MODULE 1 Unit 2: Host-Parasite Relationships Flashcards
1
Q
is largely a study of any two organisms living in close association, commonly one, the parasite, living in or on the body of the other, the host.
A
Parasitology
2
Q
The study of parasites invariably involves, firstly, the biology of [?], and, secondly, the biology of the [?] — the parasite’s environment.
A
- parasites
- host
3
Q
Parasitology can be considered to be a specialized branch of [?].
A
ecology
4
Q
means living together in close association of two phylogenetically different organisms
A
Symbiosis
5
Q
two phylogenetically different organisms, which are called the [?]
A
symbionts
6
Q
Symbiotic relationships can be characterized by specifying the nature of the [?] between the symbionts.
A
interactions
6
Q
is a relationship in which the organisms both benefit from a relationship with each other.
A
interactionsMutualism
7
Q
The symbionts in mutualism are called [?].
A
mutualists
8
Q
Mutualism is usually [?], since in most cases physiological dependence has evolved to such a degree that one mutualist cannot survive without the other.
A
obligatory
9
Q
Termites and their intestinal flagellate, [?], are an excellent example of mutualism.
A
Trichonympha
10
Q
Termites cannot digest cellulose because they cannot synthesize and secrete the enzyme [?].
A
cellulase
11
Q
The [?] in a termite’s intestine, however, synthesize cellulase and consequently digest wood eaten by their host.
A
flagellates
12
Q
The termite uses [?] excreted as a byproduct of the flagellates’ metabolism.
A
molecules
13
Q
If we kill the flagellates by exposing termites to [?], then the termites starve to death, even though they continue to eat wood.
A
high temperature or high oxygen concentration
14
Q
In commensalism, the smaller organism – [?] – benefits from the association, but the host is neither benefitted nor harmed.
A
commensal
15
Q
The term literally means “eating at the same table”.
A
Commensalism
16
Q
An example of a commensal is [?].
A
Entamoeba coli
17
Q
This Entamoeba coli lives in the [?] of man, where it feeds on bacteria and food particles, and protected from harm, while it does not cause any damage to the tissues of its host.
A
large intestines
18
Q
is a relationship in which the parasite, the smaller of the two organisms, benefits and harms the host or in some sense lives at the expense of the host.
A
Parasitism
19
Q
The host is damaged to a certain degree because of the activities of the parasite.
A
Parasitism
20
Q
One example of a parasite is [?], which derives nutrition from the human host and causes amoebic dysentery.
A
Entamoeba histolytica
21
Q
[?] exists when the two symbionts are merely “traveling together,” and there is no physiological or biochemical dependence on the part of either participant.
A
Phoresis
22
Q
The smaller one in phoresis, the [?], is carried by the larger companion, the host.
A
phoront
23
Q
This association is mechanical for the purpose of transport from one place to another.
A
Phoresis
24
An example of this is the association of a house fly that passively transfers an amoeba on its feet from contaminated feces to a plate of food.
Phoresis
25
is defined as the route a parasite follows throughout its life --- from the time of entry into the host to exit, including the [?] (outside the host) and subsequent transmission to a new host.
Parasite life cycle
| extracorporeal
26
A parasite life cycle consists of two (2) common phases:
1. phase involving the route a parasite follows when [?]
2. phase involving the route a parasite follows [?], i.e. in the outside environment or in a nonhuman host.
- in the human body.
| - independently of the human body
27
the route (and also the means) whereby a parasite gains entry into a host
1. Portal of entry
28
the developmental form of the parasite that is capable of entering its host and continuing its development within the host
2. Infective stage
29
predetermined site of development and maturation of the parasite in a host. It is also important to note how the parasite reached its final destination, since migration through the host can cause other symptoms
3. Habitat
30
the route by which the parasite escapes the host
4. Portal of exit
31
the developmental form of the parasite which leaves the host. It is routinely recognized in a biological specimen and thus is crucial in properly identifying the parasite.
5. Diagnostic stage
32
host from which the parasite is immediately transmitted to the host.
