Site icon Healthmatters.in

MEDICAL VIROLOGY: FROM PATHOGENESIS TO DISEASE CONTROL by Ashwini Suman Banerjee

health

covid19 book(modes of transmission)

 

MEDICAL VIROLOGY: FROM PATHOGENESIS TO DISEASE CONTROL

SERIES EDITOR:ASHWINI SUMAN BANERJEE

 

 

 

 

 CORONAVIRUS DISEASE 2019 (COVID 19)

MODE OF TRANSMISSION/SPREAD

 

 

 

 

 

 

 

CONTENTS

PART 1

 

PART 2

 

 

 

 

 

PART 1

Coronaviruses (CoVs) are enveloped single-stranded positive sense RNA viruses . Coronavirus belong to the Coronaviridae family in the Nidovirales order. Corona represents crown-like spikes on the outer surface of the virus; thus, it was named as a coronavirus. Coronaviruses are minute in size (65–125 nm in diameter) and contain a single-stranded RNA as a nucleic material, size ranging from 26 to 32kbs in length. The subgroups of coronaviruses family are alpha (α), beta (β), gamma (γ) and delta (δ) coronavirus. The severe acute respiratory syndrome coronavirus (SARS-CoV), H5N1 influenza A, H1N1 2009 and Middle East respiratory syndrome coronavirus (MERS-CoV) cause acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) which leads to pulmonary failure and result in fatality. These viruses were thought to infect only animals until the world witnessed a severe acute respiratory syndrome (SARS) outbreak caused by SARS-CoV, 2002 in Guangdong, China. Only a decade later, another pathogenic coronavirus, known as Middle East respiratory syndrome coronavirus (MERS-CoV) caused an endemic in Middle Eastern countries.

 

Recently at the end of 2019, Wuhan an emerging business hub of China experienced an outbreak of a novel coronavirus that killed more than eighteen hundred and infected over seventy thousand individuals within the first fifty days of the epidemic. This virus was reported to be a member of the β group of coronaviruses. The novel virus was named as Wuhan cronavirus or 2019 novel coronavirus (2019-nCov) by the Chinese researchers.

 

Fig: Structure of SARS-CoV-2 . SARS-CoV-2 has surface viral proteins,namely spike glycoprotein(S), which mediates interaction with cell surface receptor ACE2. The viral membrane glycoprotein (M) and envelope (E) of SARS-CoV-2 are embedded in host membrane –derived lipid bilayer encapsulating the helical nucleocapsid comprising viral RNA.

ANIMALS TO HUMAN

The Zoonotic origin of SARS-CoV-2 in Wuhan,China,can be strongly associated with the wet animal market since a large number of people who got an infection in the beginning were more or less exposed to it.

Current research confirms more than 95% genomic similarity between SARS-CoV-2 and bat coronavirus, indicating bats as the most probable host of the former. Besides bat, several other animal hosts were reported as a virus reservoir.  Some coronaviruses that infect animals can sometimes be spread to humans and then spread between people, but this is rare. This is what happened with the virus that caused the current outbreak of COVID-19. However, we do not know the exact source of this virus. Public health officials and partners are working hard to identify the source of COVID-19. The first infections were linked to a live animal market, but the virus is now spreading from person to person.

The virus that causes COVID-19 spreads mainly from person to person through respiratory droplets from coughing, sneezing, and talking. Recent studies show that people who are infected but do not have symptoms likely also play a role in the spread of COVID-19. At this time, there is no evidence that animals play a significant role in spreading the virus that causes COVID-19. Based on the limited information available to date, the risk of animals spreading COVID-19 to people is considered to be low.

