Origin of Viruses, Viral Diseases and Monkey Pox

Origin of Viruses, Viral Diseases and Monkey Pox 

by: 

ju-boo lim

I have been reading a lot of news about monkeypox or mpox over the last few weeks with people writing all kinds of stories about it to frighten others in the social media.

Since I have studied microbiology, virology, medicine, and on the evolution of life, I thought I should come in to share whatever I know on these subjects. I shall later write separate articles on bacteria, microfungi and parasites, some of them can cause infectious diseases.

But let me begin with viruses first before going into the current outbreak of monkeypox or mpox.

I shall introduce here a little bit about viruses, their origin, their classifications, the names of some of them and why some of them are pathogenic, and some are not. Let me give readers some examples of viruses that are pathogenic and the diseases they cause, and if they are curable.

Viruses are fascinating entities in my eyes through the lens of evolution. They are often viewed as a bridge between the living and non-living. Let’s have an overview covering their origin, classification, pathogenicity, and examples of pathogenic viruses and diseases.

Origin of Viruses

The origin of viruses is still debated, but there are three main hypotheses:

First is the regressive hypothesis (Degeneracy Hypothesis) where it is believed viruses might have evolved from more complex organisms (such as small cells) that lost cellular functions over time, retaining only the genetic machinery necessary to reproduce within a host.

Second is the cellular origin hypothesis (escape hypothesis) where scientists believe viruses may have originated from genetic material that "escaped" from cells, like plasmids or transposons, becoming independent agents capable of infecting other cells.

Evolutionists also came out with their third coevolution hypothesis where viruses and cellular life might have evolved together from a common prebiotic pool, with viruses predating or evolving alongside early forms of life.

Classification of viruses are primarily based on their genetic material. By this, I mean viruses can have DNA or RNA genomes, which may be single-stranded (ss) or double-stranded (ds). Here are two examples:

1.      DNA viruses such as the adenoviruses

2.      RNA viruses such as the coronaviruses

Shape and structure of viruses are, helical, for example tobacco mosaic virus. Then comes the icosahedral viruses such as herpesviruses. Then complex ones, which are the bacteriophages

Viruses may have or may not have an envelope presence. The enveloped viruses have a lipid layer, for example the influenza virus, whereas non-enveloped viruses lack a lipid envelope, example the norovirus.

 In term of replication strategy, viruses are classified based on their replication mechanisms according to the Baltimore Classification, which divides viruses into seven groups:

Group I: Double-stranded DNA viruses (e.g., Herpesviruses)

Group II: Single-stranded DNA viruses (e.g., Parvoviruses)

Group III: Double-stranded RNA viruses (e.g., Rotaviruses)

Group IV: Positive-sense single-stranded RNA viruses (e.g., Poliovirus)

Group V: Negative-sense single-stranded RNA viruses (e.g., Influenza)

Group VI: RNA viruses with reverse transcriptase (e.g., HIV)

Group VII: DNA viruses with reverse transcriptase (e.g., Hepatitis B virus)

Pathogenic vs. Non-Pathogenic Viruses

Most viruses are not pathogenic to humans, but some can be. Pathogenic viruses cause disease by disrupting the normal cellular function of the host, often leading to tissue damage or triggering excessive immune responses.

Non-pathogenic viruses are some viruses that may live in harmony with their hosts without causing harm. For example, bacteriophages are viruses that infect bacteria, often without directly affecting humans.

There are also pathogenic viruses.  These are harmful to humans because they interfere with cellular processes or cause excessive immune responses. Factors like how the virus enters the cell, its replication strategy, and the host's immune response determine its pathogenicity

Here are just some examples of pathogenic viruses, the diseases they cause, and whether they are curable:

 1. Dengue, especially in a tropical country like Malaysia is among the top in the list. In fact, about half of the world's population is now at risk of dengue with an estimated 100–400 million infections occurring each year. Dengue is found in tropical and sub-tropical climates worldwide, mostly in urban and semi-urban areas.

