The earthquake in Haiti has pushed this most impoverished country in the Western hemisphere into the spotlight and in doing so, has drawn attention to the Cinderella diseases of the world: neglected tropical diseases or NTDs.
Described as such by the World Health Organization (WHO) because they persist “exclusively in the poorest and most marginalized communities and have been largely eliminated elsewhere and thus are often forgotten,” NTDs affect more than 1 billion people worldwide. They are highly prevalent in countries like Haiti that have high levels of poverty and poor sanitation and medical systems.
Most NTDs kill slowly, causing life-long disabilities, which in turn have severe consequences for both human health and livelihood. Examples of these diseases are leprosy, lymphatic filariasis (elephantiasis) and trachoma, characterized by debilitation, thickening of the skin and underlying tissues, and blindness, respectively.
The irony is that most NTDs are completely preventable. However, the poor economic and political clout of their victims means that there is little pressure on national or international health care programs to prioritize funding for the control of these diseases.
At the Texas A&M University College of Veterinary Medicine & Biomedical Sciences, Dr. Christine Budke, assistant professor of epidemiology, is aiming to change this.
Budke’s research focuses on two NTDs-cystic echinococcosis (CE) or hydatid disease and neurocysticercosis (NCC). Caused by parasitic worms or helminths, CE and NCC affect both animals and humans and are prevalent in poor rural agricultural communities mainly in developing regions of the world, for example, areas of China, the Middle East, Central and South America, and Africa.
By determining the global burden of these diseases-that is, their total health, socioeconomic and financial cost to society-Budke aims to highlight and improve their pariah status.
A “two-fold hit”
“What makes [CE] exceptional…is that it is not only a substantial human health problem but also has a considerable economic effect on the livestock industries of some of the most socioeconomically fragile countries,” Budke and her coauthors explained in a paper in 2006 titled the Global socioeconomic impact of cystic echinococcosis.
NCC also causes this “two-fold hit,” as Budke describes the blow to not only human health but also livestock production inflicted by these diseases. The involvement of both animal and human hosts in the transmission cycles of CE and NCC explains this impact.
For example, the primary host of the tapeworm Echinococcus granulosus, which causes CE, is the dog. Humans generally become infected by accidentally ingesting tapeworm eggs in food or drink contaminated with dog fecal material or during direct contact with dogs. Livestock such as sheep, cattle and goats can also acquire the infection from dog fecal material ingested during grazing.
In the case of NCC, humans are the primary host of the disease-causing tapeworm Taenia solium and become infected by accidentally ingesting tapeworm eggs in food or water contaminated with human feces or by eating raw or undercooked infected pork. Pigs also become infected by ingesting eggs shed in human feces.
In both CE and NCC, the ingestion of tapeworm eggs results in the formation of larval cysts, which form in various organ systems and can have disastrous consequences for human and animal health.
“Cysts [which in the case of CE form mainly in the liver and lungs] can grow to be 12 centimeters [about 5 inches] across,” Budke says. “These slow-growing cysts are space-occupying lesions. They are almost like a cancer and they can kill you.”
Also, in both CE and NCC, cyst infestation in livestock results in economic losses due to livestock condemnation and production losses.
Pariahs for various reasons
Despite these serious consequences to both human and animal health, these diseases have not received due attention.
“The global burden of these diseases has never been determined partly because there is no framework for reporting these diseases at the regional, city or country level,” Budke says, citing one reason for the neglected status of CE and NCC.
In a paper published last year titled Zoonotic larval cestode infections: Neglected, neglected tropical diseases? Budke and her coauthors provided several reasons for the under-reporting of CE and NCC.
One is that these diseases are often undiagnosed. This is because tests for their early diagnosis, for example, abdominal ultrasound, computer tomography and magnetic resonance imaging scans, are not accessible to individuals in remote poverty-stricken communities.
CE and NCC also remain undiagnosed because of their chronic nature.
“Clinical signs associated with echinococcosis can take five to ten years to develop, with clinical signs associated with NCC also taking months or years to appear,” Budke and her coauthors explain in the paper. “For government administrations dealing with a myriad of public health crises, this lack of acute symptoms may make these conditions seem less dire than those with a shorter incubation period.”
Difficult treatment and complex control strategies have also contributed to the neglected status of these diseases.
Treatment often involves the expensive surgical removal of cysts and the administration of antihelminthic drugs for a minimum of six months, which is not always effective. Control programs, which for CE may include a combination of health education, vaccination of secondary hosts such as sheep and the deworming of dogs, are not easily implemented for various reasons.
“It is very difficult to sustain control measures,” Budke says. “A number of factors need to be considered.” For CE, these include controlling stray dog populations’ access to offal (the organs of butchered animals), the logistics of dog deworming and the cultural or religious beliefs of societies, who believe in protecting and adopting stray dogs, an important parasite reservoir.
The difficulty in addressing the abovementioned issues is compounded by the limited funding available for controlling these neglected diseases.
The way forward
“[These diseases] are really a one-health problem,” Budke says, stressing that both the human health and veterinary sectors must take responsibility for managing CE and NCC. Shared control costs and earlier detection of these zoonotic diseases are some advantages of this partnership.
Budke also stresses the importance of determining the global burden of CE and NCC, which involves estimating their health and socioeconomic costs. In addition to providing information on disease scope, global burden estimates will help raise awareness about these diseases and in doing so, make funding control measures for them a priority.
Budke and her collaborators hope that these approaches will increase the profile of CE and NCC and prevent them from being treated as “neglected stepchildren.”