Fig:  Transmission from Animals to human

 

HUMAN TO HUMAN

Data from various studies so far implicate the Zoonotic origin of SARS-CoV and SARS-CoV-2,and its fast spread among humans confirms person to person transmission. SARS being an airborne virus, transmit via the same way as cold and flu do.The virus spreads by an infected person on coughing or sneezing leaving small droplets in the air or by stool. So the person who inhales such droplets or touches the infected surfaces may also get infected. Respiratory infections can be transmitted through droplets of different sizes: when the droplet particles are >5-10 μm in diameter they are referred to as respiratory droplets, and when then are <5μm in diameter, they are referred to as droplet nuclei.1 According to current evidence, COVID-19 virus is primarily transmitted between people through respiratory droplets and contact routes.2-7 In an analysis of 75,465 COVID-19 cases in China, airborne transmission was not reported.8

Droplet transmission occurs when a person is in in close contact (within 1 m) with someone who has respiratory symptoms (e.g., coughing or sneezing) and is therefore at risk of having his/her mucosae (mouth and nose) or conjunctiva (eyes) exposed to potentially infective respiratory droplets. Transmission may also occur through fomites in the immediate environment around the infected person.8 Therefore, transmission of the COVID-19 virus can occur by direct contact with infected people and indirect contact with surfaces in the immediate environment or with objects used on the infected person (e.g., stethoscope or thermometer).

 

Airborne transmission is different from droplet transmission as it refers to the presence of microbes within droplet nuclei, which are generally considered to be particles <5μm in diameter, can remain in the air for long periods of time and be transmitted to others over distances greater than 1 m.

In the context of COVID-19, airborne transmission may be possible in specific circumstances and settings in which procedures or support treatments that generate aerosols are performed; i.e., endotracheal intubation, bronchoscopy, open suctioning, administration of nebulized treatment, manual ventilation before intubation, turning the patient to the prone position, disconnecting the patient from the ventilator, non-invasive positive-pressure ventilation, tracheostomy, and cardiopulmonary resuscitation.

There is some evidence that COVID-19 infection may lead to intestinal infection and be present in faeces. However, to date only one study has cultured the COVID-19 virus from a single stool specimen.9  There have been no reports of faecal−oral transmission of the COVID-19 virus to date.

 

 

 

 

1.3 TYPES OF TRANSMISSION – DIRECT/INDIRECT

COVID-19 spreads mainly by droplets produced as a result of coughing or sneezing of a COVID-19 infected person.

This can happen in two ways:-

 

  1. Person-to-parson contact- Infectious diseases are commonly transmitted through direct contact. Transmission occurs when an infected person touches or exchanges body fluids with someone else.This can happen before an infected person is aware of the illness. Sexually transmitted diseases(STDs) can be transmitted this way.

            Pregnant women can also transmit infectious diseases to their unborn children via the placents. Some STDs,including gonorrhoea,can be passed from mother to baby during childbirth.

 

  1. Droplet Spread- The spray of droplets during coughing and sneezing can spread an infectious disease. You can even infect another person through droplets created when you speak. Since droplets fall to the ground within a few feet,this type of transmission requires close proximity.

 

  1. Airborne transmission

 

Some infectious agents can travel long distances and remain suspended in the air for an extended period of time. You can catch a disease like measles by entering a room after someone with measles has departed.

  1. Contaminated objects

 

Some organisms can live on objects for a short time. If you touch an object, such as a doorknob, soon after an infected person, you might be exposed to infection. Transmission occurs when you touch your mouth,nose,or eyes before thoroughly washing your hands.

        Germs can also be spread through contaminated blood products and medical supplies.

 

 

  1. Food and drinking water

 

Infectious diseases can be transmitted via contaminated food and water. E.Coli is often transmitted through improperly handled produce or undercooked meat. Improperly canned foods can create an environment ripe for Clostridium botulinum, which can lead to botulism.

 

  1. Animals- to-person contact

 

Some infectious diseases can be transmitted from an animal to a person. This can happen when an infected animal bites or scratches you or when you handle animal waste. The Toxoplasma gondii parasite can be found in cat feces. Pregnant women and people with compromised immune systems should take extra care( disposable gloves and good hand hygiene) when changing cat litter, or avoid it altogether.

