----start---- Dr. Lok parasit 10/9/97 siphonaptera - fleas. highly specialized ectoparasites. again, his intro is all recap from last time. Ok. fleas are NOT very host specific. dog and cat fleas may prefer to feed on dogs or cats, but will happily take whatever they can get as far as any other warmblooded hosts in the environment. so feeding behavior is characterized by lack of host specificity. fleas are classified by degree of attachment to host. most fleas move around on the host freely in the haircoat. however, a couple of species do not. one is permanently attached to outer skin, and another actually burrows into the skin and lays eggs in subdermal pockets. but, when we're talking about where a host encounters fleas, the route of transmission is from environment to host, NOT from host to host. the source of infestation is going to be the environment. fleas do not jump from host to host. adult dog/cat fleas, contrary to popular opinion, really can't endure long periods off the host. they don't get on and off a lot. there are other kinds of fleas which can but not dog/cat fleas. once they've found a host, they rarely if ever leave it. that's not to say that the adults in the pupal case can't survive for a while off the host - they can. fleas and disease there's one highly specializd species that we call the "sticktight" flea of poultry. angular appearance of head. echidnophaga gallinacea. looks like its head was bashed in. attaches around eyes, combs, wattles of chickens where feathers are sparse. adult females stay on host. can cause ulceration, swelling on host. can cause blindness when tissue around eyes swells. tunga penetrans, the "chigo flea", is mainly a parasite of people (and shouldn't be confused with chiggers). the female fleas burrow under the outer layers of skin, lay eggs, and form a sort of subdermal pocket, which fills with eggs and feces and becomes pruritic and purulent. again, sort of an angular head more typical fleas include the dog and cat fleas, ctenocephalides felis and canis. canis has a blunt anterior end, dome shaped. felis is a bit more elongate. very similar looking. in fact, c.canis is becoming almost unknown, and c.felis is seen on dogs much more often. we think c.canis is becoming extinct. these are the common fleas of dogs and cats and will readily attack humans in the absence of the preferred host. both are intermediate hosts for tapeworm dipylidium caninum which is transmitted in cystercercoid stage by the flea. the embryonated eggs from dog feces are ingested by larval stages of fleas, which are particulate feeders with mandibular not sucking mouthparts. eggs hatch and the cystercercoid stages grow in the fleas, fleas are eaten by host, and are liberated in host GI tract. there are also rodent fleas that host rodent tapeworms. fleas are vectors of some viral pathogens: myxomatosis in rabbits also rickettsia - endemic typhus or murine typhus best known as classic vector of yersinia pestis, plague bacillus rat flea, xenopsylla cheopia, transmits the bacillus of plague into human populations. so it has to transfer between species, rats and people. remember the proventricular spines in the flea? the bacterium will cause a kind of clot or matt of cells to accumulate on the spines, clogging it up, so the flea can't feed to satiety, and the flea will regurgitate a lot of blood while it is feeding. so it will hop from host to host trying to fill itself and it will be spreading the organisms all the time. UGH. from veterinary standpoint, we know urban cycle of plague isnt well known these days, but in western US, there are many foci of rural plague. plague is enzootic in ground squirrels and prairie dogs out there, and fleas transmit it. humans get it when they blunder into animal habitats, eg in campsites or rustic cabins or something. when people come in after not being there for a while they can get infected. so if youremember anything about fleas, remember that they are enzootic and epizootic vectors of plague bacillus. flea control: we're going to have another hour on this later, so we're going to kind of skip a lot right now. three main objectives in controlling fleas exist. need lots of client education. first objective: correct acute problem. kill the adults that are on the host now. there are many ways to do this. classic ones are pyrethrin sprays applied frequently, about 1x/week. organophosphates as medallions and collars, dichlorvos (pretty toxic) used to be in flea collars. and a whole group of modern topical things - frontline (fipronil), imidacloprid (advantage) both safe and effective. problem used to be lack of residual action of topicals - didn't last long enough to break the cycle. animal would be reinfested from the environemental larvae/pupae growing up into adults. these modern topicals have residual life > 21 days, average length of flea life cycle (which is variable), so this potentially obviates the need for environmental treatment. classically, we've had to have a two pronged approach - treating animal, and treating environment to prevent reinfestation. many agents have been developed to do this - chemical pesticides to kill larvae and pupae, growth regulators to block development of larval stages, abrasive aerogels - sodium polyborate etc, abrade waxy cuticle that usually prevents water loss, causes dessication. another approach that's been used is to target the egg stages BEFORE they leave the host. the Ovitrol flea collar contains an insect hormone mimic that inhibits the embryonation of eggs. the eggs fall off host but fail to hatch. that helps break the life cycle. another approach is to use a systemic metabolic inhibitor - give