My Science School

Do you know what's common among SARS-CoV-2, HIV AIDS, Ebola, SARS, MERS, Nipah, H1N1 flu (swine flu) and H5N1 flu (bird flu)? Yes, all of these are zoonoses, that is, they are animal-bome diseases.

A zoonosis is any disease or infection that is naturally transmissible from vertebrate animals to humans. Zoonoses have different modes of transmission. In direct zoonosis, the disease is transmitted from animals to humans through air, bites or saliva. In indirect zoonoses, the transmission occurs via an intermediate species (referred to as a vector), which carries the disease pathogen. These pathogens can be viruses, bacteria, fungi or parasites.

Though the world has seen the emergence of diseases throughout history, in the last 50 years, a host of new infectious diseases has spread rapidly after making the evolutionary jump from animals to humans. According to the World Health Organisation (WHO), 70% of emerging human pathogens come from animals. In the last century, at least 10 infectious diseases jumped from animals to humans, it says.

What has led to this?

Globalisation, deforestation, encroachment of wild environments, human-animal conflicts and wildlife trade have led to the spike in zoonosis outbreak, says a report by the WHO, released in September 2019. It has also warned that the risk of a global pandemic is growing and that zoonotic diseases will continue to emerge and re-emerge.

The deadly ones

As the world grapples with the new coronavirus, which is thought to have spread from bats, let's take a look at some of the major zoonotic diseases and their outbreaks...

Bubonic plague

Bubonic plague was the cause of the Black Death that swept through Asia, Europe and Africa in the 14th Century and killed an estimated 50 million people. It took centuries for some societies to recover. Plague is a bacterial disease caused by Yersinia pestis. It is carried by rodents and cats. The infection in humans is caused by the bite of an infected flea.

HIV-AIDS

HIV, the virus that causes AIDS, originated from chimps and other primates and is thought to have first infected humans at least a century ago. However, it was first recognised only in 1981. By the end of that year, there were 270 reported cases and 121 deaths. HIV destroys the immune system, opening the door to a host of deadly infections. The virus has now mutated to a separate human-only disease. Between 1981 and 2018, the disease caused an estimated 32 million deaths worldwide.

SARS An epidemic of SARS, caused by a strain of coronavirus SARSCOV, affected 26 countries and resulted in more than 8,000 cases in 2003.

SARS-CoV is thought to have spread from bats, which, in tumn, spread to other animals (civet cats) and perhaps first infected humans in southern China in 2002.

Ebola

The 2014-2016 outbreak in West Africa was the largest Ebola outbreak since the virus was first discovered in 1976. The outbreak started in Guinea and then spread to other parts of the continent. The virus is transmitted to people from wild animals (such as chimpanzees, gorillas, monkeys, antelopes or porcupines). Human-to-human transmission happens through direct or indirect contact with the blood or bodily fluids of infected people. It is thought that fruit bats of the Pteropodidae family are natural Ebola virus hosts.

Nipah

Nipah virus (Niv) infection severely affects both animals and humans. The natural host of the virus are fruit bats. It can spread from bats to other animals to people or directly from bat to and between people. Even eating a fruit bitten by an infected bat can transfer Nipah to humans. The disease was first identified in 1998 during an outbreak in Malaysia, India has reported three NiV outbreaks in the past. The first two were in West Bengal: Siliguri in 2001 and Nadia in 2007. The third outbreak occurred in Kerala in May 2018.

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Fleas are tiny bugs. They don’t grow much larger than the tip of a pen, and they range from light brown to almost black in color. They don’t have wings, so they get around by jumping from place to place. Their thin, flat bodies and hard shells mean you often need to squeeze them between fingernails or two hard surfaces to kill them. Even then, where there is one, many often follow. Fleas reproduce quickly, especially if you have pets in the house. But even if you don’t have pets, your yard can potentially play host to fleas, and you may end up with a bunch of mysterious bites. They’re almost impossible to get rid of without a pesticide treatment.

Fleabites are pretty distinctive. They look like small, red bumps in clusters of three or four or a straight line. The bumps remain small, unlike mosquito bites. You might notice a red “halo” around the bite center. The most common places to find these bites are around the legs or ankles. Fleabites are also common around the waist, armpits, breasts, groin, or in the folds of the elbows and knees.

For humans, the risk of contracting another disease from the flea is very small. Yet bacteria can get into your body through the bite and cause an infection, especially if you scratch it. An infected bite will turn red, warm, and it may release pus. Fleabites can also cause an allergic reaction in people who are sensitive to them. Symptoms can range from raised welts on the skin to difficulty breathing. Fleabites can also cause complications in pets, such as allergic reactions and even anemia from blood loss. That’s why it’s important to take animals to a vet if they have fleas.

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A person can get it by eating food or drink contaminated with human or animal feces where the parasite is present.

