Which is a Parasite That Lives and Feeds on the Outer Surface of a Host

Ectoparasite

Ectoparasites are parasites that live on the external surface of hosts, for example fleas and lice of various terrestrial vertebrates, and Monogenea and Copepoda of freshwater and marine fishes.

From: Encyclopedia of Biodiversity , 2001

Ectoparasites

Richard J. Pollack , ... Scott A. Norton , in International Encyclopedia of Public Health (Second Edition), 2017

Abstract

Ectoparasites are a taxonomically diverse group of organisms that infest the skin of human beings and other animals. Ectoparasitic arthropods and nematodes are similar in that an individual organism can produce skin lesions that are large enough to see with the unaided eye. Ectoparasitic infestations are often intensely itchy, causing considerable annoyance and discomfort. These conditions are often focally hyperendemic in impoverished communities, with a particularly high prevalence in vulnerable families, households, and neighborhoods.

Pediculosis (infestation by head and body lice) and scabies are found to some degree in all human populations, but myiasis (fly larva infestation), tungiasis (sand flea disease), and cutaneous larva migrans occur mainly in tropical and subtropical environments. Except for body lice, the organisms discussed in this article are not vectors of pathogenic microorganisms. In other words, most ectoparasites do not carry disease-causing agents; they are, instead, the direct cause of disease. Mortality is low, but the cumulative morbidity from the direct discomfort, secondary bacterial infections, and sequelae of those infestations and infections is considerable.

Despite the abundant presence of ectoparasitic infestations across human populations, biomedical science lacks firm evidence-based practices to reliably control these organisms. In addition, head lice and scabies are developing resistance to some chemical compounds employed to treat infested individuals, prevent spread, and control outbreaks.

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Immunity to Infection

In Primer to the Immune Response (Second Edition), 2014

iii) Defense against Ectoparasites

Ectoparasites are often arthropods that attack the exterior surface of a host. For example, the common tick is the carrier of the extracellular bacterium Borrelia burgdorferi responsible for Lyme disease. The bacteria are introduced into the host when the tick bites him/her to obtain a blood meal. Large numbers of basophils, eosinophils and mast cells accumulate at the bite site to repel both the attacking bacteria and the tick. It is thought that when mast cell degranulation releases substances that increase vascular permeability, ticks have greater difficulty in locating host blood vessels. Some ectoparasites are countered by the same strategies effective against helminth worms. Antipathogen IgE bound to the surface of basophils and mast cells is critical for host defense against such invaders. For example, humans who lack adequate numbers of basophils and eosinophils develop scabies, a severe, itchy rash caused by the mite Sarcoptes scabiei. Much remains to be determined about the molecular details of immune responses to ectoparasites.

NOTE: The involvement of Th2 responses in defense against ectoparasites came from the unexpected finding of increased Demodex skin infections in mice lacking both CD28 and STAT6. CD28 is a key costimulator of Th cell activation, and STAT6 is the transcription factor required for IL-4 production by these cells.

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Communicable Diseases

Theodore H. Tulchinsky MD, MPH , Elena A. Varavikova MD, MPH, PhD , in The New Public Health (Third Edition), 2014

Ectoparasites

Ectoparasites include scabies ( Sarcoptes scabiei), the common bed bug (Cimex lectularius), fleas, and lice, including the body louse (Pediculus humanis), pubic louse (Phthirius pubis), and head louse (Pediculus humanus capitis). Their severity ranges from nuisance value to serious public health hazard. Head lice are common in schoolchildren worldwide and are mainly a distressing nuisance. The body louse serves as a vector for epidemic typhus, trench fever, and louse-borne relapsing fever. In disaster situations, disinfection and hygienic practices may be essential to prevent epidemic typhus. The flea plays an important role in the spread of the plague by transmitting the organism from rats to humans. Control of rats has reduced the flea population; however, during war and disasters, rat and flea populations may thrive. Scabies, which is caused by a mite, is common worldwide and transmitted from person to person. The mite burrows under the skin and causes intense itching. All of these ectoparasites are preventable by proper hygiene and the treatment of cases. The spread of these diseases is rapid and therefore warrants immediate attention in school health and public health policy.