6. Source of infection
33
stages where helminths and protozoa pass through during their life cycles.
developmental stages
34
The complete life cycle of helminths includes the
egg, larva, and adult
35
Life cycles involve [?] that copulate and females produce fertile eggs.
sexually differentiated adult worms
36
The eggs undergo [?] developing into a juvenile larva which will hatch out under suitable conditions. Larvae mature into several stages to adults.
embryonation
37
Although the life cycles of protozoa can vary a great deal, they are basically characterized by
trophozoite and cyst
37
are the metabolically active feeding and motile form, which are delicate and do not survive long outside the body; may encyst to become a cyst within a protective coating to tolerate harsh environments.
Trophozoites
38
are the resting, nonmotile, resistant stage of protozoa bounded by tough cell wall to survive adverse environmental conditions, such as desiccation, low nutrient supply, and even anaerobiosis
Cysts
39
can reemerge as a trophozoite when exposed to favorable conditions
Cysts
40
is a major risk factor for infections with intestinal amoebae (e.g., Entamoeba histolytica) or flagellates (e.g., Giardia lamblia)
Ingestion of contaminated water
41
Liquid or semi-formed samples may show trophozoites if the intestinal motility is [?].
rapid
42
Cysts will form, on the other hand, if the intestinal motility is [?] and be passed in formed stool.
normal
43
There are two life cycle patterns, namely:
1. Direct life cycle
| 2. Indirect life cycle
44
when a parasite requires only single host to complete its development cycle, e.g. Trichomonas vaginalis requires only a human host to complete its life cycle.
1. Direct life cycle
45
when a parasite requires two or more species of host to complete its development.
2. Indirect life cycle
45
is a host that harbors the adult stage of the parasite or where the parasite undergoes a sexual method of reproduction. It is also known as the final host.
1. Definitive host -
46
Sexual reproduction has not been clearly shown in some parasites— such as most protozoa (except the [?])—and in these cases we arbitrarily consider the definitive host the one most important to humans.
apicomplexans
47
is a host in which the larval stage of the parasite lives or where asexual mode of reproduction takes place. In some parasites, two different intermediate hosts may be required to complete different larval stages. These are known as first and second intermediate hosts, respectively.
2. Intermediate host
48
Example of life cycle with one (1) intermediate host.
Taenia species
49
are often but not necessarily vertebrates; malaria parasites, Plasmodium spp., reach sexual maturity and undergo fertilization in mosquitoes, which are therefore by definition their definitive hosts, whereas humans are the intermediate hosts.
Definitive hosts
50
is a host in which the parasite does not undergo further development
but remains viable and infective to another host.
3. Paratenic host
51
It is not necessary for the completion of the parasites life cycle but serves as a temporary refuge and vehicle for reaching an obligatory host, usually the definitive host, thus it is also known as the transport host or phoretic host
3. Paratenic host
52
Example: Fasciola hepatica eggs ingested by humans in contaminated animal liver, being not infective to man, will remain in the same stage of parasite without change and detected in human feces. In this case, [?] serve as a paratenic host.
humans
53
is a host harboring parasites that are parasitic for humans and from which humans may become infected
4. Reservoir host -
54
Example: Fasciola hepatica are primarily parasites of [?], most commonly, sheep, cattle, and goats, which serve as their reservoir hosts.
domestic and wild ruminants
55
is a host that is naturally infected with certain species of parasite
5. Natural host
56
Example: Dogs (also cats) are the normal hosts for [?]. The parasite is transmitted between hosts by ingesting the dog or cat flea containing the [?]
Dipylidium caninum
| cysticercoid larvae
57
is a host that is, under normal circumstances, not infected with the parasite. It is also known as incidental host
6. Accidental host
58
Example: Humans are accidental hosts of Dipylidium caninum acquired by ingesting the infected flea, possibly due to [?] with flea-infested pets.
close contact
59
is a host that generally does not allow transmission of the parasite to the next host, thereby preventing the parasite from completing its development.
