Arthropods

 Chapter -11 

Arthropods

• Parasitic arthropods are ectoparasites that have a temporary or permanent association with their hosts. Their considerable medical significance is due to their capability to cause nuisance or skin diseases in humans and to act as vectors of viruses, bacteria, protozoa, or helminths. Some species or stages of arthropods are capable of penetrating to deeper skin layers or into body openings or wounds, where their effect is similar to that of endoparasites. Only a small selection of medically important arthropods will be described in the following chapter, in particular those that are of significance in central Europe. The reader is referred to the literature for more detailed information.

Arachnida
Ticks (Ixodidae)

• General. The order Ixodida includes two important families, the Agamidae (soft ticks) and Ixodidae (hard ticks). The latter is the most significant group worldwide. We will only be considering the Ixodidae here.

• Approximately 20 hard tick species are indigenous to western and central Europe, belonging to the genera Ixodes, Rhipicephalus, Dermacentor, and Hemophilic. The most important species is Ixodes Ricinus that accounts for about 90% of the tick fauna in this region. For this reason, human tick bites in central Europe are in most cases caused by I. Ricinus and only occasionally by other tick species.

Ixodes Ricinus

Vector of the causative agents of Lyme borreliosis and tickborne encephalitis

• Morphology. Male: about 2–3 mm long with a highly chitinized scutum covering the entire dorsal surface. Female: 3–4 mm, up to 12 mm when fully engorged after a blood meal; the scutum covers only the anterior portion of the body. Adults and nymphs (the latter about 1 mm long) have four pairs of legs, the smaller larvae (about 0.5 mm long) only three pairs. Ticks possess characteristic piercing mouthparts.

• Biology. The various stages of I. ricinus are dependent on blood meals from vertebrates throughout their developmental cycle. Having selected a suitable location on a host, a female tick inserts her piercing mouthparts into the skin within about 10 minutes. Using clawlike organs at the tip of stylettelike mouthparts, the chelicerae, the tick cuts a wound into which the unpaired, barbed, pinecone-shaped hypostome is then inserted to anchor the parasite in the skin. While sucking blood, ticks secrete large amounts of saliva, containing cytolytic, anticoagulative, and other types of substances. They ingest blood, tissue fluid and digested tissue components. The weight of the female increases considerably during a blood meal. When completely engorged, the tick resembles a ricinus seed. The epidemiologically important factor is the possible ingestion of pathogens with the blood meal, which can, at a following blood meal in the tick’s next developmental stage, be inoculated into another vertebrate host (horizontal transmission). Female ticks even transmit certain pathogens by the transovarial route to the next generation of ticks (vertical transmission).

• Epidemiology. I. ricinus occurs widely in Europe, both in lowland and mountainous regions up to 800–1000 m above sea level, occasionally even higher. The habitats preferred by this species include coniferous, deciduous, and mixed forests with plentiful underbrush and a dense green belt. The different stages of ticks inhabit grass, ferns, and branches in this low vegetation either quite close to the ground (mainly larvae and nymphs) or somewhat higher (up to about 80–100 cm, mainly adults) in questing for suitable hosts. When hosts approach, the ticks either let themselves drop onto them or cling to the skin on contact. I. ricinus becomes active at 7–10 8C. Maximum tick activity is registered in the periods May-June and August-October.

• Diagnosis. Identification of I. ricinus is either done macroscopically or with the help of a magnifying glass. Differential species identification requires the skills of a specialist. Skin reactions, in particular the erythema chronicum migrans resulting from a borreliosis infection, often provide indirect evidence of an earlier tick bite.

• Tick bite prevention. Tick habitats with dense undergrowth, ferns, and high grasses should be avoidedas faraspossible.Ifthis isunavoidable,proper clothing must be worn shoes, long socks, long trousers (tuck legs of trousers into socks), long sleeves that fit closely around the wrists. Additional protection is providedbysprayingtheclotheswithacaricides, especiallypyrethroids,which havea certainrepellenteffect(e.g.,flumethrin). The effect of repellents applied to the skin (see malaria) is in most cases insufficient to protect against ticks.