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Infectious Endophthalmitis

Travis A. Meredith , J. Niklas Ulrich , in Retina (Fifth Edition), 2013

Ectoparasites

Ectoparasites are organisms that live on the skin of a host, from which they derive their sustenance. The phylum Arthropoda includes the two-winged, or dipterous, flies. The larvae or maggots of these flies may invade living or necrotic tissue of animals and humans, producing myiasis. Multiple dipterous flies are thought to be capable of producing ocular myiasis. It is thought that the larvae are imbedded in the eye, that they burrow directly through the sclera and then under the retina. Typically, they leave asymptomatic tracks throughout the fundus, but a number of cases of destructive endophthalmitis have been reported, particularly from Scandinavia.

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Self-Defense

Michael D. Breed , Janice Moore , in Animal Behavior, 2012

Pathogen Avoidance

Although many behavioral biologists like to think about lions and tigers more than tapeworms and ticks, parasites, by definition, have negative effects on fitness. The ways that animals alter behavior so as to avoid infection are just now becoming apparent to behavioral biologists. Humans tend to think of host defense as something that happens after an animal acquires a parasite, when the immune system is activated. That certainly occurs, and it has behavioral components that will be addressed shortly. However, even as hiding successfully from a predator may be less risky than fighting against one, so, too, the use of behavior to avoid infection altogether can be at least as valuable as fighting off the infection.

Ectoparasites provide some of the best examples of parasite avoidance. Although humans are inclined to view ectoparasites as more of an annoyance than a serious threat, this (again) is not representative of the vast majority of animals that have no shelter from, say, biting flies, and no medicines with which to combat the diseases that they transmit. To most animals, ectoparasites can be a substantial threat and are worth avoiding. Indeed, fly swatting by howler monkeys (Alouatta palliata) proves this point nicely: these monkeys engaged in over 1,500 slaps or other avoidance maneuvers during a 12-hour period, using 24% of their metabolic budget in the process (less basal metabolism). ⁴⁴ For smaller animals, blood loss itself can be significant. Wood rats can use bay leaves—nibbling them so as to release the volatile chemicals they contain—to "fumigate" their nests, probably reducing the number of flea larvae in the nest. ⁴⁵

Key Term

An ectoparasite lives on the outside of its host; a flea is an example of an ectoparasite. Endoparasites, such as tapeworms, live within their host.

Parasite avoidance could have some serious implications for behavioral ecology. It is clear, for instance, that organisms may change habitat preference in an attempt to avoid parasites. Like many animals, juvenile stickleback fish (Gasterosteus spp.) frequented areas near the bottom and near vegetation in a tank that was devoid of the branchiuran parasite Argulus canadensis. In the presence of the parasite, however, the fish spent more time near the surface and in open areas, where the parasite was less abundant. ⁴⁶ Clearly, the presence or absence of the parasite would influence a study of stickleback habitat preference.

Social behavior is affected by parasites, much as it is affected by predators. Both the dilution effect and the selfish herd principle (see Chapter 13) can be seen in animal responses to biting flies. During fly season, many animals "bunch," that is, form larger and tighter herds. In experimental tests of bunching, repellant-sprayed Holstein heifers did not form groups as often as control (water-sprayed) ones did. ⁴⁷ Group formation may lower the likelihood of any one individual being bitten.

Even camouflage, so prominent in predator avoidance, may function in parasite avoidance as well. In 1981, Jeffrey Waage hypothesized that the stripes of zebras may contribute to protection from tsetse flies, which have distinct preferences for some patterns over others and, in general, prefer large, dark objects to lighter ones. ⁴⁸ (The boldest zebra patterns co-occur with tsetse.)