 

  1. Animal reservoirs

 

Animal-to-animal disease transmission can sometimes transfer to humans .Zoonosis occurs when diseases are transferred from animals to people. Zoonotic diseases include:

 

  1. Insect bites (Vector-borne disease)

 

Some Zoonotic infectious agents are transmitted by insects, especially those that suck blood. These include mosquitos, fleas and ticks. The insects become infected when they feed on infected hosts, such as birds,animals and humans. The disease is then transmitted when the insect bites a new host.

  1. Environmental reservoirs

 

Soil, water, and vegetation containing infectious organisms can also be transferred to people. Hookworm, for example, is transmitted through contaminated soil. Legionnaires’ disease is an example of a disease that can be spread by water that supplies cooling towers and evaporative condensers.

 

 

                    

 

 

                                                                                         

Expiration /Evaporation
Inhalation/spray

spray

 

 

 

 

 

 

 

 

 

 

Fig : COVID -19 infection:Transmission

 

 

 

 

 

 

 

 

 

COVID-19 affects different people in different ways. Most infected people will develop mild to moderate illness and recover without hospitalization. Seek immediate medical attention if you have serious symptoms. Always call before visiting your doctor or health facility.

People with mild symptoms who are otherwise healthy and have strong immune system should manage their symptoms at home.

On average it takes 5–6 days from when someone is infected with the virus for symptoms to show, however it can take up to 14 days.

 

Viruses work by hijacking cells in the body. They enter host cells and reproduce. They can then spread to new cells around the body.

Coronaviruses mostly affect the respiratory system, which is a group of organs and tissues that allow the body to breathe.

Respiratory illnesses affect different parts of this respiratory system, such as the lungs. A coronavirus typically infects the lining of the throat, airways, and lungs.

Early symptoms of coronavirus may include coughing or shortness of breath. In some cases, it can cause severe damage to the lungs. People with COVID-19 may or may not show features of earlier or later phases;

 

 

Phase 1; Cell invasion and viral replication in the nose

Both SARS-CoV-2 and SARS-CoV gain entry via a receptor called ACE2. More commonly known for their role in controlling blood pressure and electrolytes, these receptors are also present in the lungs, back of the throat, gut, heart muscle and kidneys, In SARS , there are hardly any upper respiratory tract symptoms and viral units are rarely present outside the lungs. This fact initially took the focus away from continuing to look for ACE2 receptors in the nose. Scientists have found ACE2 receptors in the mouth and tongue, potentially indicating a hand-to-mouth route of transmission.

 

Phase 2: Replication in the lung and immune system alerted

The viral load study in Germany showed that active viral replication occurs in the upper respiratory tract. Seven out of nine participants listed a cough among their initial symptoms.In two individuals with some signs of lung infection, the virus in sputum peaked at day 10-11. It was present in the sputum up to day 28 in one person.

In the lung, the ACE2 receptor sits on top pf lung cells called pneumocytes. These have an important role in producing surfactant- a compound that coats the air sacs(alveoli), thus helping maintain enough surface tension to keep the sacs open for the exchange of oxygen and carbon dioxide.

 

 

 

Phase 3: Pneumonia

Pneumonia in COVID-19 occurs when parts of the lung consolidate and collapse. Reduced surfactant in the alveoli from the viral destruction of pneumocytes makes it difficult for the lungs to keep the alveoli open.

As part of the immune response, white blood cells, such as neutrophils and macrophages, rush into the alveoli. Meanwhile, blood vessels around the air sacs become leaky in response to inflammatory chemicals that the white blood cells release. This fluids puts pressure on the alveoli from outside and, in combination with the lack of surfactant , causes them to collapse.

 

Phase 4: Acute respiratory distress syndrome , the cytokine storm, and multiple organ failure

 

The most common time for the onset of critical disease is 10 days, and it can come on suddenly in small proportion of people with mild or moderate disease. In severe acute respiratory distress syndrome(ARDS), the inflammation stage gives way to the fibrosis stage. Fibrin clots form in the alveoli

Cytokines are chemical mediators that white blood cells such as macrophages release, and they can engulf infected cells. These cytokines – which have names such as IL1, IL6 AND TNFa- have actions that include dilating the vessel walls and making them more permeable. In extreme circumstances , this can lead to a collapse of the cardiovascular system.