Mites

Sarcoptic scabies

• Infestation with Sarcoptic scabies var. hominis causes human scabies, a condition characterized by pronounced pruritus, epidermal mite burrows, nodules, and pustules. Transmission is person to person. Various mite species that parasitize animals may also infest the human skin without reproducing, causing the symptoms of “pseudo scabies.”

• Occurrence. Scabies caused by Sarcoptic scabies var. hominis does not occur frequently in Europe, although occasional outbreaks are seen in school classes, families, senior citizens’ homes, and other groups

• Morphology and biology. Sarcoptic scabies: mites about 0.2–0.5 mm long with ovoid bodies. The adults and nymphs have four pairs of leg, the larva has three pairs of legs. Following transmission to a human host the female mites penetrate into the epidermis and begin to tunnel. The resulting winding burrows are usually 4–5 mm and sometimes as long as 10 mm. Oviposition begins after only a few hours. Six-legged larvae hatch from the eggs after a few days. In further course of development involving moldings, the larvae transform into protonymphs (nymph I), then deutonymphs (nymph II), and finally adult males and females. The entire life cycle takes two to three weeks. The lifespan of the female mites is four to six weeks

• Epidemiology. Transmission is by close contact (sexual partners, family members, school children, healthcare staff) from person to person, whereby female mites translocate to the skin of a new host. Indirect transmission on clothes (underclothes), bed linens, etc. is not a primary route, but should be considered as a factor in control measures. Without a host, mites usually die off within a few days. Mite infections can also be acquired from animals to which humans have close skin contact.

• Clinical manifestations. An early sign of an initial infestation with Sarcoptes mites is the primary efflorescence with mite tunnels up to 2–4 mm and sometimes 10 mm long—threadlike, irregularly winding burrows reminiscent of pencil markings. The female mite is found at the end of the burrow in a small swelling.

• Following an inapparent period of about four to five weeks, during which time a hypersensitivity response to mite antigens develops, the scabies exanthema manifests in the form of local or generalized pruritus, which is particularly bothersome in the evening when body heat is retained under the bedcovers. The evolving skin lesions are papulous or papulovesicular exanthema and reactions due to scratching. In adults, these lesions are seen mainly in the interdigital spaces and on the sides of the fingers, on the wrists and ankles and in the genital region. Children also occasionally show facial lesions.

• Diagnosis and control. Case history and clinical manifestations provide important diagnostic hints that require etiological confirmation by identification of the parasites. A papule is removed by tangential scalpel excision, whereupon the specimen is macerated in 10% potassium hydroxide (KOH), and then examined for mites under a microscope. Mites can also be isolated from skin tunnels after scarification with a needle or by pressing adhesive tape onto the skin. Therapy requires topical application of c-hexachlorocyclohexane (lindane), permethrin or crotamiton in strict accordance with manufacturer’s instructions. A recent development is peroral therapy with ivermectin. Underclothing and bed linens must be washed at a minimum temperature of 50 8C.

Insects

Lice (Anopluran)

• Head lice and crab lice occur more frequently in central Europe and elsewhere than is generally assumed and must therefore always be taken into consideration when diagnosing skin diseases.

• Parasite species. Two species of lice infest humans, one of which is divided into two subspecies

• General morphology and biology. Lice are dorsoventrally flattened insects, about 1.5–4 mm in length, wingless, with reduced eyes, short (five-segmented) antennae, piercing and sucking mouthparts, and strong claws designed to cling to hairs

• Lice develop from eggs (called nits) glued to hairs. The hatched louse grows and molts through three larval stages to become an adult. Lice remain on a host permanently; both males and females are hematophagous and require frequent blood meals. Lice are highly host-specific, so that animals cannot be a source of infestation for humans

• Medical significance. Among the various species of lice only the body louse is a vector of human diseases. It transmits typhus fever (caused by Rickettsia prowazekii), relapsing fever (caused by Borrelia recurrentis), and trench fever (caused by Bartonella quintana). In central Europe, the medical importance of lice is not due to their vector function, but rather to the direct damage caused by their bites (see below).

