www.pediagenosis.com Open in urlscan Pro
2a00:1450:4001:801::2013  Public Scan

Form analysis
1 forms found in the DOM

GET /search

<form action="/search" id="search-form" method="get">
  <input name="q" placeholder="Search here and hit enter..." required="required" type="search">
  <input name="max-results" type="hidden" value="20">
  <button class="close" type="button">×</button>
</form>

Text Content

Agents of Infectious Disease - pediagenosis

Knowledge about Organs system, Anatomy Physiology, Health, Medicine,
Microbiology,Cardiovascular, Digestive, Endocrine, Immunology, Integumentary,
Reproductive, Reproductive, Musculoskeletal, Sensory, Nervous, Urinary,
Endocrine, Abdomen, Back Spinal Cord, Head, Lower Limb, Pelvis Perinium, Thorax,
Upper Limb, Cell, Haematology, Pediatrics, Emergency, Tranplatation Atc



 * Organs System
   * Cardiovascular System
   * Digestive System
   * Endocrine System
   * Immunology System
   * Integumentary System
   * Musculoskeletal System
   * Nervous System
   * Reproductive System
   * Sensory System
   * Respiratory System
   * Urinary System
 * Anatomy Physiology
   * Abdomen
   * Back Spinal Cord
   * Cell
   * Head Neck
   * Lower Limb
   * Pelvis Perineum
   * Thorax
   * Upper Limb
 * Health
   * Haematology
   * Pediatrics
 * Medicine
   * Emergency
   * Pharmacology
   * Tranplantation
 * Food
 * 



×

Article Update
 * Anatomy of the Basal Ganglia and Related Structures
 * Ventilatory Patterns and the Apnea Test
 * Brain Death
 * Vegetative State and Minimally Conscious State
 * Hypoxic-Ischemic Brain Damage
 * Atrial Enlargement
 * Axis Deviation in Normal Electrocardiogram
 * Cardiac Depolarization and Repolarization and Mean Instantaneous Vectors
 * Electrocardiogram
 * Specialized Conduction System
 * Cardiac Catheterization
 * Physiologic Changes During Pregnancy
 * Neural and Humoral Regulation of Cardiac Function
 * Cardiovascular Examination
 * Innervation of Heart
 * MECHANICAL VENTILATION
 * TRACHEAL RESECTION AND ANASTOMOSIS
 * ENDOTRACHEAL SUCTION
 * MORBIDITY OF ENDOTRACHEAL INTUBATION AND TRACHEOSTOMY
 * TRACHEOSTOMY
 * ENDOTRACHEAL INTUBATION
 * SECURING AN EMERGENT AIRWAY
 * UPPER AIRWAY OBSTRUCTION AND THE HEIMLICH MANEUVER
 * POSTURAL DRAINAGE AND BREATHING EXERCISES
 * CHEST-DRAINING METHODS

Sunday, 16 January



Home Immunology Organ science Agents of Infectious Disease


TUESDAY, AUGUST 7, 2018


AGENTS OF INFECTIOUS DISEASE

pediagenosis    August 07, 2018    Immunology , Organ , science   



Agents of Infectious Disease
The agents of infectious disease include prions, viruses, bacteria,
Rickettsiaceae and Chlamydiaceae, fungi, and parasites. A summary of the salient
characteristics of these human microbial pathogens is presented in Table 12.2.



Prions
In the past, microbiologists have assumed that all infectious agents must
possess a genetic master plan (a genome of either ribonucleic acid [RNA] or
deoxyribonucleic acid [DNA]) that codes for the production of the essential
proteins and enzymes necessary for survival and reproduction. However, it is now
known that infection can be transmitted solely by proteins and no nucleic acid.
Prions, protein particles that lack any kind of a demonstrable genome, are able
to transmit infection. A number of prion-associated diseases have been
identified, including Creutzfeldt-Jakob disease and kuru in humans, scrapie in
sheep, chronic wasting disease in deer and elk, and bovine spongiform
encephalopathy (BSE or mad cow disease) in cattle. The various prion-associated
diseases produce very similar pathologic processes and symptoms in the hosts and
are collectively called transmissible neurodegenerative diseases (see Fig.
12.1). All are characterized by a slowly progressive, noninflammatory neuronal
degeneration, leading to loss of coordination (ataxia), dementia, and death over
a period ranging from months to years. In fact, evidence indicates that scrapie
prion proteins (called PrPSC) are actually altered or mutated forms of a normal
host protein called cellular PrPC. Differences in the posttranslational
structure cause the two proteins to behave differently. The PrPSC is resistant
to the action of proteases (enzymes that degrade excess or deformed proteins)
and aggregates in the cytoplasm of affected neurons as amyloid fibrils. The
normal PrPC is protease sensitive and appears on the cell surface.



