Helminth Parasites and Arthropod Vectors

Trematode pathogens

Schistosoma mansoni (schistosomiasis, snail fever)

Reduviidae

"Kissing bug"

Class Arachnida

spiders, mites, ticks 8 legs (4 pairs) as adults, 2 body segments

Cestodes

tapeworms

Schistosoma japonicum

the only human blood fluke that occurs in China, Philippines, Sri Lanka Asia and Lindu Lake .(Found by Markus Kleemann[1] in a Rainforest Lake) It is the cause of schistosomiasis japonica, a disease that still remains a significant health problem especially in lake and marshland regions. Schistosomiasis is an infection caused mainly by three schistosome species; Schistosoma mansoni, Schistosoma japonicum and Schistosoma haematobium. S. japonicum being the most infectious of the three species.[2] Infection by schistosomes is followed by an acute Katayama fever. Historical accounts of Katayama disease dates back to the discovery of S. Japonicum in Japan in 1904. The disease was named after an area it was endemic to, Katayama district, Hiroshima, Japan.[3] If left untreated, it will develop into a chronic condition characterized by hepatosplenic disease and impaired physical and cognitive development. The severity of S. japonicum arises in 60% of all neurological diseases in schistosomes due to the migration of schistosome eggs to the brain.

Rickettsia prowazekii

typhus

Trematodes

Flukes

tsetse fly

Trypanosoma brucei (African Sleeping Sickness)

Life cycle of Cestodes

Egg is released from feces Embryonated eggs or proglottids are ingested by secondary host ( cattle or swine) Onchosphere is formed and enter circulation cysticercus forms in muscles Muscle is ingested by human Scolex attaches to intestine grows proglottids.

Xenopsylla cheopis,

Fleas are small flightless insects that form the order Siphonaptera. As external parasites of mammals and birds, they live by consuming the blood of their hosts. Adults are up to about 3 mm (0.12 in) long and usually brown. Bodies flattened sideways enable them to move through their host's fur or feathers; strong claws prevent them from being dislodged. They lack wings, and have mouthparts adapted for piercing skin and sucking blood and hind legs adapted for jumping. The latter enable them to leap a distance of some 50 times their body length, a feat second only to jumps made by froghoppers. Larvae are worm-like with no limbs; they have chewing mouthparts and feed on organic debris.

Scolex head

Head of tape worm. Attaches to intestinal mucosa.

Trematode distinguishing features

Leaf-shaped, short, non-segmented bodies

Cestodes distinguishing features

Long, flat, segmented bodies; scolex = head, segments = proglottids

Nematode distinguishing features

Long, slender, non-segmented bodies

Enterobium vermicularis

Other than human, Enterobius vermicularis were reported from bonnet macaque.[8] Other species seen in primates include Enterobius buckleyi in Orangutan [9] and Enterobius anthropopitheci in chimpanzee. Enterobius vermicularis is common in human children and transmitted via the faecal-oral route. Humans are the only natural host of Enterobius vermicularis.[10] Enterobius gregorii, another human species is morphologically indistinguishable from Enterobius vermicularis except the spicule size.[11] Throughout this article, the word "pinworm" refers to Enterobius. In British usage, however, pinworm refers to Strongyloides, while Enterobius is called threadworm.[12]

Enterobium vermicularis

Pinworm infection, also known as enterobiasis, is a human parasitic disease caused by the pinworm.[3] The most common symptom is itching in the anal area.[1] This can make sleeping difficult.[1] The period of time from swallowing eggs to the appearance of new eggs around the anus is 4 to 8 weeks.[2] Some people who are infected do not have symptoms.[1] The disease is spread between people by pinworm eggs.[1] The eggs initially occur around the anus and can survive for up to three weeks in the environment.[1] They may be swallowed following contamination of the hands, food, or other articles.[1] Those at risk are those who go to school, live in a health care institution or prison, or take care of people who are infected.[1] Other animals do not spread the disease.[1] Diagnosis is by seeing the worms which are about one centimeter or the eggs under a microscope.[1][6]

Hermaphroditic proglottids

Segments of tape worm body having both male and female reproductive organs. both eggs and proglottids are shed in the feces and enter the environment

Cestodes Pathogens

Taenia saginata (beef tapeworm), T. solium (pork tapeworm)

Ticks

Western black-legged tick (Ixodes) - Borrelia burgdorferi (Lyme disease), Rickettsia rickettsii (Rocky Mountain Spotted Fever) are small arachnids, part of the order Parasitiformes. Along with mites, they constitute the subclass Acari. Ticks are ectoparasites (external parasites), living by feeding on the blood of mammals, birds, and sometimes reptiles and amphibians. Ticks had evolved by the Cretaceous period, the most common form of fossilisation being immersed in amber. Ticks are widely distributed around the world, especially in warm, humid climates.

