The Top 10 Infectious Diseases
Which pathogen tops the list as the most deadly
In a world that some mistakenly called post-Covid, it’s easy to forget that before Covid came onto the scene there was a whole raft of other diseases vying for the title of deadliest disease.
Diseases include communicable diseases (those caused by viruses, bacteria, and the variety of single cells or multi-cellular parasites) and non-communicable diseases (which are chronic but not contagious) both of which damage health. While heart disease (non-communicable) is the biggest killer worldwide (responsible for an estimated 8.5 million deaths annually), it is not transmissible person to person and so not included here. In this round-up we will only include communicable infectious diseases.
The second clarification required is whether by deadly we mean those diseases that have killed the most people, those that have the highest mortality rate, or even those who killed quickest.
While there were certainly fascinating diseases in each of these categories (which I will explore with rather too much relish in future articles) for now I will limit myself to the biggest killers globally, and annually.
I had also better lay my cards on the table to say that infectious diseases are one of my favorite topics, that is to say, I find them fascinating. For all of the fascination however these diseases affect real people with horrific consequences, and all efforts can and are being taken to eradicate them. For that, we should also be thankful for organizations like the Center for Disease Control, the Crick Institute, the London and Liverpool Schools of Tropical Medicine, and the Bill and Melinda Gates Foundation among others.
So let’s dive in by looking at the Top 10 infectious diseases. What are they? Where do they originate? What are the symptoms? What are the consequences for individuals, communities, and countries?
Spoiler alert………. There’s a new kid on the block.
10 MRSA — problem of our own creation.
MRSA (methicillin-resistant Staphylococcus aureus) is an antibiotic-resistant bacteria that is the direct evolutionary result of our over-dependence and usage of antibiotics, both in human and animal populations.
Through the indiscriminate use of antibiotics, we have provided an evolutionary pressure towards resistance against the very drugs which should protect us against infection and allowed these pathogens to flourish. Even more alarmingly MRSA is only one of a class of antibiotic-resistant bacterial infections. A study from Oxford University has put the total figure for this class of pathogens at over 1.2 million deaths per year.
MRSA is present on our skin without any consequences, but once inside our bodies, these bacteria rapidly multiply causing swelling, and redness which can lead to septicemia, pneumonia, and endocarditis (infection of the heart valves), all of which can be fatal. It may be at 10 now but antibiotic resistance is one of the problems that will only get worse in the future.
9 Measles.
It’s a sad fact that despite the safe and reliable vaccines, Measles still kills an estimated 140,000 people per year, mostly children under five.
Caused by a virus in the Para via family measles is one of the most contagious diseases lingering in the air and on surfaces for hours before it can reach it reinfects. In fact, it has an up to 90% infection rate, according to one source. Often the symptoms are mild with a runny nose, fever, and the characteristic rash. But in the very young and adults over 30, it can lead to blindness, pneumonia, and encephalitis, and as a result, in death. While measles has been all but eradicated from many countries, it is still common in Brazil, India and Sub Saharan Africa, China, and Russia.
The good news is that The WHO is moving to eradicate measles. The bad news is that wars and natural disasters are slowing down their work which is further exacerbated by misinformation.
8 Cholera.
Cholera is a disease with a historical pedigree that can be traced through at least seven separate pandemics. It is by bacteria and remains very much a disease of poverty, conflict, and natural disasters.
Spread through contaminated water, food, and water and closely associated with poor sanitation and a lack of clean drinking water the symptoms range from mild, if unpleasant to severe with diarrhoeal causing dehydration which left untreated will kill rapidly.
Presently there are over four million cases annually resulting in between 21,243 thousand deaths per year. The good news is that cholera can be successfully treated with an oral rehydration solution and worldwide there has been a steady decline in cases.
7. Diarrhoeal Diseases
Diarrhoeal disease is the second largest killer of children under five, killing an estimated 525,000 each year out of 1.7 billion individual infections. Caused by a range of infectious agents diarrhoeal diseases should be easy to prevent through access to safe drinking water, basic hygiene, and adequate nutrition. But these things are sadly lacking in too many areas.
It is also easy to treat in many cases through basic nutrition and rehydration therapy. The solutions to prevent deaths from diarrhoeal diseases sound simple and yet conflict and climate disruption are out of the reach of many and beyond the political will of those that could make a difference.
