The virus is a set of gene. Typical viruses multiplication cycle is divided into six phases: 1. Absorption to the human cell, which is referred to as host cell; 2. Penetration or entry to the human cell; 3. Uncoating to release the genomes; 4. Viruses or virion components production; 5. Assembly; and 6. Released from the human cell.

This series of events, sometimes with a slightly variation. The viral infection of the cells may be productive (lytic response) or nonproductive (no response).

The outcome of an infection depends on the particular virus-host combination. This means, it depends on the relationship, the viruses have with our body cells.

The viruses need to undergo only one stage between the productive and nonproductive. This kind of viruses are called virulent virus or angry virus.

Those viruses that can undergoes both productive and nonproductive, are referred to as temperate viruses. Some of the temperate viruses can be reactivated or induced to leave a latent state (sleeping state), and they enter to a productive state or virulent stage.

The remainder of this article is concerned with the details of the steps of the virulence state. The next article will jump to routes of infectious diseases transmission.


The first steps for viruses to multiply in any viral infections is the attachment known as adsorption of the infecting particles to the surfaces of the cell.

The prerequisites for this interaction is a collision between the virus and the human cell. Only a small fraction of the collisions between a virus and its host cell lead to a successful infections.

The viruses need to have attachment proteins known as receptors. These receptors are more similar to human fingers and hands for grabbing. This is because the virus uses these receptors to attach on human cell.

You still remember enveloped and naked viruses

All enveloped viruses that are causing diseases in humans, contain the attachment proteins which are receptors. Some of the viral receptors are also found on human red blood cells of certain species. Such receptors are responsible for hemagglutination.

The particular kind of a virus is capable of inflecting only a limited spectrum of of cell types called its host range. This kind of cell host range is very important in determining the pathology of the infection ( the steps in which the virus under go in order to cause an infection).

The entry and uncoating

Once the virus has attached on the human cell, penetration which is the entry into the inside of the cell, the virus is no hidden from the immune system.

The uncoating stage happens simultaneously with the entry or may happened in series of steps. Here we will discuss two type of viral entry and uncoating.

1. The enveloped human viruses

Two basic mechanisms for the entry of an enveloped human viruses into the cell. Both of the mechanisms involve fusion of the viral envelope with a cellular membrane, and the release of the free nucleic capsid into the cytoplasm.

The envelopes of these viruses contain protein spikes (hands finger like) that promote fusion of viral envelopes with the plasma membrane of the cell, releasing e nucleic capsid directly into the cytoplasm.

2. The naked capsid human viruses

Viruses may undergoes dissolution, getting dissolved by binding on the human cell membrane or skin. The nuclei acid is directly deposited to the targeted sites. Now let get to refresh our understand, that viruses are separated into RNA viruses and DNA viruses.

So, most RNA viruses replicate or multiply on the cytoplasm, with the exception of influenza virus (flue) and the retrovirus (HIV). Influenza virus, retrovirus, and other DNA viruses except poxvirus replicate or multiply in the nucleus of the human cell.

Genomic structures replication (multiplying)

The human cells obviously contain the enzymes and tons of protein accessories required for the replication of the DNA.

The smallest DNA viruses like parvovirus, they depends on the infected human cell so that if that infected cell divide thus the virus divide too.

This also occurs with some of RNA viruses, the good example of this kind is HIV. That is the reason why it is not easy to clear or eliminate it. Topic on HIV will be discussed in depth later.

Assembly of viral particles

Remember that we said one human cell is infected by a virus and human cells are naturally multiplying by division. So now the virus is inside the cell that is prone to multiply by division.

The genomes of the viruses and that of the human cell are now one (integrated), the first thing to divide is the cytoplasm, which is a fluid inside the cell. Followed by the nucleus inside the cell. Once all of this is done.

The overall cell divides with the the virus in it. So now more of the infected human cells are thus produced.

Assembly stage the place when each of the new cell’s proteins are coming together to make new infected cells. Note: it is not simple as in this generalization to describe this phenomenon.

Release of new viruses

Once the viral particles have been assembly, now new baby viruses causing infection and diseases are ready to be released from the mother host cell.

This all happens by escape from the infected cell through coding for enzymes that lysis the cell. These enzymes weaken the cell wall by cleaving specific bonds in peptidoglycan layer. The weakened cells burst as a result of the osmotic pressure.