Cimex lectularius

bed bugs; hypersensitivity to bites; pesticide resistant

cercaria larvae

fluke larvae that infect humans by penetrating the skin in contaminated water. These larvae develop into adult flukes with in the circulatory system where they mate, and female adult flukes lay eggs in the blood vessel walls. The eggs migrate to the urinary system or intestine to be shed onto the environment

cysticercus larvae

form of tape worm that is ingested by humans

miracidia larvea

free swimming fluke larvae that hatch from from eggs that have made their way to an aquatic environment. The miracidia then penetrate the tissue of fresh water snails and reproduce asexually to form cercaria larvae

Pediculus humanus capitis

head louse

Class Insecta

insects 6 legs (3 pairs), 3 body segments, antennae, often wings Pathogens: Mosquitoes: malaria, W. bancrofti, WNV, Yellow Fever -Flies: tsetse fly - Trypanosoma brucei (African Sleeping Sickness) -Bugs: reduviids (kissing bugs) - T. cruzi (Chagas disease) -Fleas: rat fleas - Yersinia pestis (bubonic plague) -Lice: body lice - Rickettsia prowazekii (typhus) -Botflies (secrete antibiotic and anesthetic) -Maggot therapy for wound debridement -Cimex lectularius = bed bugs; hypersensitivity to bites; pesticide resistant

Wuchereria bancrofti

is a human parasitic roundworm that is the major cause of lymphatic filariasis. It is one of the three parasitic worms, together with Brugia malayi and B. timori, that infect the lymphatic system to cause lymphatic filariasis. These filarial worms are spread by a variety of mosquito vector species. W. bancrofti is the most prevalent of the three and affects over 120 million people, primarily in Central Africa and the Nile delta, South and Central America, the tropical regions of Asia including southern China, and the Pacific islands.[1] If left untreated, the infection can develop into a chronic disease called elephantiasis.[2] In rare conditions it also causes tropical eosinophilia, an asthmatic disease. There is no commercially available vaccine, however high rates of cure have been achieved with various anti-filarial regimens and lymphatic filariasis is the target of the WHO Global Program to Eliminate Lymphatic Filariasis with the aim to eradicate the disease as a public health problem by 2020

Pediculus humanus humanus

is a louse that infests humans. The condition of being infested with head lice, body lice, or pubic lice is known as pediculosis.[2] Body lice are vectors for the transmission of the human diseases epidemic typhus, trench fever, and relapsing fever.

Maggot therapy

is a type of biotherapy involving the introduction of live, disinfected maggots (fly larvae) into the non-healing skin and soft tissue wound(s) of a human or animal for the purpose of cleaning out the necrotic (dead) tissue within a wound (debridement) and disinfection. There is evidence that maggot therapy may help with wound healing

Microfilaria

is an early stage in the life cycle of certain parasitic nematodes in the family Onchocercidae.[2] In these species, the adults live in a tissue or the circulatory system of vertebrates (the "definitive hosts"). They release microfilariae into the bloodstream of the vertebrate host. The microfilariae are taken up by blood-feeding arthropod vectors (the "intermediate hosts"). In the intermediate host the microfilariae develop into infective larvae that can be transmitted to a new vertebrate host. The presence of microfilariae in the host bloodstream is called "microfilaraemia". The success of filariasis eradication programs is typically gauged by the reduction in numbers of circulating microfilariae in infested individuals within a geographic area.