Prion diseases present significant challenges for management due to the
pathogenic structure of PrPSC. It is very stable and, therefore, is resistant to
many antibiotics. Studies investigating transmission of prion diseases in
animals clearly demonstrate that prions replicate, leading researchers to
investigate how proteins can reproduce in the absence of genetic material. Based
on current models, it is believed that PrPSC binds to the normal PrPC on the
cell surface, causing it to be processed into PrPSC, which is released from the
cell and then aggregates into amyloid-like plaques in the brain. The cell then
replenishes the PrPC and the cycle continues. As PrPSC accumulates, it spreads
within the axons of the nerve cells, causing progressively greater damage of
host neurons and the eventual incapacitation of the host. Prions lack
reproductive and metabolic functions, so the currently available antimicro- bial
agents are useless against them.


Viruses
Viruses are the smallest obligate intracellular pathogens. They have no
organized cellular structures but instead consist of a protein coat, or capsid,
surrounding a nucleic acid core, or genome, of RNA or DNA never both (Fig.
12.2). Some viruses are enclosed within a lipoprotein envelope derived from the
cytoplasmic membrane of the parasitized host cell. Enveloped viruses include
members of the herpesvirus group and paramyxoviruses (e.g., influenza and
poxviruses). Certain enveloped viruses are continuously shed from the infected
cell surface enveloped in buds pinched from the cell membrane.



The viruses of humans and animals have been categorized somewhat arbitrarily
according to various characteristics. These include the type of viral genome
(single-stranded or double-stranded DNA or RNA), physical characteristics (e.g.,
size, presence or absence of a membrane envelope), the mechanism of replication
(e.g., retroviruses), the mode of transmission (e.g., arthropod-borne viruses,
enteroviruses), target tissue, and the type of disease produced (e.g., hepatitis
A, B, C, D, and E viruses), to name just a few.
Viruses are incapable of replication outside of a living cell. They must
penetrate a susceptible living cell and use the biosynthetic structure of the
cell to produce viral progeny.



The process of viral replication is shown in Figure 12.3. Not every viral agent
causes lysis and death of the host cell during the course of replication. Some
viruses enter the host cell and insert their genome into the host cell
chromosome, where it remains in a latent, nonreplicating state for long periods
without causing disease. Under the appropriate stimulation, the virus undergoes
active replication and produces symptoms of disease months to years later.
Members of the herpesvirus group and adenovirus are examples of latent viruses.
Herpesviruses include the viral agents of chicken- pox and zoster
(varicella–zoster), cold sores (herpes simplex virus [HSV] type 1), genital
herpes (HSV type 2), cytomegalovirus infections, roseola (human herpesvirus 6),
infectious mononucleosis   (IM)   (Epstein-Barr   virus   [EBV])   (see Fig.
12.4), and Kaposi sarcoma (herpesvirus 8). The resumption of the latent viral
replication may produce symptoms of primary disease (e.g., genital herpes) or
cause an entirely different symptomatology (e.g., shingles instead of
chickenpox).