The causative agent is the dengue virus (DENV), which has four distinct serotypes (DENV-1, DENV-2, DENV-3, and DENV-4). Infection with one serotype provides lifelong immunity to that serotype but not to the others. The virus is primarily transmitted to humans through the bites of infected Aedes mosquitoes, mainly Aedes aegypti and Aedes albopictus. These mosquitoes are most active during the daytime.

The symptoms for dengue are, in mild cases, fever, headache, pain behind the eyes, joint and muscle pain, rash, and mild bleeding (e.g., gums or nosebleeds). In severe cases (Dengue Hemorrhagic Fever/Dengue Shock Syndrome). There may be severe abdominal pain, persistent vomiting, rapid breathing, bleeding gums, fatigue, and restlessness. This can lead to shock, organ damage, or death if untreated.

There is no specific antiviral treatment for dengue. Supportive care involves fluid management, pain relievers (like acetaminophen), and monitoring for signs of severe dengue. Severe dengue requires hospitalization for proper medical care, which can significantly reduce fatality rates. The prevention for dengue is vector (Ades mosquitoes) control, which is crucial, including reducing mosquito breeding sites (stagnant water) and using mosquito repellents or nets. The Dengvaxia vaccine is available but only recommended for individuals who have had previous dengue infections, as vaccination can lead to more severe illness in those who have not been previously exposed.

2.  Influenza virus (Flu)

Classification: Group V, RNA virus, enveloped

The disease they cause is seasonal flu. The symptoms they cause are fever, cough, sore throat, body aches. They are curable using antiviral drugs like oseltamivir that can reduce severity, and vaccines prevent infection.

3. Human Immunodeficiency Virus (HIV)

Classification: Group VI, retrovirus (RNA)

The disease they cause is acquired immunodeficiency syndrome (AIDS). Here the symptoms are immune system failure, opportunistic infections. AIDS is not curable, but manageable with antiretroviral therapy (ART), allowing patients to live long, healthy lives. 

4. Hepatitis B Virus (HBV)

Classification: Group VII, DNA virus

The disease they cause is hepatitis B (liver inflammation). The symptoms presented are jaundice, fatigue, and liver damage. There is no complete cure for hepatitis B, but antiviral drugs can control the infection, and vaccines prevent it.

5. SARS-CoV-2 (Coronavirus)

Classification: Group IV, RNA virus, enveloped.

 The disease it causes is Covid-19. Here the symptoms for Covid-19 are fever, cough, respiratory issues, loss of taste/smell. There is no specific cure for Covid-19 but vaccines and treatments like antivirals (remdesivir) can reduce the severity.

6. Herpes Simplex Virus (HSV)

Classification: Group I, DNA virus, enveloped

The disease they cause is oral/genital herpes. Here the symptoms are painful blisters. There is no cure for herpes simplex, but antiviral drugs (acyclovir) can control outbreaks.

7. Rabies Virus

Classification: Group V, RNA virus

The disease caused is rabies. The symptoms for rabies are fever, hydrophobia, and encephalitis. There is no cure for rabies. It is fatal once symptoms appear, but vaccines can prevent it if administered after exposure.

8. Human Papillomavirus (HPV)

Classification: Group I, DNA virus.

Here for human papillomavirus the disease is, warts, cervical cancer. The symptoms presented are genital warts and cancer risk. There is no cure for the infection itself, but vaccines prevent cancer-causing strains.

Having very briefly said the above, let us now go into those non-pathogenic viruses. Examples of viruses that do not typically cause diseases in humans include the bacteriophages that infect bacteria and may play beneficial roles in ecosystems and even human health by regulating bacterial populations.

There are also certain plant viruses like the cucumber mosaic virus, which do not affect humans.

But why are some viruses pathogenic? Scientists tell us there are 3 reasons for this. Firstly, we call this as host tropism. Some viruses have evolved to target specific host cells, leading to infection and damage.

Second reason is viral replication. The rapid reproduction of viruses can overwhelm the host's immune system, leading to disease.

The third reason is immune response. In some cases, the body's response to the virus (inflammation, fever) can contribute to the symptoms and pathology of the disease.

