GENERAL CHARACTERS OF RADIATA

SUPERPHYLUM RADIATA

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The radiata is a superphylum which includes both the echinoderms, cnidarians and ctenophores and is not part of the usual classification system and is not used by the biologists. The group includes radially symmetric animals of Eumetazoa[1]. The echinoderms, however, are members of the Bilateria, because they exhibit bilateral symmetry in their developing stages. Their radial symmetry is secondary.

In 1983 Thomas defined a sub-kingdom called Radiata Consisting of the phyla porifera, myxozoa, placozoa, cnidaria and ctenophore (that is, all the animals that are not in bilateria). The five kingdom classification of Lynn Margulis and K. V. Schwartz keeps only Cnidaria and Ctenophora in Radiata.

We will deal hear with the Cnidaria and Ctenophora with respect to their general characters.

COELENTRATA (OR CNIDARIA)

The cnidarians[2] are an aquatic group of organisms, commonly known as hydroids, jellyfish, sea anemone and corals. They are tentacle bearing, radial or biradial animals with sac-like body composed of two basic cell layers. The inner layer of cells, called the gastrodermis, lines the hollow space, the coelenterons, which functions in digestion and transport and into which there is single opening, the mouth. The outer cell layer consists of an epidermis. The gastrodermis and epidermis are separated by a thin, acellular matrix or mesolamella or by a jelly-like material containing cells called the mesoglea or mesenchyme.

All Cnidaria are constructed from eight basic cell types – epithelial, muscular, nervous, glandular, reproductive, interstitial, mesenchyme and cnidoblasts. Cnidoblasts are most frequently present on tentacles and contain stinging structures – the nematocysts which function in defence and in the capture of food; all cnidarians are carnivorous in habit.

All cnidarians have tissue level of organization having, epiderma, nervous, digestive and muscular tissues, but lacking specialized organ system. Fundamentally two body forms are repre: Polyp and Medusa (we will talk about these later)

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EXTERNAL MORPHOLOGY

Coelenterates are a acoelomate and radially symmetrical lower invertebrates (Radiata). The coelenterates are represented by two morphologically different types of individuals, polyps and medusa.

Polyps are sessile with a tubular body (eg. Hydra, Metridium (Sea anemone))

Medusa are free swimming umbrella or bell-shaped body.

Some coelenterates pass through both stages in their life cycle with an alternation of generations.

INTERNAL STRUCTURE

Internal structure of Cnidarians can be understood by studying the histology of Hydra.

GASTROVASCULAR CAVITY

Almost all cnidarians have a central cavity called coelenterons, functionally referred to as gastrovascular cavity. It has only one opening – the mouth. There is no anus and no excretory pore. The undigested food and wastes exit the cavity through the mouth opening.

BODY WALL

There body wall is composed of two layers of cells, outer layer is called epidermis and the inner layer is called gastrodermis/endodermis. The two layers are separated from each other by a thin delicate, non-cellular gelatinous layer called mesoglea or supporting lamella.

1. EPIDERMIS

The epidermis is composed of small, more or less cuboidal cell. It is a protective and sensory layer. The epidermis is covered externally by a thin coating of cuticle. It has various types of cells as follows.

a. Epithelio-muscle cells

Most of epidermis is composed of epithelio-muscle cells that helps in both muscular contraction and epithelial covering. The epithelial part extends up to body surface and the basal muscular part is drawn out into two muscle processes along the longitudinal axis. Muscle process contains contractile fibril, the myoneme.

b. Gland cells

These are tall cells found chiefly on pedal disc and around mouth region. These secrete a mucus-like sticky material which serves for attachment and protection.

c. Interstitial cells

They are present in the interstitial spaces between epithelio-muscle cells. They are small round undifferentiated cells and are capable of developing any other kind of cells, such as reproductive, glandular, stinging etc.

d. Cnidoblasts

Many of the interstitial cells of epidermis develop into specialized cells called cnidoblasts. These are specially present on the tentacles arranged in clusters or batteries. They are oval shaped cells with basal nucleus and possess a sac-like organoid – the nematocyst. It is like a capsule enclosing a coiled tube or thread.

e. Sensory cells

They occur scattered throughout the epidermis among epithelio-muscle cells and are specially found on tentacles, hypostome and pedal disc.

f. Nerve cells

Throughout the evolutionary trend, true nerve cells or ganglion cell occurs for first time in coelenterates. They are derived from interstitial cells of epidermis. They occur at the base of epithelio-muscle cells just above their muscle processes..

g. Germ cells

During summer, interstitial cells of some regions of body, divide repeatedly and proliferate like reproductive cells forming gonads, which later differentiate into testes and ovaries.