Human viruses are furthermore released as follows:

1. Cell death

The mother infected cell or host infected cell dies after giving birth to the new infected cells or viruses.

Presumably because the viral genetic program is dominant and precludes the continuation of normal cell functions required for survival.

The naked capsid human viruses lack specific mechanisms for lysing the infected cell and apparently are released into the extracellular milieus simply as a consequence of cell death.

2. Budding

With the exception of other viruses, all enveloped human viruses acquire their membrane by budding either through the plasma membranes. In the case of herpes viruses, ultimately escape from the cell after budding through nuclear membrane is unclear (more research is required).

For viruses that bud, it is important to note that the plasma membranes of the infected cells contains virus-specific glycoproteins that represent foreign antigens. This means your infected cells become the target of your own immune system.


Protection from viral infection is to be accomplished at the level of antibodies binding to the viruses, it must occur before adsorption and prevent viruses from attaching to and penetrating our cells.

Most enveloped viruses acquire an envelope during released by budding. Retroviruses except HIV reproduce without cell death.

Genomic structures: viruses causing infection and diseases

From previous page posted, we introduced the meaning of viruses, their sizes and design . Now on the next topic we will be looking at genome structure, of which is the one that make viruses very difficult to respond very well on treatment or get cleared from our system.

Viral genomics structure

Structural diversity among the viruses is the most obvious, when the make-up of the viral genomes is considered. Genomes can be made of ribonucleic acid (RNA) or deoxyrionucleic acids (DNA) and be either double stranded or single stranded.

For viruses with single-stranded genomics, the nucleic acid can be either of the same polarity (indicated by a + or – for a different polarity) from that of the viral messenger-RNA (mRNA) produced during the viruses causing infection and diseases.

Two types of genomics structure are known, the linear and the circular. Most viruses have a single nucleic acid molecules for their genomics structures, in some cases several pieces of nucleic acid constitute the complete genome.

Viruses as such have segmented genomes. One virus class which is retrovirus (e.g.HIV) carries two identical copies of its genomics structures and is therefore diploid.

This is what is rarely and complicated about HIV. A few viral genomes such as picornaviruses, hepatitis B virus, and adenoviruses contain covalently attached protein on the ends of the polynucleotide chains.

Viral genomics subunit structure of Capsids

The capsid of all viruses are composed of many copies of one or at most several kinds of protein subunits.This fact follows from:

1. All viruses code for their own capsid proteins, and it turns out that even if the entire coding capacity of the genomics structures were to be used to specify a single giant capsid protein, the protein would not be large enough to enclose the nucleic acid genomes.

This lead to multiple protein copies required. The simplest spherical virus contains 60 identical protein subunits.

2. Viruses are such highly symmetric structures that it is not uncommon to visualize naked capsid viruses in the electron microscope as a crystalline arrays.

The presence of many identical protein subunit in viral capsids or the existence of many identical spikes in the membrane of enveloped viruses has important implications for adsorption, hemagglutination, and recognition of viruses by neutralizing antibodies

Viruses genomics cylindrical shape

A cylindrical shape is the simplest structure for a capsid. The first virus to be crystallized and studied was a plant virus, which is tobacco mosaic virus (TMV).

The capsid of a TMV is shaped like a rod or, a cylinder, with the RNA genomics structure wound in a helix inside it. The capsid is composed of many copies of a single kind of protein subunit arranged in a closed packed helix, which places every subunit in the same microenvironment.

Because of the helical arrangement of the subunits, viruses that have this type of design are often said to have helical symmetry. Thus, the nucleocapsids of influenza, measles, mumps, rabies, and poxviruses are probably constructed with a helical arrangement of protein subunit in close association with the nucleic acid genomics structures.

The viruses genomics spherical shape

Construction of a spherical shaped virus similarly involves the packing together of many identical subunits, but in case the subunits are placed on the surface of a geometric solid called an icosahedron.

Because the icosahedron belong to the symmetric structural group, the spherically shaped viruses are said to have cubic symmetry (note that the term ‘cubic’, used in these contexts, has nothing to do with the more familiar shape called cube).

When viewed in the electron microscope, many naked capsid viruses and some nucleocapsids appear as spherical particles with a surface topology that makes it appear that they are constructed of identical ball-shped subunits.