7. Dead-end host
60
Example of life cycle with two (2) intermediate hosts.
Fasciola hepatica
61
Example of life cycle with natural hosts.
Dipylidium caninum
62
Example of life cycle with accidental hosts.
Dipylidium caninum
63
Example of life cycle with Dead-end hosts.
Trichinella spp.
64
Trichomonas vaginalis resides in the female [?] and the male [?], where it replicates by binary fission .
lower genital tract
| urethra and prostate
65
The parasite does not appear to have a cyst form, and does not survive well in the external environment.
Trichomonas vaginalis
66
is transmitted among humans, its only known host, primarily by sexual intercourse .
Trichomonas vaginalis
67
Malaria parasite, [?], requires both human host and mosquito to complete its life cycle.
Plasmodium sp.
68
Adult worms of Ascaris lumbricoides live in the small intestine of man. Therefore, man serves as its
definitive host
69
Taeniasis is the the infection with the adult worm of [?] in the small intestine of human.
Taenia solium or Taenia saginata
70
Humans are the only definitive hosts of these species .
Taenia solium or Taenia saginata
71
Eggs [?] are passed in feces.
(orgravid proglottids)
72
[?] is the intermediate host of T. solium, and cattle for T. saginata. They become infected by ingesting vegetation contaminated with eggs or gravid proglottids .
Pig
73
In the animal’s intestine, the oncospheres hatch , invade the intestinal wall, and migrate to the striated muscles, where they develop into [?]. Humans become infected by ingesting raw or undercooked infected meat .
cysticercus larvae
74
In the human intestine, the cysticercus develops over 2 months into an [?], which can survive for years.
adult tapeworm
75
Trichinellosis is transmitted between animals by consuming infected meat or meat products containing
encysted larvae
76
Humans acquire trichinellosis by consuming [?] infected with the Trichinella larvae.
raw or undercooked meat
77
When a human or animal eats meat which is infected, the larvae are released from the [?] as it is digested and invade the small bowel where they develop into adult worms.
muscle
78
The female worms release larvae that migrate to [?] where they encyst.
striated muscles
79
Because humans typically do not get eaten by other animals, thus will not allow transmission to another host, humans are [?] hosts for Trichinella spp.
dead-end
80
Aside from the taxonomic classification of parasites, parasites can also be categorized according to:
1. Pathogenicity
2. Necessity for host
3. Number of host(s) required
4. Habitat
81
is a parasite that causes injury to the host.
a. Pathogenic parasite
82
is a parasite that does not cause injury to the host; is also termed as commensal.
b. Nonpathogenic parasite
83
a parasite that is absolutely dependent on the host during a segment or all of its life cycle to complete their development and propagate their species.
a. Obligate parasite
84
have developmental forms outside the host, including some periods of time in the external environment.
a. Obligate parasite
85
is one that is capable of independent or a parasitic existence.
b. Facultative parasite
86
Example: Strongyloides stercoralis' life cycle alternates between
free-living in the soil and parasitic cycles when the filariform
larvae penetrate the human skin and mature in the small
intestine.
b. Facultative parasite
87
Example of life cycle with Facultative parasite -
Strongyloides stercoralis
88
refers to nonparasitic stages of active existence, which live independent of the host
c. Free-living parasite
89
Example: Naegleria fowleri are living in the environment --- in fresh water, soil, thermal discharges of power plants, geothermal wells, and poorly-chlorinated recreational and tap water. They are only opportunistically parasitic.
c. Free-living parasite -
90
a parasite that enters or attaches to the body of a species of host different from its normal one. A parasite may or may not continue full development in an accidental host. It is also known as incidental parasite
d. Accidental parasite
91
Example: Dipylidium caninum is an accidental parasite of human following incidental ingestion of infected dog or cat fleas.
d. Accidental parasite
92
is one that remains on or in the body of the host for its entire life.
e. Permanent parasite
93
is one that remains on or in the body of the host for its entire life.