In response to infection,ACE1 creates excess angiotensin 2 from angiotensin1. Angiotensin 2 directly damages the lungs, causes blood vessel constriction, and makes the blood vessels leaky.

 

 

QUESTIONNAIRE ON COVID-19

  1. Is coronavirus a bacteria or virus?
  2. Can humans become infected with the COVID-19 from an animal source?
  3. What is the mode of transmission? How easily get it spread?
  4. When is a person infectious?
  5. Are children also at risk of infection and what is their potential role in transmission?
  6. What is the risk of infection in pregnant women and neonates?
  7. How long does the virus survive on surfaces?
  8. Can I catch coronavirus from the feces of someone with the disease?
  9. Can antibiotics treat the coronavirus disease?
  10. What are the effects of organism on Human body?
  11. What do you mean by Viral organisms?
  12. Explain in detail about types and mode of transmission of disease?

 

 

 

 

 

 

 

 

 

 

PART 2

 

An incubation period is the time between when you contract a virus and when your symptoms start.

Currently, according to the Centers for Disease Control and Prevention (CDC), the incubation period for the novel coronavirus is somewhere between 2 to 14 days after exposure.

According to a recent report, more than 97 percent of people who contract SARS-CoV-2 show symptoms within 11.5 days of exposure. The average incubation period seems to be around 5 days. However, this estimate may change as we learn more about the virus.

For many people, COVID-19 symptoms start as mild symptoms and gradually get worse over a few days.

 

 

 

 

 

 

COVID-19 has more respiratory symptoms than a cold, which usually causes a runny nose, congestion, and sneezing. Also, a fever isn’t too common with a cold.

 

The flu has similar symptoms to COVID-19. However, COVID-19 is more likely to cause shortness of breath and other respiratory symptoms.

About 80% of people recover from the symptoms of COVID-19 without needing any special medical treatment.

However, some people can become seriously ill after contracting COVID-19. Older adults and people with compromised immune symptoms are at the highest risk of developing more severe symptoms.

On average it takes 5-6 days from when someone is infected with the virus for symptoms to show, however it can take up to 14 days.

 

 

 

 

If you think you have symptoms of COVID-19, stay home and call your doctor. Let your doctor know:

 

You may need to be evaluated if:

  1. Your symptoms are severe
  2. You’re an older adult
  3. You have underlying health conditions
  4. You’ve been exposed to someone with COVID-19

 

Your doctor will determine if you need testing and what type of treatment is best.

If your symptoms are mild and you have no underlying health conditions , your doctor may tell you to just stay home, rest, stay hydrated, and to avoid contact with other people.

If your symptoms get worse after a few days of rest, its important to get prompt medical care.

 

 

Coronavirus tests done by the Indian Council for Medical Research as part of its efforts to map the spread of the disease in India have found a significant proportion of people contracted the infection despite having no recent international travel history or contact with confirmed cases.

             ICMR labs tested 5,911 samples taken from patients with severe acute respiratory infections in 52 districts in 21 states and Union Territories between February 15 to April 2. In these tests, 104 samples, or 1.8% of the patients , tested positive for coronavirus.

                Only one of positive samples came from a patient with recent international travel history, two from those who were in contact with a laboratory confirmed case. Forty cases, or 39.2% of the dataset, did not have any travel or contact history. There was no data available for as many as 59(58.7%) of the cases.

 

*COMMUNITY TRANSMISSION

            The Council had initiated these tests as part of sentinel surveillance to detect community transmission of covid-19 in India. Community transmission is said to take place when the source of infection for a large number of cases in an area cannot be traced, when individuals pick up the infection without having travelled to countries where the virus is circulating or having been in contact with known confirmed cases.

