Demodex Folliculorum. 2 Slides: Section in Situ, Whole Mount
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Phylum Arthropods Study Material: Demodex folliculorum. 2 slides: section in situ, whole mount. Sarcoptes scabei. 1 slide, wholemount. Dermanyssus gallinae. 1 slide, wholenount. Argas persicus. 1 slide, wholemount. Dermacentor andersoni. 1 slide, wholemount. Amblyomma americana. 1 slide, wholemount. Rhipicephalus sanguineus. 1 slide, wholemount. Boophilus annulatus. 2 slides: male and female, wholemount. Xenopsylla cheopis. 2 slides: male and female, wholemount. Pediculus humanis. 2 slides: male and female wholemount. Phthirius pubis. 1 slide. Class Arachnida, Subclass Acari|Mites and ticks. Like other arachnids the body is divided into prosoma (Cephalotho- rax) and opisthosoma but the division is not clear as in spiders. More often the most evident division is between an anterior re- gion (gnathosoma) bearing the mouthparts and the rest of the body (idiosome). There are eight legs in adults but typically larvae have only 6 legs. Most classifications recognize two major lineages: Acariformes and Parasitiformes. Acariformes includes Sarcoptiform and Trom- bidiform mites, many of which are free living, feeding on soft bodied organisms, plants or fungi. The group also includes many parasitic species, among them Sarcoptes, Demodex, Oribates and the like. Parasitiformes includes mesostigmatid mites, which are pri- marily predaceous (but include some parasites such as Der- manyssus) and the ticks (Argasidae and Ixodidae) all of which are parasitic. As their name suggest, mites are the smallest members of the Acari. But "mites" occur in both Parasitiformes and Acari- formes, and the term mite therefore does not describe a natural group. Superorder Acariformes. 1 2 Demodex folliculorum and D. brevis. Both species occur on hu- mans: D folliculorum inhabits hair follicles whereas D. brevis inhabits sebaceous glands. Both prefer skin of the face (eye- brows, eyelashes and the skin on either side of the nose). Adults periodically leave the follicle to mate or locate a new follicle, and are most active at night. Eggs are laid within the follicle (or sebaceous gland in the case of D. brevis). There are two slides to examine: a whole mount of the or- ganisms and a section of the skin showing the parasites in situ. The mites are unmistakeable with their cigar shaped bodies and stubby legs. In the section, locate the epidermal layers of the skin and look for a hair follicle. Note the segmented mites in the follicle. They are about 1/4 mm in length. Infections are more common in older hosts and prevalence of infection increases with age. Most infections are asymptomatic although in some cases mites cause a dermititis. Other species of Demodex spp. occur in wildlife and a common species, Demodex canis infects dogs and can give rise to serious mange (demodectic mange). Sarcoptes scabei. This species is the causative agent of scabes, a disease in humans characterized by small pimple like lesions on the skin especially between the fingers, on the wrists, ankles and elbows and in the groin region. Lesions itch intensely and can easily become secondarily infected leading to future compli- cations. The disease is easily treated with skin lotions such as lindane cream. Sarcoptes spp. are tiny mites with round bodies (in dorsoven- tral view) and 4 pairs of tiny legs. Males and females mate on the host skin and females then burrow into the skin (remaining in upper skin layers) deposited eggs periodically as she moves along. Larval mites hatch from the eggs and climb onto the surface of the skin to mature and mate. Scabes is a disagreeable infection and causes intense itching. As in demodectic mange, the main dangers of Sarcoptes infection arise through the potential for secondary infection. Treatment involves a cream containing miticide (e.g pyrethrin). More re- cently Ivermectin, developed for veterinary use has been found to be effective and safe in humans; the drug is taken as a pill. 3 Sarcoptic mange in wild and domestic animals is caused by a very similar species (or perhaps a physiological race of the same species) and humans can acquire infections from these animals although most commonly human infections are acquired from other infected humans. Superorder Parasitiformes: Order Mesostigmata. Dermanyssus gallinae, aka red chicken mite, is a relatively large mite that occurs on birds, notably chickens. The mite is proba- bly more accurately described as a micropredator since they live off the host during the day and attach to the host only for their blood meals in the evening. Large numbers can cause nest aban- donment and destruction of young. Infections are most comon in Europe and primarily in layer hens which are held in dense confinement. Treatment includes insecticide sprays which must be used carefully because of their toxicity. But the risk of infec- tion is effectively