Sarcoptes scabies

or the itch mite is a parasitic mite (an arthropod) that burrows into skin and causes scabies. The mite is found in all parts of the world. Humans are not the only mammals that can become infected. Other mammals, such as wild and domesticated dogs and cats (in which it is one cause of mange) as well as ungulates, wild boars, bovids, wombats, koalas, and great apes are affected. Devastating for AIDs sufferers

Taenia solium

pork tapeworman intestinal zoonotic parasite found throughout the world, and is most prevalent in countries where pork is eaten. The adult worm is found in humans and has a flat, ribbon-like body, which is white in color and measures 2 to 3 m in length. Its distinct head, the scolex, contains suckers and a rostellum as organs of attachment. The main body, the strobila, consists of a chain of segments known as proglottids. Each proglottid is a complete reproductive unit; hence, the tapeworm is a hermaphrodite. It completes its life cycle in humans as the definitive host and pigs as intermediate host. It is transmitted to pigs through human feces or contaminated fodder, and to humans through uncooked or undercooked pork. Pigs ingest embryonated eggs called morula, which develop into larvae, the oncospheres, and ultimately into infective larvae, cysticerci. A cysticercus grows into an adult worm in human small intestines. Infection is generally harmless and asymptomatic. However, accidental infection in humans by the larval stage causes cysticercosis. The most severe form is neurocysticercosis, which affects the brain and is a major cause of epilepsy. Human infection is diagnosed by the parasite eggs in the faeces. For complicated cysticercosis, imaging techniques such as computed tomography and nuclear magnetic resonance are employed. Blood samples can also be tested using antibody reaction of enzyme-linked immunosorbent assay. Broad-spectrum anthelmintics such as praziquantel and albendazole are the most effective medications.

Nematodes

roundworms

Schistosoma mansoni

schistosomiasis, snail fever

Schistosoma haematobium

urinary blood fluke) is species of digenetic trematode, belonging to a group (genus) of blood flukes (Schistosoma). It is found in Africa and the Middle East. It is the major agent of schistosomiasis, the most prevalent parasitic infection in humans.[1] It is the only blood fluke that infects the urinary tract, causing urinary schistosomiasis, and is the leading cause of bladder cancer (only next to tobacco smoking).[2][3] The diseases are caused by the eggs. Adults are found in the venous plexuses around the urinary bladder and the released eggs travels to the wall of the urine bladder causing haematuria and fibrosis of the bladder. The bladder becomes calcified, and there is increased pressure on ureters and kidneys otherwise known as hydronephrosis. Inflammation of the genitals due to S. haematobium may contribute to the propagation of HIV.[4] S. haematobium was the first blood fluke discovered.

tsetse fly

are large biting flies that inhabit much of tropical Africa they have a prominent economic impact in sub-Saharan Africa as the biological vectors of trypanosomes, which cause human sleeping sickness and animal trypanosomiasis.

Ixodidae

Almost all ticks belong to one of two major families, the Ixodidae or hard ticks, which are difficult to crush, and the Argasidae or soft ticks. Adults have ovoid or pear-shaped bodies which become engorged with blood when they feed, and eight legs. As well as having a hard shield on their dorsal surfaces, hard ticks have a beak-like structure at the front containing the mouthparts whereas soft ticks have their mouthparts on the underside of the body. Both families locate a potential host by odour or from changes in the environment. Ticks have four stages to their lifecycle, namely egg, larva, nymph, and adult. Ixodid ticks have three hosts, taking at least a year to complete their lifecycle. Argasid ticks have up to seven nymphal stages (instars), each one requiring a blood meal. Because of their habit of ingesting blood, ticks are vectors of at least twelve diseases that affect humans and other animals.

Arthropod vectors

Animals with exoskeletons (chitin) and jointed appendages = insects, arachnids, crustaceans -Humans = source of blood meals Class Insecta (insects) Class Arachnida (spiders, mites, ticks)

Nematode Pathogens

Ascaris lumbricoides (intestinal obstruction; f/o - typically on vegetables fertilized with night soil), Enterobium vermicularis (pinworm; f/o), cat/dog heartworms, Wuchereria bancrofti (filiariasis, elephantiasis; insect vector); Dracunculus medininsis (arthropod "vector"); Trichinella spiralis (food borne)

Xenopsylla cheopis,

The oriental rat flea, is a vector of Yersinia pestis, the bacterium which causes bubonic plague. The disease was spread by rodents such as the black rat, which were bitten by fleas that then infected humans. Major outbreaks included the Plague of Justinian and the Black Death, both of which killed a sizeable fraction of the world's population.

Enterobium vermicularis

The pinworm (species Enterobius vermicularis), also known as threadworm (in the United Kingdom and Australasia) or seatworm, is a parasitic worm. It is a nematode (roundworm) and a common intestinal parasite or helminth, especially in humans.[5] The medical condition associated with pinworm infestation is known as pinworm infection (enterobiasis)[6] (a type of helminthiasis) or less precisely as oxyuriasis in reference to the family Oxyuridae.[7]

Botflies

Their larvae are internal parasites of mammals, some species growing in the host's flesh and others within the gut. The Dermatobia hominis is the only species of botfly known to parasitize humans routinely, though other species of flies cause myiasis in humans.