• Pediculus humanus capitis (Head Louse)

• Morphology and biology. Oval body, length 2.2–4.0 mm, morphology very similar to the body louse. Nits are 0.5–0.8 mm long. Localization is mainly in the hair on the head, occasionally also on other hairy areas of the head or upper body. The nits are glued to the base of the hair near the skin. Duration of development from nit to adult is 17 days. The lifespan of adults on human host about one month, survival off host at room temperature is for up to one week

• Occurrence and epidemiology. Occurs worldwide; in central Europe it is not frequent, but epidemic-like outbreaks of head louse infestation are observed regularly, especially in schools and kindergartens, homes, groups of neglected persons, etc. Children and women are most frequently infested. About 60% of persons with lice show low levels of infestation with <10 adult lice, the others higher levels (up to >1000 lice). According to official statistics, head louse infestation in the UK increased between 1971 and 1991 about sevenfold; in 1997, about 18.7% of the schoolchildren in Bristol were infested with lice.

Clinical manifestations

• Pruritus and excoriations in the scalp area, nits on hairs, especially in the retro auricular area. 

• In some cases scalp dermatitis, especially at the nuchal hair line: small papules, moist exanthema, and crusting. 

• Occasionally also generalized dermatitis on other parts of the body caused by allergic reactions to louse antigens. 

• Both objective and subjective symptoms may be lacking in up to 20% of cases.

• Diagnosis. Determination of symptoms and detection (direct or with magnifier) of lice and/or nits, especially around the temples, ears, and neck.

• It is important to clarify the epidemiological background regarding all possible sources of infestation (e.g., in schools). Some countries have introduced regulations on control of outbreaks of louse infestation in schools and other community institutions.

• It is important to clarify the epidemiological background regarding all possible sources of infestation (e.g., in schools). Some countries have introduced regulations on control of outbreaks of louse infestation in schools and other community institutions.

• Control. Clothing, pillows, etc. that have been in contact with lice must be decontaminated: wash laundry at 60 8C; keep clothes and other objects in plastic bags sealed with adhesive tape for four weeks or deep-freeze the bags for one day at –10 to –15 8C. Clean upholstered furniture, mattresses, etc. thoroughly with a vacuum cleaner and decontaminate as necessary (consult an expert for pest control).

• Occurrence, morphology, and biology. The crab louse occurs with some regularity in central Europe. Infestations are more frequent in adults than in children and in men more frequently than in women. This louse species can be readily differentiated from the head or body louse: small, length 1.3–1.6 mm, with trapezoid or crablike body form (Fig. 11.1d). The parasites are most often found on hair of the pubic and perianal region, more rarely on hairy areas of the abdominal region, hairs around the nipples, beard hairs, eyelashes, and eyebrows. The life cycle takes three to four weeks. Deprived of a host, crab lice die at room temperature within two days.

• Epidemiology. Transmission of crab lice is almost solely by way of close body contact (sexual intercourse in adults or parent-child contact). Indirect transmission on commonly used beds, clothes, etc. is possible, but is not a major factor.

• Myiasis. Larvae (maggots) of various fly species can penetrate and colonize the skin, skin lesions, and body orifices, thereby causing the type of tissue damage known as myiasis. There are various forms of myiasis, the most important of which are summarized in Table 11.4. Cases of imported myiasis and autochthonous wound myiasis have increased in central Europe in recent years. Diagnosis: inspection and identification of the larvae. Therapy: mechanical removal of the parasites, control of secondary infections, if required oral therapy with ivermectin (extralabel drug use).

• ldwide. About 100 of these occur in central Europe, of which the medically important species belong mainly to the families Pulicidae and Ceratophyllidae. Encounters with Pulex irritans, the so-called “human flea,” are rare, but humans are often bitten by flea species normally found on animals, e.g., the dog flea (Ctenocephalides canis), cat flea (Ctenocephalides felis felis), hedgehog flea (Archaeopsylla erinacei), and European chicken flea (Ceratophyllus gallinae). All flea species show low levels of host specificity and therefore may infest various animal species as well as humans.

