Arthropods
The arthropods are a group characterized by exoskeletons, segmentation and jointed appendages. They are a very diverse group.
From the tree of life project, a web site that summarizes the most current classification scheme for most groups, a phylogeny for Arthropods. http://tolweb.org/Arthropoda/2469.
To help you understand the arthropod taxonomy please go to the following web site. http://evolution.berkeley.edu/evolibrary/article/_0/arthropods_0
Work through the pages and activities covering arthropod characteristics (through an arthropod checklist). Answer question 1.
The major parasites that plague humans or their domesticated animals are found among the Crustacea, Insecta (a subgroup of the Hexapoda) and Arachnida.
Crustacea: Pentastomida
What are pentastomids? Adult pentastomids, or tongue worms,are highly modified crustaceans. They usually reside in the respiratory tract of their reptile, bird or mammal end hosts. Larvae live in the internal organs of vertebrate or arthropod intermediate hosts. Most of the species that ultimately find their way into humans or their domesticated animals are zoonotic species that usually infect reptilian species kept as pets, or utilized in local customs and rituals. All pentastomids have five appendages. . One is the mouth; the others are two pairs of hooks which they use to attach to the host. This arrangement led to their scientific name, meaning five openings. In an experiment where pentastomids were implanted in a gecko’s stomach, the parasites invaded the lungs in as little as four hours. In humans, infections are usually asymptomatic. There is growing concerns that because of the snake trade, human may become infected with larger loads, or less tolerated species, and develop the respiratory problems that characterize some pentastomid infections of reptiles.
Life cycle of a pentastomid that can infect humans. From the Encyclopedia of life: Pentastomida, Overview.
Review the life cycle above of a pentastomid and then visit this website that gives more information on pentastomids. You will not be responsible for classification of pentastomids. https://en.wikipedia.org/wiki/Pentastomida Answer question 2.
Many different crustacean groups have adapted a parasitic life cycle. Many copepods are external parasitic as adults on fish. Most crustacean parasites, however, infect other invertebrates often causing bizarre behavioral changes in morphology and behavior. For example, as exampled in your text pgs. 110-112, some barnacle parasites infect crabs, castrating males and taking over the reproductive function of males and females who will produce and disperse only young of the parasite for the rest of their lives.
Insecta
Among the Insecta, it is the wasps and flies that contain the most parasitic species.
Wasps: Hymenoptera
There are many parasitic wasps. They are mainly threats to other insects and each other. In fact it is not uncommon to find a series where one wasp that infects a other insect such as a moth caterpillar. Its larvae in turn can be infected by another wasp which in turn can be infected by yet another smaller wasp. Entomologists sometimes term the type of relationship wasp parasites have with their hosts as a parasitoid relationship. A parasitoid is a parasite that ultimately sterilizes or kills or even consumes its host after spending a significant portion of its life on that host.
Cotesia glomerata impregnates a cabbage white caterpillar with her eggs. Up to 60 individual larvae can develop in the helpless victim.
View this parasitic relationship at http://www.youtube.com/watch?v=vMG-LWyNcAs Answer question 3.
Flies: Diptera
The dipterans or flies are a different matter. Myiasis (burial of larvae in tissue) is an obligatory step in the life cycle of some flies and incidental for others. Some species that cause myiasis in the Americas are Cochliomyia (Screw worm fly), Calliphora, Oestrus, Sarcophaga, and Gastrophilus. Larvae can burrow through necrotic or healthy tissue using their mandibular hooks aided by proteolytic enzymes. They can cause mechanical damage and the affected area may be the site of a secondary infection.
Botflies: Dermatobia hominis or the human bot fly. Life cycle diagrammed at http://www.cdc.gov/dpdx/myiasis/index.html
View the videos at these two web sites. http://www.youtube.com/watch?v=V2Ac6RYSvo8
https://www.youtube.com/watch?v=90exkFR2iSM Answer question 4a.
Screwworms: Cochliomyia hominovorax or Chrysoma bezziana
These flies lay their eggs in the vicinity of wounds of the host and so need only one host to complete their life cycle.
View the video at https://www.youtube.com/watch?v=AXvObw8yuzs and read pgs. 98-104 in your textbook. Answer question 4b and c.