Reduviidae

They are mainly found and widespread in the Americas, with a few species present in Asia, Africa, and Australia. These bugs usually share shelter with nesting vertebrates, from which they suck blood. In areas where Chagas disease occurs (from the southern United States to northern Argentina), all triatomine species are potential vectors of the Chagas disease parasite Trypanosoma cruzi, but only those species (such as Triatoma infestans and Rhodnius prolixus) that are well adapted to living with humans are considered important vectors. Proteins released from their bites have been known to induce anaphylaxis in sensitive and sensitized individuals

Ascaris lumbricoides

a roundworm, infects humans when an ingested fertilised egg becomes a larval worm (called rhabditiform larva) that penetrates the wall of the duodenum and enters the blood stream. From there, it is carried to the liver and heart, and enters pulmonary circulation to break free in the alveoli, where it grows and molts. In three weeks, the larva passes from the respiratory system to be coughed up, swallowed, and thus returned to the small intestine, where it matures to an adult male or female worm. Fertilization can now occur and the female produces as many as 200,000 eggs per day for a year. These fertilized eggs become infectious after two weeks in soil; they can persist in soil for 10 years or more.[5] The eggs have a lipid layer which makes them resistant to the effects of acids and alkalis, as well as other chemicals. This resilience helps to explain why this nematode is such a ubiquitous parasite.

Schistosoma mansoni

a water-borne parasite of humans, and belongs to the group of blood flukes (Schistosoma). The adult lives in the blood vessels (mesenteric veins) near the human intestine. It causes intestinal schistosomiasis

Echinococcus granulosus

also called the hydatid worm, hyper tape-worm or dog tapeworm, is a cyclophyllid cestode that parasitizes the small intestine of canids as an adult, but which has important intermediate hosts such as livestock and humans, where it causes cystic echinococcosis, also known as hydatid disease. The adult tapeworm ranges in length from 3 mm to 6 mm and has three proglottids ("segments") when intact—an immature proglottid, mature proglottid and a gravid proglottid.[1] The average number of eggs per gravid proglottid is 823. Like all cyclophyllideans, E. granulosus has four suckers on its scolex ("head"), and E. granulosus also has a rostellum with hooks. Several strains of E. granulosus have been identified, and all but two are noted to be infective in humans.[2] The lifecycle of E. granulosus involves dogs and wild carnivores as a definitive host for the adult tapeworm. Definitive hosts are where parasites reach maturity and reproduce. Wild or domesticated ungulates, such as sheep, serve as an intermediate host.Transitions between life stages occur in intermediate hosts. The larval stage results in the formation of echinococcal cysts in intermediate hosts. Echinococcal cysts are slow growing,but can cause clinical symptoms in humans and be life-threatening.[4] Cysts may not initially cause symptoms, in some cases for many years. Symptoms developed depend on location of the cyst, but most occur in the liver, lungs, or both.

Taenia saginata

beef tapeworm It is an intestinal parasite in humans causing taeniasis (a type of helminthiasis) and cysticercosis in cattle. Cattle are the intermediate hosts, where larval development occurs, while humans are definitive hosts harbouring the adult worms. It is found globally and most prevalently where cattle are raised and beef is consumed. It is relatively common in Africa, Europe, Southeast Asia, South Asia, and Latin America. Humans are generally infected as a result of eating raw or undercooked beef which contains the infective larvae, called cysticerci. As hermaphrodites, each body segment called proglottid has complete sets of both male and female reproductive systems. Thus, reproduction is by self-fertilisation. From humans, embryonated eggs, called oncospheres, are released with faeces and are transmitted to cattle through contaminated fodder. Oncospheres develop inside muscle, liver, and lungs of cattle into infective cysticerci.

