It is believed that around half the US adult population will be obese (肥胖的) by 2030, while one in four will fall into the severely obese category. This is according to a new study led by the Harvard T.H. Chan School of Public Health, which found that levels of obesity are increasing in every state. Indeed the predictions show that levels of severe obesity could be higher than 25 percent in half of states.

“Especially striking was our finding that among adults with very low income (less than $20,000 per year), severe obesity is predicted to be the most common in 44 states—almost everywhere in the US,” a researcher said.

The research was carried out to inform state policymakers—and perhaps help change the tendency. The study authors say the best form of attack is prevention. Limiting intake of sugar is stressed as one of the most effective and cost-effective methods for reducing obesity levels, and a tax likely to save more money than it costs.

Sugar (and the sugar industry) has come under fire for its role in promoting obesity. Indeed, one recent study published in September 2019 puts responsibility for today’s obesity epidemic (流行病) firmly on the shoulders of sugar, concluding high-sugar diets during childhood in the seventies and eighties could be behind the rise.

“We knew from previous work that obesity is increasing in the US, and that some states and demographic groups (人群) are at higher risk, but we were surprised that even the states with the lowest obesity will be above 35 percent in 2030—a level currently considered high, a researcher told Newsweek. What is clear is that we will not be able to treat our way out of this epidemic—achieving and keeping weight loss is difficult—so prevention efforts will be key to making progress in this area.”

In autumn of 1975, two mothers in Lyme, Connecticut, were desperate for answers their doctors could not provide. Their families and others in the Lyme area were suffering from a mysterious(神秘的)illness. Two doctors from Yale, Allan Steere and Stephen Malawista, began an investigation that would result in a groundbreaking medical discovery.

The doctors began by conducting individual examinations of each patient. They found patients of all ages were suffering from a set of symptoms (症状) rarely observed together. Blood samples revealed no virus that offered a clue about the cause. However, they found fruitful information in their interviews with patients: one quarter of them recalled a skin rash (皮疹) with a bull’s-eye pattern about four weeks before other symptoms arose.

Armed with this new clue, the Department of Health worked with the Yale doctors, conducting surveys to learn where the disease was most widely seen. It seemed that the majority of patients lived in heavily wooded areas, who spent a good deal of time outdoors, gardening, landscaping, or playing. The symptoms were nearly always experienced for the first time during summer. Crucially, some recalled having been bitten by a tick (蝉), which feeds mostly on the blood of mammals and birds.

By 1977, investigators confirmed that the deer tick was responsible. But no one could say why it was causing the illness or how patients could be treated. In 1982, a scientist named Willy Burgdorfer discovered a specific type of bacteria (细菌), carried by the deer tick, which was causing the disease. But how did the deer tick acquire the bacteria in the first place? Finally, scientists determined that the ticks picked up the bacteria from their hosts. As its name suggests, the deer tick often feeds on deer, carriers of the Lyme disease bacteria. Scientists concluded that the bacteria passed from wildlife to ticks to humans. All lived closely among one another in the area.

How could a disease from a common parasite（寄生虫）spring up so suddenly? Many areas of the northeast, including Lyme, were once farmland. The farmland was replanted with trees. After the forest grew in, the area was then developed with houses. Gradually, neighborhoods pushed deeper into the habitat of deer ticks and, more importantly, the wildlife they fed upon. As humans encountered more ticks, they became more likely to contract the disease.

One of the remaining mysteries about Lyme disease is where and when it truly began. This puzzle may never be solved. Today, Lyme disease——if caught early—is easily treated with antibiotics, thanks to the hard work of many scientists, doctors, and patients.

An infectious disease is a disease that is caused by the invasion of a host by pathogens（病原体）whose activities harm the host’s tissues and can be spread to other individuals.

Microorganisms（微生物）capable of causing disease are called pathogens. A true pathogen is an infectious agent that causes disease in any possible host. The terms “infection” and “disease” are quite different. In order to cause disease, pathogens must be able to enter the host body, stick to specific host cells, invade and multiply and do damage to host tissues.

Pathogens may be spread through either direct or indirect contact. Direct contact occurs when an individual is infected by contact with the infection source. It also includes taking in the infectious droplets released by sneezing or coughing. Indirect contact occurs when a pathogen can survive the environment outside its host for a long period of time. So lifeless objects that are polluted by direct contact with the infection source may be the indirect contact for easily infected group.

Public health measures typically involve killing the pathogen from its source or from its route of spread. Those measures include ensuring a safe water supply, effectively treating waste water, and initiating animal control and vaccination（疫苗）programs, etc. Personally, the first line of defense is to keep pathogen at bay by following good personal hygiene（卫生）habits. Prevent infection before it begins and avoid spreading it to others with some easy measures, such as washing hands, getting vaccinated and so on.

Man never stops fighting against all kinds of infectious diseases. But in the past two decades at least a dozen “new” disease have been identified, and traditional diseases that appeared to be “on their way out” are re-emerging. Globally, infectious diseases remain the leading cause of death. Clearly, the ballet has not been won. Nevertheless, it is increasingly difficult for most of us to deny the claims of science. We are continually presented with great amounts of relevant scientific and medical knowledge, which encourages us to take more responsibility for our own health.