Global Health Snapshot: Neglected Tropical Diseases
They disfigure, blind, disable, stigmatize and kill an estimated 1 billion people worldwide—the poorest of the poor. Yet neglected tropical diseases (NTDs) have traditionally ranked low on health agendas.
WHO’s first report on 17 NTDs—published in October 2010—rejects the notion of “waiting for the diseases to gradually disappear as countries develop.” Instead, it recommends preventive chemotherapy, intensified case management, vector control, veterinary public health, and safe water, sanitation and hygiene.
Buoyed by new interventions and research, as well as recent support from donors, pharmaceutical companies and NGOs, WHO asserts that control of NTDs is possible and elimination is a feasible goal.
Why do the diseases still exist? One reason is that they lack the attention given high-mortality diseases, says International Health professor William Brieger, DrPH ’92, MPH. “Of course, there are societal costs of disabilities, but they’re not as widely documented as deaths from HIV, TB and malaria,” Brieger explains .
Another reason is that health services are difficult to access in remote areas and urban slums. Surgery is an option in some cases, but medical facilities and health workers are in short supply. Brieger recently returned from Chad, where there are only several hundred doctors serving 11 million people. “And about 20 percent of the health facilities are not functional,” he says. “When a situation is that extreme, how can you deliver the services?”
Trachoma
A chronic conjunctivitis caused by the bacterium Chlamydia trachomatis and transmitted by contact with infected secretions.
Symptoms: Inflammation under eyelid. Multiple untreated infections can cause scarring, inturned eyelashes leading to corneal damage and, ultimately, blindness.
Treatment: Community-wide administration of single-dose antibiotics; surgery for inturned eyelashes
Prevention: Hand- and face-washing; sanitation improvements
Location: Concentrated in Africa
Prevalence: 41 million cases
Trending: Prevalence has fallen sharply since 1985 when 360 million people were infected.
Fact: Women are four times more likely to have blinding trachoma than men (largely because of frequent proximity to children, who are reservoirs of infection).
Target the Community: “Antibiotics, increased water availability and keeping face, hands and clothes clean are really what I see as the approach targets to removing infection in these communities.”
Sheila West has conducted clinical trials on trachoma treatments for the disease in Tanzania, Ethiopia and Niger.
Lymphatic Filariasis
The disease, which can lead to elephantiasis, is caused by parasitic worms and transmitted by mosquitoes. Adult worms nest in a person’s lymphatic system, producing millions of larvae that circulate in the blood.
Symptoms: Swollen arms, legs or genitals; also damage to kidneys and lymphatic system
Treatment: Swelling of arms and legs can be reduced by rigorous hygiene or reduction surgery.
Prevention: Mass administration of drugs to at-risk populations to reduce parasite burden and interrupt transmission via mosquitoes
Location: Africa, Southeast Asia and South America
Prevalence: 120 million cases in 81 countries
Trending: WHO aims to eliminate it by 2020.
Fact: Over half of infected people have no outward signs of infection.
Secretive Parasites: “[I study] how filarial parasites establish decades-long infections and not generate a reaction that causes them either to be rejected or cause significant pathology.”
Alan Scott focuses on the immunobiology of host-parasite interactions.
Leprosy
A chronic bacterial infection caused by Mycobacterium leprae and transmitted by droplets from the nose and mouth. The pathogen has an incubation period of about five years.
Symptoms: Mild skin lesions. Untreated, leprosy can cause severe and disfiguring skin lesions and permanent damage to nerves, upper respiratory tract and eyes.
Treatment: Multidrug therapy
Prevention: Early diagnosis and treatment of infected individuals
Location: Mainly Asia and Africa
Prevalence: 211,903 registered cases worldwide (2009)
Trending: New cases dropped 4 percent between 2007 and 2008.
Observation: Some new leprosy cases in China appear to have been transmitted via infected water or soil, not by close contact with leprosy patients-—the traditional route.
Early Detection: “Our research focuses on developing a diagnostic test to detect the disease early enough and start treatment before the nerve-damaging lesions occur.”
Ying Zhang, an expert on drug-resistant TB, is conducting leprosy research in southern China, with Huan-Ying Li, MD, MPH, ’52.
Leishmaniasis
A spectrum of diseases caused by the protozoan parasites (Leishmania), transmitted by sand flies.
Symptoms: Four types of disease range in severity, from skin sores on exposed areas to lesions that can destroy mucous membranes. In severe form, parasites cause swelling of spleen and liver.