e. Permanent parasite
94
is one that lives on the host only for a short period of time, such as a mosquito or bedbug, only feeds on the host and then leaves
f. Temporary parasite
95
intermittent parasite
f. Temporary parasite
96
is a parasite that is found in or migrates to an organ which is not its usual habitat. It is also referred to as erratic parasite or wandering parasite.
g. Aberrant parasite
97
Example: Toxocara canis or Toxocara cati are intestinal parasites of dogs and cats, respectively. Human become accidental host by ingestion of the eggs from the animal feces. In humans, the eggs hatch and larvae penetrate the intestinal wall and are carried by the circulation to a variety of tissues (liver, heart, lungs, brain, muscle, eyes). The larvae do not undergo any further development in these sites, and cause local reactions and mechanical damage.
g. Aberrant parasite
98
is a parasite that passes through the digestive system without infecting the host
h. Spurious parasite
99
Example: After ingestion of poorly cooked liver from an infected animal harboring eggs of Fasciola hepatica, eggs are transiently present in the stool (spurious or false infection). True fascioliasis is acquired through the ingestion of metacercariae encysted on edible aquatic plants such as Ipomea obscura ("kangkong") and Nasturtium officinale (watercress).
h. Spurious parasite
100
is one that requires only one (1) host to complete the life cycle.
a. Monoxenous parasite
101
is one that requires more than one (1) host to complete the life cycle. Some heteroxenous parasites pass their life cycles in two (2) hosts, namely a definitive host and a n intermediate host; others, in three (3) hosts, a definitive host and two (2) intermediate hosts -- a first intermediate host and a second intermediate host.
b. Heteroxenous parasite
102
is one that uses a single host as definitive host and intermediate host; the definitive host of one generation becomes the intermediate host of the next generation.
c. Autoheteroxenous
103
Example: Trichinella spiralis whereby adult worms and encysted
larvae develop within a single vertebrate host, and an infected
animal serves as a definitive host and potential intermediate
host. A second host is required to perpetuate the life cycle
of Trichinella.
c. Autoheteroxenous
104
is a parasite that is attached to the outer surfaces of its host.
a. Ectoparasite
105
is a parasite that lives within the body of its host.
b. Endoparasite
106
is a parasite that inhabits a cavity of the host's body.
i. Coelozoic
107
is a parasite that dwells within tissues of the host.
ii. Histozoic
108
is one that parasitic within a cell.
iii. Cytozoic
109
is parasite in the intestine of the host.
iv. Enterozoic
110
is a parasite that lives in the blood.
v. Hematozoic
111
is a parasite living in fecal matter.
vi. Coprozoic
112
Monoxenous [Greek monos, one, unique + Greek xenos, foreign]
113
Enterozoic [Greek [?] , intestine + Greek zôion, animal]
énteron
114
Heteroxenous [Greek [?], other party, another + Greek [?], foreign]
heteros
| xenos
115
Hematozoic [Greek [?] , blood + Greek zôion, animal]
haima
116
Coelozoic [Greek [?], hollow, concave + Greek zôion, animal]
koilos
117
Coprozoic [Greek [?], excrement + Greek [?], animal]
kópros
| zôion
118
refers to any animate or inanimate object from which the parasite is immediately transmitted to the human host.
source of parasitic infection
119
The most common sources of parasitic infections are
contaminated soil and water
120
Infective stages of parasites may be ingested from contaminated soil, especially among children who play in the contaminated soil and then put their hands in their mouths without washing them (e.g., embryonated eggs of [?]) , or contaminated water (e.g., cysts of [?]); or infective larvae in soil (e.g., [?]) or in water (e.g., cercariae of [?] directly penetrate exposed skin.
- Ascaris lumbricoides
- Giardia lamblia
- filariform larvae of hookworm
- Schistosoma spp.
121
are called geohelminths. In all of them, eggs passed in feces undergo maturation in soil. This means that the soil plays a major role in the development and transmission of the parasite.
Soil-transmitted helminths (STH)
122
are those that are acquired from contaminated water.