A family of viruses that has gained a great deal of attention is the
Orthomyxoviridae or flu viruses. There has been attention focused on the H5N1
variant, commonly known as the avian influenza virus, and the H1N1 variant,
commonly known as swine flu. The avian influenza viruses differ from the usual
human influenza viruses by the hosts they normally infect.
Avian influenza viruses typically infect wild birds. However, on occasion a new
virus may result from genetic rearrangements that make it better fit to infect
humans. When this occurs, the human population is more susceptible because the
virus is unfamiliar to most of our immune systems. The H1N1 or swine flu was
most notable in 2009. This influenza A virus was susceptible to oseltamivir
(Tamiflu), but resistant to amantadine. Rapid influenza diagnostic tests (RITs)
have been developed to diagnose a person with H1N1 and other influenza viruses.
Since the early 1980s, members of the retrovirus group have received
considerable attention after identification of the human immunodeficiency
viruses (HIV) as the causative agent of acquired immunodeficiency syndrome
(AIDS). The retro-viruses have a unique mechanism of replication. After entry
into the host cell, the viral RNA genome is first translated into DNA by a viral
enzyme called reverse transcriptase. The viral DNA copy is then integrated into
the host chromosome where it exists in a latent state, similar to the
herpesviruses. Reactivation and replication require a reversal of the entire
process. Some retroviruses lyse the host cell during the process of replication.
In the case of HIV, the infected cells regulate the immunologic defense system
of the host, and their lysis leads to a permanent suppression of the immune
response.

In addition to causing infectious diseases, certain viruses also have the
ability to transform normal host cells into malignant cells during the
replication cycle. This group of viruses is referred to as oncogenic and
includes certain retroviruses and DNA viruses, such as the herpesviruses,
adenoviruses, and papovaviruses. Human papillomaviruses (HPVs), members of the
papovavirus family, cause cutaneous and genital warts, and several genotypes are
associated with cervical cancer. The first vaccine (Gardasil) to prevent
cervical cancer, precancerous genital lesions, genital warts, and anal and
oropharyngeal cancers due to HPV types 6, 11, 16, and 18 was developed in 2006.


Bacteria
Bacteria are autonomously replicating unicellular organisms known as prokaryotes
because they lack an organized nucleus. Compared with nucleated eukaryotic
cells, the bacterial cell is small and structurally relatively primitive.
Similar to eukaryotic cells, but unlike viruses, bacteria contain both DNA and
RNA. They are the smallest of all living cells and range from 0.1 to 10 µm. They
contain no organized intracellular organelles, and the genome consists of only a
single chromosome of DNA. Many bacteria transiently harbor smaller
extrachromosomal pieces of circular DNA called plasmids. Occasionally, plasmids
contain genetic information that increases the virulence or antibiotic
resistance of the organism.
The prokaryotic cell is organized into an internal compartment called the
cytoplasm, which contains the reproductive and metabolic machinery of the cell.
The cytoplasm is surrounded by a flexible lipid membrane, called the cytoplasmic
membrane. This in turn is enclosed within a rigid cell wall. The structure and
synthesis of the cell wall determine the microscopic shape of the bacterium
(e.g., spherical [cocci], helical [spirilla], or elongate [bacilli]). Most
bacteria produce a cell wall composed of a distinctive polymer known as
peptidoglycan. This polymer is produced only by prokaryotes and is therefore an
attractive target for antibacterial therapy. Several bacteria synthesize an
extracellular capsule composed of protein or carbohydrate. The capsule protects
the organism from environmental hazards such as the immunologic defenses of the
host.

Certain bacteria are motile as the result of external whiplike appendages called
flagella. The flagella rotate like a propeller, transporting the organism
through a liquid environment. Bacteria can also produce hairlike structures
projecting from the cell surface called pili or fimbriae, which enable the
organism to adhere to surfaces such as mucous membranes or other bacteria.
Most prokaryotes reproduce asexually by simple cellular division. The manner in
which an organism divides can influence the microscopic morphology. For
instance, when the cocci divide in chains, they are called streptococci; in
pairs, diplococci; and in clusters, staphylococci. The growth rate of bacteria
varies significantly among different species and depends greatly on physical
growth conditions and the availability of nutrients. In the laboratory, a single
bacterium placed in a suitable growth environment, such as an agar plate,
reproduces to the extent that it forms a visible colony com- posed of millions
of bacteria within a few hours (Fig. 12.5).