These visible structures are referred to as morphological subunits. Morphological subunits are composed of either five or six individual protein molecules, each one referred to as a structural subunit, or promoter.

In the simplest case of a virus with a cubic symmetry, I’ve promoters are placed on each 12 vertices of the icosahedron forming a pentamer. While, the capsid is composed of a total of 60 promoters.

This arrangement places every promoter in the same microenvironment as every other promoter in the case of helical symmetry.To accommodate the larger cavity required by viruses with large genomics structures, the capsid’s contain many more promoters.

These viruses are based on a variation of the basic icosahedron in which the construction involves a mixture of pentamers and hexamers instead of only pentamers. A detailed description of is higher level of virus structure is beyond the scope of this text.

Special surface genomics structures

Many viruses have structures that protrude from the surface of the virion. These genomics structures are important for the two earliest steps of infection, adsorption, and penetration.

The examples of the surface structure include the spikes of adenovirus and the glycoprotein spikes found in the membrane of enveloped viruses.

Even viruses without obvious surface extensions probably contain short projections, which is more of the obvious spikes, are involved in the specific binding of the virus to the cell surface.

Classification of viruses causing infection and diseases in human

Table 1 Represent classification of RNA and DNA human viruses causing diseases

Table 1.

Table 1 present a classification scheme for human viruses that is based solely on their genomics structure. The viruses are arranged in order of increasing genomics structural size.

It is important to bear in mind that phylogenetic relationships cannot be inferred from this taxonomic scheme. The tables should not be memorized, but instead used as a reference guide to viruses structures.


The terminal protein molecules as well as other special genomics structures found in other viruses play key roles in the replication process.

In general, viruses with similar genomics structures exhibit similar replication strategies.

See the next article, where we will be discussing viruses multiplication, viral infection of cells may be productive or none productive, animal viruses may cause oncogenic transformation.

Microorganism the cause of infection leading to a disease

People get sick and die because of microorganisms. What are microorganisms? Microorganisms are normally known as germs in simple english.Microorganisms can not be seen by our necked eyes, we can only see them by the use of a microscopy.

When we talk of microorganisms, we simple talk about bacteria, viruses, fungi, and others .

Microorganisms can be classified as bad and good. We have good microorganisms, that are used in our food, medicine and cleaning materials. We can also find very bad microorganisms that make humans, plants and animals sick. 

Where can microorganisms be found?

Microorganisms can be found everywhere, all over human skin; inside ones mouth, and nose; sexual organs (private parts); inside the stomach and intestine; on our hands; food we eat; soil, air, and water.

Good microorganisms that are found as normal micro flora in our body, have an ability to harm us. Remember our body are made of sterile environment and none sterile environment.

So if the harmful microorganisms get access to the sterile part of our body such as blood circulatory system, that is where a person is defined as infected by microorganisms. At that stage it is not a diseases, it is just an infection.

What is an infection? An infection is defined by the present of a bacteria or any other microorganisms being a foreigner or an antigen in our body, where now antibodies which are normal known as body soldiers or defense system recognises antigens.

Human body defend itself from microorganisms

Human bodies are made of defense mechanism which is immune system. Immune system consists of antibodies and a lot of immune cascades which we are not going to talk about in this posts.

Our skin, mouth, eyes, noise, vagina and penis possesses first layer of defense mechanisms. Skin itself is our first protector/ barrier from foreign microorganisms. If the first immune barrier fails or over powered by microorganisms.

The second defense barrier which are antibodies come on board. If the antibodies fails too, that is where infection manifest leading to a disease. 

A broader discussion on immunology will cover this part of antibodies or immune system as a whole.

Microorganisms cause infections and diseases

Once the immunity fail to defend the body from these very bad microorganisms, the sickness begins. Once a person shows signsvand symptoms, it is when we use a term called disease.

A disease can be infectious or none infectious. The infectious diseases are caused by microorganisms such as viruses, very bad bacteria, very bad fungi and parasites.

Microorganisms that cause diseases are called pathogens. Pathogens have an ability to cause to cause infections that lead to diverse diseases. 

For detailed information on viruses see Genomic structures: viruses causing infection and diseases

Microorganisms can enter the body through the four sites such as respiratory tract (mouth and nose) e.g. influenza virus that causes the flu. Gastrointestinal track (mouth oral cavity) e.g. vibrio cholerae which causes cholera.

