Epidemiology
The World Health Organization defines tropical disease as a group of communicable diseases that prevail in tropical and subtropical conditions in 149 countries affecting more than one billion people and cost developing economies billions of dollars every year.
They mainly affect populations living in poverty,
without adequate sanitation and in close contact with infectious vectors and domestic animals (1,
2,
3).
The so-called "neglected tropical diseases" are composed of 13 conditions among the most common chronic infections in the world’s poorest people,
which include parasitic infections (helminths and protozoan) and bacteria.
These diseases are considered neglected because they are not highly visible since they do not kill large numbers of people,
they don’t tend to cause explosive outbreaks and they usually affect those in absolute poverty.
Additionally,
there is no monetary incentive for the development of new diagnostic tools and drugs for these diseases.
In particular,
endemic countries have limited resources to invest in health (1,
2).
Nevertheless,
an expanded list of the most common tropical diseases includes fungal,
viral and ectoparasitic infections,
such as: Tuberculosis,
Malaria,
Dengue and a spectrum of new viruses (1,
2) [Table 1]:
• Ascarisis
• Trichuriasis
• Schistosomiasis
• Amebiasis
• Strongyloidiasis
• Hookworm infection
• Lymphatic Filariasis
• Onchocerciasis
• Chaga’s Disease
• Leishmaniasis
• Leprosy & Trachoma
• Leptospirosis
• Neurocysticercosis
• Scabies
• Influenza
• Ebola & West Nile virus
• Dracunculiasis
• African trypanosomiasis
Tropical diseases were originally thought to affect only the geographical area between the tropics of Cancer and Capricorn.
However,
these pathologies have now spread worldwide due to reasons such as global warming and globalization.
This means that borders are now more easily crossed (1,
3) [Fig.
1].
Migration is not only possible by infected human beings,
but also by arthropods that have been known to migrate and adapt alongside human populations.
Such is the case of the aedes aegypti mosquito,
the known vector for Yellow Fever,
Dengue,
Chikunguyna and Zika,
which have been registered in locations remote from the warmer tropics (1,
2).
The major neglected tropical diseases by prevalence are Ascariasis,
with a global prevalence of around 800 million and with a population at risk of 4.2 billion; and Trichuriasis,
with a global prevalence of around 600 million and with a population at risk of 3.2 billion,
among others.
These diseases are particularly prevalent in vulnerable populations such as: children,
marginalized,
immigrants and victims of violence.
They also affect mostly females and uneducated populations in low-income areas (1,
4,
5).
Refugees are in a particular high risk of contracting this parasites [Fig.
2].
Note that this particular group of refugees arrived to Minnesota,
and had a prevalence of over 20% for any nematode infection.
In the US,
the incidence of some tropical diseases has increased in recent years,
being as high as 4 million for ascariasis.
The incidence for toxocariasis is as elevated as 1.3 to 2.8 million; for strongyloidosis 100,000 and for cysticercosis is 150.000 cases.
Among tropical viral infections Dengue fever 110.000-200.000 (4,
5).