 

 

 

  1. What is contact Tracing?

     Contact tracing is the process of identifying , assessing, and managing people who have been exposed to a disease to prevent transmission. As per ICMR guidelines, which are also directions that have sound public health sense behind them, people who may have been exposed to the virus are to be followed for 28 days from the date of the probable last exposure/arrival from affected countries. Any person who has had contact with the index patient under investigation/treatment for suspected, probable or confirmed cases of SARS-COV-2, should be monitored for the appearance of symptoms.

 

  1. Who is a Contact?

     Anyone who provided care for the suspect or confirmed case, including a health care worker (including those involved in cleaning, waste management, laboratory technicians, doctors) or family member , or any one who had close physical contact; anyone who stayed at the same place( lived with, or visited) while the index patient was symptomatic.

         If symptoms appear within the first 28 days following the contact, the individual should be considered a ‘ probable’ case and reported through the Integrated Disease Surveillance Programme network to the National Centre for Disease Control.

 

 

 

 

 

                   CONCLUSIONS

 

Based on the available evidence , including the recent publications, mentioned above, WHO continues to recommend droplet and contact precautions for those people caring for COVID-19 patients. WHO continues to recommend airborne precautions for circumstances and settings in which the aerosol generating procedures and support treatment are performed, according to risk assessment. These recommendations are consistent with other national and international guidelines, including those developed by the European Society of Intensive care Medicines and Society of Critical Care Medicines and those currently used in Australia, Canada and United Kingdom.

              WHO recommend airborne precautions for any situations involving the care of COVID-19 patients, and consider the use of medical masks as an acceptable option in case of shortages of respirators(N95, FFP2, FFP3).

                Current WHO recommendations emphasize the importance of rational and appropriate use of all PPE, not only masks, which requires correct and rigorous behaviour from health care workers, particularly in doffing procedures and hand hygiene practices. Finally WHO continues to emphasize the utmost importance of frequent hand hygiene, respiratory etiquette, and environmental cleaning and disinfection , as well as the importance of maintaining physical distances and avoidance of close, unprotected contact with people with fever or respiratory symptoms.

 

 

 

 

 

REFERENCES / BIBLIOGRAPHY

 

  1. WHO Infection Prevention and Control Guidance for COVID – 19 available at

https://www.who.int/emergencies/diseases/n coronavirus-2019/technical-guidance/infection-prevention-and-control

 

  1. Coronavirus disease (COVID-19): For health professionals.

https://www.canada.ca/en/public-health/services/diseases/2019-novel-coronavirus-infection/health-professionals.html

 

  1. Guidance on infection prevention and control for COVID-19

https:www.gov.uk/government/publications/novel-coronavirus-infection-prevention-and-control

 

  1. Infection prevention and control for COVID-19 in healthcare settings

https://www.ecdc.europa.eu/en/publivations-data/infection-prevention-and-control-covid-19-healthcare-settings

 

  1. World Health Organization. Infection prevention and control of epidemic – and pandemic-prone acute respiratory infections in health care. Geneva: World Health Organization;2014 Available from: https://apps.who.int/iris/bitstream/handle/10 sequence=1

 

 

 

 

 

QUESTIONNAIRE ON COVID-19

 

  1. What are the symptoms of COVID-19 Infection?
  2. Is headache a symptom of the coronavirus disease?
  3. What is the recovery time for the coronavirus disease?
  4. What is the incubation period of the coronavirus disease?
  5. Which are the first symptoms of the coronavirus disease?
  6. Can Coronavirus disease be caught from a person who has no symptoms?
  7. How long does coronavirus stay on surfaces?
  8. Are there differences between symptoms caused by the flu and COVID-19?
  9. Can a person exposed to coronavirus transmit it to others if he/ she uses a swimming pool?
  10. Should people avoid eating meat- based food to prevent transmission?
  11. What is Contact tracing?
  12. Who is a Contact?

 

 

Exit mobile version