In nature, however, bacteria rarely exist as single cells floating in an aqueous
environment. Rather, bacteria prefer to stick to and colonize environmental
surfaces, producing structured communities called biofilms. The organization and
structure of biofilms permit access to available nutrients and elimination of
metabolic waste. Within the biofilm, individual organisms use chemical signaling
as a form of primitive intercellular communication to represent the state of the
environment. These signals inform members of the community when sufficient
nutrients are available for proliferation or when environmental conditions
warrant dormancy or evacuation. Examples of biofilms abound in nature and are
found on surfaces of aquatic environments and on humans. Eighty percent of all
chronic infections are due to the presence of biofilms.
The physical appearance of a colony of bacteria grown on an agar plate can be
quite distinctive for different species. Bacteria are also identified according
to how they divide. Some bacteria produce pigments that give colonies a unique
color; some produce highly resistant spores when faced with an unfavorable
environment. The spores can exist in a quiescent state almost indefinitely until
suitable growth conditions are encountered, at which time the spores germinate
and the organism resumes normal metabolism and replication.
Bacteria are extremely adaptable life forms. They are found not just in humans
and other hosts but in almost every environ- mental extreme on earth. However,
each individual bacterial species has a well-defined set of growth parameters,
including nutrition, temperature, light, humidity, and atmosphere. Bacteria with
extremely strict growth requirements are called fastidious. For example,
Neisseria gonorrhoeae, the bacterium that causes gonorrhea, cannot live for
extended periods outside the human body. Some bacteria require oxygen for growth
and metabolism and are called aerobes. Others cannot survive in an
oxygen-containing environment and are called anaerobes. An organism capable of
adapting its metabolism to aerobic or anaerobic conditions is called
facultatively anaerobic.
In the laboratory, bacteria are generally classified according to the
microscopic appearance and staining properties of the cell. The Gram stain is
the most widely used staining procedure. Bacteria are designated as
gram-positive organisms if they are stained purple by a primary basic dye
(usually crystal violet). Those that are not stained by the crystal violet but
are counterstained red by a second dye (safranin) are called gram-negative
organisms. Staining characteristics and microscopic morphology are used in
combination to describe bacteria. For example, Streptococcus pyogenes, the agent
of scarlet fever and rheumatic fever, is a gram-positive streptococcal organism
that is spherical, grows in chains, and stains purple by Gram stain. Legionella
pneumophila, the bacterium responsible for Legionnaire disease, is a
gram-negative rod.
Another means of classifying bacteria according to microscopic staining
properties is the acid-fast stain. Because of their unique cell membrane fatty
acid content and composition, certain bacteria are resistant to the
decolorization of a primary stain (either carbol fuchsin or a combination of
auramine and rhodamine) when treated with a solution of acid alcohol. These
organisms are termed acid-fast and include a number of significant human
pathogens, most notably Mycobacterium tuberculosis and other mycobacteria.
For purposes of taxonomy (i.e., identification and classification), each member
of the bacterial kingdom is categorized into a small group of biochemically and
genetically related organisms called the genus and further subdivided into
distinct individuals within the genus called species. The genus and species
assignment of the organism is reflected in its name (e.g., Staphylococcus
[genus] aureus [species]).


Spirochetes. The spirochetes are an eccentric category of bacteria that are
mentioned separately because of their unusual cellular morphology and
distinctive mechanism of motility. Technically, the spirochetes are
gram-negative rods but are unique in that the cell’s shape is helical and the
length of the organism is many times its width. A series of filaments are wound
about the cell wall and extend the entire length of the cell. These filaments
propel the organism through an aqueous environment in a corkscrew motion.
Spirochetes are anaerobic organisms and comprise three genera: Leptospira,
Borrelia, and Treponema. Each genus has saprophytic and pathogenic strains. The
pathogenic leptospires infect a wide variety of wild and domestic animals.
Infected animals shed the organisms into the environment through the urinary
tract. Transmission to humans occurs by contact with infected animals or
urine-contaminated surroundings. Leptospires gain access to the host directly
through mucous membranes or breaks in the skin and can produce a severe and
potentially fatal illness called Weil syndrome. In contrast, the borreliae are
transmitted from infected animals to humans through the bite of an arthropod
vector such as lice or ticks. Included in the genus Borrelia are the agents of
relapsing fever (Borrelia recurrentis) and Lyme disease (B. burgdorferi).
Pathogenic Treponema species require no intermediates and are spread from person
to person by direct contact. The most important member of the genus is Treponema
pallidum, the causative agent of syphilis.


