During the 20th century, the scientific community made great strides toward the eradication of certain dangerous diseases. This was accomplished, in part, through improvements in sanitation and vaccinations, the invention of antibiotics, and advancements in medical technology. But we have still yet to realize a world completely devoid of illness.

There are a variety of reasons for this, and some of the fault inevitably lies with the human population: Overconsumption and the prevalence of an inactive lifestyle have resulted in skyrocketing rates of obesity and the illnesses related to it. And some believe that parents who ignore vaccination recommendations are keeping certain childhood maladies alive that could be eliminated. This past October, the Wildlife Conservation Society (WCS) issued a list of the "deadly dozen" pathogens, including SARS, avian flu, bubonic plague, and hemorrhagic fevers such as Ebola and yellow fever, that could gain strength and trigger pandemics in the future due to climate change. For the present, here are four dangerous diseases that continue to rise:

Tuberculosis. The World Health Organization (WHO) estimates that one in three people worldwide has been exposed to tuberculosis. One of the oldest known diseases, it primarily attacks the lungs but can also affect the brain, kidneys, and spine. For nine in 10 of those with a latent infection, the bacteria will remain dormant; however, in 2006 approximately 9.6 million people were diagnosed with tuberculosis, and 1.5 million died. While the detection rate of new tuberculosis cases was halved between 2005 and 2006, it continues to increase at about 3 percent a year. What most concerns the medical community is the rise of drug-resistant strains of tuberculosis, which have a much higher mortality rate, especially among people whose immune systems are already compromised by disease or age.

Diabetes. According to a recent study released by the Centers for Disease Control & Prevention (CDC), reported cases of diabetes, the seventh leading cause of death in the United States, have nearly doubled over the past 10 years across the nation-from 5 in 1,000 people in the mid-1990s to 9 in 1,000 in the mid-2000s. Approximately 90 percent of those diagnosed with the disease suffer from type 2 diabetes, which is often caused by obesity and lack of exercise because an abundance of fatty tissue can encourage one's cells to become insulin-resistant.

Whooping Cough. The number of people infected by this highly contagious respiratory tract infection, which resembles the common cold in its initial stages but progresses in about a week's time to severely constrict the trachea and bronchi, had fallen to just 1,000 in the United States in 1976. But it has since rebounded, with more than 25,000 cases reported in 2004. Some experts blame this increase on parents who fail to get their children immunized, especially in light of the recent controversy over the supposed link between vaccinations and autism. 

Salmonella and E. coli. Each year, food-borne illnesses affect as many as 80 million Americans and take the lives of about 9,000. As the global reach of food industries increases, so too do incidences of salmonellosis and E. coli infections. In fact, reported cases of salmonellosis have doubled over the past few decades, and the disease is now among the most commonly reported infections. In 2007, E. coli, which has only been recognized as a pathogen since 1982, was the cause behind an increasing number of meat and produce recalls associated with outbreaks.