Viruses vary greatly in their complexity and effects. While many are harmless or even beneficial, pathogenic viruses can cause serious diseases, some of which are curable, while others are only manageable. The classification of viruses helps in understanding their behaviours and impacts on hosts.

I have only given a very brief introduction on viruses, and only some of the diseases they cause. Let's now go and explore mpox (monkeypox) which is what I actually wanted to write here.  

Monkeypox (mpox) is a viral zoonosis, meaning it can be transmitted from animals to humans. It is caused by the monkeypox virus, which belongs to the Orthopoxvirus genus, the same family as the variola virus (which causes smallpox). Mpox is less severe compared to smallpox, but outbreaks have become more common, particularly in recent years.

Transmission and Infectivity

Mpox spreads through close contact with an infected person or animal, or through contaminated materials (e.g., bedding, clothing). Human-to-human transmission occurs primarily through 4 routes below:

There is also direct contact through skin lesions, bodily fluids, or respiratory droplets.

Fomite infection is through contaminated objects like towels or bedding.

Respiratory droplets can also be another source of infection. This is through prolonged face-to-face contact (though less efficient than smallpox).

There is also through animals called zoonotic transmission.  Contact with animals like rodents or monkeys in endemic areas.

However, mpox  is less contagious than smallpox and typically spreads through direct contact, not casual interactions. The virus can enter the body through broken skin, respiratory tract, or mucous membranes (eyes, nose, mouth).

But what are the symptoms of Mpox? Mpox symptoms are similar to, but milder than, smallpox symptoms. The incubation period ranges from 5 to 21 days. Here are some mpox symptoms.

Prodrome stage (early symptoms) are fever, headache, muscle aches (myalgia), fatigue and swollen lymph nodes (lymphadenopathy), which distinguishes mpox from smallpox

There will be rash and lesions within 1-3 days of the fever, a rash develops, often starting on the face and spreading to other parts of the body. The rash progresses through stages such as, macules (flat lesions), papules (raised lesions), vesicles (fluid-filled blisters), pustules (filled with pus), and scabs that eventually fall off. The lesions can be painful and may leave scars.

As far as infectivity and severity are concerned, mpox is not highly contagious compared to airborne viruses like COVID-19. It spreads through close contact and is considered moderately infectious. Household members or caregivers in close contact with infected individuals are at higher risk.

Furthermore, mpox is generally not highly lethal. The case fatality rate (CFR) varies depending on the strain. The West African clade has lower mortality rate (around 1%-3%) compared to the Congo Basin clade where the mortality rate is higher (up to 10%)

Most people asked me if mpox is curable? As far as I know, while there is no specific cure for mpox, the disease is usually self-limiting and resolves on its own within 2 to 4 weeks. However, some treatments and preventive measures are available.

Here are some of them to include antiviral treatments. Antiviral drugs like tecovirimat (TPOXX), initially developed for smallpox, have shown promise in treating severe cases of mpox.

There are of course symptomatic management and supportive care, such as pain relief, hydration, and treatment of secondary infections. These are essential. Vaccines such as smallpox vaccine (particularly the newer MVA-BN or JYNNEOS) have been shown to be effective in preventing mpox infection. Post-exposure vaccination (within 4 days of exposure) can reduce severity.

But prevention and control are always better than cure. The prevention of mpox involves avoiding contact with animals in endemic areas. Proper hygiene and protective measures when caring for infected individuals. The use of smallpox vaccines in outbreak settings to control transmission.

Today, mpox has spread outside its traditional endemic regions in Central and West Africa, causing concern. In 2022, and currently in 2024, multiple outbreaks occurred in non-endemic countries, raising awareness of the need for vigilance and control measures.

Let me summarize mpox

1.      Transmission is close contact with infected individuals or animals.

2.      Symptoms are fever, swollen lymph nodes, rash, and painful skin lesions.

3.      Severity: Not highly lethal, with case fatality rates between 1-10%, depending on the strain.

In terms of curability, there is no specific cure, but the disease is usually self-limiting. Antivirals and vaccines can help manage or prevent severe cases.