Waterborne parasites
123
Distribution of parasites in soil and water is associated with
poor sanitation.
124
generally refers to the provision of facilities and services for the safe disposal of human urine and feces.
Sanitation
125
Lack of access to toilets or latrines is a motivation by compulsion for people to practice the following:
```
Open defecation (OD)
Use of night soil
```
126
```
Open defecation (OD)
Use of night soil
```
127
the human practice of defecating outside (in the open environment) such as in fields, bushes, forests, ditches, streets, canals or other open space. This leaves feces exposed in ways that can easily lead to other people coming into contact with fecal pathogens.
Open defecation (OD)
128
It became a primary means of waste disposal in areas without sanitation facilities; its use is a risky practice as it may contain disease-causing pathogens. Although controlled by government regulations, it is still widespread in some developing nations.
Use of night soil
129
used as fertilizer for food crops.
human excrement
130
[?] nonhuman hosts containing infective stage of parasite is consumed as food by human.
Raw or undercooked
131
```
Examples of these food sources and foodborne parasites are:• Kangkong, watercress: Fasciola hepatica
• Pork:
• Beef:
• Freshwater fish:
• Crabs:
• Snail (kuhol):
```
* Pork: Taenia solium (pork tapeworm)
* Beef: Taenia saginata (beef tapeworm)
* Freshwater fish: Capillaria philippinensis
* Crabs: Paragonimus westermani
* Snail (kuhol): Echinostoma ilocanum
132
Humans can also acquire parasitic infections if they swallow food or vegetables that have come in contact with contaminated soil and consume them without [?] or washing them with contaminated water.
proper washing
133
is an invertebrate, an arthropod or mollusc, that transmits an infection from one host to another.
vector
134
is a vector which not only assists in the transfer of parasites between hosts but also in which the parasite goes through morphological or physical changes.
135
A certain period has to elapse after the parasite enters the vector, undergoes a developmental process before it becomes infective.
Biological vector
135
A certain period has to elapse after the parasite enters the vector, undergoes a developmental process before it becomes infective.
Biological vector
136
The vector assists in the completion of the life cycle of the parasite.
Biological vector
137
```
Examples of biological vectors and vector-borne parasites are:
• Mosquito:
• Dog/cat flea:
• Sandflies:
• Reduviid bugs:
```
* Mosquito: Plasmodium spp.
* Dog/cat flea: Dipylidium caninum
* Sandflies: Leishmania spp.
* Reduviid bugs: Trypanosoma cruzi
138
is a vector which assists in the transfer parasitic form between hosts but is not essential in the life cycle of the parasite.
Mechanical vector
139
Example of mechanical vectors is:
| • Housefly:
• Housefly: Amoebiasis
140
is a human infection caused by an organism which occurs naturally in other animals
zoonosis
141
Zoonotic diseases can be caused by
viruses, bacteria, parasites, and fungi
142
For zoonotic diseases that are caused by parasites, they are from a variety of [?].
domestic and wild animals
143
While some are foodborne zoonotic parasites, others are a group of so-called [?] whose infective form is introduced into the environment while already primed for infection and can be transmitted to humans under certain conditions.
“contact” parasites
144
* Canids:
| * Felids:
* Canids: Echinococcus granulosus, Toxocara canis
| * Felids: Toxoplasma gondii, Toxocara cati
145
People who have a parasitic disease or are carriers of parasites are sources of infection. Persons with [?] are obvious sources of infection.
frank symptomatic infection
146
a person who is harboring a parasite but exhibiting no clinical signs or symptoms, and can transmit parasite to others, are unfortunately very difficult to discover and control.
carrier
147
is where the infected person himself is the source of infection. It is a reinfection by parasites that are already present within the body of the host.
Autoinfection
148
This is due to the ability of parasites to complete the life cycle within a single host, without the involvement of another host. This explains persistent infections in individuals for a long time even without additional exposure. The build-up of parasites within the host causes hyperinfection.