Avoidance of microscopic parasite propagules is more difficult to study; if nothing else, time and extent of exposure are frequently unknown. Nonetheless, parasite avoidance has been hypothesized to account for xenophobia; when strangers are kept away from the group, so are their pathogens. Hygienic behavior is also widespread, and many animals are fastidious about where they deposit urine or feces. This may be in part related to the function of each in identification and territory marking, but in addition, some species will not forage where they have defecated. Social insects have developed special alarm behaviors to alert nestmates to contagion. ⁴⁹

Sexual selection can be influenced by parasites. There are several reasons why choice of a parasite-free mate is beneficial: first, the absence of parasites may indicate "good genes," that is, a genetically based resistance to parasites. Second, a parasite-free mate will not transmit parasites to mates or offspring. Parasite-free mates may also be better at parental care, if such exists.

Of Special Interest: Parasites and Behavior

As we have noted (see Chapter 9 on foraging), parasites are adept at manipulating host behavior, and they often do so in ways that enhance parasite transmission. Perhaps the most surprising manipulation is that of reduced antipredator behavior. This has been seen in a wide range of parasite and host taxa, ranging from isopods parasitized by acanthocephalans (they are more likely to be around a fish predator) to fish with cestodes (they recover more quickly from fright response). However, in no system has this phenomenon been more thoroughly investigated than in rodents with Toxoplasma gondii. This protistan parasite can infect a variety of hosts but undergoes a sexual phase in felids. We have known since 1980 that mice with Toxoplasma were less fearful, but recent studies on rats have revealed an even more amazing scenario: rats infected with Toxoplasma are not only unafraid of cat urine, but are actually attracted to it. In addition, this is not because of a general reduction in fear; the infected rats continued to display more general fear responses (e.g., edge preference, shock avoidance) and spatial learning was unaffected. Although the parasites were encysted in a variety of areas of the brain, they were most concentrated in the amygdala (see Chapter 2). ⁵⁰ What have you learned in earlier chapters about the amygdala that makes this fact particularly intriguing?

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Introduction to Ectoparasitic Diseases

James H. Diaz , in Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases (Eighth Edition), 2015

Mechanisms of Ectoparasite-Borne Diseases and Injuries

The arthropod ectoparasites can threaten human health directly by burrowing into, feeding, dwelling, and reproducing in human skin and orifices (mites, fleas, and flies) or by blood or tissue juice sucking (fleas, lice, mites, and ticks). The arthropod ectoparasites can also threaten human health indirectly by infectious disease transmission (fleas, mites, and ticks). Ticks are the most versatile ectoparasitic arthropods and can transmit a variety of infectious diseases (viral, bacterial, and protozoan) and even inject paralytic toxins (tick paralysis) during their prolonged blood meals. Unlike other ectoparasites, ticks can be infective as males and females at birth (by transovarial pathogen transmission) and throughout all stages of their development (by trans-stadial pathogen transmission). The most commonly encountered arthropod ectoparasites, excluding ticks, and the major clinical manifestations of their infestations are featured in Table 293-2.

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Integumentary System Diseases of Nonhuman Primates

Joshua A. Kramer , Joseph Bielitzki , in Nonhuman Primates in Biomedical Research (Second Edition), Volume 2, 2012

Parasitic Disease

Ectoparasites are infrequently reported in nonhuman primates depending on rearing and housing method. Three types of mite infestations are of concern: demodectic, psoregatic, and sarcoptic. Demodex sp. lesions are nonpruritic (Loebel et al., 1973; Hickey et al., 1983). A new species of Demodex was recently identified in rhesus macaques and named Demodex macaci (Karjala et al., 2005; Starost et al., 2005). In rhesus macaques, Demodex mites seem to preferentially occupy hair follicles of the perianal and facial skin (Figure 11.10). Psorobia (formerly Psorergates sp. produced rough, scaly, elevated, circumscribed, variably pruritic papules usually on the face (Lee et al., 1981; Baskin et al., 1984; Atkins et al., 2008). Lesions in the periorbital area caused by Psorobia may result in a yellow discoloration of the skin (Raulston, 1972). Infestation with Sarcoptes scabiei is infrequent but papular, erythematous, and frequently pruritic lesions have been reported (Graczyk et al., 2001; Kalema-Zikusoka et al., 2002). Zoonotic transmission of scabies has been reported (Goldman et al., 1949).