2. GASTRODERMIS

The coelenterons is internally lined by gastrodermis. It is formed chiefly of large, columnar cells. This layer is mainly nutritive in function. The gastrodermis is composed of following types of cells.

a. Endothelio-muscle or nutritive cells

These are most abundant cells forming bulk of gastrodermis. These resemble the epithelio-muscle cells of epidermis except that their basal contractile processes are single, more delicate and oriented at right angles to the processes of the epithelio-muscle cells. There contraction reduces the diameter of the body and tentacles, which becomes narrower and longer.

The free end may bear two whip-like flagella and blunt pseudopodia like projections. The movement of flagella keeps the food in the coelenterons in motion. The pseudopodia like projections can engulf food particles.

b. Endothelial-gland cells

They are smaller than nutritive cells and occurs scattered among nutritive cells. They lack muscle tails at basal end, but may bear one or two flagella. The gland cells are absent in the tentacles. They are of two types.

· Enzymatic gland cells: secrete digestive enzymes into gastrovascular cavity for extracellular digestion.

· Mucous gland cells: secrete a slimy fluid serving as lubricants.

c. Interstitial cells

A few interstitial cells occur between the bases of nutritive cells. These are totipotent cells and thus can transform into all other type of cells.

d. Sensory cells

Sensory cells are found in between nutritive cells. They are supposed to be stimulated on entry of prey into gastrovascular cavity.

e. Nerve cells

These are similar to those present in epidermis, except that they are present here in fewer no. than epidermis.

3. MESOGLEA

It is non-cellular thin layer secreted by both epidermis and endodermis and separates the epidermis and gastrodermis. It serves for attachment of cellular layers.

 

TO BE CONTD…..

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[1] Eumetazoa is a clade which includes all major animal phyla 

Technorati Tags: CNIDARIA,RADIATA,CTENOPHORA

except sponges.

[2] Cnidos, thread; Gk

Giardiasis: General Introduction

1.      INTRODUCTION

Giardiasis (popularly known as beaver fever)[i] is a zoonoticparasitic disease caused by the flagellate protozoan Giardia lamblia(also sometimes calledGiardia intestinalis and Giardia duodenalis).[ii] The Giardia inhabits the small intestine of its host(variety of domestic and wild animals species, as well as humans). It is attached to the surface of columnar epithelial cells of intestine. It may penetrate down into the secretory tubules of mucosa and may also be found sometimes in the gall bladder and biliary drainage. It is one of the most common pathogenic parasitic infections in humans worldwide; in 2013, there were about 280 million people worldwide with symptomatic giardiasis.

2.      HISTORY

The trophozoite form of Giardia was first observed in 1681 by Antonie van Leeuwenhoek in his own diarrhea stools. The genus was chosen to honour Professor Alfred Mathieu Giard of Paris. In 1998, a highly publicised Giardia and Cryptosporidium outbreak was reported in Sydney, Australia, but it was found to be due to mismeasurement of the concentrations of microbes in the water supply. A 2004 outbreak in Bergen (Norway) hastened work on adding UV treatment to the water facilities[iii]. In 2008, Giardia was identified as one of the causes of the dysentery[1] afflicting Crusaders in Palestine in the 12th and 13th centuries.

3.      CAUSATIVE AGENT

Giardia lamblia exists in two forms

a.       The trophozoite: it is a pear-shaped and motile organism. It is 10-20 micrometer long and 7-10 micrometer in diameter. The body is tear drop shaped with convex dorsal. The trophozoite possess 8 flagella and two nuclei. The anterior portion of ventral surface of the organism is modified to form a sucking disc which serves for attachment of organism.

b.      The cyst: the cyst is oval and measures 8-14 micrometer in length and 7-10 micrometer in width. It has four nuclei, flagella and blepharoplast. The cyst is smooth and colourless. It represents the resting stage of organism. Its rigid outer wall protects the organisms from unfavourable conditions. It has been observed that the cyst hatches only after exposure to acidic conditions of stomach.

4.      SOURCE OF INFECTION AND TRANSMISSION

Giardia lamblia is transmitted through fecal-oral route with the ingestion of cysts. Primary route are personal contact and contaminated water and food. The cyst is transmitted from individual to individual by water and food contaminated by faecal matter. After the cyst is ingested, its cytoplasm differentiates into two motile, fully formed trophozoites. These then come out of the cyst wall and attach themselves to the epithelial surface of the small intestine. Subsequently they multiply by binary fission.

Within days after infection, millions of trophozoites develop. These may completely cover a party of epithelial surface of small intestine. Giardia lamblia is not considered as tissue parasite, but its ability to adhere closely to the columnar cells at the level of microvilli results in antigenic stimulations of the host. The cysts are formed in the small intestine.

5.      SYMPTOMS

Symptoms might include watery diarrhoea alternating with greasy stools. Fatigue, cramps and belching gas also may occur. Some people have no symptoms.