Mycoplasmas. The mycoplasmas are unicellular prokaryotes capable of independent
replication. These organisms are less than one third the size of bacteria at
approximately 0.3 µm at their largest diameter and contain a small DNA genome
approximately one half the size of the bacterial chromosome. The cell is
composed of cytoplasm surrounded by a membrane but, unlike bacteria, the
mycoplasmas do not produce a rigid peptidoglycan cell wall. As a consequence,
the microscopic appearance of the cell is highly variable, ranging from coccoid
forms to filaments, and the mycoplasmas are resistant to cell-wall–inhibiting
antibiotics, such as penicillins and cephalosporins.
The mycoplasmas affecting humans are divided into three genera: Mycoplasma,
Ureaplasma, and Acholeplasma. The first two require cholesterol from the
environment to produce the cell membrane; the acholeplasmas do not. In the human
host, mycoplasmas are commensals. However, a number of species are capable of
producing serious diseases, including pneumonia (Mycoplasma pneumoniae), genital
infections (Mycoplasma hominis and Ureaplasma urealyticum), and maternally
transmitted respiratory infections to infants with low birth weight (U.
urealyticum). not produce disease in the cells of certain arthropods such as
fleas, ticks, and lice. The organisms are accidentally transmitted to humans
through the bite of the arthropod (i.e., the vector) and produce a number of
potentially lethal diseases, including Rocky Mountain spotted fever and epidemic
typhus. Rocky Mountain spotted fever is a reportable disease that has increased
in frequency over the last decade from two cases in 1 million people to eight
cases in 1 million people. However, the death rate has decreased to
approximately 0.5%.
The Chlamydiaceae are slightly smaller than the Rickettsiaceae but are
structurally similar and are transmitted directly between susceptible
vertebrates without an intermediate arthropod host. Transmission and replication
of Chlamydiaceae occur through a defined life cycle. The infectious form, called
an elementary body, attaches to and enters the host cell, where it transforms
into a larger reticulate body. This undergoes active replication into multiple
elementary bodies, which are then shed into the extracellular environment to
initiate another infectious cycle. Chlamydial diseases of humans include
sexually transmitted genital infections (Chlamydophila trachomatis), which are
the most common of the bacterial sexually transmitted infections (STIs)10;
ocular infections and pneumonia of newborns (C. trachomatis); upper and lower
respiratory tract infections in children, adolescents, and young adults
(Chlamydophila pneumoniae), which generally does not cause severe disease unless
there is an underlying pulmonary disorder2; and respiratory disease acquired
from infected birds (Chlamydia psittaci).
Organisms within the family Anaplasmataceae (including the reorganized genera
Ehrlichia, Anaplasma, Neorickettsia, and Wolbachia) are also obligate
intracellular organisms that resemble the Rickettsiaceae in structure and
produce a variety of veterinary and human diseases, some of which have a tick
vector. These organisms target host mononuclear and polymorphonuclear white
blood cells for infection and, similar to the Chlamydiaceae, multiply in the
cytoplasm of infected leukocytes within vacuoles called morulae. Unlike the
Chlamydiaceae, however, the Anaplasmataceae do not have a defined life cycle and
are independent of the host cell for energy production. Ehrlichia sennetsu,
which is primarily restricted to Japan, produces a disease called sennetsu fever
that resembles IM. Disease caused by this organism differs from other
Anaplasmataceae because it is associated with eating raw fish infested with E.
sennetsu–infected parasites. The most common infections caused by
Anaplasmataceae are human monocytic and granulocytic ehrlichiosis. Human
monocytic ehrlichi-osis is a disease caused by Ehrlichia chaffeensis and E.
canis that can easily be confused with Rocky Mountain spotted fever.