to the host, called lufenuron (Program), and it inhibits the synthesis of chitin, the polysaccharide used in insect eggs and cuticles. when fleas bite the host, they get a dose of lufenuron. eggs laid by that flea won't be able to make chitin to have normal shell. those eggs won't be viable. embryos in that egg also grow abnormally. Fipronil is active ingredient in frontline - has residual activity about a month or more, so treating animals topically with this (or imidocloprid) can break environmental cycle alone. animal is so well protected for so long that the new fleas can't parasitize the host and they also die. vaccines against fleas are being addressed as well. they are directed at flea salivary secretions, which enable fleas to feed, and also the concept of desensitizing hosts to the allergens in flea saliva. so those are the three main brainches of flea control. (um. that didn't seem like three to me, but whatever.) LICE phthiraptera- another order in the insecta consider comparisons and contrasts between fleas and lice. lice are wingless ectoparasites but are not laterally compressed - are dorsoventrally flattened. legs are modified for clinging to hair, not for jumping. they have a sort of thumb/finger thing to grab onto hair. fleas are highly mobile jumpers, and lice are more couch potatoes. (hair potatoes?) they are annoying, cause blood loss, and act as pathogen vectors. depending on taxonomist, lice in some cases may be split into two orders, but we consider lice to be a single order containing two suborders. morphology: eggs of lice are laid in haircoat and entire life cycle occurs in haircoat of host. eggs are pasted into hairshafts. eggs = "nits+ and are operculate. nymphal louse emerges through operculum. nymph resembles adult. two suborders: anoplura - piercing/sucking mouthparts. mallophaga - chewing. anoplura: can recognize it by looking at the narrow head, which is narrower than the thorax. mallophaga: biting/chewing lice - have mandibulid mouthparts, two opposing mandibles capable of chewing. feed on dander, skinflakes, etc. can chew feathers, etc. some can rasp integument and get blood, but not usually blood feeders. head is broader than thorax. life cycles: simple metamorphosis nymphs emerge from eggs, feed on same substrate as adults. series of molts to adult stage. whole thing occurs on host. not capable of existing off host for more than a few hours. so route of transmission must be by direct host/host contact. this is important for clients to understand. the other thing to remember is that ths whole thing occurs at host body temperature. so this always takes about 3 weeks - whereas flea life cycle varies with temp and humidity in environment which is less consistent. lice hardly ever leave host. another corrollary to the point that this all occurs on the host is the possibility for a geometric growth of these parasites. females are prolific and numbers can increase amazingly. starting with 2 lice in october, by april you can have almost 24 million lice. it's not an accident that they did this experiment over the winter. that is the time when lice grow at high rates in livestock - haircoats are heavier, thicker, animals are brought inside and into close contact with eachother. adult lifespan is about 1-2 mos. see handout: list of genera and species FOR REFERENCE ONLY. the host species that are subject to being parasitized by chewing and sucking lice should be known: cattle, swine, horses, sheep and dogs all get sucking lice (anoplura). pediculosis is the term for louse infestation. in cows, we see unthriftiness, thin haircoat, scratches, emaciation, maybe anemia. hematopinus spp parasitize pigs and horses and cows. is important in pigs economically. has all the hallmarks of a sucking anoplurid louse. lice, unlike fleas, are exquisitely host specific. the hematopinus of cows will not be found in pigs and vice versa. human anoplurid parasites: anoplurid genera pthirus and pediculus. pthirus pubis - crab louse, pubis louse. people can NOT get this from pets. there was once a transient infection in a dog - and the people in the house insisted that the dog was the source of the infection in the people...but that's not possible. this louse is transmitted by close physical contact. pediculus humanus humanus - body louse. not common in affluent populations. epidemic among homeless people and underdeveloped countries. vectors of many rickettsial dzs - epidemic typhus, trench fever, relapsing fever. people who are crowded together and can't bathe a lot get lice - warfare, natural disasters, social upheaval - when people are forced to live in close confinement. pediculus humanus capitis: head louse. unlike humanus humanus, this louse is seen in very affluent populations. is the great socioeconomic leveller. seen in schoolchildren without regard to race, creed, color, and so forth. head lice have not been incriminated as vectors of any human pathogens. mallophagans: primarily of poultry - pests of fowl chewing lice divided into amblycera and ischnocera based on antenna morphology. amblycera - mainly fowl. the ischnocera do contain genera that parasitize dogs, cats, goats, sheep, horses, and cattle. chewing lice are intermediate hosts for dipylidium caninum. how do you control lice? much more straightforward for lice than fleas. no environmental component to worry about. treat the host. agents used on livestock are usually applied fall-midwinter. usually organophosphates eg raybon, vapona. young dairystock can be treated with methoxychlor- a DDT derivative. it is much more easily biodegraded than DDT. dogs/cats usually treated with carbamate based shampoos or lotions. ---end----