Emerging Infectious Diseases

As the name suggests, an emerging infectious disease is indeed one that follows an upward rising curve on the most contacted infections lately graph. However, there are a few more other specifications that differentiate emerging infectious diseases from the generically prevailing ones. Foremost among these specs is the time factor. A disease is recognized as an emerging one if its incidence has seen a spurt in the last 20 years, and is extrapolated to continue to increase in frequency and intensity in the near future. Besides time, a lot of other factors also determine whether or not a particular disease qualifies as an emerging infectious disease. Let's first take a look at these other determining factors, before going on to casting a glance at the various infectious diseases that are included within the scope of emerging or re-emerging infectious diseases.

Various Determining Factors

Besides the time period during which a spurt is seen in the incidence of a particular infection, other factors that determine whether or not an infectious disease qualifies to be touted as emerging, include the following:

    Pathogen Status - An infectious disease may be deemed as emerging if the microbial pathogen was previously unknown (meaning a new species/genus altogether), a newly discovered strain of an existing pathogen, an existing and known pathogen causing a new kind of disease owing to an evolutionary leap in its genetic architecture, re-emergence of a known infection owing to development of resistance to traditional methods of treatment, etc.

    Geographic Coverage - A previously-region-bound infectious disease may assume the emerging status if it begins to move to other geographic regions as well, owing to changes in climatic conditions and human activities such as frequent and increased volume of travels and emigration / immigration, etc.

    Susceptibility Factors - Any kind of change in susceptibility levels in host populations (be it human or animal) towards a particular infectious pathogen can cause the emergence or re-emergence of an infectious disease to significant levels. For instance, mass immunocompromization owing to such diseases as AIDS, Herpes, etc., have led to an increase in the occurrence of opportunistic infections over the last couple of decades.

    Development of Economic Sectors - Economic sectors that contribute to the food production and processing industry such as agriculture, animal husbandry for producing meat, dairy and poultry for consumptions, etc., use a lot of chemicals and antibiotics to ensure the health and fitness of their stock and keep them disease free. These medications and their effects get carried over to the end consumers of these products. Unnecessary consumption of anti-infectants and antibiotics develop resistance towards these drugs even without the consumer being aware of this. This leads to the emergence or re-emergence of a lot of infectious diseases in the consumer population.

    Violence and Mass Mortal Threats - Deliberate violent human activity such as war, bio-terrorism, and natural calamities such as flood, famine, etc., cause a lot of new types of infectious diseases to emerge, while bringing certain bygone infectious disease to the fore all over again.

Emerging Infectious Diseases List

Here's a list of some significant infectious diseases that have emerged and re-emerged in the last couple of decades.

    West Nile Disease - causes encephalitis like symptoms and is a neuroinvasive disease.

    Hepatitis C and E - both diseases affect the liver, leading to inflammation and scarring of this organ.

    Mumps - it is characterized by inflammation of the salivary glands which can be quite painful, as well as testicular swelling in males, the latter being less usual than the former.

    Staphylococcus Aureus Infections - the Staph bacteria causes a lot of infections and diseases like impetigo, cellulitis, pneumonia, mastitis, endocarditis, sepsis, etc., though skin related infections are most common.

    Acanthamebiasis - a group of diseases caused by the Acanthamoeba genus of protozoa and may include infection of dermal and organic tissues as well as the meninges.

    Lyme Disease - caused by ticks as the bacterial parasite is transmitted through the bite of ticks. Fever, fatigue, depression, headaches and skin rashes are chief symptoms.

    Exanthema Subitum - skin rash seen in many infants which is caused by Herpesvirus-6.

    Kaposi's Sarcoma - is indicated by cancerous growths on connective tissues and is caused by Herpesvirus-8.

    Enterovirus 71- causes hand, foot and mouth diseases, and is also known to cause neurological diseases in young children.

    Helicobacter Pylori Infection - indicated by stomach ulcers and chronic gastritis.

    Australian Bat Lyssavirus - this close relative of the rabies virus induces symptoms similar to rabies (partial paralysis, convulsions and delirium), and results in death of the carrier within a couple of weeks to 20 days.

    Encephalitozoon Hellem - a unicellular fungal species that causes opportunistic infections in immunocompromized individuals. It mostly affects the eyes, respiratory tract and genitourinary tract of the infected.

    Tuberculosis (in geographic regions facing breakdown in public health, such as Zimbabwe) - a bacterial infection of the lungs caused by mycobacteria, leading to gradual cellular death of lung and respiratory organ tissues.

    Immunodeficiencies (mass immunocompromization in various geographic regions such as Namibia, Swaziland, Botswana, South Africa, etc., where the percentage of individuals suffering from HIV / AIDS are maximum in the whole world.) - diseases of the immune system that weaken the immune defenses such as AIDS, leukemia, various types of cancers, etc.

    Clostridium Difficile Infection - causes diarrhea and intestine diseases as a result of beneficial bacteria that naturally occur in the gut getting cleared out by antibiotics.

    Henipavirus Infection - causes meningitis, pulmonary edema and hemorrhage, encephalitis and pulmonary congestion in various mammals, including humans.

    Severe Acute Respiratory Syndrome - a kind of pneumonia caused by the SARS coronavirus.

    Anthrax - bacterial infection of the skin and gastrointestinal tracts as well as the lungs, more often than not leading the infected to mortality. It saw a re-emergence when spore contaminated letters were sent to media offices and two senators in the US post 9/11 as an act of bio-terrorism.

    Babesiosis - a disease of the blood caused by parasitic protozoan, leading to anemia due to abnormal break down of red blood cells.

    Enterocytozoon Bieneusi Infection - diarrhea and intestinal lesions caused by the parasitic fungus Enterocytozoon Bieneusi

    Ehrlichiosis - bacterial infection transmitted through tick bites which kills white blood cells of the host.

    Avian and Swine Flu - both types of influenza are caused by the Influenza A virus, and have the infected exhibit the typicla influenza symptoms of fever, headaches, malaise, runny nose, sore throat, muscle ache, with more intense respiratory discomfort with or without diarrhea.

    Creutzfeldt-Jakob Disease - human variant of the mad cow disease, where the neural degeneration of the brain and spinal cord takes place.

    Shingles - viral infection of the skin, characterized by appearance of dermal blisters and painful rashes.

    Smallpox - a viral disease infecting the small blood vessels located under the skin, leading to dermal rashes and appearance of fluid-filled blisters in the later stages.

    Botulism - bacteria induced muscular paralysis which starts with the face and spreads to the limbs and other organs. Infection usually occurs from consuming contaminated food or contamination of open wounds.

    Dengue - a viral disease caused by the dengue virus which is transmitted from the bite of carrier mosquitoes. The symptoms are similar to those of malaria.

Wondering why HIV/AIDS didn't make it to this list? Well, the first officially recorded case of HIV/AIDS dates back to the year 1959. Although at that time, the pathogen was misdiagnosed, later tests on preserved tissues of the subject tested positive for HIV. So you see, it's not so much of a New Age disease, as many make it out to be!

Of all the above mentioned and other infectious diseases, the spots for the top 10 emerging infectious diseases go to anthrax, tularemia, dengue fever, Lyme disease, SARS, prion triggered diseases (such as Creutzfeldt-Jakob disease and bovine spongiform encephalopathy), Hepatitis, E. Coli, Influenza-A infections and tuberculosis. Besides these, owing to growing resistance to various antibiotics (due to extensive administration to livestock reared for food), infections caused by Strep and Staph bacteria are going on an upward trend on the emerging infectious diseases curve.