• Morphology. The fleas in this group are about 2–5 mm long, laterally flattened, wingless and have three pairs of legs, the hindmost of which are highly adapted for jumping. The mouthparts form a beaklike proboscis for bloodsucking, the antennae are short. Combs of spines (ctenidia) can adorn the head and first thoracic segment (

• Life cycle. Fleas are ectoparasites in humans and vertebrate animal species. Frequent blood meals are needed during the one to three month egg-laying period. Most of the eggs fall off the host and continue to develop in cracks and crevices (e.g., between floorboards, under rugs, under dog or cat cushions or in birds’ nests). The life cycle from egg to adult includes three larval stages and one pupal stage and takes three to four weeks under ideal conditions. This time period can also be extended by a matter of weeks depending on the environmental conditions. The lifespan of an adult flea varies from a few weeks to one year including longer starving periods as well as egg and pupa survival maxima of eight and five months, respectively. This explains why dog and cat flea populations can persist in human dwellings for months if control measures are not taken.

• Epidemiology. The fleas in this group are periodic ectoparasites. The adult stages remain for the most part on the host while the larvae and pupae live in the vicinity of their hosts in the so-called “nest habitat.” In certain regions, fleas serve as vectors for viruses, bacteria, rickettsiae, protozoa, and helminths. Fleas are best-known as the vectors of the causative agent of plague, Yersinia pestis (rodent-infesting fleas of the genus Xenopsylla, among others).

• Clinical manifestations. Dermal reactions to fleabites go through several phases:

• Early reaction: within five to 30 minutes after the bite, a dotlike hemorrhage (at the site of the bite) and a reddening (erythema) with or without a central blister are formed, accompanied by pruritus

• Late reaction: after 12–24 hours, itching papules form, surrounded by erythemas up to palm-size, some with a central blister or purulent pustule; this reaction persists for one to two weeks.

• Predilection sites for lesions: extremities, neck, nape of neck, shoulders, less often the trunk. Reactions are usually in multiple groups, sometimes in rows.

• Diagnosis and control. A diagnosis is reached based on the skin lesions and the case history. Fleas are rarely found on the human body. It is important to find the potential source of flea infestation on animal hosts (dog, cat, hedgehog, birds, etc.) or in their environment, and to identify the fleas found. Once the species is known, specific control measures can be carried out.

Fleas of the Family Tungidae (Sand Fleas)

• Morphology and biology. Tunga penetrans, the chigoe, jigger, or sand flea, infest humans and animal species, for example dogs. The males, young females, and other stages live in sandy soil. Fertilized females are highly active in questing for a host. If they succeed, they penetrate the skin head first, then swell up within one to two weeks, sometimes reaching the size of a pea, from their original size of 1–2 mm in length. They lay eggs over a period of about two weeks, and then die while still under the skin.

Clinical manifestations

• Lesions, mainly on the soles of the feet and between the toes, more rarely on other parts of the body.

• Formation of reddened, pea-sized, painful nodules with a craterlike central depression. Inflammatory and sometimes purulent infiltration of the lesion.

• Diagnosis, therapy, and prevention. The diagnosis is based on the characteristic skin lesions and can be confirmed by parasitological or histological examination of the material removed from the sores. Treatment consists of mechanical removal of the female flea under local anesthesia and control of the secondary infection. Topical application of ivermectin is also effective. Prevention demands that shoes that fit and close properly be worn.

Laboratory Diagnosis of Parasitoses

• This section contains short instructions for sampling and shipment of specimens to diagnostic laboratories and describes current options of diagnosing parasitoses. Readers are referred to the specialized literature for more detailed information.

• In addition to the usual patient data, a diagnostic laboratory requires in particular information on previous stays in foreign countries, especially travel to tropical or developing countries, as well as any clinical symptoms or previous treatments.

Shipment of Materials

• Proper shipment of specimens is an important precondition to obtain reliable results! Request specific instructions from officially recognized (accredited) analytical laboratories. The following specimen types are suitable as test materials for the various parasites

Stool

• & Intestinal protozoa (Entamoeba, Giardia, Cryptosporidium, Sarcocystis, Cyclospora, Microspora): stool specimen preserved in SAF solution. Add about 1 g of fresh (body-warm!) stool to 10 ml SAF solution (sodium acetate–acetic acid–formalin), shake vigorously, and submit to laboratory. If the test result is negative and an infection is still suspected, repeat the test once or twice on different days. Request transport tubes and solution from the laboratory. Commercial test kits are also available for shipment and processing of stool specimens.

