Pork tapeworms and international fellows
Every year the Wellcome Trust offers fellowships to support scientists at different career stages. Professor Hector H. Garcia from the Universidad Peruana Cayetano Heredia and the Instituto de Ciencias Neurologicas in Lima, Peru, is the first ever Wellcome Trust Senior Fellow in Public Health and Tropical Medicine (for Researchers from Developing Countries).
Professor Garcia works in Peru on the brain disease neurocysticercosis, a tapeworm that humans catch from eating infected pork. It infects the nervous system, causing epilepsy. I spoke to him about his work.
What is human neurocysticercosis?
Cysticercosis is an infection by the larvae of a parasite (Taenia solium, the pork tapeworm). Neurocysticercosis (NCC) is when it infects the human nervous system. This infection can cause epilepsy and other neurological symptoms and is present in most developing countries. It also shows up in industrialised countries because of immigration and travel.
Three out of every ten cases of epilepsy in Peru (and in other countries) are caused by NCC.
How does it cause acquired epilepsy?
The parasite attempts to hide from the host immune system using a series of evasion mechanisms, but the immune system eventually finds the cysts and triggers an inflammatory reaction aimed to kill the larvae. This inflammatory reaction temporarily damages the brain tissues, causing seizures and other neurological symptoms.
What interested you about this particular area of research?
Besides being a serious and poorly studied public health problem in Peru, the clinical manifestations of NCC are extremely varied. The symptoms depend on how many cysts there are, where they are located, their size, whether they are alive, dying or dead (and calcified), and the immune response of the host. Neurological symptoms reflect the affected area of the nervous system, so with all these variables almost any neurological symptom can be caused by NCC. It is a fascinating subject.
What does your research focus on?
We work as a multidisciplinary, multi-institution group in Peru: the Cysticercosis Working Group. Across the group we work in almost every area of research about Taenia solium, from basic sciences (antigen and mechanism identification, vaccine candidates), pharmacology (new potential therapeutic agents), diagnosis, treatment, and control. My work focuses more on clinical and diagnostic trials. The research I will be doing under the Wellcome Trust Senior Fellowship is focused on determining the impact and burden of NCC in seizure disorders in Peru, how this decreases after elimination, and how old, calcified parasite scars still cause seizures.
What have you found so far?
Research by our group has made substantial contributions to the field. This includes characterising the serological assay (method of diagnosis) of choice, finding effective treatment for infected pigs, performing the only double-blind, randomised clinical trial of antiparasitic drugs in brain cysts, and performing the first wide-scale elimination program which was developed from 2003 to 2010 in Northern Coastal Peru.
The research we are now focusing on has demonstrated that when a patient with old, calcified brain lesions has a seizure, 50 per cent of the time there is a surrounding area of edema (likely inflammation) around one calcification. There are several implications of this: it may identify a mechanism of seizures, it may provide a target for therapy, and it may unveil a significant contributor to poor neurological health in endemic areas.
Is it possible that cysticercosis could be eradicated?
Yes. Long ago, a series of experts published a paper arguing that it was possible. It is based on several biological facts:
- There is a single host for the adult tapeworm – humans – which is the source of infection for pigs and humans. Human faeces containing the parasite’s eggs are released into the environment, and often contaminate food or water.
- The intermediate host or reservoir (the pig) is domestic. An intermediate host is a host that harbours the parasite for only a short transition period; pigs ingest food or water containing the eggs of the parasite, which then hatch inside their bodies and attach to their muscles as cysticerci. Humans become infected when they eat undercooked infected pig meat.
- There are basically no wild reservoirs (there are a few, but they are occasional and do not really contribute to the cycle)
- There are good treatments for tapeworm infections and other control tools.
Our work in Tumbes, Peru provided proof of the concept that elimination, which is the initial step towards eradication, is feasible.
Considering that cysticercosis is endemic to many countries, including Peru, do you think that research into it has been somewhat neglected?
All of us working with parasites other than malaria are already resigned to the idea. In the particular cases of cysticercosis and hydatid disease, another disease caused by tapeworms, they are doubly neglected: often they are not even included in lists of ‘neglected tropical diseases’.
What other challenges do you face?
Research in developing countries always faces a scarcity of resources, equipment and trained staff. Another, less recognised, obstacle is the fragility and poor stability of government institutions in many developing countries. Frequent political changes make it difficult to sustain good work long-term.