Tinea capitis
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Ringworm, also known as Tinea, is a contagious (excluding tinea versicolor[1]) fungal infection of the skin. Contrary to its name, ringworm is not caused by a worm.
Ringworm is very common, especially among children, and may be spread by skin-to-skin contact, as well as via contact with contaminated items such as hairbrushes. Ringworm spreads readily, as those infected are contagious even before they show symptoms of the disease. Participants in contact sports such as wrestling have a risk of contracting the fungal infection through skin-to-skin contact.
Tinea capitis
Ringworm is also a common infection in domestic animals, especially cattle and cats. Humans can contract ringworm from animals; cats, cattle and dogs are common sources owing to close association with humans.
Giardia affects humans. It is also one of the most common parasites infecting cats. Mammalian hosts also include cows, beaver, deer, dogs and lambs.
Infection causes giardiasis, a type of gastroenteritis that manifests itself with severe diarrhea and abdominal cramps. Other symptoms can include bloating, flatulence, fatigue, nausea, vomiting and weight loss. In some patients, vomiting or nausea is the major symptom. The symptoms usually manifest themselves about seven to ten days after ingestion. Giardia is a major cause of intestinal disease worldwide and the most frequent non-bacterial cause of diarrhea in North America. Nonetheless, the basic biology of this parasite is poorly understood.
Parasite life cycle.
Giardia belongs among the diplomonads.
Infection from giardia can occur from consuming contaminated food or water; this includes clean-looking mountain streams. It can also be transferred from animal or human feces. Not every person displays symptoms of infection, but they can still serve as a carrier of the disease. Giardia infection is a concern for people camping in the wilderness or swimming in contaminated streams or lakes, especially the artificial lakes formed by beaver dams (hence the popular name for giardiasis, "Beaver Fever").
Giardia may be ingested at camping areas, day care centers, waterborne outbreaks, and is also highly infectious to other family members once one individual is infected. Other causes can be uncooked food, contaminated wells and failed municipal water systems.
The life cycle begins with a noninfected cyst being excreted out through feces of an infected individual. Once out in the environment, the cyst becomes infected. A distinguishing characteristic of the cyst is 4 nuclei and a retracted cytoplasm. Once ingested by a host, the trophozoite emerges to an active state of feeding and motility. It feeds on mucous inside the digestive tract and causes the host to have epigastric pain, excessive gas, and diarrhea with fat and mucous but no blood. This can last from 2 - 4 weeks but for a lactose intolerant individual, it can last up to six months.
After the feeding stage, the trophozoite undergoes asexual replication through longitudinal binary fission. The resulting trophoziotes and cysts then pass through the digestive system in the feces. Distinguishing features of the trophozoites are large karyosomes and lack of peripheral chromatin, giving the two nuclei a halo appearance. This is a primitive form of protozoa and also lacks mitochondria.
Nomenclatures for Giardia species are hard since humans and other animals appear to have morphological identical parasites. Cats can be cured easily, lambs usually just lose weight, but in calves the parasites can be fatal and often are not responsive to antibiotics or electrolytes. Carriers among calves can also be asymptomatic. Dogs have the most problems since usually 30% of the population under one year old is infected in kennels. It is more a "puppy problem" than an adult one. Moreover, this parasite is deadly for chinchillas, so make sure you take extra care to provide them with safe water.
Treatment in kennels can be done by identifying the infected dogs and isolating them or just a mass treatment, followed by cleaning the entire kennel with bleach or other cleaning disinfectants. The grass area used for exercise should be considered contaminated for at least one month since cysts can survive in the environment for that long. Prevention can be achieved by quarantine for at least 20 days and managing the water supply to be clear of too many cysts.
Filter use or boiling is recommended for water purification of drinking water in wilderness conditions.
Treatment of drinking water for Giardia typically involves some form of high efficiency filtration and/or chemical disinfection such as chlorination or ozonation. Treatment is necessary throughout North America. Scooping water from the top is not an effective way to avoid Giardia.
This picture shows multiple views of a single Giardia lamblia (intestinalis)
cyst as imaged at different instrument settings by confocal microscopy.Bar
= 10 micrometres.
(A) is the cyst imaged by transmission (differential interference
contrast), only.
(B) is the cyst wall selectively imaged through use of fluorescent-labelled
(TRITC) antibody that is cyst wall specific.
(C) is the cyst imaged through use of carboxy fluorescein diacetate, a
viability stain.
(D) is a composite image of (B) and (C).
(E) is a composite image of (A), (B), and (C).
Under a normal compound light microscope, Giardia often looks like a "clown face," with two nuclei outlined by adhesive discs above dark median bodies that form the "mouth." Cysts have four nuclei.