FIGURE 11.10. Numerous Demodex macaci mites in cross section within a hair follicle on the skin of the lower lip from an adult rhesus macaque.

Demodex infestation has caused severe eosinophilic and lymphocytic perifolliculitis. Classically, Demodex mites are cigar-shaped (inset).

The nematode Anatrichosoma cutaneum has been reported as causing subcutaneous migration tracts, which are most evident in the palmar and plantar surfaces. The affected skin is dry, white, and scaly (Breznock et al., 1975; Harwell et al., 1979; Anonymous, 1980; Kessler, 1982).

Clinical signs of pruritic dermatitis with hair loss and variable hyperkeratosis have been reported in a variety of new and world species secondary to pediculosis. Infection is transmitted both from infected humans and between animals, likely through grooming behavior. Infestation with a variety of louse species has been reported including Anoplura and Pediculus spp. Zoonotic transmission is possible (Wimsatt et al., 1988; Mader et al., 1989; Cohn et al., 2007).

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Parasites of the Giant Panda: A Risk Factor in the Conservation of a Species

Tao Wang , ... Robin B. Gasser , in Advances in Parasitology, 2018

2.1.3 Ixodidae (Hard Ticks)

Other ectoparasites that can affect the health of the giant panda are (blood-feeding) hard ticks. Since the first description of tick infection by Haemaphysalis warburtoni (Wu and Hu, 1985a), an increasing number of hard tick species have been identified on giant pandas in the last two decades (Lai et al., 1990; Ma, 1987; Qiu and Zhu, 1987; Yu et al., 1998). To date, 13 species representing 3 genera of hard ticks have been proposed as recorded (from rescued, sheltered or dead, wild giant pandas). These ticks include members of the genera Haemaphysalis (9 species), Ixodes (3 species) and Dermacentor (1 species) (Table 2). Of these ticks, Haemaphysalis flava has been most commonly reported in giant panda populations (Cheng et al., 2013; Ma, 1987; Qiu and Zhu, 1987). Recently, molecular tools have also been employed for the genetic characterisation of ticks from the giant panda. Using mitochondrial and ribosomal DNA markers as well as key morphological characters, H. flava was identified to predominate on giant pandas in the Qinling mountain range (Cheng et al., 2013). Although there is no report on mortality caused by such hard ticks, morbidity involving dermatitis and/or weight loss has been recorded in infested giant pandas (CCRCGP, unpublished records). Similar to the treatment of C. panda, ivermectin and selamectin are the compounds most commonly used against ticks in breeding centres and zoos (CCRCGP, unpublished clinical records). To date, there are no reports of any associated tick-borne diseases in the giant panda.

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Laelapid and Dermanyssid Mites of Medical and Veterinary Interest

Antonella Di Palma , Annunziata Giangaspero , in Encyclopedia of Infection and Immunity, 2022

Host range, host location and distribution

Mammalian ectoparasites can be monoxenous (occurring on a single species of host), oligoxenous (occurring on a few host species), and polyxenous (capable of infesting a broad array of host taxa). Polyxenous ectoparasites may be limited to host species that are closely related phylogenetically or may parasitize unrelated hosts that share ecological or behavioral similarities.

Regarding laelapid species obligate hematophagous of small mammals, it is under discussion whether there is a single polixenous species that parasites a variety of hosts, or whether there are cryptic species highly host-specific. Recent studies strongly indicate that they are primarily monoxenous (e.g., Gettinger, 1992; Martins-Hatano et al., 2002; Lareschi and Velazco, 2013) and when mites, initially assigned at the same species, infest more than one host species, an examination of the morphological variation within and among mite specimens support the hypothesis that mites infesting different hosts are reproductively isolated populations or species complex (Gettinger, 1992; Gettinger et al., 2011; Nava and Lareschi, 2012; Lareschi et al., 2013; Lareschi and Galliari, 2014). Host switching of mites among rodents has probably taken place, followed by speciation (Lareschi et al., 2013; Lareschi and Galliari, 2014; Silva-de la Fuente et al., 2020). Since some laelapids are vectors of pathogens, these processes of the new host colonization are also important from an epidemiological point of view.