The screwworm was thought eradicated but recently some outbreaks have been recorded.
View this film on a florida outbreak https://www.youtube.com/watch?v=0rGbnTLKg3U Answer question 4d.
Most dipterans cause concern, not because they are parasites themselves, but because they can transmit pathogens and other parasites to humans on contact. Houseflies can leave bacteria on food and other items that ultimate cause disease. Of more concern, are mosquitoes and some other flies that while feeding on blood can inject serious disease causing organisms into the animal they are feeding upon. We have already examined some of these species in guide five.
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Lice
Lice taxonomy has been revised, but the old literature is still relevant. The lice we will be examining belong to the subgroup Anoplura. Interestingly many of the other subgroups such as the old Mallophaga, (now Ischnocera and Amblycera) mainly parasitize birds, which are suspected to be the first host for any louse. Some species of Rhynchophthirinal parasitize elephants and warthogs.
Examine the information on lice on the CDC website and then read and watch the video which relate lice's historical impact on man and how they are being used to understand more about our own evolution. Most of the latter work is possible because different lice species have very narrow host tolerances and may starve if placed on the wrong host. Answer questions 5.
http://www.cdc.gov/parasites/lice/
http://blogs.scientificamerican.com/guest-blog/2011/02/14/of-lice-and-men-an-itchy-history
Lice tell a tale about clothing. http://www.pbs.org/wgbh/nova/evolution/lice.html
The diagram below indicates where our species of lice came from, you guessed it, other primates.
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Fleas
Fleas are wingless, dark colored small ectoparasites. In the United States the Dog Flea, Ctenocephalides canis, is the one of concern for most pet owners as adults will try to feed on or bite humans and this species can transmit tapeworms to dogs and cats. Some individual dogs or humans may be very allergic to some of the substance in flea saliva. The reaction by their immune system to the bite may last for weeks after a bite.
http://www.merckvetmanual.com/mvm/integumentary_system/fleas_and_flea_allergy_dermatitis/flea_allergy_dermatitis.html
The most serious flea borne disease in history was Yersinia pistes, or plague (known in the Middle Ages as the Black Death). This is a disease of rats and other rodents, and rodent fleas can transmit it to man. Plague carried in this way has probably caused more deaths than all the wars in history. According to the World Health Organization, there are 1,000 to 3,000 cases of bubonic plague worldwide each year. A few cases still reported from time to time in the US. Interestingly, it is known that squirrels and prairie dogs or more correctly their fleas act as reservoirs for the disease in the US. The human flea, Pulex irritans, is anything but that, and actually found on many wild mammals besides humans,such as skunks, foxes and coyotes. The flea in the US more recently associated with carrying the plague is the rock squirrel flea, Diamanus montanus which is primarily found on rodents. Fleas have taken center stage in California and a few other states as possible carriers of new emerging and potential epidemic diseases, because of the flea's short life cycle and the ability of adults to live for months without a blood meal.
Examine this CDC pamphlet and answer question 6 a and b.
There is a serious dermatological disease cause by a flea, Tungiasis. Visit the websites below and answer question 6c.
Insects are a diverse group and many subgroups of insects do have parasitic forms. Various bugs, Hemiptera, are parasitic or are vectors for unicellular parasites. Bedbugs are on the rise in the United States and although they do not carry any disease can cause great suffering for their human hosts. You will read more about them in chapter six, There are also whole groups that are parasitic that we have not even mentioned because they pose no threat to humans or their domesticated animals. Strepsiptera are small insects and most species spend their lives as endoparasites in other insects.
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We will now examine a whole new group of arthropods, those vectors of disease or ectoparasite belonging to the Arachnida. This group contains the spiders, some scorpions and other creatures of nightmares. Although treated last, it is these ectoparasites, ticks and mites, that carry diseases that are spreading, cause mortality, and so a cause of major concern in the US.
