Animal Diversity (Non Chordates) : Entamoeba histolytica- structure, life cycle, disease, therapy and prevention

 

Introduction

Entamoeba histolytica was first discovered by Lambl in 1859 and its pathological nature was described by a Russian Zoologist ‘Friedrick Losch’ in 1875. He discovered this protozoan in the faeces and intestinal ulcers of a dysentery patient and succeeded in transferring it to puppies.

Classification

Phylum-          Protozoa

Class-              Rhizopoda

Order-             Amoebida

Genus-            Entamoeba

Species-          histolytica  

Distribution

Entamoeba histolytica is cosmopolitan i.e., found everywhere and all most all parts of the world.

Example- Mexico, China, India, South America, Philippines etc.

Particularly it is found in tropical and subtropical areas. It is more common in backward countries, where sanitation is not proper.

Habit and Habitat

Entamoeba histolytica is an endoparasite. It is found in the intestine of man and other vertebrates. It lives in the colon of man.

Enton = within

Amoebae = change

Histos = tissue

Lysis = dissolve  

Entamoeba dissolves intestinal mucosa and feed up on the tissue debris of mucosa. It produces ulcers and secrete pus from intestinal mucosa. It enters in brain, lungs and liver in chronic patients. It produces Amoebic dysentery or Amoebiasis in man.

Infants under a year old are rarely infected with it, while children and young adults are very susceptible to the parasite.

Entamoeba is monogenetic, it found in man, pig, gorilla, dog and buffalo also.

Structure

Entamoeba histolytica is found in three forms according to shape and size.

1.       Trophozoite form or Magna form

2.       Minute form or pre-cystic form

3.       Cystic form

 

1.       Magna form-

This form is large and motile. It is 20-30 micron in size. Due to large size, it is called magna form. It produces disease in man. The cytoplasm of magna form is clearly divisible into ectoplasm and endoplasm. Single pseudopodia is found, hence it is monopodial species.

In the endoplasm, food vacuoles, RBCs and bacteria are found. Contractile vacuole absent. Nucleus is large 4-6 micron in size. Below nuclear membrane chromatic granules are found. In the center, a round endosome or karyosome is present. Around endosome, a clear area is present called Halo.

Nucleoplasm is in the form of striations like spokes of cycle.

It produces disease in man or in vertebrate because it is ficolin form. It feeds on tissue of intestinal mucosa.

 

Entamoeba histolytica: Vesicular nucleus 

2.       Pre-cystic form or minute form-

This form is smaller than magna form. It lives in the cavity of large intestine. It is non-feeding form. It is 15-20 micron in size. It is produced by trophozoite form. Nucleus is familiar to the nucleus of trophozoite form.

 

3.       Cystic form-

Minute form because round and secretes a hard cyst with single nucleus is called monocystic form. Nucleus of monocystic form divides to form two nucleus. It is called binucleated cystic form. The two nucleus of binucleate cystic form divides to form four nucleus, now it is called tetranucleate or quadrinucleate cystic form. One or two glycogen masses found in cyst as reserve food materials. All three forms mononucleate, binucleate and tetranucleate cystic form are present in the cavity of large intestine. These comes out from the faeces of host (man).

 

Entamoeba histolytica: Structure of three stages of life cycle 

 

 

Reproduction and Life Cycle of Entamoeba histolytica

Entamoeba histolytica is mono-genetic because it completed its life cycle in single host (man).

Magna form is found to attached with intestinal mucosa, it feeds and grows. It divides by binary fission. Division is like mitosis. Single entamoeba produces two amoebae. It grows to form again magna form. Some of magna form becomes smaller and form minute form. It do not feed. It lies in the cavity of intestine.

Minute form becomes cystic form because it’s cyst is protecting the parasite from digestive enzymes of the host. All these forms comes out from the faeces of man. Cyst is hard, light and greenish in colour.

On faeces, flies sit and flies carries the cyst to open food and water and vegetables. In this way food and water becomes contaminated and it infect new host (man).

In the tetranucleate cystic stage is ingested through contaminated food and water. It reaches to the stomach but there are no effect of gastric juice on cyst. When cyst reaches to intestine. It ruptures by the action of intestinal juice and tetra nucleate stage comes in the lumen (cavity) of host. This stage is called metacystic stage. Metacystic stage with four nucleus divides and redivides to form eight amoebae. Each becomes large and form magna form. Magna form attaches with the intestinal mucosa. It feeds on mucosal cells or intestinal cells. Sometimes, it rupture the intestinal wall and reaches to blood streams. It may reaches to liver and brain. It produces hepatitis and secondary complications. From the intestinal mucosa blood with mucus comes out and passes through anus along with stool.

