Biological Sciences
Vector Transmission
Vector transmission refers to the process by which infectious agents, such as viruses or bacteria, are transmitted from one host to another through the bite of a vector organism, such as mosquitoes or ticks. The vector acts as a carrier for the pathogen, allowing it to be transferred to a new host during feeding. This mode of transmission is common in the spread of many diseases, including malaria and Lyme disease.
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8 Key excerpts on "Vector Transmission"
eBook - PDF- Nagalingam, Mohandoss(Authors)
- 2018(Publication Date)
- Daya Publishing House(Publisher)
In mechanical transmission two types of vectors operate in disease transmission: 1. The frst type collect the agent in their mouth parts and directly transfer it to the next host e.g. Blood sucking arthropods described as living needle. 2. The others are those vectors which pick up the causal agent in their legs, body hairs or proboscis as by fies and moths. They are designated as living swabs. In both the cases infection is being brought about by mere surface contact with the contaminated media. Infectivity of a mechanical vector declines sharply with time and becomes totally ineffcient within a short time. Mechanical transmission is a character of the pathogen and not of the vector. Elimination of the vector need not totally eliminate the infection but will only reduce the incidence rate. Another factor which infuences the effcacy of spread of a disease here is the role of an organic medium which favours the spread of mechanical transmission. In biological transmission, intervention of a vector seems mandatory for an effcient spread of the pathogen. The role of insects, therefore, is very important here and their control is a major weapon in disease control. Biologically transmitted pathogens undergo a cycle of development in the vector. Consequently there is a period of incubation during which the This ebook is exclusively for this university only. Cannot be resold/distributed. infection does not spread. When this period is over, the vector is infective and remains so for the rest of its life. Vectors transmitting pathogens by biological means are in strict sense the definitive hosts. Broadly, fve factors infuence the process of dissemination and establishment of the disease. 1. The manner in which the agent is released from the vertebrate host: If the pathogen is restricted to blood or tissues and are to be transmitted by blood sucking or biting arthropods, the process is designated as ‘active egress’.
eBook - ePub- Gary R. Mullen, Lance A. Durden(Authors)
- 2002(Publication Date)
- Academic Press(Publisher)
epidemiology deals with the natural history and spread of diseases within human and animal populations. Vector-borne diseases consist minimally of a triad that includes an arthropod vector, a vertebrate host, and a parasite. The spread of pathogens by arthropods is especially complex, because in addition to interactions between the vertebrate host and the parasite, an arthropod is required for transmission of the parasite to uninfected hosts. Environmental factors such as temperature and rainfall impact these processes by affecting the rate of parasite maturation within the arthropod host, as well as arthropod abundance in time and space.A vector is an arthropod responsible for the transmission of parasites among vertebrate hosts. Vectors transmit parasites, not diseases. Disease is the response of the host to invasion by or infection with a parasite. A parasite is any organism, including viruses, bacteria, protozoa, and helminths, that is dependent upon the host for its survival. Parasites may or may not cause disease. When a parasite injures its host and causes disease, it is referred to as a pathogen or disease agent. A vector-borne disease , therefore, is an illness caused by a pathogen that is transmitted by an arthropod. Facultative parasites have both free-living and parasitic forms, whereas obligate parasites are totally dependent upon their host(s) to provide their requirements for life. Ectoparasites live on or outside the host, whereas endoparasites live inside the host. When interacting with their hosts, ectoparasites produce an infestation that typically remains topical or peripheral, whereas endoparasites produce an infection upon invasion of host tissues. The occurrence and severity of disease depends upon the host-parasite interaction after infection. A host carrying a parasite is infected , whereas an infected host capable of transmitting a parasite is infective. A host capable of parasite maintenance without clinical symptoms is a carrier.