6. Pneumonia.
Accounting for 14% of all deaths under five pneumonia is another preventable disease that wrecks families. Which wrecks lives, destroys families, and stifles economic growth. Caused by a range of infections, viral, fungal, and bacterial pneumonia is characteristically characterized by acute respiratory infections causing the alveoli (air sacs) in the lungs to fill with pus or fluid, preventing breathing and killing through asphyxiation.
A disease of poverty exacerbated by indoor air pollution, smoking, and crowded living conditions Pneumonia looks set to continue to affect millions for many years to come.
5. Malaria.
Caused by a single-celled organism called Plasmodium Malaria is spread by a mosquito vector. With symptoms starting with headaches which then progress to fevers, Malaria can result in death or serious long-term debilitating illness. Malaria remains a significant problem for the 241 million people infected each year killing an estimated 627,000 annually.
Malaria has seen a surge in numbers due to the Covid pandemic and there are concerns that climate change could extend the range of the Anopheles mosquito vector reintroducing malaria, to countries like southern Europe that have been malaria-free for many decades.
Our main lines of defense against malaria are those that target mosquito vectors and antimalarial drugs. Vector controls include the removal of standing water insecticides and impregnated Nets which have proved extremely effective. Antimalarial drugs are also effective but are expensive and some mosquito populations have developed resistance to them. There are hopes that a vaccine, developed in 2021 could be rolled out more widely.
At present, despite nine more countries being certified malaria-free since 2015, the goal of eradicating malaria remains elusively unattainable.
4. HIV
Having claimed 36.3 million lives, HIV is very much a global pandemic. Despite the fact that for some with access to retroviral drugs and advanced healthcare systems, HIV has become a manageable condition for 680,000. People still died of HIV-related causes in 2020. The HIV virus targets the immune system infecting the very white blood cells that should be fighting off infections, leaving the body unable to fight off subsequent infections and some cancers.
HIV is spread through bodily fluids, including semen, breast milk, blood, and vagina secretions and despite widespread information campaigns the combined effects of the Covid pandemic, economic downturns, and conflicts have led to a surge in HIV cases. Sadly there is a very real prospect of seven million AIDS-related deaths in the next decade.
3. Hepatitis B
Infecting 296 million people and killing 820,000 hepatitis B is one of the biggest global health problems and yet one of the least understood. A virus that attacks the liver, hepatitis B causes jaundice, fatigue, vomiting, liver failure, and cancer.
Endemic throughout. In the Western Pacific and Africa, Hepatitis B is commonly spread from mother to child at birth or horizontally between infected and noninfected children. It is also sexually transmitted and spread amongst intravenous drug users through contaminated needles.
Although treatable at the early stages of infection, the later stages are untreatable. Problems arise, however, because at the early stages, there are few symptoms and few people are aware that they are infected until it is too late leaving transmission routes open and any chance of treatment severely compromised.
There is a vaccine for Hepatitis B however the challenge lies in reaching those populations that are most in need.
2. TB
Until recently, TB was the world’s top infectious killer with an annual death toll of 1.5 million people, and may well reclaim that unenviable position soon. Infecting more than 10 million people per year TB is present in all countries and in all age groups, and has been, it has been estimated that one-quarter of the world’s population carries the infection even if they show no symptoms.
Caused by a bacteria, with an air Bourne infection route, many of the symptoms are familiar to us from books and films. Coughing up blood is the most obvious example however the symptoms include fever, night sweats, and chest pains.
The problem arises however because the early symptoms are mild, resulting in poor rates of detection before the disease is progressed. TB is treatable and preventable however a lack of resources or healthcare means 95% of all deaths occur in developing nations. Sadly this situation has only been made only worse by the prevalence of HIV and antibiotic-resistant strains in many of these same countries.
1. COVID-19
And here it is, out of nowhere, to the world’s biggest killer. Covid 19.
This airborne Coronavirus has to date had 500 billion confirmed cases and six million deaths. As I write it continues to wreak havoc on the world, despite the availability of vaccines. With the current outbreak in China of most concern
Mild symptoms are most common, tiredness and loss of smell, but for a significant minority, COVID leads to shortness of breath, confusion, and respiratory failure. So how will this pandemic pan out? No one can yet tell. Most countries of the world (with the noticeable exception of African countries) have vaccinated a large proportion of their populations, but new variants continue to emerge. And it is not beyond the realms of possibility that a new variant may render our vaccines useless and throw the whole world back into lockdown.
So there we have it the Top ten infectious diseases in the world. A list of misery and disease all of which continue to hold nations back and blight lives. The only hope is that the nations of the world can work together to produce and deliver vaccines, and medicines to those that need them most, and together we can combat these deadly killers that plague humanity.