People may experience:

Pain areas: in the abdomen

Gastrointestinal: diarrhoea, belching, bloating, indigestion, nausea, passing excessive amounts of gas, vomiting, or flatulence

Whole body: fatigue, loss of appetite, malaise, or malnutrition

Also common: cramping, failure to thrive, malodorous stool, or weight loss

6.      PREVENTION/PROPHYLAXIS

Proper maintenance of water supply systems. Washing of hands and avoiding potentially contaminated food and untreated water.

7.      TREATMENT

Giardia lamblia is difficult to diagnose, which often leads to delay in treatment or misdiagnosis. Several tests should conducted over one-week period for proper detection. The Giardia lamblia infection can be diagnosed by examination of stool for motile trophozoites or for distincitive oval cysts of Giardia lamblia. Modern tests like ELISA are capable of detecting even minor infections of Giardia lamblia.

Treatment is not always necessary, since the infection usually resolves on its own. However if infection is acute or symptoms persists then nitroimidazole medication is used such as metronidazole, tinidazole, secnidazole or ornidazole.

During pregnancy, paromomycin is preferred treatment drug because of its poor intestinal absorption and thus less exposure to the foetus.

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[1] Dysentery, is a type of gastroenteritis, that results in diarrheawith blood

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[i]  "Giardiasis (beaver fever)". New York State Department of Health. October 2011. Retrieved21 June 2015.

[ii] Esch KJ, Petersen CA (January 2013). "Transmission and epidemiology of zoonotic protozoal diseases of companion animals". Clin Microbiol Rev.26 (1): 58–85.

[iii] Nygård K, Schimmer B, Søbstad Ø, Walde A, Tveit I, Langeland N, Hausken T, Aavitsland P (2006). "A large community outbreak of waterborne giardiasis-delayed detection in a non-endemic urban area". BMC Public Health. 6 (1): 141. doi:10.1186/1471-2458-6-141. PMC 1524744. PMID 16725025.

AMOEBIASIS: GENERAL INTRODUCTION

1.     INTRODUCTION

Amoebiasis is also known as entamoebiasis. It is an infection caused by any of the amoeba of the Entamoeba group. But the symptoms are most common on infection of Entamoeba histolytica. Amoebiasis can be present with no, mild or severe symptom. Symptoms may include abdominal pain, mild diarrhoea, bloody diarrhoea or severe colitis[1] with tissue death and perforations.

2.     HISTORY

The most dramatic incident was Chicago World’s Fair Outbreak in 1933 in USA. It was caused by contaminated drinking water; defective plumbing. There were 100 cases (with 58 deaths).

In 1998 there was an outbreak of amoebiasis in the republic of Georgia; 188 cases were reported, including 71 cases of intestinal amoebiasis and 106 probable causes of liver amoebiasis.

3.     CAUSATIVE AGENT

In humans for species of Genus Entamoeba have been reported to cause amoebiasis – E. gingivalis, E. coli, E. hartmanni, E. histolytica.

E. histolytica has world wide distribution. It parasitizes various primates and rodents. It inhabits the lumen and mucosa of large intestine, predominantly colon. It is capable of invading virtually any tissue and organ of the body. The most predominantly infected organ other than colon is liver. The cystic stage is formed in the lumen of gut and occurs in the stool of chronic dysenteric patients and carriers.

4.     SOURCE OF INFECTION AND TRANSMISSION

It is usually transmitted by the fecal-oral route, but it can also be transmitted indirectly through contact with dirty h ands or objects. Infection is spread through ingestion of the cyst form of the parasite[2].  Any non-encysted amoeba, or trophozoites[3] , die quickly after leaving the body but may also be present in stool – these are rarely the source of new infection. Members of both sexes of human are infected by this parasite. There is, however, a higher prevalence of amoebiasis in adult males in the agricultural occupation who have increased risk of exposure. 

5.     SYMPTOMS

Most infected people (about 90%) are asymptomatic, but this disease has the potential to make sufferer dangerously ill. It is estimated that about 40,000 to 100,000 people die annually worldwide due to amoebiasis[i]. Infection can sometimes last for years. Symptoms can develop after days or few weeks of infection. But usually it is about two to four weeks. Symptoms can range from mild diarrhoea to severe dysentery with blood and mucus. The blood comes from lesions formed by the amoeba invading the lining of large intestine. In about 10% infection the amoeba enters the bloodstream and may travel to other organs in the body. Most commonly liver is infected[ii]. In asymptomatic infection the amoeba lives by eating and digesting bacteria and food particles in the gut[4]. It does not usually come in contact with the intestine. Disease occurs when amoeba comes in contact with the intestinal lining. Amoeba secrets the same enzyme and destroys the mucosa and ingests the destroyed cells. Theoretically the ingestion of one viable cyst can cause amoebiasis.