Urogenital tract e.g. Escherichia coli which causes cystitis. Sex organs (vagina and penis) e.g. Neisseria gonorrhoeae which causes gonorrhea.

Where can microorganisms reside and multiply

Microorganisms are found every where in our planet and everywhere on/in our body except in sterile environment like blood circulatory system and central nerveous system (CNS).

In none sterile environment such as vagina, penis, anus, mouth, nose and skin, microorganisms can reside and multiply.

Viruses are microorganisms that can only survive and multiply inside leaving cells

Mostly once a virus is inside a human cell, it incorporate it own DNA with that of a human cell to multiply and further infect other neighbouring cells, thus far initiate an infection that later become a disease if not diagnosed and get eliminated or treated early.

Bacterial microorganisms can survive and multiply in any environmental given. Such that, there are bacteria that survive in harsh temperatures, very hot conditions more than a thousand degrees Celsius.

Some bacteria can be found residing and multiplying in very cold environment like negative 80 degrees Celsius. This proves how stubborn are microbes, which is a reason why people, animals and plants succumb from them if not cleared.

A glance on antibiotics

Thousands of companies are manufacturing antibiotics/ antimicrobial such as antivirals, antifungal and others.

Antimicrobials are developed in order to treat, eliminate and monitor infectious microorganisms. Not forgetting that natural human immunity also play a pivotal role in eliminating and clearing microbes in our body systems.

Keeping in mind that antibiotics have side effects, those effect slightly affect human bodies negatively. Our bodies are like motor vehicles, regularly requires services.

Human body services goes along with the use of antimicrobial agents but the over used of antibiotics lead to microbial resistance to them. How microorganisms resist antibiotics, will be discussed in our next topic.

Good microorganisms go bad too

Microbiotas are not all so bad, some bacteria are good for our health but in excess are dangerous. Microorganisms called normal microflora are not that bad, they protect us from so many things.

Take an example of Mutans streptococcus which is mostly found residing in our mouth. It is responsible for keeping pH balance in our oral environment.

By keeping pH balance, our teeth are protected from an automatic demineralization (breaking down). Despite that, we still get oral conditions such as dental caries which are caused by species of Mutans streptococcus, due to our diet imbalance.

Consumption of sucrose rich nutrients lead to super activation of normal flora (Mutans streptococcus species) microorganisms to multiply excessively and uncontrollable. That way oral infection such as dental caries is manifested.

Looking at a female sex canal, it naturally possess a fungi called Candida Albicans, which is a very good microorganisms but but under unbalance pH environment, the fungal infection immerge, which is called Candidiasis.

Candidiasis cause a discharge through the vagina. Which is a very uncomfortable discharge in a woman’s private part. This fungal infection is infectious, it can be transmitted from one person to another via unprotected sexual activities. We will discuss more of sexual transmitted diseases in the next post.

Commercial uses of microorganisms

Microorganisms that are found residing in our body can be used commercially to manufacture food that we love and eat everyday, for example cheese, yogurt etc. This topic will be discussed later.


humans have both good and bad relationship with microorganisms. Good microorganisms are beneficial to human, while bad ones are harming our health. The over use of antibiotics leads to microbes being resistance.

Have it ever cross your mind? The human microorganisms diversity: the offense

Any one can get sick due to many unforeseen reasons. You can come across your own normal flora (get details on the next topic); you can come across microorganisms like infectious bacteria from the air, soil, water, and through other human beings.

We are surrounded by trillions of microorganisms that survive in diverse environment. Some of these microorganisms are good for our health and some are very bad, culprits of our death cause. On the following topics we will discuss the basics of microorganisms diversity.

This will include entry into the microbial world, roles of microorganisms in nature, microbial adaptation to diverse environment, microorganisms that plants interact with and use of microbial diversity by humans.

The entry of microbial into the world

The purpose is to show how diverse are microorganisms

Definition of microorganisms diversity, and how are interconnected with one another.Before birth, all normal infants are protected from the environment by the placental of the mother and her immune system.

Immediately, the unborn child decide to escape the womb, that is where an enormously complex microbial world that had evolved past trillions years ago enters or evade an infant.

Most of these microorganisms are free living but a few have ecological niches in the external, mucosal, and other surfaces of humans and other creatures. Often these microorganisms have a mutual benefit.