eBook - PDF- Michael Thrusfield(Author)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
Mechanical vector: an animal (usually an arthro-pod) that physically carries an infectious agent to its primary or secondary host (e.g. mosquitoes and fleas transmitting myxomatosis virus between rab-bits). The infectious agent neither multiplies nor develops in the mechanical vector. Biological vector: a vector (usually an arthropod) in which an infectious agent undergoes either a necessary part of its life-cycle, or multiplication, before transmission to the natural or secondary host. Three types of biological transmission occur: (1) developmental transmission: with an essential phase of development occurring in the vector (e.g. Dirofilaria immitis in mosquitoes); (2) propagative transmission: when the agent multi-plies in the vector (e.g. louping ill virus in ixodid ticks); (3) cyclopropagative transmission: a combination of (1) and (2) (e.g. Babesia spp. in ticks). Development in the vector involves migration of the infectious agent. Thus, two types of transmission are identified in the life-cycles of members of the protozoan genus Trypanosoma. The African try-panosomes that parasitize the blood and tissues of infected animals are ingested by insects of the genus Glossina, in which they undergo a developmental cycle that involves migration from their initial focus of infection in the midgut and back to the salivary glands, from which infective forms are released; this is salivarian transmission. In contrast, members of the species Trypanosoma cruzi (the cause of Chagas' disease in man in South America, with dogs, cats and some wild animals implicated as reservoirs) are ingested by bugs of the family Reduviidae, from which infective forms are shed in the faeces, human infection occurring by contamination of wounds and the eyes; this is stercorarian transmission. Biological vectors are frequently either definitive or intermediate hosts; for example mosquitoes are biological vectors and the definitive hosts of Plasmodium spp.
eBook - PDFVector-Borne Diseases
Recent Developments in Epidemiology and Control
- David Claborn, Sujit Bhattacharya, Syamal Roy, David Claborn, Sujit Bhattacharya, Syamal Roy(Authors)
- 2020(Publication Date)
- IntechOpen(Publisher)
The ability to transmit a pathogen biologically varies greatly among species of arthropods and even among geographical strains within a species [16]. Four types of biological transmission have been described according to the type of biological development the pathogen undergoes in the body of the arthropod vector: i. Propagative transmission occurs when the organism ingested with the blood meal undergoes simple multiplication in the body of the arthropod. ii. Cyclopropagative transmission in which the pathogen undergoes a develop-mental cycle (changes from one stage to another) as well as multiplication in the body of the arthropod. iii. Cyclodevelopmental transmission: the pathogen undergoes developmental changes from one stage to another but does not multiply. iv. Vertical and direct transmission occurs either via the transovarial route or by infection of eggs from female after oviposition, both leading to venereal transmission. Vector-Borne Diseases - Recent Developments in Epidemiology and Control 10 The second way of transmission called mechanical transmission consists of a simple transfer of the organism on contaminated mouthparts or other body parts. No multiplication or developmental change of the pathogen on or in the arthropod takes place during this type of transmission. The relative infection of the vector is usually of short duration in such cases because the vector is mere a pathogen carrier. Successful mechanical transmission depends on the degree of contact insects have with the vertebrate hosts and on feeding behavior [16]. The vector and pathogen interactions greatly affect the dynamics of VBDs and explain many of the particular characteristics of each infection and its epidemics. Vector-borne pathogen transmission occurs when host, vector, and pathogen inter-act in space and time within a permissive environment.
- Edward T Ryan, David R Hill, Tom Solomon, Naomi Aronson, Timothy P Endy(Authors)
- 2019(Publication Date)
- Elsevier(Publisher)
Most vector-borne pathogens are zoonoses (pathogens of animals) and have a primary vertebrate reservoir host and a primary arthropod vector that maintains the transmission cycle in nature; this is usually via horizontal transmission but is sometimes facilitated by transovarial or vertical transmission (see later). This primary cycle is usually inapparent in humans and domestic animals. On occasion, the pathogen may be introduced into the peridomestic or urban environment by secondary vectors or by the vertebrate host, which often establishes a secondary transmission cycle involving other vertebrate hosts and arthropod vectors. Humans and domestic animals are usually infected by bridge vectors from these secondary cycles and are often dead-end or incidental hosts, not contributing to the transmission cycle. Recent studies suggest, however, that humans may in fact play a previously unappreciated role as reservoir during the transmission of pathogens and parasites in what is typically referred to as anthropogenic transmission (e.g., visceral leishmaniasis caused by Leishmania donovani in India and Sudan). A basic vector-borne pathogen transmission cycle is shown in Fig. 147.1. An arthropod can transmit a pathogen from one person or animal to another in one of two basic ways. Fig. 147.1 Transmission cycles for arthropod-borne infections. Mechanical Transmission Defined as transfer of a pathogen present on contaminated mouthparts or other body parts. There is no multiplication or developmental change of the pathogen on or in the insect. Examples include some enteroviruses, bacteria, and protozoa of human and veterinary importance. Insects, such as houseflies, can become contaminated with such pathogens while feeding on feces and transfer them to food