Many parasitic worms enter their hosts by active invasion. Their transmission success is often based on a mass production of invasive stages. However, most stages show a highly specific host-finding behaviour. Information on host-finding mechanisms is available mainly for trematode miracidia and cercariae and for nematode hookworms. The larvae find and recognise their hosts, in some cases even with species specificity, via complex sequences of behavioural patterns with which they successively respond to various environmental and host cues. There is often a surprisingly high diversity of host-recognition strategies. Each parasite species finds and enters its host using a different series of cues. For example, different species of schistosomes enter the human skin using different recognition sequences. The various recognition strategies may reflect adaptations to distinct ecological conditions of transmission. Another question is how, after invasion, parasitic worms find their complex paths through their host's tissues to their often very specific microhabitats. Recent data show that the migrating parasite stages can follow local chemical gradients of skin and blood compounds, but their long-distance navigation within the host body still remains puzzling. The high complexity, specificity and diversity of host-recognition strategies suggest that host finding and host recognition are important determinants in the evolution of parasite life cycles.

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Amebiasis is a parasitic infection of the intestines caused by the protozoan Entamoeba histolytica, or E. histolytica. The symptoms of amebiasis include loose stool, abdominal cramping, and stomach pain. However, most people with amebiasis won’t experience significant symptoms.

The cause of amebiasis is infection by the protozoan parasite Entamoeba histolytica. It begins when a person drinks contaminated water or eats foods contaminated with the cystic form (infective stage), comes in contact with contaminated colonic irrigation devices or the fecally contaminated hands of food handlers, or by oral-anal sexual practices.

The cystic form changes into trophozoites (invasive form) in the ilium or colon and invade the mucosal barrier, leading to tissue destruction and diarrhea. These trophozoites can reach the portal blood circulation to the liver and eventually go to other organs. It only infects humans, and the CDC does not classify it as a free-living organism.

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A parasite is an organism that lives in another organism, called the host, and often harms it. It depends on its host for survival.

The parasite uses the host’s resources to fuel its life cycle. It uses the host’s resources to maintain itself.

Parasites vary widely. Around 70 percentTrusted Source are not visible to the human eye, such as the malarial parasite, but some worm parasites can reach over 30 meters in length.

Parasites are not a disease, but they can spread diseases. Different parasites have different effects.

There are many types of parasite, and symptoms can vary widely. Sometimes these may resemble the symptoms of other conditions, such as a hormone deficiency, pneumonia, or food poisoning.

Parasitic infections cause a tremendous burden of disease in both the tropics and subtropics as well as in more temperate climates. Of all parasitic diseases, malaria causes the most deaths globally. Malaria kills more than 400,000 people each year, most of them young children in sub-Saharan Africa.

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Children face special risks from air pollution because their lungs are growing and because they are so active and breathe in a great deal of air.

Several studies have found air pollution linked to harm to children while they are still in the womb. A large study in California found that higher particle pollution levels increased the risk of preterm birth.5 Pregnant women exposed to even low levels of particle pollution had higher risk for preterm birth in a Boston study.6 Preterm births occurred more frequently when particle pollution spiked, as an Australian study found, even when they controlled for other risk factors.

Further evidence that cleaner air provides real benefits to children’s health came in a 2016 report from the same study exploring changes to 4,602 children’s respiratory symptoms such as coughing, congestion and phlegm. The study looked at the changes in these symptoms in three groups of children living in Southern California over different periods of time when air quality also differed (1993-2001, 1996-2004, and 2003-2012). As air quality improved, the children in the study suffered fewer bronchial symptoms whether they had asthma or not. In communities where the air quality improved the most, the children experienced even fewer symptoms.

So, does cleaning up the air really improve children’s health? In 2017, the researchers reviewed these long-term studies of children in Southern California and the impact of improvements in air quality on their health. They concluded that the 20 years of collected data provided strong evidence of the potential to improve children’s health by reducing some of the most common outdoor air pollutants.

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PM 2.5 refers to a category of particulate pollutant that is 2.5 microns or smaller in size. The average cross-section of a human hair is 50 microns. PM stands for “particulate matter.” The EPA and many health organizations categorize particulate matter by size because different size particles have different health effects. For instance, PM 10 particles (particles less than 10 microns in size) can irritate your nose and eyes, but fewer of these particles penetrate deep into your lungs, so they do not cause the same health problems that smaller micron particles can, although they do increase rates of respiratory disease 

PM 2.5 particles are complex because they can be made up of numerous types of chemicals and particles, and they can be partly liquid, as opposed to solid, like a common dust particle. Particulate pollutants that are entirely or partly made up of liquid droplets are known as an aerosol. Natural kinds of aerosols include dust, sea salt and volcanic ash, whereas man-made sources include factory and auto emissions, coal combustion and biomass burning for clearing land or farming.