Entamoeba histolytica: Reproduction and life history 

Disease

This disease is called blood dysentery. It produces abdominal pain and host appetite. Sometimes produces anemia due to loss of blood. In this way loss of weight is common. Patients want to continued in the lavatory. Frequent intestinal pain takes place.

Diagnosis

In a simple way, the microscopical detection of trophozoites or cysts in faecal smears.

Therapy

Treatment of amoebic dysentery is not very difficult but the permanent cure is sometimes hard to achieve as relapses do occur. For temporary relief, an alkaloid Emetine is effective. A synthetic derivative of Emetine, called Dehydroemetine, is equally effective. The antimalaria drug, chloroquine is effective against amoebic abscesses in the liver but not elsewhere. Some of the latest iodine compounds, such as Vioform , Chiniofon, Diodoquin, etc., have shown more lasting results. Certain antibiotics, such as Fumagillin, Terramycin, Erythromycin and Aureomycin have proved to be effective in the eradication of the parasite.

Prevention

It is the matter of personal as well as municipal hygiene.

For personal hygiene, we need to follow following habits-

1.       Protection of food and water from contamination by houseflies, cockroaches, etc.

2.       Cutting finger nails regularly.

3.       Washing hands with soap and water after handling dirty articles, before taking meals and after using toilet.

4.       Avoiding use of unboiled water and improperly washed vegetables and raw salads.

5.       Avoiding passing out of stool on open grounds, street sides or vegetables fields.

 

The municipal hygiene is the responsibility of the town areas. They must take the following preventive measures-

1.       Proper disposal of sewage.

2.       Purification of drinking water.

3.       Chemical treatment of human faeces to be used as fertilizer.

4.       Proper sanitation of roads, streets, lanes and open drains.

 

Biodiversity: Types, Patterns, Values/Importance, Loss and Causes

 

Introduction

• Every organism of the living world, whether it is a plant, an animal or a microorganism (viruses, bacteria, unicellular eukaryote) is unique in itself. This uniqueness of individuals is the basis of the diversity that is shown by the living organisms.
• Biodiversity is the variety of the world’s organisms, including their genetic diversity and the assemblage they form.

                          Number of species of bacteria, fungi, plants and animals in the world

Taxon	Number of Species
Higher plants	2,70,000
Algae	40,000
Fungi	72,000
Bacteria (including cyanobacteria)	4,000
Viruses	1,550
Mammals	4,650
Birds	9,700
Reptiles	7,150
Fishes	26,959
Amphibians	4,780
Insects	10,25,000
Crustaceans	43,000
Molluscs	70,000
Nematodes & worms	25,000
Protozoa	40,000
Others	1,10,000

 

Types of Biodiversity

1.       Species Diversity-

• Species is the basic unit of classification and is defined as a group of similar organisms that mate and produce offspring’s with one another, thus, share a common lineage. The number of species of plants and animals that are present in a region constitutes its species diversity.
• A natural forest has a higher species diversity as compared timber plantation, which is usually a monoculture. In the natural system, there are a large number of non-wood products that people depend on such as fruit, fuelwood, fodder, fiber, gum, resin and medicines. Timber plantations do not provide such goods for local consumption.

 

2.       Genetic Diversity-

• Genetic diversity refers to the variations between individuals of a species characteristics passed down from parents to their offspring.
• This is the variability among individuals of a species, e.g., each human being differs widely from all others. This diversity is due to a large number of combinations possible in our genes that give us specific characteristics. This genetic variability is essential for a healthy breeding population of a species. If the number of breeding individuals is reduced, then in-breeding occurs. Eventually , it can lead to the extinction of the species.

3.       Ecosystem or Community Diversity-

• There are a large variety of different ecosystems on earth which have their own complement of distinctive inter linked species based on the differences in the habitat. Ecosystem diversity can be described for a specific geographical region, or a political entity such as a country, a state or a taluka.
• Distinctive ecosystems include landscapes such as forests, grasslands, deserts, mountains, etc. as well as aquatic ecosystems such as rivers, lakes, and the sea.
• There are three perspectives-

(a)    Alpha Diversity- It is the biodiversity within a particular area, community or ecosystem. It is usually expressed by the number of species (i.e., species richness) in that ecosystem. This can be measured by counting the number of taxa (distinct groups of organisms) within the ecosystem (e.g. families, genera and species).