eBook - PDF- Patricia Marques(Author)
- 2020(Publication Date)
- Delve Publishing(Publisher)
Recent studies have emphasized that the majority of the last pandemics have been originated by zooneses in the wild. The participation of vectors in the spread of zoonotic diseases was estimated to occur in about one fourth of pathogen outbreaks during the last century [1]. Importantly, human related activities are contributing to increase the impact of vector-borne diseases by increasing vector density (e.g. irrigation, urbanization, dam construction) or by introducing pathogens into areas in which they had been hitherto absent [2]. As a result, there has been the need to control the population of blood-feeding arthropods to reduce epidemiologic risks because they may harbor pathogens responsible for serious infectious diseases such as malaria, viral encephalitis, West Nile virus, Chagas disease, Lyme disease or African sleeping sickness. Although pathogen prevalence in vectors is usually low, Disentangling Vector-Borne Transmission Networks: A Universal DNA... 137 a correct understanding of vector-hosts interactions is crucial to predict transmission patterns and for the development of efficient control policies. The enhancement of species identification since the advent of molecular methods has revolutionized our view of such complex ecological networks at the same time that it has contributed to gain insights on the co-evolutionary relationships between vectors, pathogens and their hosts [reviewed in 3]. The emerging of international initiatives such as the Consortium for the Barcode of Life (www.barcoding.si.edu) is expected to greatly expand the benefits of molecular methods in this field. The DNA barcoding project aims to establish a 648-bp fragment of the Cytochrome c Oxidase Subunit I (COI) mitochondrial gene as universal method for the taxonomic classification of biodiversity [4], [5].
eBook - ePubViruses
From Understanding to Investigation
- Susan Payne(Author)
- 2017(Publication Date)
- Academic Press(Publisher)
Chapter 5Virus Transmission and Epidemiology
Abstract
Viral epidemiology is the study of the relationships among viruses and their hosts. An important aspect of viral epidemiology is spread. Viral epidemiologists try to predict the potential for development of an epidemic or pandemic and to determine appropriate interventions to contain an outbreak. Epidemiologists must try to account for a variety of factors involving both host and virus. These include, but are not limited to: mode of transmission, length of infection, and window of transmissibility, population density, living conditions, environment (climate, season), and stability of the virus. Modes of viral transmission include direct contact, exchange of body fluids, contact with infected fomites, inhalation, ingestion of contaminated food or water, and insects. Insect transmission can be complicated as the virus may replicate in the insect host or be passed vertically through eggs that survive for long periods in the environment. While medical personnel are interested in cases of disease, the epidemiologist must also consider infections that are silent or inapparent. Serological surveys are an important tool for detecting past viral infections.
eBook - PDFThe Mycoplasmas V3
Plant and Insects Mycoplasmas
- R.F. Whitcomb(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
The cells were more susceptible to virus inoculations and yielded more virus. 9 / Vector Transmission of Mycoplasmal Agents 293 Despite the promise offered by tissue culture studies, these methods have not been successfully applied to plant mycoplasmas. For example, a monolayer cell culture from C. montanus was established and maintained for over 2 years, but attempts to inoculate the cell cultures with WXMs failed (Richardson and Jensen, 1971). Also, McBeath (1974) was unable to infect cells of D. elimatus with the CSA. VIM. FACTORS AFFECTING THE TRANSMISSION OF PROKARYOTES BY VECTORS The effectiveness of transmission of a pathogen depends upon both biological and physical factors. Some factors may indirectly affect patho-gen transmission through direct action on the vectors, and others may directly affect both the vector and the pathogen. Although the potential rate of spread of a pathogen between plants depends on the size and mobility of the vector populations, the actual performance is governed by biological as well as physical factors. Several biological factors such as age, sex, biotype of vectors, number of generations per year, age of plants, and circadian periodicity are known to affect the transmission of prokaryotes by vectors. In general, nymphs of Homoptera are more efficient vectors than adults (Chiykowski and Sinha, 1970; Chiykowski, 1974, 1976), but in some cases adults have been reported to be better transmitters (Sinha and Chiykowski, 1967b; Chiykowski and Sinha, 1969; Gold, 1974). The transmission efficiency of females is usually higher than that of males regardless of age (Chiykowski, 1967, 1974, 1977; Sinha and Chiykowski, 1967b; Chiykowski and Sinha, 1970), but this may also occasionally be reversed (Chiykowski, 1976). Differences in the ability of insect biotypes to transmit prokaryotes have been observed in some instances (Severin, 1950a; Lindsten, 1962; Gold, 1974).
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