geographic ranges. There are many knowledge gaps in our understanding of risk o...
Lyme disease is the most commonly reported vector-borne disease in the United States, and the number of cases reported each year continues to rise. The complex nature of the relationships between the pathogen (Borrelia burgdorferi sensu stricto), the tick vector (Ixodes scapularis Say), multiple vertebrate hosts, and numerous environmental factors...
Candidatus Rickettsia mendelii is a novel rickettsial species recently identified in Ixodes ricinus. In this study, Ixodes brunneus collected from wild birds (n = 77 ticks) or vegetation (n = 4 ticks) in southeastern Virginia were surveyed for rickettsial agents. Candidatus Rickettsia mendelii was confirmed in I. brunneus through sequencing of the...
Cases of morphological anomalies in the blacklegged tick, Ixodes scapularis (Acari: Ixodidae), have recently been reported from the Northeastern and upper Midwestern United States, potentially complicating identification of this important vector of human disease-causing pathogens. We hereby report a case of a morphological anomaly in I. scapularis,...
Dermacentor variabilis, a common human-biting tick found throughout the eastern half and along the west coast of the United States, is a vector of multiple bacterial pathogens. Historically, D. variabilis has been considered a primary vector of Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever. A total of 883 adult D. varia...
Understanding tick-transmitted pathogens in tick infested areas is crucial for the development of preventive and control measures in response to the increasing cases of tick-borne diseases. A stochastic model for the dynamics of two pathogens, Rickettsia parkeri and Rickettsia amblyommii, in a single tick, Amblyomma americanum, is developed and ana...
A mathematical model for a two-pathogen, one-tick, one-host system is presented and explored. The goal of this model is to determine how long an invading pathogen persists within a tick population in which a resident pathogen is already established. The numerical simulations of the model demonstrate the parameter ranges that allow for coexistence o...
Zika is a flavivirus transmitted to humans through either the bite of infected Aedes mosquitoes or sexual intercourse with infected individuals. In this paper, we present a mathematical model based on these two modes of transmission. Using the next-generation matrix method, a threshold parameter called basic reproduction number is determined. Sensi...
The hard (ixodid) ticks Amblyomma americanum and Amblyomma maculatum are found throughout the southeastern United States. To study the effects of water inundation, which is an increasingly common phenomenon in many coastal areas, unfed adult A. americanum and A. maculatum ticks were tested for survival by submergence in three water conditions: fres...
Tick population control technologies have been studied for several decades but no method is successful in all situations. The success of each technology depends on tick species identity and abundance, host species identity and abundance, phenology of both ticks and hosts, geographic region, and a multitude of other factors. Here we review current t...
The first mathematical models for an argasid tick are developed to explore the dynamics and identify knowledge gaps of these poorly studied ticks. These models focus on Ornithodoros moubata, an important tick species throughout Africa and Europe. Ornithodoros moubata is a known vector for African swine fever (ASF), a catastrophically fatal disease...
We formulate and analyse a stochastic epidemic model for the transmission dynamics of a tick-borne disease in a single population using a continuous-time Markov chain approach. The stochastic model is based on an existing deterministic metapopulation tick-borne disease model. We compare the disease dynamics of the deterministic and stochastic model...
Human use of the ocean and its ecosystems continues to degrade coastal habitats around the world. Assessing anthropogenic impacts on these environments can be costly and manpower-intensive; thus, the development of rapid, remote techniques to assess habitat quality is important. We employed autonomous hydrophone receivers to record the soundscapes...
The recent spread of mosquito-transmitted viruses and associated disease to the Americas motivates a new, data-driven evaluation of risk in temperate population centers. Temperate regions are generally expected to pose low risk for significant mosquito-borne disease; however, the spread of the Asian tiger mosquito (Aedes albopictus) across densely...
Proportion of the human population infected with Zika virus in New York City as a function of Ph (proportion of blood meals on humans) and season length.
From left to right, 90-day, 120-day, and 150-day peak mosquito seasons are shown. As season length increases, the percent of serious outbreaks increases and the needed percent of human feeding to...
Summary results for our quantities of interest, R0 and total number of people infected, for each scenario (city, season length, virus).
(XLSX)
Proportion of the human population infected with chikungunya at the end of the 90-day season in Atlanta as a function of R0 and Ph (proportion of blood meals that are human).
The red line is at R0 = 1.
(TIFF)
Distribution of chikungunya R0 across ranges of human feeding rates, Ph, for New York City.
(TIFF)
Summary of references and data used to determine parameter values.
(XLSX)
Proportion humans infected with chikungunya as a function of number of bites per person per day and R0.
The solid line is at R0 = 1.
(TIFF)
Proportion of the population infected with chikungunya in New York City as a function of Ph (proportion of blood meals on humans) and season length.
From left to right, 90-day, 120-day, and 150-day peak mosquito seasons are shown.
(TIFF)
Detailed description of the model and parameter values used for simulations.
(PDF)
The recent invasion of the hard tick Ixodes affinis, a sylvatic vector of Borrelia burgdorferi, into the Mid-Atlantic region of the United States has prompted questions as to the origin of these ticks, and the possibility of connectivity with presumed ancestral populations in Central and South America. To assess connectivity and ancestry of I. affi...
A cholera model with continuous age structure is given as a system of hyperbolic (first-order) partial differential equations (PDEs) in combination with ordinary differential equations. Asymptomatic infected and susceptibles with partial immunity are included in this epidemiology model with vaccination rate as a control; minimizing the symptomatic...