The spiny rat mite, L. echidninus, and the smaller species, Laelaps nuttalli Hirst, 1915, are cosmopolitan ectoparasites. Laelaps echidninus is associated primarily with murid synanthropic rodents like the black rat (Rattus rattus Linnaeus 1758) and the Norway rat (Rattus norvegicus Berkenhout 1769). Moreover, it has been detected on Sigmodon, on the house mouse Mus musculus Linnaeus, 1758, and rarely on laboratory rodents (Pratt, 1963; Lareschi and González-Acuña, 2010; Mullen and Oconnor, 2019). Laelaps nuttalli is commonly found on commensal and wild Rattus species, while both (L. echidninus and L. nuttalli) can occasionally bite humans (Mullen and Oconnor, 2019).

Members of the family Dermanyssidae are primarily parasitic on birds, but contains a few species readily found on rodents. Rodent associated dermanyssids are in the genus Liponyssoides, while species in the genus Dermanyssus are primarily parasites of birds; occasionally they have been collected from rodents and other mammals (Moss, 1967, 1968, 1978; Radovsky, 1985; Dowling, 2006; Lindquist et al., 2009b; Mullen and Oconnor, 2019).

Liponyssoides sanguineus, has been collected from many species of mammals throughout the world. The common house mouse, Mus musculus, is the preferred host, but this mite occurs also on peridomestic rats (R. norvegicus and R. rattus), diverse laboratory rodents, and rodents sold in pet stores. It readily attacks human beings as well (Fischer and Walton, 2014; Mullen and Oconnor, 2019; Eremeeva and Muniz-Rodriguez, 2020).

Dermanyssus species show a rather low host-specificity with multiple host associations and a rather wide geographic distribution (Moss, 1978). For example, Dermanyssus gallinae is largely considered an avian-specific ectoparasite of farmed birds (e.g., chickens, turkeys, and ducks), as well as wild and synanthropic birds (e.g., pigeons, sparrows, starlings, and doves). However, it can occasionally feed on a range of mammals, such as cats (Guin, 2005; Di Palma et al., 2018), dogs (Ramsay et al., 1975; DeClerq and Nachtegaele, 1993; Friesen et al., 2011), gerbils (Lucky et al., 2001), other rodents (Allymehr et al., 2012; Kowal et al., 2014), goat (Dorny et al., 1994), horses (Mignon and Losson, 2008), and humans (reviewed by Cafiero et al., 2019).

However, studies in the last decade have shown that most of the Dermanyssus species actually have more restricted host ranges than first believed (Roy et al., 2009b). In particular, D. gallinae might not be the only Dermanyssus parasitizing laying hens but that some other closely related species might often have been confused with this species (Roy and Chauve, 2007). Recent research based on morphological and molecular data (Roy et al., 2009a, 2010b; Roy and Buronfosse, 2011) has shown that D. gallinae is actually a species complex including at least two cryptic species. In particular, D. gallinae s. str. Appears to be the only pest in poultry houses, as well as on other bird species except pigeons, while D. gallinae special lineage L1 is restricted to pigeons only.

