From smallpox to AIDS, how the world has battled infectious diseases

 

If we are to save the world from the threat of infectious diseases, we need to learn the lessons of past outbreaks.

 A group of people from a camp  in Palestine being vaccinated against smallpox.          Image credit: Wellcome Library/Wikimedia Commons 

 In 2013, the World Health Organisation declared  antibiotic resistance was a threat to global health security. It can  seem hard to believe that in the 21st century infectious diseases remain  such a profound existential risk. But this declaration highlights the  ever-lingering threat of infectious diseases and our dependence on  antibiotics to stave off their impact on human and animal health and industry.It  also reminds us to appreciate antibiotics as one of many advances in  infectious diseases and public health during the past century, and  reflect on some of the greatest, still persistent, infectious disease challenges facing us today.Here  we explore our past and present struggles with four of the most  significant infectious diseases human beings have faced, some of the  progress we’ve made in prevention and treatment, and possible future  directions. 

 Infectious disease deaths. Reprinted with permission from Macmillan  Publishers Ltd: Nature. Paulson T. Epidemiology: a mortal foe. Nature  2013. 

 

Tuberculosis

Tuberculosis or TB has been responsible for the death of more people than any other infectious disease in history; over a billion deaths in the past 200 years. Its origin is unclear, but it infects a number of other species, including cattle.Today, about a third of the world’s population  is thought to be infected with TB, in its dormant form. This means the  bacteria is present but it’s controlled by the immune system, the  infected person has no symptoms, and it can’t be spread to others. The  bacteria will reactivate in a small proportion of people and they may  develop symptoms including fever, sweats, weight loss, fatigue, cough, and haemoptysis (coughing up blood).TB  occurs in every country, including Australia, but mostly occurs in  people born in countries where TB is more common, due to the  reactivation of dormant TB infection. Patients with weakened immune systems due to chemotherapy, HIV or other medical illnesses are at higher risk of TB.In 2015, there were 10.4 million new cases of TB,  and 1.8 million TB-related deaths around the world?, with the vast  majority of cases in developing countries. The infection and death rate  have been declining internationally since the early 1900s.Long  before the availability of treatment options, improvements in  sanitation, housing, and vaccination led to a reduction in the rates of  TB in some countries. But antibiotics made it a curable disease; without  them, up to 70% of people with active infection die from TB.But  treatment is complicated, and typically involves taking four  medications for two months, then two medications for a further four  months. These medications are not without side effects, and can be  poorly tolerated. Unfortunately, when medications are not taken or  prescribed properly, the TB bacteria can become resistant to these  treatments.In recent years, drug-resistant TB has been documented all over the world, but is much more common in people previously treated for TB, and in Russia, China and India.Treatment  of resistant TB is much more complicated, takes longer, is more prone  to failure, and often uses more toxic drugs. New rapid tests can  diagnose TB, and whether or not the bacteria will be resistant to our  first-line drugs.A vaccine for TB has been available for around a century, but is most effective in preventing severe TB infection in children. The vaccine’s efficacy is much less clear in adults.Despite advances in treatment, tuberculosis continues to occur disproportionately in the developing world. Although progress is being made,  ongoing and increased political and financial support is essential to  ensure coordinated diagnosis, surveillance and care strategies, and  universal access to these. Similarly, continued investment is needed for the development of new tools to detect and treat TB.

Smallpox

Smallpox was caused by the variola virus,  which plagued humanity for millennia and had a lasting impact on human  history. As late as the 1960s, smallpox was still endemic in Asia and  Africa, with an estimated two million deaths occurring annually.Smallpox  was spread easily between people by sneezing or shared contact, leading  swiftly to the characteristic disfiguring pustular lesions on the skin.  The disease was severe, with about 30% of affected people dying,  while the rest were left with complications associated with infection.  These included a multitude of scars, blindness, infections and  arthritis.Those who survived, however, were generally protected from reinfection. Building on observations  that milkmaids were protected from smallpox, Edward Jenner, an 18th  century British physician, developed and popularised a technique called  “vaccination” whereby he deliberately inoculated a patient with cowpox, a  closely related virus the milkmaids were exposed to. This led to protection from smallpox.While  a popular origin story, alternative approaches to protection, such as  inhaling dried smallpox lesions, had likely been practised in China and  India for many years previously,  and had already been introduced into the United Kingdom. However,  inoculation with smallpox came with a risk of severe infection in a  significant number of recipients, and Jenner’s safer approach was  adopted for larger scale immunisation programs.In 1980, smallpox  became the first, and so far only, human infectious disease to be  declared eradicated by the World Health Organisation. This came about  via a coordinated international response, led by an Australian microbiologist, Frank Fenner.  This involved mass-vaccination, along with public health surveillance  and preventative measures, which aimed to educate communities, and  identify and contain individual cases.The last case of smallpox was reported in Somalia in 1977, with the unfortunate death of medical photographer Janet Parker in 1978 serving as a final warning of this deadly condition.Smallpox may be gone as a disease, but the variola virus controversially remains, kept secure in laboratories in Russia and the US. Concern has emerged about the prospect of smallpox as a weapon of bioterrorism. The impact of such an event could be devastating, given people are no longer routinely immunised against smallpox.

