Parasites|Parasites in humans|Are parasites animals|Medical world

Parasites in humans

Parasites consists of the following terms-

Plasmodium species

Malaria, an infection caused by plasmodium app., has affected mankind for millennia. The word malaria means 'bad air' , and refers to the association between the illness and the marshes where Anopheles mosquitoes breed. Although malaria has virtually disappeared from Europe and the USA , it remains a major problem in tropical countries where it causes an estimated 216 million cases and 655000 deaths per year.

Plasmodium species

plasmodium spp. Cause human infection:

P.falciparum can invade RBCs of all ages, may be drug-resistant, and is responsible for most severe, life-threatening infections. It does not produce dormant liver stages or cause relapse.

P.vivax and P.ovale cause clinically similar milder infections. They produce hypnozoites and may cause relapse months after the initial infections.

P. malariae rarely cause acute illness in normal hosts, does not produce hypnozoites, but may persist in the bloodstream for years.

Life cycle

Humans acquire malaria from sporozoites transmitted by the bite of the female Anopheles mosquito. Sporozoites travel through the bloodstream and enter hepatocytes.

Here they mature into tissue schizonts which rupture and release merozoites into the bloodstream.

These invade RBCs and mature into ring forms, then trophozoites, and finally schizonts, before rupturing to release merozoites. Alternatively ,some erythrocytic parasites develop into geametocytes, which are ingested by the mosquito and complete the sexual life. In P. Ovale infections, some parasites remain dormant in the liver as hypnozoites for months, before they mature into tissue schizonts.

Epidemiology

The epidemiology of malaria varies and depends on a number of factors: climate, plasmodium spp. And life cycle, efficiency of transmission by factors, and drug resistance.

Are parasites animals?

Babesia

Babesiosis is a zoonotic infection caused by babesia spp., a malaria like parasites that parasitizes erythrocytes of animals and causes fever, haemolysis, and haemoglobinuria. It typically causes mild illness in humans, but fulminant disease may occur in asplenic or immunosuppressed patient

The parasites

There are >70 babesia spp. Worldwide that infect a wide range of mammals and birds. Babaesia spp. Have traditionally been classified into four clades:

• Clade 1 contains Babesia micro spp. That cause disease in the USA and Japan;
• Clade 2 contains Babesia Duncani and B. Duncani-like organism that cause disease in the western USA;
• Clade 3 contains Babesia divergence that cause disease in the cattle in Europe.

Epidemiology

The first fatal human case of babesiosis was reported in 1996. Since then, >2700 cases have been reported worldwide, most from north-eastern coastal regions of the USA. Based on seroprevalence data, most infections appear to be subclinical.

Transfusion-associated , transplacental , and perinatal transmission may occur. The clinical feature of babesiosis very markedly regions.

Toxoplasma gondii

Toxoplasmosis is a zoonotic infection caused by T.gondii, a coccidian parasite of cats that effects humans and other mammals as intermediate hosts. Although infections with T.gondii is a common. It rarely causes disease, apart from in congenitally acquired infection and in patients with cell-mediated immunodeficiency, especially AIDS.

Classification

T. Gondii belongs to subphylum Apicomplexa , class sporozoa and exists in three forms-

• The oocyst
• The tissue cyst
• The tachyzoite

Life cycle

Oocyst are produced in the cat's intestine and shed in its faeces. Once once outside the cat, the oocysts sporulate and develop sporozoites. Oocysts are ingested by other animals and release sporozoites, which develop into tachyzoites.

These infect a wide variety of cells, multiply rapidly to form rosettes, lyse the cells, and spread to other cells or parts of the body. In the tissues, formation of tissue cysts may occur, with slowly replicating bradyzoites inside them.

Epidemiology

Toxoplasmosis is a worldwide zoonosis infecting a wide variety of mammals. Human infection occurs through the ingestion of:

• Tissue cysts in raw or undercooked meat;
• Food or water contaminated with oocysts;Transplacental transmission from mother to foetus;

Cryptosporidium

Cryptosporidium is an intracellular protozoan, first described in 1907 in mice and thought to be rare and clinically insignificantfor 50 years. It has since been recognised as a common enteric pathogen and is associated with waterborne outbreaks and diarrhoea in children and adults.

It infects and replicate in epithelial cells of the digestive and respiratory tract of most vertebrates. Twenty species are recognised; Cryptosporidium parvum is the most important species.

Life cycle

Ingestion of oocysts is followed by encystation, usually following exposure to digestive enzymes or bile acids, then release of four sporozoites which attach to the epithelial cell wall. Sporozoites mature asexually into meronts and release merozoites intraluminally . Some of these re-invade the host cels while others mature sexually into oocysts which are excreted in the faeces.

Epidemiology

Cryptosporodium is a ubiquitous enteric pathogen of all age groups. Transmission occurs by person to person, animal-to-person, waterborne, or, less commonly, food-borne spread. The prevalence of faecal oocyst excretion varies from 1-3% in industrialised countries to 5-10% in Asia and Africa. Seroprevalence in Europe and North America.

Cyctoisospora

Cystoispora belli is a coccidian GI parasite. First described in 1915.

Epidemiology

C.belli is found worldwide but predominantly causes infections in tropical and subtropical climates. Infection may occur in immunosuppressed patients and immunocompetent patients. Transmission is by the face-oral rate with ingestion of sporulated oocysts in contaminated food and water.

Leishmania

Leishmaniasis is caused by various Leishmania spp. That vary in their geographical distribution and clinical features. There are three clinical syndromes, each of which may be caused by several species:

• Visceral leishmaniasis;
• Cutaneous leishmaniasis;
• Mucosal leishmaniasis
• Post-kala-azar dermal leishmaniasis

The parasite

Leishmania spp. Have a dimorphic life cycle and live in macrophages as intracellular amastigotes in mammalian hosts and extracellular promastigotes in the gut of their sandfly vectors. Leishmania spp. Cannot be differentiated on the basis of morphology speciation was initially based on epidemiological and clinical features; several molecular assays are now used.

Epidemiology

Visceral leishmaniasis has a wide geographical distribution. It is caused by leishmania Donovani spp. Leishmania infonaut, or leishmania chagasi . Rarely, leishmania omanzonesis or leishmania tropica may cause visceral leishmaniasis

Cutaneous leishmaniasis is also widely distributed. The classic form of Old World cutaneous leishmaniasis, the oriental sore, is found in the Middle East, the Mediterranean, Africa and Asia. It is usually caused by L.Major, L.tropica, leishmania brazilensis, leishmania Mexican, leishmania panamensis and occasionally by L. Chagasi.