6.     PREVENTION/PROPHYLAXIS

Wash hands thoroughly with soap and hot running water for at least 10 seconds after before handling food.

Clean bathrooms and toilets often, pay particular attention to toiled seats and taps.

Avoid sharing towels or face washers.

Avoid raw vegetables when in endemic areas, as they may have be fertilized using human faeces.

Boil water or treat with iodine tablets.

Avoid eating street foods, especially in public areas where others are sharing sauces in one container.

7.     TREATMENT

E. histolytica infection occurs in both the intestine and tissues of intestine or liver. So two different classes of drugs are needed. One for each location. Thus there are two major components of treatment.

* Elimination of tissue invading organisms

* Elimination of organisms from the lumen of intestine

The drugs commonly used are:

Iodoquinol

Metronidazol

Emetine

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[1] Inflammation of colon

[2] A semi dormant and hardy structure found in faeces.

[3] a growing stage in the life cycle of some sporozoan parasites, when they are absorbing nutrients from the host

[4] the stomach or belly.

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[i] Atlas of human infection diseases, first edition. Heiman F. L. Wertheim, Peter Horby and John P. Woodall., 2012, Black well publishing ltd.

[ii] Nespola e tal., 2015, First case of amebic liver abscess 22 years after first occurrence. Parasite 22: 20

TYPHOID

1.      HISTORY

In 430 BC, a plague, which some believed to have been typhoid, killed one-third of the population of Athens, including the leader Pericles. Some historians believe that English colony of Jamestown Virginia, died out due to typhoid. Typhoid fever killed more than 6000 settlers in new from 1607 to 1624 [43]. During the Spanish-American war, American troops were exposed to typhoid fever due to inadequate sanitation system. Consequently more soldiers died of typhoid than the war wounds.

            The most notorious incident of typhoid was Mary Mallon (a cook in New York), also known as typhoid marry. She was the first carrier of typhoid in USA in 1907. She was found to be closely associated with 53 typhoid cases and 3 deaths [47]. The public health authorities asked Mary to quit her job or have her gall bladder removed, as she had chronic infection that kept her active as a typhoid disease carrier. Mary quit her job but returned late under a false name. But she was detained and quarantined after another typhoid outbreak. She died of pneumonia after 26 years of quarantine[i].

2.      CAUSATIVE AGENT

It is caused by Salmonella typhi. However, the organisms like Salmonella paratyphi and Salmonella schottmilleri may also cause this disease. The Salmonella vary in length. Most of these are motile and have peritrichous flagella. They grow readily on simple media.

3.      SOURCE OF INFECTION AND TRANSMISSION

The bacterial infection takes place through food and water contaminated by human faeces. The infection my occur through milk and other dairy products. The infectious dose seems to be quite high and may be more than 10⁵ organisms. In areas with very poor sanitation, the bacteria may get transmitted through house flies.

4.      SYMPTOMS

The salmonella reach the small intestine and from there they penetrate the epithelial lining. Then the bacteria are phagocytozed by the macrophages, within which they actively multiply. The macrophages transmit the salmonellae throughout the body. These even occur during first week of infection which is accompanied by fever, aches and pains.

Extended bacteremia[ii] occurs in the second week. Generally the gall bladder becomes infected. From the gall bladder the bacteria may shed into the intestinal lumen. During this time, ulcerative lesions (rose spots) appear on the lower chest and abdomen in some patients.

In untreated cases, the patients is exhausted by the third week.

After people recover from clinical disease, the S. Typhi may continue to multiply in the gall bladder, who may become chronic carrier and serve as source of future typhoid outbreaks.

Upto 10% of patients may die of this disease.

5.      PREVENTION

a.       Proper sewage treatment

b.      Pasteurization of milk

c.       Vaccines: although killed vaccines have been used for many years, they are of limited value. The vaccine reduces the chances of getting typhoid disease to 30-70 %.

6.      TREATMENT

Antibiotics like ampicillin and chloramphenicol are used for the treatment of typhoid fever. Treatment must be continued for several weeks to ensure killing of bacteria that becomes sequestered[iii] in the body.

Trimethoperim, sulfamethoxazole and mumoxillin are excellent alternatives to ampicillin.

7.        

          REFERENCES/FURTHER STUDIES

1.        Sobti, R. C., Medical Zoology

2.        Byrne, Joseph Patrick (2008), Encyclopedia of pestilence, pandemics and plagues: ISBN 0-313-34102-8

3.        Nova: the most dangerous women in America

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[i] A state or place of isolation in which people or animal exposed to infectious diseases is placed.

[ii] the presence of bacteria in the blood

[iii]  Isolated and hidden away.