Giardia alternates between two different forms — a hardy, dormant cyst that contaminates water or food and an active, disease-causing form that emerges after the parasite is ingested. National Institute of General Medical Sciences grantee Dr. Frances Gillin of the University of California, San Diego and her colleagues cultivated the entire life cycle of this parasite in the laboratory, and identified biochemical cues in the host's digestive system which trigger Giardia's life cycle transformations. They also uncovered several ways in which the parasite evades the defenses of the infected organism. One of these is by altering the proteins on its surface, which confounds the ability of the infected animal's immune system to detect and combat the parasite. Gillin's work reveals why Giardia infections are extremely persistent and prone to recur. In addition, these insights into Giardias biology and survival techniques may enable scientists to develop better strategies to understand, prevent, and treat giardia infections.
The trophozoite form of Giardia was first observed in 1681 by Anton van Leeuwenhoek in his own diarrheal stools. His observations were recreated, using a single lensed microscope of the kind used by Leeuwenhoek, by British microbiologist Brian J. Ford who showed how clearly one could view Giardia through a primitive microscope
Entamoeba histolytica is an anaerobic parasitic eukaryote protozoan, part of the genus Entamoeba. It infects predominantly humans and other primates. Diverse mammals such as dogs and cats can become infected but usually do not shed cysts (the environmental survival form of the organism) with their feces, thus do not contribute significantly to transmission. The active (trophozoite) stage exists only in the host and in fresh feces; cysts survive outside the host in water and soils and on foods, especially under moist conditions on the latter. When swallowed they cause infections by excysting (to the trophozoite stage) in the digestive tract.
Entamoeba histolytica, as its name suggests, can actually bore through the enteric walls (histolysis = destroying tissue) and reach the blood stream. From there, it can reach different vital organs of the human body, like the liver, lungs, brain, eyes etc. A typical effect is a liver abscess caused by such migrating Entamoeba histolytica, which can be fatal. Ingested red blood cells are sometimes seen in the cytoplasm.
Entamoeba histolytica infection can lead to amebiasis or amebic dysentery. Symptoms include fulminating dysentery, diarrhea, weight loss, fatigue, abdominal pain, and amebomas.
It can be diagnosed by stool samples. Trophozoites should be seen in a fresh fecal smear and Cysts in an ordinary stool sample. ELISA or RIA can also be used.
Strongyloides stercoralis is the scientific name of a human parasitic roundworm causing the disease of strongyloidiasis.
This 2 mm-long worm is found both free-living in soil, and as a parasite of humans, other primates, and dogs. The free-living male and female worms are not infectious, however, their offspring all develop to infectious larvae. These infectious larvae penetrate the skin when there is contact with the soil. Some of them enter the superficial veins and ride the blood vessels to the lungs, where they enter the alveoli. They are then coughed up and swallowed into the gut, where they parasitise the intestinal mucosa (duodenum and jejunum). However, research in dogs has shown that most of the larvae that penetrate the skin migrate randomly through the body until they reach the small intestine. Only females will reach reproductive adulthood in the intestine. Female strongyloides reproduce through parthenogenesis. The eggs hatch in the intestine and young larvae are then excreted in the feces. It takes about two weeks to reach egg development from the initial skin penetration. By this process, S. stercoralis can cause both respiratory and gastrointestinal symptoms. Adult worms can live up to a year in dogs.
Autoinfection can also occur when the larvae which hatch from the eggs in the small intestine have time to mature to infectious larvae before being excreted. They penetrate the wall of the lower ileum or colon or the skin of the perianal region, enter the circulation again, up to the lungs, and back down to the small intestine thus repeating the cycle. Because of autoinfection, humans have been known to still be infected up to 50 years after they were first exposed to the parasite. Immunosuppressive drugs, such as those used for tissue transplantation, (especially corticosteroids) can increase the rate of autoinfection to the point where there is an overwhelming number of larvae migrating through the lungs, and in many cases this can prove fatal. Additionally, diseases such as HTLV-1 (Human T-cell Lymphotropic Virus 1), which enhance the Th1 arm of the immune system and lessen the Th2 arm, increase the disease state. While there are a number of drugs which will kill the adult worms, these drugs have little effect on the majority of these autoinfective larvae during their migration through the body.
Sacculina is a genus of barnacles that are parasitic on crabs. The adults bear no resemblance to the barnacles that cover ships and piers; they are recognised as barnacles because their larval forms are like other members of the barnacle class Cirripedia.
The female Sacculina larva finds a crab and walks on it until it finds a joint. It then molts, injecting its soft body into the crab while its shell falls off. The Sacculina grows in the crab, emerging as a sac, known as an externa, on the underside of the crab's rear thorax, where the crab's eggs would be incubated.
When a female Sacculina is implanted in a male crab it will interfere with the crab's hormonal balance. This sterilizes it and changes the bodily layout of the crab to resemble that of a female crab by widening and flattening its abdomen, among other things. The female Sacculina has even been known to cause the male crabs to perform mating gestures typical of female crabs.
The male Sacculina looks for a female Sacculina adult on the underside of a crab. He then enters and fertilizes her eggs. The crab (male or female) then cares for the eggs as if it were its own, having been rendered infertile by the parasite.