Clinical disease severity ranges from mild to life threatening. Manifestations
include generalized malaise, anorexia and nausea, fever, and headache. Decreases
in white blood cells (leukopenia) and platelets (thrombocytopenia) often occur.
Severe sequelae include severe respiratory failure, encephalopathy, and acute
renal failure. The disease is usually more severe in older adults and people
with compromised immune function. Evidence validates  the  importance  of 
empirical antibiotic treatment when one suspects ehrlichiosis since a fulminant
and life-threatening infection is likely with immu- nocompromised people. Human
granulocytic ehrlichiosis, which is caused by two species (Anaplasma
phagocytophilum and Ehrlichia ewingii), is also transmitted by ticks. The
symptoms are similar to those seen with human monocytotropic ehrlichiosis.

The genus Coxiella contains only one species, C. burnetii. Like its rickettsial
counterparts, it is a gram-negative intracellular organism that infects a
variety of animals, including cattle, sheep, and goats. In humans, Coxiella
infection produces a disease called Q fever, characterized by a nonspecific
febrile illness often accompanied by headache, chills, and mild pneumonia-like
symptoms. The organism produces a highly resistant sporelike stage that is
transmitted to humans when contaminated animal tissue is aerosolized (e.g.,
during meat processing) or by ingestion of contaminated milk.


Fungi
The fungi are free-living, eukaryotic  saprophytes  found in every habitat on
earth. Some are members of the normal human microflora. Fortunately, few fungi
are capable of causing diseases in humans, and most of these are incidental,
self-limited infections of skin and subcutaneous tissue. Serious fungal
infections are rare and usually initiated through puncture wounds or inhalation.
Despite their normally harmless nature, fungi can cause life-threatening
opportunistic diseases when host defense capabilities have been disabled.
The fungi can be separated into two groups, yeasts and molds, based on
rudimentary differences in their morphology. The yeasts are single-celled
organisms, approximately the size of red blood cells, which reproduce by a
budding process. The buds separate from the parent cell and mature into
identical daughter cells. Molds produce long, hollow, branching filaments called
hyphae. Some molds produce cross walls, which segregate the hyphae into
compartments, and others do not. A limited number of fungi are capable of
growing as yeasts at one temperature and as molds at another. These organisms
are called dimorphic fungi and include a number of human pathogens such as the
agents of blastomycosis (Blastomyces dermatitidis), histoplasmosis (Histoplasma
capsulatum), and coccidioidomycosis (Coccidioides immitis).
The appearance of a fungal colony tends to reflect its cellular composition.
Colonies of yeast are generally smooth with a waxy or creamy texture. Molds tend
to produce cottony or powdery colonies composed of mats of hyphae collectively
called a mycelium. The mycelium can penetrate the growth surface or project
above the colony like the roots and branches of a tree. Yeasts and molds produce
a rigid cell wall layer that is chemically unrelated to the peptidoglycan of
bacteria and is therefore not susceptible to the effects of penicillin-like
antibiotics.
Most fungi are capable of sexual or asexual reproduction. The former process
involves the fusion of zygotes with the production of a recombinant zygospore.
Asexual reproduction involves  the  formation  of  highly  resistant  spores 
called conidia or sporangiospores, which are borne by specialized structures
that arise from the hyphae. Molds are identified inthe laboratory by the
characteristic microscopic appearance of the asexual fruiting structures and
spores.
Like the bacterial pathogens of humans, fungi can produce disease in the human
host only if they can grow at the temperature of the infected body site. For
example, a number of fungal pathogens called dermatophytes are incapable of
growing at core body temperature (37°C), and the infection is limited to the
cooler cutaneous surfaces. Diseases caused by these organisms, including
ringworm, athlete’s foot, and jock itch, are collectively called superficial
mycoses. Systemic mycoses are serious fungal infections of deep tissues and, by
definition, are caused by organisms capable of growth at 37°C. Yeasts such as
Candida albicans are commensal flora of the skin, mucous membranes, and
gastrointestinal tract and are capable of growth at a wider range of
temperatures. Intact immune mechanisms and competition for nutrients provided by
the bacterial flora normally keep colonizing fungi in check. Alterations in
either of these components by disease states or antibiotic therapy can upset the
balance, permitting fungal overgrowth and setting the stage for opportunistic
infections.