Ticks:Acari
Ticks can carry a variety of serious diseases. Visit this website for a list of the more serous found in the United States. http://www.cdc.gov/ticks/diseases/ These diseases are very difficult to diagnose as the tick before symptoms arise has detached and most simple resemble the flu. It is only when the infected individual does not get better but worst as time progresses that medical providers may consider a tick-transmitted disease. http://www.cdc.gov/ticks/life_cycle_and_hosts.html
There are actually two types of ticks, hard (Ixodidae) and soft (Argasidae) ticks. Ixodidae species are those that transmit most diseases of public concern. However, the soft body ticks Ornithodoros hermsi and O. turicata, are vectors of tick-borne relapsing fever (TBRF) spirochetes.
Tick species actually vary in the number of hosts they can have. Also even when they have three hosts, the cycle does not have to involve different species of host or even different individuals. This type of flexibility in life cycle increases their probability of survival and potential for disease transmission.
Examine this website https://www.cdc.gov/ticks/life_cycle_and_hosts.htmlfor general information about ticks. Answer questions 7a-c.
Then examine the following website, focusing on ticks that may cause diseases in North Carolina.
https://www.cdc.gov/ticks/geographic_distribution.html
Fill out the table to answer 7d.
Lyme disease is on the rise in the US. Efforts to control it, remain problematic.
There is a vaccine for Lyme's. However, it requires booster shots and there are other problems limiting its distribution. Examine the sources below and answer question 7e.
https://www.historyofvaccines.org/content/articles/history-lyme-disease-vaccine
MITES
There are many species of mites, most are predators or scavengers. Those involved in symbiotic relationships are for the most part commensalistic. but there are a few parasitic species that plague humans and many that present serious threats to domesticated animals.
We tend not to think about insects as domesticated, but the European honeybee (named after the continent of its origin) is as domesticated a species as the horse and sheep. It not only is a source of honey and other products, but many of our cereal crops depend on it for pollination. Of prime concern then are mites that has at times threatened to destroy this multi-million dollar industry. Read pages 87-92 in your text and answer Questions 8a.
On the list are Follicle mites or Demodex species. Of interest is that for the most part these exist for the most part as harmless commensals on most humans and we are unaware of their existence. See pictures at https://www.cdc.gov/dpdx/scabies/index.html Click on the image gallery to see pictures of scabies mites and demodex mites.
There are sites such as http://www.ophthalmologymanagement.com/issues/2010/september-2010/do-you-know-demodex that does connect overpopulation of these mites with eye problems.Yet another species Demodex canis can cause mange in some dogs.http://www.petmd.com/dog/general-health/evr_dg_demodectic_mange_in_dogs
You should be aware of this genus of mite. There are articles that claim all humans have at least of few of these. We find them when individuals in my invert class choose to look, although I do not encourage pulling of eyelashes and eyebrow hair. Yet many dogs I have known that have become infected to their species have had to be euthanized.
Probably the most problematic mites for humans and dogs are those that bury under the skin causing types of scabies. One of the symptoms of scabies is intense itching. Different scabies or mange mites infect different domesticate mammals and wildlife, most are highly contagious and cause extensive inflammation.
Visit the following websites after reading chapter 6. They will help you answer questions relating to this chapter.
http://www.cdc.gov/parasites/scabies/ and http://www.cdc.gov/dpdx/scabies/
Most mite infections, although definitely most unpleasant do not carry any risk of diseases transmitted by the action of the mites, although serious secondary bacterial infections caused by animal scratching in response to the intense itching and inflammation caused by the mite can occur. There are exceptions. For example a recent typhus local epidemic in Thailand was traced to chiggers or mites whose nymphs are the parasitic stage. The chiggers were past to children from small mammals reservoirs. http://wwwnc.cdc.gov/eid/article/19/5/12-1445_article.htm
Most of us react with horror at the chance of contacting ticks mites, lice or other parasites that live on or just the skin. This is somewhat to be expected, these ecto and endo parasites are attacking our largest organ, and our main organ of protection against any pathogen. It is expected that our bodies would in some sense over respond to these invaders. It is then to be expected that some individuals would suspect parasites even if they were not there. There is concern that the incidence of individuals that believe they have parasitize despite lack of clinical confirmation is growing. http://www.dermnetnz.org/arthropods/parasitophobia.html
This condition besides other tales of "itchy" parasites are covered in Chapter 6 of your textbook. Read this chapter and then answer the rest of Question 8 using information obtained from your text.