Treatment: Antimony-containing compounds; also used: amphotericin B and fluconazole
Prevention: Bednets
Location: Southeast Asia, Middle East and South America
Prevalence: 12 million people infected worldwide
Trending: 1 to 2 million new cases each year
Fact: Drug-resistant Leishmania strains have been identified; need for new therapies is growing.
Devastating Loss: “As a student, I was struck by the amount of tissue destruction this parasite can cause. Skin breakdown [sometimes] can result in permanent disfigurement.”
Jay Bream focuses on the role of cytokines (soluble proteins) in disease susceptibility.
Chagas Disease
A life-threatening illness caused by the parasite Trypanosoma cruzi and transmitted by the feces of the blood-sucking triatomine, known as the “kissing bug.”
Symptoms: Fever, headache and muscle pain; also can be asymptomatic in acute phase. In latent phase, parasites hide in heart and other cells, often leading to cardiac arrest and premature death.
Treatment: Benznidazole and nifurtimox for acute phase
Prevention: Insecticides (indoor), blood-bank screening, screening of pregnant women and children of infected women
Location: Mainly in Latin America
Prevalence: 10 million people infected
Trending: Decreased from 20 million cases in 1981 to 10 million in 2009
Fact: Of 10 million people infected, 2 to 3 million will die prematurely of heart disease.
Better, Safer Drugs: “At least 60 percent of children with chronic T. cruzi infection can be cured, and treatment of adults decreases progression and mortality. But the drugs have significant toxicity and better, safer drugs are urgently needed.”
Robert Gilman, a tropical disease expert, conducted research in Peru for more than 25 years.
Dengue
A mosquito-borne viral infection causing a severe, flulike illness. Multiple infections may lead to the potentially lethal dengue hemorrhagic fever.
Symptoms: Flulike symptoms; severe form may result in shock caused by leaking blood vessels
Treatment: No specific treatment; supportive care only
Prevention: Insecticides and environmental management; personal protection
Location: Originally concentrated in Southeast Asia, it has spread rapidly to Central and South America over the past 20 years, as well as India, Australia and the Caribbean (most recently, Florida).
Incidence: 50 to 100 million dengue infections worldwide every year
Trending: 30-fold increase in incidence in last 50 years
Fact: Virus comprises four serotypes. After infection with one serotype, an infection by another increases risk of dengue hemorrhagic fever.
A Quadruple Threat: “A vaccine has to protect against all four serotypes. If it doesn’t,
you could actually set up a vaccinated population to have more severe disease [later]. That’s not something we see with other human diseases.”
Anna Durbin is collaborating on a clinical trial in Brazil that tests the safety of a tetravalent vaccine against dengue.
Buruli Ulcer
A severe skin disease caused by Mycobacterium ulcerans.
Symptoms: Toxin mycolactone, produced by M. ulcerans, causes large, deep ulcers that can attack muscles and bones. Untreated, it can cause permanent disability.
Treatment: Antibiotics streptomycin and rifampicin; surgery for advanced cases
Prevention: Researchers are working to understand how infection is transmitted and to develop a vaccine.
Location: Mainly in West Africa, including Ivory Coast, Ghana and Benin
Prevalence: Very little accurate information; disease has been reported in 33 countries.
Trending: No clear trend; increase in cases in West Africa in past decade
Fact: Method of transmission is unclear, however, most patients live in marshy areas, indicating that infections may occur in aquatic environments.
A Disease of Development: “I think there is a lot of evidence that development in rural areas [including construction that creates slow-moving water and bad drainage] has a role in the expansion of the disease.”
Jacques Grosset is an international authority on Buruli ulcer and is developing an early diagnostic test and a shorter treatment course.
Other NTDs cited in WHO's 2010 report on Neglected Tropical Diseases
• Cysticercosis
• Dracunculiasis (guinea-worm disease)
• Echinococcosis
• Endemic treponematoses
• Foodborne trematode infections
• Human African trypanosomiasis (sleeping sickness)
• Onchocerciasis (river blindness)
• Rabies
• Schistosomiasis
• Soil-transmitted helminthiases (intestinal parasitic worms)
Sources:
Jay Bream, PhD, assistant professor, Molecular Microbiology and Immunology (MMI); Paul Converse, PhD ’84, MHS ’80, research associate, Johns Hopkins Center for Tuberculosis Research; Anna Durbin, MD, associate professor, International Health; Robert Gilman, MD, professor, International Health; Jacques Grosset, MD, professor, Johns Hopkins Center for Tuberculosis Research; Alan Scott, PhD, professor, MMI; Sheila West, PhD, PharmD, professor, Epidemiology, El-Maghraby Professor of Preventive Ophthalmology, Wilmer Eye Institute; Ying Zhang, MD, PhD, professor, MMI