In general, blood-feeding ectoparasites utilize a variety of cues such as body heat, CO₂, and host-specific kairomones to locate their host. Regarding the ability of laelapid parasites to locate the host, some studies (Mitchell, 1968) highlighted the combination of responses toward carbon dioxide and blood as an important advantage for a nest-dwelling mite in actively seeking suitable hosts. Investigations on the host-searching process in dermanyssids have shown that mite-related cues (aggregation pheromones) and host-related cues (kairomones) mediate the behavior of the poultry mite (Koenraadt and Dicke, 2010) while foreleg tarsal sense organs are involved in stimuli perceiving (Soler Cruz et al., 2005). A gradual increase of CO₂ concentration, heat, and vibrations are powerful activating stimulus (Kilpinen, 2001, 2005) guiding mites toward the host thanks to the heat transmitted through the substrate or the exhaled air (as an indication that a potential host is near). After the mites have moved close to the potential host, recognition may be facilitated by skin lipids of birds, which are known to act as feeding stimulants to poultry red mites (Zeman, 1988). Anyway, CO₂ can elicit contrast behavior: mites "freeze" (i.e., they become motionless) in response to a quick increase of CO₂ when in light conditions (probably as a defensive strategy to avoid being eaten by the host) (Kilpinen, 2005). Thus, responses of mites toward CO₂ are likely to be dose and context-dependent. After the blood meal, D. gallinae forms aggregations of mixed developmental stages and thigmokinesis (i.e., increased locomotion in response to changes in contact with the immediate physical environment), and pheromones are thought to play a role in this (Entrekin and Oliver Jr, 1982; Koenraadt and Dicke, 2010). However, as nests are discontinuous and temporary microhabitats, an important adaptation of mite parasites involves the use of the host to disperse (Martins-Hatano et al., 2011).

Among laelapine nest mites, the female is usually the dispersal stage and most often found on the host, while males and immatures are presumed to be restricted to the nest of the host. In this way, dispersion is primarily vertical, between hosts of the same species (parents and young) occupying the same nest. The same happens with dermanyssids with females representing the dispersal stage most often collected on the host (Radovsky, 1985, 1994). Moreover, many families of Mesostigmata, including Laelapidae and Dermanyssidae, have established close phoretic relationships with other arthropods (Krantz, 2009b). Examples of phoretic behaviors on insects by D. gallinae have been reported twice (Flechtmann and Baggio, 1993; Pavlović et al., 2016). In this way, arthropods can contribute to mite distribution in the near vicinity, including houses and farms.

Anyway, there are parasite species whose presence is strongly related to human activities (i.e., D. gallinae). In this case, the most important aspect for their distribution, at least in Europe, has become trade flows (and not wild bird) that seem to be the routes that are the most often used by mites to disseminate. Mites use cages, birds, personnel that are carried by trucks during transfer as a spreading mean at high geographical scales (dozens to hundreds of kilometers) (Øines and Brännström, 2011; Roy and Buronfosse, 2011; Marangi et al., 2014).

Moreover, recent morphological studies explained the previously observed observed ability of some dermanyssoids (e.g., D. gallinae) to climb upwards on slippery surfaces as well as on a wide range of material, in the "off-host" environments (Mul et al., 2016), thanks to adaptations on the distal region of the legs (Di Palma and Mul, 2019). Such adaptations would have initially evolved in "wild-living" but would also prove beneficial for movement within poultry houses and thus explaining the possible active colonization of different facilities using the ventilation systems, wall fans, wall inlets, and air chimneys (Mul et al., 2009).

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Ectoparasites, Cutaneous Parasites, and Cnidarian Envenomation

Ellen Thompson , Andrea Kalus , in The Travel and Tropical Medicine Manual (Fifth Edition), 2017

Etiology

Ticks are ectoparasites found worldwide, encompassing more than 800 recognized species. Ticks feed by anchoring mouth parts in the skin and inserting a hollow proboscis to suck blood. They are members of the class Arachnida and are divided into two families: Ixodidae, or hard-bodied ticks, and Argasidae, or soft-bodied ticks.

Ixodidae live in forest and grassland areas, attach to warm-blooded hosts, and remain on the skin for days to weeks before dropping off. Ixodid ticks are vectors for Lyme disease (Chapter 24), ehrlichiosis, Rocky Mountain spotted fever, babesiosis, Colorado tick fever, tick-borne encephalitis, and other infectious diseases. The Argasidae are mainly parasites of birds and live in nesting areas. They feed rapidly at night, often on several hosts in succession. Argasid ticks are vectors for relapsing fever and other illnesses.

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