Trichinella spiralis

can live the majority of its adult life in the intestines of humans. To begin its life cycle, Trichinella spiralis adults will invade the intestinal wall of a pig, and produce larvae that invade the pig's muscles. The larval forms are encapsulated as a small cystic structure within a muscle cell of the infected host. When another animal (perhaps a human) eats the infected meat, the larvae are released from the nurse cells in the meat (due to stomach pH), and migrate to the intestine, where they burrow into the intestinal mucosa, mature, and reproduce.[3] Juveniles within nurse cells have an anaerobic or facultative anaerobic metabolism, but when they become activated, they adopt the aerobic metabolism characteristics of the adult.[2] Trichinella spiralis lifecycle Female Trichinella worms live for about six weeks, and in that time can produce up to 1,500 larvae; when a spent female dies, she passes out of the host. The larvae gain access to the circulation and migrate around the body of the host, in search of a muscle cell in which to encyst .[3] The migration and encystment of larvae can cause fever and pain, brought on by the host inflammatory response. In some cases, accidental migration to specific organ tissues can cause myocarditis and encephalitis that can result in death.

lymphatic filariasis

caused by Wuchereria bancrofti

Botflies

deposit eggs on a host, or sometimes use an intermediate vector such as the common housefly, mosquitoes, and, in the case of Dermatobia hominis, a species of tick. They are common in Belize. The smaller fly is firmly held by the botfly female and rotated to a position where the botfly attaches some 30 eggs to the body under the wings. Larvae from these eggs, stimulated by the warmth and proximity of a large mammal host, drop onto its skin and burrow underneath.[6] Intermediate vectors are often used, since a number of animal hosts recognise the approach of a botfly and flee.[7] Eggs are deposited on animal skin directly, or the larvae hatch and drop from the eggs attached to the intermediate vector: the body heat of the host animal induces hatching upon contact or immediate proximity. Some forms of botfly also occur in the digestive tract after ingestion by licking. Ox warble fly (Hypoderma bovis) Myiasis can be caused by larvae burrowing into the skin (or tissue lining) of the host animal. Mature larvae drop from the host and complete the pupal stage in soil. They do not kill the host animal, thus they are true parasites.

Schistosoma japonicum

is an important parasite and one of the major infectious agents of schistosomiasis.This parasite has a very wide host range, infecting at least 31 species of wild mammals, including 9 carnivores, 16 rodents, one primate (Human), two insectivores and three artiodactyls and therefore it can be considered a true zoonosis.

Trichinella spiralis

is an ovoviviparous[1] nematode parasite, occurring in rodents, pigs, horses, bears, and humans, and is responsible for the disease trichinosis. It is sometimes referred to as the "pork worm" due to it being typically encountered in undercooked pork products. It should not be confused with the distantly related pork tapeworm.

Ascaris lumbricoides

is the "large roundworm" of humans, growing to a length of up to 35 cm (14 in).[1] It is one of several species of Ascaris. An ascarid nematode of the phylum Nematoda, it is the most common parasitic worm in humans. This organism is responsible for the disease ascariasis, a type of helminthiasis and one of the group of neglected tropical diseases. An estimated one-sixth of the human population is infected by A. lumbricoides or another roundworm.[2] Ascariasis is prevalent worldwide, especially in tropical and subtropical countries.[3] According to the latest research, Ascaris lumbricoides and Ascaris suum (pig roundworm) are the same species.

Dracunculus medinensis

larvae are found in fresh water, where they are ingested by copepods of the genus Cyclops. Within the copepod, the D. medinensis larvae develop to an infective stage within 14 days.[5] When the infected copepod is ingested by a mammalian host, the copepod is dissolved by stomach acid and the D. medinensis larvae migrate through the wall of the mammalian intestine, and mature into adults. One hundred days after infection, a male and female D. medinensis meet and sexually reproduce within the host tissue. The male dies in the host tissue while the female migrates to the host's subcutaneous tissue. Approximately one year after infection, the female causes the formation of a blister on the skin's surface, generally on the lower extremities, though occasionally on the hand or scrotum. When the blister ruptures, the female slowly emerges over the course of several days or weeks.[5] This causes extreme pain and irritation to the host. When the host submerges the affected body part in water, the female expels thousands of larvae into the water. From here, the larvae infect copepods, continuing the life cycle

Helminths

mutlicellular , eukaryotic worms, some of which cause parasitic infections in humans.

Dracunculus medinensis

or Guinea worm is a nematode that causes dracunculiasis, also known as guinea worm disease.[1] The disease is caused by the female[2] which, at up to 800 mm (31 in) in length,[3] is among the longest nematodes infecting humans.[4] In contrast, the longest recorded male Guinea worm is only 40 mm (1.6 in).[3] The common name "guinea worm" is derived from the Guinea region of Western Africa.