Parasites
In a strict sense, any organism that derives benefits from its biologic
relationship with another organism is a parasite. In the study of clinical
microbiology, however, the term parasite has evolved to designate members of the
animal kingdom that infect and cause disease in other animals, and includes
protozoa, helminths, and arthropods.
The protozoa are unicellular animals with a complete complement of eukaryotic
cellular machinery, including a well-defined nucleus and organelles.
Reproduction may be sexual or asexual, and life cycles may be simple or
complicated, with several maturation stages requiring more than one host for
completion. Most are saprophytes, but a few have adapted to the accommodations
of the human environment and produce a variety of diseases, including malaria,
amebic dysentery, and giardiasis.2 Protozoan infections can be passed directly
from host to host such as through sexual contact, indirectly through
contaminated water or food, or by way of an arthropod vector. Direct or indirect
transmission results from the ingestion of highly resistant cysts or spores that
are shed in the feces of an infected host. When the cysts reach the intestine,
they mature into vegetative forms called trophozoites, which are capable of
asexual reproduction or cyst formation. Most trophozoites are motile by means of
flagella, cilia, or ameboid motion.
The helminths are a collection of wormlike parasites that include the nematodes
or roundworms, cestodes or tapeworms, and trematodes or flukes. The helminths
reproduce sexually within the definitive host, and some require an intermediate
host for the development and maturation of offspring. Humans can serve as the
definitive or intermediate host and, in certain diseases such as trichinosis, as
both. Transmission of helminth diseases occurs primarily through the ingestion
of fertilized eggs (ova) or the penetration of infectious larval stages through
the skin directly or with the aid of an arthropod vector. Helminth infections
can involve many organ systems and sites, including the liver and lung, urinary
and intestinal tracts, circulatory and central nervous systems, and muscle.
Although most helminth diseases have been eradicated from the United States,
they are still a major health concern of developing nations.
The parasitic arthropods of humans and animals include the vectors of infectious
diseases (e.g., ticks, mosquitoes, biting flies) and the ectoparasites. The
ectoparasites infest external body surfaces and cause localized tissue damage or
inflammation secondary to the bite or burrowing action of the arthropod. The
most prominent human ectoparasites are mites (scabies), chiggers, lice (head,
body, and pubic), and fleas. Transmission of ectoparasites occurs directly by
contact with immature or mature forms of the arthropod or its eggs found on the
infested host or the host’s clothing, bedding, or grooming articles such as
combs and brushes. Many of the ectoparasites are vectors of other infectious
diseases, including endemic typhus and bubonic plague (fleas) and epidemic
typhus (lice).



Share with your friends



Related Posts


ANATOMY OF THE BASAL GANGLIA AND RELATED STRUCTURES




VENTILATORY PATTERNS AND THE APNEA TEST




BRAIN DEATH


Home

Give us your opinion






POPULAR POSTS

 * URETHRAL ANOMALIES VERUMONTANUM DISORDERS
   
 * Agents of Infectious Disease
   
 * Rectus Sheath: Cross Section Anatomy
   
 * Foramina and Canals of Cranial Base: Inferior View Anatomy
   


LABELS

Abdomen AnatomyPhysiology BackSpinalCord Cardiovascular Cell Digestive Emergency
Endocrine Haematology HeadNeck Health Immunology Integumentary LowerLimb
Medicine Musculoskeletal Nervous Organ Pediatrics PelvisPerineum Pharmacology
Reproductive Respiratory science Sensory Thorax Transplantation UpperLimb
Urinary




 * About
 * Contact
 * Disclaimer
 * Privacy Policy
 * Sitemap


Copyright © 2022 pediagenosis All Right Reserved

Notification
This is just an example, you can fill it later with your own note.
Done

Diese Website verwendet Cookies von Google, um Dienste anzubieten und Zugriffe
zu analysieren. Deine IP-Adresse und dein User-Agent werden zusammen mit
Messwerten zur Leistung und Sicherheit für Google freigegeben. So können
Nutzungsstatistiken generiert, Missbrauchsfälle erkannt und behoben und die
Qualität des Dienstes gewährleistet werden.Weitere InformationenOk