HIV/AIDS

In the early 1980s, a small number of gay men in the United States started presenting with unusual infections, previously only seen in people with severe immune deficiencies. Over the subsequent years, the human immunodeficiency virus or HIV was discovered, and its global burden was recognised.The virus, which had most likely originated in primates in Africa, had probably been infecting humans for close to a century, and had spread  across the globe. Untreated HIV causes a slow destruction of the  infected person’s immune system, leading to a plethora of opportunistic  infections and cancers, known as the acquired immunodeficiency syndrome  or AIDS.Without treatment, almost all people with HIV progress to AIDS, and die. At its peak in the 1990s, around 1,000 Australians a year died from HIV/AIDS. 

 AIDS awareness painting on wall in Chimoio town, Mozambique. The text  reads: "Be careful, always use a condom". (Photo: Ton RulkensFlickr) 

 HIV/AIDS mobilised western communities to act like never before. In Australia,  a grassroots campaign led by communities most deeply affected resulted  in a number of public health interventions and legislative changes. This  included safe sex campaigns, needle exchange programs, and mandatory  condom use and STI testing for commercial sex workers.These  changes led to reductions in rates of new HIV cases, while global  investment in research and public health led to the development of  “antiretroviral” drugs, which stopped the virus from replicating, helped  control HIV infection, and markedly reduced the risk of progression to AIDS.To date, about 40 million  people have died from AIDS, and an estimated 36.7 million are living  with HIV. Nevertheless, most people affected by HIV in western countries  live a long and healthy life.Although an effective vaccine for HIV is not available, progress is being made in diagnosis, reducing transmission and improving the health of those affected.Treating those with HIV to a point where the virus isn’t detectable in their blood reduces the possibility of onward transmission  by 90-95%. And it leads to numerous individual health benefits for the  infected individual. In contrast, uninfected people at high risk of  contracting the virus can take antiviral medications known as pre-exposure prophylaxis that prevent infection. These have shown to be highly effective if taken properly.There are hopes these treatments will end the epidemic by 2030.

Influenza

It’s  easy to forget about the danger of influenza. In most cases, this virus  is responsible for a respiratory illness of varying severity that  generally doesn’t require treatment. However, influenza has been responsible for more deaths in the last century than HIV/AIDS.Usually, seasonal influenza outbreaks occur annually and affect around four million people, with about 250,000 deaths worldwide.  Typically older patients, with pre-existing illnesses such as heart  failure or chronic lung disease, and pregnant women are at the greatest risk of death.Many  people have a degree of immunity, due to vaccination or previous  infection. It’s worth noting that although safe, the influenza vaccine  is imperfect; it’s developed using strains of influenza virus  circulating in winter, in the opposite hemisphere, and is about 50%  effective at preventing infection.  But vaccination is still an important strategy to protect those at risk  of most severe infection. It reduces hospital admission and symptomatic  infection.Occasionally, an influenza virus not usually seen in  humans is transmitted from its reservoir in aquatic birds, poultry or  pigs, to humans. As a consequence, those exposed have no natural  immunity, and are not protected by the vaccine at all. If this virus  evolves to readily infect and spread between humans, it can have  devastating consequences.In the last century, this has happened several times, with numerous fatalities. The Spanish influenza pandemic of 1918 led to the deaths of more than 40 million people; more than double  the number of fatalities in the First World War in the preceding four  years. It progressively spread around the globe, with the modernisation  of transport and trade systems, and mass-movement of military troops.In more recent times, smaller outbreaks have occurred, with bird flu and swine flu. There is an ever-lingering threat  of a repeat influenza pandemic, due to the industrial scale farming of  chickens and pigs, that are also susceptible to infection and the close proximity of humans to these animals.Due to the rapid and fluid movement of people around the globe for business and leisure, a new pandemic virus could easily be transported around the world. In recent years, countries have stockpiled influenza medications and vaccines in preparation for a possible influenza pandemic.These  are only four of the infectious diseases that have shaped the last  century. In reality, there are a number that could have been included in  this list of threats including polio, malaria, cholera and syphilis.Each  of these diseases is very different, and as such, our responses to them  have been very different too. In part this is because quite different  organisms cause these infections, but it’s also because the social  context in which diseases happen is critical.If we are to save  the world from the threat of infectious diseases, we need to learn the  lessons of past outbreaks, including the value of international  collaboration, perseverance and commitment to humanity.