(b)    Beta Diversity- It is a measure of biodiversity which works by comparing the species diversity between ecosystem or along environmental gradients. This involves comparing the number of taxa that are unique to each of the ecosystems. It is the rate of change in species composition across habitats or among communities. It gives a quantitative measure of diversity of communities of that experience changing environments.

(c)     Gamma Diversity- It refers to the total species richness over a large area or region. It is a measure of the overall diversity for the different ecosystems within a region. It is the product of a diversity of component ecosystems.

Patterns of Biodiversity

Latitudinal gradients − 

• The plants and animals are not distributed evenly worldwide. The diversity of living forms decreases as we go from the equator towards the poles. A huge amount of plants and animals are concentrated in the tropical region because of the following reasons.
• Tropical environment is less seasonal and almost constant and predictable as compared to temperate environment.
•  Tropics receive the major part of the solar energy, which contributes to great productivity.
• Speciation is dependent upon time. Tropical areas have remained undisturbed for millions of years unlike temperate regions, which have experienced frequent glaciations in the past.

      Species-Area relationships − Alexander von Humboldt observed that biodiversity increases with increase in explored area. This relationship can be given by,

log S = log C + Z log A

Where,

S = Species richness

A = Area

Z = Slope of the line (regression co-efficient)

C = Y-intercept

Value of Z is found to lie in the range of 0.1 to 0.2 for comparatively smaller areas such as countries while for very large areas such as entire continents, the slope of the line is much steeper with Z value lying from 0.6 to 1.2.

Values/Importance of Biodiversity

The value of the earth’s biological resources can broadly be classified into the following two categories.

(a)Direct values-

• one of the most important values of biological resources is in providing the food.
• Many other values of biological resources is in providing medicines, fuel, building materials, fiber for clothing and industrial products.
• Originally, plants were consumed directly from the wild.
• Ornamental plants are lucrative commodity today. 

(b) Indirect value-

• At the other end of spectrum, biological resources provide values which are not immediately seen but have far- reaching impact on our living conditions. Indirect benefits of biodiversity can be enumerated as follows:
• Protecting areas from soil erosion, floods and other harmful weather condition.
• Reducing the risk of local and global climate change.
• Recycling nutrients.
• Monitoring the health of the environment.
• Pollination, gene flow, etc.
• Absorbing and decomposing pollutants.
• Preserving recreational, aesthetic, socio-cultural, scientific educational, ethical and historical value of natural environments.

Loss of Biodiversity 

• The International Union for Conservation of Nature (IUCN) notes that many species are threatened with extinction. In addition, at threat of extinction are-

       1 out of 8 birds

       1 out of 4 mammals

       1 out of 4 conifers

      1 out of 3 amphibians

     6 out of 7 marine turtles

• 75% of genetic diversity of agricultural crops has been lost.
• 75% of the world’s fisheries are fully or over exploited.
• Up to 70% of the world’s known species risk extinction if the global temperatures rise by more then 3.5°C.
• 1/3^rd of reef- building corals around the world are threatened with extinction.
• Over 350 million people suffer from severe water scarcity.
• The International Union for Conservation of Nature (IUCN) maintains the Red list to assess the conservation status of species, subspecies, varieties and even selected subpopulations on a global scale.
• Extinction risks out pace any conservation successes. Amphibians are the most at risk of extinction in recent years. The reasons vary from overuse of resource by humans, climate change, fragmented habits, habitat destruction, ocean acidification and more.

Causes of Biodiversity Losses

The main cause of the loss of biodiversity can be attributed to influence of human beings on the world’s ecosystem. In fact human beings have deeply altered the environment and have modified the territory, exploiting the species directly for example by fishing and hunting, changing the biogeochemical cycles and transferring species from one area to another of the planet. The threats to biodiversity can be summarized in the following main points.

• Habitat loss and fragmentation − This is the major cause for loss of biodiversity. Habitat destruction is caused by human activities such as deforestation and increasing pollution, leading to the loss of many plants and animals.
• Over-exploitation − Humans due to their greed and increased exploitation of natural resources have contributed to the endangerment of commercially important species of plants and animals. Example − Species such as Steller’s sea cow and passenger pigeon have been extinct due to over exploitation by humans.
• Alien-species invasion − The unintentional or deliberate introduction of alien species causes the declination of the indigenous species. Example − Nile perch introduced in Lake Victoria led to the extinction of more than 200 species of cichlid fish in the lake.
• Co-extinction − When a plant or animal becomes extinct, another plant or animal which is dependent on it in an obligatory way also becomes extinct. Example − In case of plant-pollinator mutualism, the extinction of one partner will eventually lead to the extinction of other also.