• Helminth eggs (without Enterobius): one to two specimens of SAF stool, or better yet 10–20 g fresh stool. With larger amounts of fresh stool, concentration methods can be used, thus improving the chances of parasite detection.

• Enterobius (oxyurid) eggs: adhesive tape on slide. In the morning, press the adhesive side of a piece of transparent adhesive tape about 4 cm long and 1 cm wide onto the perianal skin, then strip it off and press the adhesive side smoothly onto a slide. Submit to laboratory or examine under a microscope.

• Larvae of Strongyloides or hookworms: about 10–20 g fresh stool (unrefrigerated) for examination using the Baermann technique and for preparing a larval culture.

• Coproantigens: parasite antigens excreted in stool (coproantigens) can be detected using predominantly the ELISA. Laboratory procedures or commercial kits are now available for diagnosing various intestinal parasites, including Giardia, Cryptosporidium, Entamoeba, and Taenia.

• Blood

• Malaria plasmodia

• Important: the blood specimen must be taken before commencement of malaria therapy, if possible at the onset of a febrile episode. Send the material to the laboratory by the fastest means available!

• 5–10 ml EDTA blood (to test for Plasmodium falciparum antigen, for blood smears and “thick film” preparations).

• If possible, add two to four thin, air-dried blood smears (for Giemsa staining and detection/identification of Plasmodium

• Other blood protozoa (trypanosomes, Babesia): 5–10 ml EDTA blood.

• Microfilariae: 5–10 ml blood with EDTA. Important: take blood samples in accordance with periodicity of microfilariae, either at night or during the day.

Serum

• Antibodies to various parasites: 2–5 ml serum or 5–10 ml of whole blood (both without additives)

Cerebrospinal fluid

• Antibodies to Taenia sodium (suspected cysticercosis): 1–2 ml of cerebrospinal fluid, no additives

• Trypanosomes: 1–2 ml of cerebrospinal fluid, no additives

Bronchial Specimens

• Microspora and Pneumocystis carinii: induced sputum or 20 ml of bronchial lavage.

• Urine

• Schistosoma eggs and microsporidia: sediment (about 20 ml) from 24-hour urine.

Cultivation

• Visceral leishmaniosis: sample obtained under aseptic conditions by puncture from lymph nodes or bone marrow must be transferred immediately to culture medium (order from laboratory

• Cutaneous leishmaniosis: take specimen tissue from the edges of the lesion (following surface disinfection) and transfer to culture medium.

• Acanthamoebas: 1–2 ml of contact lens rinsing liquid or conjunctival lavage, no additives.    

• Material for Polymerase Chain Reaction (PCR)

• The PCR (see p. 409) is now used to detect or identify species or strains of different parasites, including for example Leishmania, Toxoplasma, Microspora, Echinococcus, Taenia, and filarial worms. For analysis with this technique, the following materials can be sent to the laboratory, depending on the parasite species involved: biopsy or tissue specimens from hosts, blood (with EDTA or heparin added), sputum, fecal specimens or other materials in native condition, and parts of parasites (for example proglottids of Taenia). Some specimens can also be fixed in 70% ethanol (consult with the laboratory).

Tissue Specimens and Parasites

• Skin snip: for detection of microfilariae in skin. Remove about a 5 mm2 surface skin specimen using a scalpel and needle, without opening any blood vessels, at the pelvic crest, thigh or other suitable localization, transfer immediately to 0.9% NaCl solution and transport to laboratory immediately or send by express delivery.

• Surgical preparations and biopsies: either by standard method fixed in 4% formalin or finished section preparations.

• Surgical preparations and biopsies: either by standard method fixed in 4% formalin or finished section preparations.

Immunodiagnostic and Molecular Techniques

• A number of parasitosis can be diagnosed by immunological techniques (detection of antibodies or circulating antigens in serum or of coproantigens in stool) and/or by DNA analysis using the PCR or another technique. Table 11.5 provides an overview of selected options.