Autoinfection
149
Parasites causing autoinfection are:
* Enterobius vermicularis
* Strongyloides stercoralis
* Capillaria philippinensis
* Cryptosporidium parvum
* Taenia solium
* Hymenolepis nana
150
occurs when the parasite infective stage passes out from the host and re-enters the host. One way by which reinfection occurs is perianal-to mouth via finger transmission.
External autoinfection
151
is when the parasite repeats the life cycle without leaving the host.
Internal autoinfection
152
[?] migrates nocturnally outside the anus and oviposit on the perianal area. The eggs become infective in [?] under optimal conditions. Infection occurs via transferring eggs to the mouth with hands that have scratched the perianal area ([?]) or through exposure to eggs in the e n v i r o n m e n t , o r b y retroinfection,--- the migration of newly hatched larvae from the anus back into the intestine ([?]).
Gravid female Enterobius vermicularis
4 to 6 hours
external autoinfection
internal autoinfection
153
is an inanimate object that becomes contaminated with and transmits pathogens to the host.
fomite
154
Example: Eggs from louse-infested clothing or other personal articles also may be sources of infection; body lice may be acquired from sitting on cloth-covered seats in public places, such as theaters or waiting areas.
Fomites
155
is the site or route through which the parasite gains access into the human body.
portal of entry
156
Parasites have a preferred portal of entry that is a prerequisite to their being able to become established within the host, and some to cause disease. The preferred portals of entry for some common parasites are:
1. Gastrointestinal tract
2. Skin and mucous membranes
3. Respiratory tract
4. Genitourinary tract
5. Others
157
This is the most common portal of entry of the parasites.
1. Gastrointestinal tract
158
Parasites gain access to the gastrointestinal tract by way of the
mouth
159
Ingestion of infective stages in contaminated food, water, contaminated fingers or fomites.
1. Gastrointestinal tract
160
1. Gastrointestinal tract: Ingestion
```
Examples:
Entamoeba histolytica
Giardia lamblia
Ascaris lumbricoides
Trichuris trichiura
Taenia spp.
```
161
Person-to-person orally by kissing or fomites (such as eating utensils).
1. Gastrointestinal tract
162
1. Gastrointestinal tract: Person-to-person orally by kissing or fomites
Examples:
Entamoeba gingivalis
Trichomonas tenax
163
The [?]usually serves as a barrier to infection. However, it is an important portal of entry of some parasites to the blood from which they can spread to other sensitive internal organs.
skin skin
164
By penetration of the unbroken skin by larvae once they make contact with the host.
2. Skin and mucous membranes
165
2. Skin and mucous membranes: By penetration of the unbroken skin by larvae once they make contact with the host.
Examples:
Filariform larvae of hookworms while walking barefoot on the soil
Cercaria of Schistosoma spp. while swimming in water
166
By the aid of vector that transmits infective stage of the parasite when it feeds upon the host
2. Skin and mucous membranes
167
2. Skin and mucous membranes: By the aid of vector
Examples:
Plasmodium spp. (malaria) are injected via the mouth part of female Anopheles mosquito during a blood meal
(inoculative method)
```
Trypanosoma cruzi (Chagas' disease), during a blood meal of a reduviid bug, are
released in the bug's feces and enter the host through the bite wound or intact mucosal membranes, such as the conjunctiva
(contaminative method)
```
168
[?] eggs deposited in the perianal region of the host can easily contaminate the surrounding environment (underwear and beddings)and may become airborne and be inhaled and swallowed to initiate intestinal infection.
Enterobius vermicularis
169
infect humans by penetrating the nasal mucosa, usually during swimming or sinus irrigation, and migrating to the brain via the olfactory nerves causing primary amebic meningoencephalitis (PAM).
Naegleria fowleri trophozoites
170
is a portal of entry for parasites that are contracted sexually.
genitourinary tract
171
4. Genitourinary tract spp
Example: Trichomonas vaginalis
172
5. Others
* Transplacental
| * Transmammary
173
by which the parasite leaves its host is usually but not always the same as the portal of entry; determine how parasites spread in a population.
portal of exit
174
refers to the manner in which transmission takes place.