lowered by clean housing practices and regular inspection of stock for the presence of the mites. Superorder Parasitiformes: Order Ixodida. Ticks are dis- tinguished from mites by their larger size and by the fact that the hypostome is armed (i.e. covered with posteriorly directed spines or hooks). In addition all ticks have a unique chemosen- sory organ, Haller's organ, a pit like structure on the dorsal surface of the first pair of walking legs. Ticks are important pathogens in livestock and especially so in the subtropic and tropics where transmission can occur through- out the year and large populations of ticks can build up. Ticks feed on blood and large numbers can elicit anemia. Tick feed- ing holes compromise the value of the hide of stock animals and ticks are also important disease vectors: Lyme disease, Rocky Mountain spotted fever, Typhus, Tularemia, etc. Some ticks produce toxins that have profound effects on their hosts: tick paralysis is an ascending paralysis that can be provoked by as few as a single tick; the effects recede completely after removal of the tick. Most ticks belong to the famiy Ixodidae, the hard ticks, but 5 genera are included in the Argasidae. In Argasids the capitulum is subterminal; it lies in a groove on the ventral side of the 4 idiosome which overhangs it. This the capitulum cannot be seen in dorsal view. Hard ticks have only one nymphal stage and feed 3 times in their life: once as larvae, once as nymphs and finally once as adults; each feeding involves full engorgement. Argasids have many nymphal stages and feed repeatedly; their feeding is of short duration and they spend most of their time off the host in the nest or burrow. Ixodids may be one host, two host or three host ticks depending on whether they take their three feedings on one, 2 or three different hosts. Argasids are many host ticks as their feeding habits would suggest. Study the tick species provided and be sure you are able to use the attached key to identify them to genus. Family Argasidae. Argas persicus. , the chicken tick, is cosmopolitan in poultry. It is most important as a vector of fowl disease (e.g., Fowl spirochaetes) and this more commonly in the tropics. It is rela- tively unimportant in more temperate climates. Other members of this genus feed on bats and birds and may also feed on hu- mans but they are not important vectors of tick born zoonotic diseases in humans. Family Ixodidae. Dermacenter andersoni, the Rocky Mountain wood tick, occurs west of the great divide in North America. It is a 3 host tick meaning that it colonizes a new host for each blood meal; larvae feed on small rodents, nymphs on medium sized rodents and adults on medium to large mammals, including humans. This species can cause tick paralysis. Not the prominent festoons on the posterior border of the abdomen. Amblyomma americana, the Lone star tick, has one or more sil- ver spots on the dorsal surface of its abdomen. This species is one of the few temperate species in the genus which is otherwise more common in tropical hosts. The Lone star tick feeds on a wide variety of potential hosts including humans and transmits a number of diseases including Tularemia and rocky mountain spotted fever. 5 Rhipicephalus sanguineus, the brown dog tick, is cosmopolitan. It has been introduced into all continents and is arguably the most widespread tick. It shows a marked preference for dogs and all stages feed on dogs. The tick is easily recognized by the presence of festoons and the fact that the basis capitulum has spur-like lateral extensions. Note that some of the slides of Boophilus and Rhipicephalus have been mislabelled. You should be able to correctly identify the material using the key we provide at the end of this document. Boophilus annulatus. , the American cattle tick, used to occur throughout the southern USA, Mexico and Central and South America as well as Africa and Asia. It has been eradicated in most areas of the USA but remains common elsewhere. The basis capitulum is similar to that in Rhipicephalus but there are no festoons. Other Ixodid ticks not represented in lab material. Ixodes scapu- laris is the vector of Lyme disease in eastern North America. Lyme disease is caused by Borrelia burgdorferi, a spirochaete that is primarily parasitic in rodents. Ixodes scapularis feed as larvae on rodents and then move onto larger hosts (normally deer but also potentially man) as nymphs and adults and this is how humans acquire Lyme disease. A related species, I. paci- ficus, is a potential Lyme disease vector on the West coast of north America. Luckily however its feeding habits (it prefers lizards over rodents) are such that it rarely acts as a vector. Class Insecta. Order Siphonaptera. Fleas are affiliates of flies (Order Diptera) but do not develop wings. Adults feed on blood and lays eggs that hatch to produce larvae that live in the nest or litter associ- ated with the host.