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A 2013 assessment by WHO’s International Agency for Research on Cancer (IARC) concluded that outdoor air pollution is carcinogenic to humans, with the particulate matter component of air pollution most closely associated with increased cancer incidence, especially lung cancer.

The Board meets regularly, bringing together ministers from the health and environment sectors to address important issues in the WHO European Region.

Evidence published by WHO/Europe earlier this year, as part of the international project to review evidence on health aspects of air pollution (REVIHAAP), confirmed the importance of outdoor air pollution as a risk factor for health, and strengthened the causal link between fine particles (PM2.5) and cardiovascular and respiratory ill health. It also showed that long-term exposure to PM2.5 can trigger a range of problems, such as atherosclerosis, adverse birth outcomes and childhood respiratory diseases, and suggested possible links with neurological development, cognitive function and diabetes.

IARC’s recent classification provides indisputable evidence that air pollution is carcinogenic, and adds to the compelling evidence for taking action to improve air quality in order to reduce this important burden of disease in Europe.

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When we talk about greenhouse gases, we often think of carbon-dioxide (CO2). But did you know nitrous oxide (N2O), also called laughing gas, is a potent greenhouse gas, with ozone-depleting property?

You must be aware that a greenhouse gas is a gas that traps heat in the atmosphere and keeps the planet warm. This process called the greenhouse effect is a good thing. Without it the world would be a frozen, uninhabitable place. However, too much greenhouse gases in the atmosphere can cause the temperature to increase out of control. The more greenhouse gases in the atmosphere, the hotter the earth will become. It changes the Earth's climate system and affect all forms of life.

The main gases responsible for the greenhouse effect include carbon dioxide, methane, nitrous oxide, and water vapour. While carbon dioxide and to some extent methane have gained the recognition as climate change villains, N20 emission has largely been ignored in climate policies, despite its significant contribution to climate change.

A 2020 review of nitrous oxide sources and sinks found that emissions rose 30% in the last four decades. Nitrous oxide is responsible for roughly 7% of global warming since preindustrial times. Most N20 emissions have come from emerging countries like India, China and Brazil.

What are the sources of N20?

Nitrous oxide in the atmosphere comes from both natural and anthropogenic sources. The largest source of nitrous oxide is agriculture (73%), and the majority of agricultural emissions result from usage of nitrogen fertilizers and ill-management of animals waste.

Fossil fuel combustion and industrial processes are the other important source of nitrous oxide emissions. Biomass burning, atmospheric deposition and wastewater treatment are the other sources.

Why is N20 a cause for concern?

Like other greenhouse gases, nitrous oxide absorbs radiation and traps heat in the atmosphere. N20 has a long lifespan in the atmosphere-about 114 years.

N20 is nearly 300 times more potent at warming the planet than carbon dioxide, which means that even small sources of emissions can have a significant impact on the climate.

N20 has emerged as the most critical ozone depleting substance. It is stable in the lowest level of the atmosphere, the troposphere and acts like a greenhouse gas. When it migrates up to the stratosphere, it reacts with ozone and depletes it.

The growing demand for food and feed for animals and increased usage of fertilizers will further increase global nitrous oxide emissions.

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Recently, the Chinese government disclosed that a 41-year-old man had contracted what might be the world's first human case of H10N3 strain of bird flu. It was quick to add that the risk of large-scale spread was, however, low.

In a world already reeling under the misery caused by the COVID-19 pandemic, the news was met with trepidation.

The World Health Organisation (WHO) said that while the source of the patient's exposure to the H10N3 virus was not known, there are no other cases of human-to-human transmission among the local population yet.

H10N3 is a rare virus that usually affects poultry. There is a whole bunch of avian influenza viruses that have an impact on birds, and can be serious in people, such as the H7N9 strain that claimed almost 300 lives in China during the winter of 2016-2017. According to the WHO, there had been only rare instances of person-to person spread of the H7N9 virus.

Experts say that cases like the new H10N3 infection occur occasionally in China, which has huge populations of both farmed and wild birds of many species, and that with growing surveillance of avian influenza in the human population, more infections with bird flu viruses are being picked up.

In February this year, Russia reported the first human infection with the H5N8 virus that caused huge damage to poultry farms across Europe, Russia and East Asia last winter. News emerged that seven people infected with the virus were asymptomatic.

As long as avian influenza viruses circulate in poultry, sporadic infection of avian influenza in humans is not surprising. It is a vivid reminder that the threat of an influenza pandemic is persistent.

Though the H10N3 strain is not a common virus, flu viruses can mutate rapidly and mix with other strains circulating on farms or among migratory birds. This leads to "reassortment", meaning they could make genetic changes that pose a transmission threat to humans.

The genetic sequence of the virus that infected the patient has not been released by China. Scientists are keen to know how easily H10N3 can infect human cells to determine if it could become a greater risk. They are still waiting for details.

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