Mode of transmission
175
Parasites can be transmitted from host to host by four (4) principal modes.
1. Contact transmission
2. Airborne transmission
3. Vehicle transmission
4. Vectorborne transmission
176
This is the spread of the parasite by direct contact, indirect contact, or droplet transmission.
1. Contact transmission
177
also known as person-to-person transmission, is the transmission of a parasite by physical contact between an infected individual and a susceptible host; no intermediate object is involved
a. Direct contact transmission
178
The forms of direct contact transmission are:
* Horizontal transmission
| * Vertical transmission
179
refers to the spread of a parasite through a population from infected individual to another. This includes touching, kissing, and sexual intercourse
• Horizontal transmission
180
signifies transmission of the parasite from parent to offspring, e.g., transplacental or transmammary.
• Vertical transmission
181
occurs when the parasite is transmitted from the infected host to the next susceptible host by means of intermediary nonliving object, fomite.
b. Indirect contact transmission
182
is a type of transmission in which parasites are spread in droplets of saliva or mucus that are discharged into the air by coughing, sneezing, laughing, or talking.
c. Droplet transmission
183
Though the route is through the air, this is not regarded as airborne transmission because these particles are large (greater than [?]), travel a short distance (less than [?]) from the source, and quickly settle out of air. Since droplets fall to the ground within a few feet, this type of transmission requires close proximity.
5 µm
| 1 meter
184
is the transmission of a parasite that is suspended in air contained within droplet nuclei or dust
Airborne transmission
185
are small particles (1-4 µm in diameter) that represent what is left from the evaporation of larger droplet particles. They are small enough to remain suspended in air for prolonged periods and travel 1 meter or more from the source.
Droplet nuclei
186
is the transmission of parasite by a common inanimate reservoir where the parasite can normally be found, such as soil, water, and food, or other media including blood and other body fluids, drugs, and intravenous fluids.
Vehicle transmission
187
are the most important group of vectors that carry parasites from one host to another.
Arthropods
188
Arthropod vectors transmit disease by two general methods:
* Biological transmission
| * Mechanical transmission
189
is an active process and is more complex. The arthropod bites an infected person or animal and ingests some of the infected blood. The parasites then reproduce in the vector, and the increase in the number of parasites increases the possibility that they will be transmitted to another host.
• Biological transmission
190
Some parasites reproduce in the gut of the arthropod and can be passed in feces; if the arthropod defecates while biting the host, the parasites enter the bite wound [?], e.g., Trypanosoma cruzi (Chagas' disease) from reduviid bug.
(contaminative method)
191
Some parasites reproduce in the vector's gut and migrate to the salivary gland; these are directly injected into a bite [?], e.g., Plasmodium spp. (malaria) from female Anopheles mosquito.
(inoculative method)
192
the passive transport of the pathogens on the insect's feet or other body parts . If the insect makes contact with a host's food, pathogens can be transferred to the food and later swallowed by the host. Houseflies, for instance, can transfer the amoebae from the feces of infected people to food.
• Mechanical transmission
193
A knowledge of the life cycle of parasites and their methods of infecting the host is of paramount importance in determining methods of prevention and formulating effective [?]. It helps to ascertain the weakest or most vulnerable point at which the parasite can be attacked.
control measures
194
1. A nonpathogenic parasite.
COMMENSAL
195
2. Has a direct life cycle.
MONOXENOUS
196
3. Passes through the GIT without infecting the host.
SPURIOUS
197
4. Capable of independent or a parasitic existence
FACULTATIVE
198
5. Attached to the outer surfaces of its host.
ECTOPARASITE
199
6. Inhabits a cavity of the host's body.
COELOZOIC
200
7. Soil-transmitted helminth.
GEOHELMINTH
201
8. Actively motile and feeding form of protozoa.
TROPHOZOITE
202
9. Stage of helminth harbored by intermediate host.
LARVA
203
10.Transmitted by blood-sucking arthropods.
VERTOR BORNE