Few minority became unwelcome guests on human bodies through the expression of specialized features that give them a capacity to injures thus cause an infection. Understanding how microorganisms cause an infection that lead to a diseases is the major goal of this website.

The role of microorganisms in nature

Microorganisms are defined as  living things that are invisible to the human unaided eyes, can only be seen by the use of microorganisms.

There are responsible for the breakdown and natural recycling of organic material in the environment. Some can fix atmospheric nitrogen and synthesize nitrogen a containing inorganic and organic compounds that contribute to the nutrition of living things that lack this ability.

Some can use atmospheric carbon dioxide as a source of carbon for organic compounds. Others like oceanic algae produce oxygen through their use of atmospheric carbon dioxide for photosynthesis.

Thus , microorganisms play central roles in the nitrogen and carbon cycles and contribute to maintaining the atmospheric oxygen level.

The microbial adaptation to diverse environment

Very few areas on the surfaces of the earth do not supports microbial life.

Microorganisms have amazing range of metabolic and energy yielding ability. Many have an ability to exist under conditions that are lethal to other life forms.

For example, some bacteria can oxidize inorganic compounds such as sulphur and ammonium ions to generate energy. Some  can survive and multiply in hot springs at temperature above 75 degrees Celsius.

Many microorganisms can metabolize only fermentatively. Using substances other than oxygen as terminal electron acceptors, and can thus multiply under highly reduced conditions.

Some of these are callulolytic and can multiply rapidly in masses of decaying vegetation in the absence of oxygen. To many, oxygen is lethal.

The microorganisms that plants interact with

Some microbial species have adapted to a symbiotic relationship with higher forms of life. For example, bacteria that can fox atmospheric nitrogen colonize root systems of legumes.

When the plant dies or is plowed under, the fertility of the soil is enhanced by nitrogenous compounds originally derived from the metabolism of the bacteria. These few examples demonstrate the nature of microbial life and their essential place in our ecosystem.

The use of microbial diversity by humans

The metabolic diversity of microorganisms have led to their application to humans purposes. These uses include alcoholic fermentation in the production of wines and beers.Also the production of complex molecules such as vitamin12 and various antibiotics.

Through the use of recombinant DNA techniques, genes encoding the synthesis of substances such as human growth hormone and some immunologic mediators have been added to the genomes of bacteria, or yeasts, which then synthesize the desired products in the culture.

Because of this relatively simple and manipulable genetic structure, molecular biology studies on bacteria continue to help illuminate the complexities of cellular regulation and differentiation in higher life forms.


To study microorganisms and their role in nature is very interesting and important.

This website, however has a narrower focus since it only concerned with those microorganisms that are directly involved in the maintenance of human health and causation of infection leading to a diseases.

Within this context, we considers the four broad classes of microorganisms that interact with humans: Bacteria, Fungi, Viruses, and Protozoa.

We will then extend our knowledge to include some multicellular parasites, the helminths and fluke, that are macroscopic at some stages of their life cycles.

The bacteria ate generally smaller, simpler and probably more primitive than the fungi. Their nuclear material comprises of a single, double stranded, but very large DNA molecules withouts a structural nuclear membrane.

There are described as prokaryotic and haploid with nontrue sexual mode of reproduction. They possess autonomous self replicating smaller circular DNA molecules, termed plasmid.

An image to show a virus at it active stage of attachment to a human cell
Viruses images

The viruses, are totally different group of infectious agents.

There are strictly intracellular parasites of other living cells.Not only human cells and plants but also for bacteria.

The viruses are simple forms of replication, biological active particles that carry genetic information in either DNA or RNA molecules but never both.

Most matured viruses have protein coat over their nucleic acid and sometimes a lipid surface membrane. Which is derived from the cell that they infect.

They lack the protein synthesizing enzymes and structural apparatus necessary for their own replication. They bear essentially no resemblance to a true eukaryotes or prokaryotic cell.

Viruses replicate by using  their genetically active nucleric acids to subvert the metabolic activities of the cell that they infect to bring about the synthesis and reassembly of their component parts.

A cell infected with the single viral particle may thus yield many thousands of viral particles, which can be assembled almost simultaneously under viral nucleic acid.

See the next publication Genomic structures: viruses causing infection and diseases