The recent spread of mosquito-transmitted viruses and associated disease to the Americas motivates a new, data-driven evaluation of risk in temperate population centers. Temperate regions are generally expected to pose low risk for significant mosquito-borne disease, however, the spread of the Asian tiger mosquito ( Aedes albopictus ) across densel...
Human use of the ocean and its ecosystems continues to degrade coastal habitats around the world. Assessing anthropogenic impacts on these environments can be cost and manpower intensive; thus, developing rapid, remote techniques to assess habitat quality has become increasingly important. We employed autonomous hydrophone receivers to record the s...
Parasites and pathogens are increasingly recognized as significant drivers of ecological and evolutionary change in natural ecosystems. Concurrently, transmission of infectious agents among human, livestock, and wildlife populations represents a growing threat to veterinary and human health. In light of these trends and the scarcity of long-term ti...
Ectoparasites frequently vector pathogens from often unknown pathogen reservoirs to both human and animal populations. Simultaneous identification of the ectoparasite species, the wildlife host that provided their most recent blood meal(s), and their pathogen load would greatly facilitate the understanding of the complex transmission dynamics of ve...
Arguably one of the most important effects of climate change is the potential impact on human health. While this is likely to take many forms, the implications for future transmission of vector-borne diseases (VBDs), given their ongoing contribution to global disease burden, are both extremely important and highly uncertain. In part, this is owing...
The Companion Animal Parasite Council hosted a meeting to identify quantifiable factors that can influence the prevalence of tick-borne disease agents among dogs in North America. This report summarizes the approach used and the factors identified for further analysis with mathematical models of canine exposure to tick-borne pathogens.
Background/Question/Methods
In order to meet the challenges in the classroom, funding agencies, professional associations, and departments have organized efforts to bring together experts in content, cognition, and instructional technologies to create instruction that is innovative, learner-centered, and strategically focused on integrating conte...
Citations
... Species distribution modeling is an intuitive approach to delineating vector-borne disease ranges that is logistically feasible, particularly when surveillance programs or capacity for pathogen testing are limited. When faced with multiple unknowns (e.g., unknown transmission cycles, emerging novel pathogens, etc.), the distribution of vectors on the landscape are sometimes used in a public health context to approximate risk of exposure to pathogens (Lippi et al., 2021b;Lippi et al., 2021c). ...
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... Geographic range of the Gulf Coast tick, Amblyomma maculatum, is expanding in multiple directions [141]. Historical range of this species in the United States was the southeastern states bordering the Gulf of Mexico to the Atlantic coast of South Carolina with a 150 miles inland extension along that range [142,143]. ...
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... In 2021, Lippi et al. (2021a) re-examined the distribution of D. variabilis and the R. montanensis-infected niche in the United States, both to understand whether predicted risk of suitability for tick encounters or infected tick encounters were distinct, and to explore and compare multiple modeling approaches for assessing the distribution of this tick vector. The 2021 study leveraged the original dataset used in the 2016 study, and used a refined set of environmental predictors to compare a suite of SDM approaches. ...
... For example, paints and inks have been used to successfully mark various invertebrates, and are generally inexpensive and durable (Harman 1975;McIntosh 1999;Opp & Prokopy 1987). However, these methods can be tedious to apply, have low durability over time, can be toxic to study organisms, and have limitations for batch marking organisms (Southwood 1978;Wineriter & Walker 1984;White et al. 2020). Dust/powder marking also has many advantages in that it can be easily applied to large batches, is inexpensive, and environmentally safe (Hagler & Jackson 2001;Miller 1993). ...
... In some cases, this change is not gradual, but rapid (Indeck et al. 2015, Butler et al. 2016, Gordon et al. 2018. The biological impacts of noise pollution are also becoming clear. ...
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... Named Entity Recognition (NER) aims at recognizing mentions of rigid designators from text belonging to predefined semantic types such as person, location, and organization [6]. In general, the entities appearing in natural language can be beyond the scope of these named entities, such as domain knowledge entities [7], biomedical entities, and materials compositions [8]. A simple rule-based extractor such as a grammar-based noun phrase chunker does not generalize well because the text span of an object name or an aspect can be a subphrase or a superphrase of another phrase. ...
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... In White et al. [2], this model was further developed to include the dynamics of two pathogens. Very complicated extensions (with various variables and parameters) were suggested and analyzed in [3][4][5]. ...
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... Population growth and expansion of its range within the northeastern US as well as outward to new regions, driven in large part by reforestation and often accompanied by the spread of pathogens, is increasing concern about the future of I. scapularis-borne illness in the US and abroad [4][5][6][7][8]. Closely related species and disease vectors in the American southeast and Europe, Ixodes affinis and Ixodes ricinus (respectively), are also on the rise [9,10]; indeed, the genus Ixodes could be considered a "global menace" [11]. At the same time, new tick-borne diseases continue to emerge [12]. ...
... As ectotherms, key processes such as rates of development (e.g., eclosion, molting) vary with temperature (Lindsay et al. 1995;Ogden et al. 2004) and so ticks are thought to be unable to complete their lifecycle in areas that are too cold (Ogden et al. 2005;2005). Within these developmental constraints, climatic conditions are thought to limit tick distributions and abundances more directly, though mortality (e.g., Ginsberg et al. 2014;Johnson et al. 2018;Gaff et al. 2020;Ogden et al. 2021). Laboratory studies show that both high and low temperature extremes, as well as low humidity, are lethal to several species in the genus Ixodes (reviewed by Ostfeld and Brunner 2015). ...
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... In [38] this model was further developed to include the dynamics of two pathogens. Very complicated extensions (with various variables and parameters) were suggested and analysed in [33], [39] and [26]. ...
