Antiparasitic drugs in neurocysticercosis: albendazole or praziquantel?

Present-day anthelmintics and perspectives on future new targets

In absence of vaccines for the majority of helminths, chemotherapy is still the mainstay for controlling human helminthiases. However, a limited number of drugs are available in the market to combat parasitic helminths in human. Besides, the development and spread of drug resistance have declined the use of most currently available anthelmintics. Clearly, availability of new anthelmintic agents will be essential in the next few years. More research into the mechanisms of drug actions and their targets are eminent for the discovery and development of novel anthelmintic agents. Recent drug discovery techniques mostly rely on mechanism-based screening of compounds on heterologously expressed targets in bacterial, mammalian or yeast cells. Although this is usually a successful approach, it is money- and time-consuming; meanwhile, pharmaceutical companies prefer the tested target that is chosen based on basic research. The nervous system is the site of action of several chemotherapeutics including pesticides and antinematode drugs; accordingly, the nervous system continues to be a promising target. Recent advances in exploring helminths' nervous system, neurotransmitters and receptors have paved the way for the development of potential agents targeting the nervous system and its components.

Efficacy of diverse antiparasitic treatments for cysticercosis in the pig model

Taenia solium cysticercosis infects pigs and humans. Because antiparasitic treatment for human cysticercosis has sub-optimal efficacy, alternative regimes are needed. Seven antiparasitic regimens were tested in 42 naturally infected pigs with cysticercosis, and compared with prednisone alone (n = 6) or no treatment (n = 6). The numbers of viable cysts in muscles and in the brain were examined after necropsy and were significantly decreased in pigs receiving combined albendazole plus praziquantel, albendazole alone, or oxfendazole. Pigs receiving praziquantel alone and nitazoxanide had numerous surviving cysts. Control (untreated) pigs and prednisone-treated pigs had many more viable cysts, suggesting no effect. Combined albendazole plus praziquantel, and oxfendazole, showed a strong cysticidal effect and provide suitable alternative treatments to be further explored for their use for treatment of human neurocysticercosis.

Hydrocephalus in neurocysticercosis

INTRODUCTION

Cysticercosis (CC) is the most important of the parasitic diseases of the central nervous system due to its high incidence in the world. CC is the infection with the larval cysts of Taenia solium. It is the most common helminthic infection of the nervous system and is endemic in most underdeveloped countries as well as in industrialized nations. It is estimated that approximately 50,000 people die every year from neurocysticercosis (NCC) worldwide.

DISCUSSION

Humans with CC are incidental intermediate hosts, which replace the pig in the life cycle of the T. solium. Children are more frequently affected by parenchyma infestation of cysticercus, of which the main clinical manifestation is epilepsy. Hydrocephalus is more common in adults and is caused by cerebrospinal fluid blockage by ventricular cysts and inflammatory reactions (ependimitis/arachnoiditis). Treatment should be individualized based on clinical presentation, degree of infestation, location and viability of cysticercus, and host response. Hydrocephalus can be controlled only by removal of obstructive intraventricular cysts or associated with either ventriculoperitoneal shunt or endoscopic third ventriculostomy. The degree of infestation and complications related to the shunt represents the most important prognostic factors in the outcome of NCC.

Neurocysticercosis

Neurocysticercosis (NCC) is the most common cause of acquired epilepsy in developing countries. It can present variably depending on the location and stage of cysts in the nervous system, and the host immune response. The most common presentation of parenchymal NCC is with seizures that are usually focal and brief; status epilepticus occurs in some cases. About a third of cases have headache and vomiting. Diagnosis is made by either CT or MRI. Single, small, contrast enhancing lesions are the most common; visualization of a scolex is diagnostic. Some cases have multiple cysts with a characteristic starry-sky appearance. Although treatment with cysticidal therapy continues to be debated, there is increasing evidence that it helps through increased and faster resolution of CT lesions; whether there is any improvement in long-term seizure control needs further study. It should not be used in cysticercus encephalitis or in ophthalmic NCC and used with caution in extraparenchymal NCC. It is of no use in calcified lesions. Corticosteroids are used simultaneously to reduce cerebral oedema. Seizures respond well to a single antiepileptic, and the seizure recurrence rate is low in cases with single lesions; those with multiple, persistent or calcified lesions usually have recurrent seizures. Extraparenchymal NCC is often associated with intracranial hypertension, hydrocephalous and chronic meningitis; it has a guarded prognosis; surgical intervention is required in many cases. Management of NCC needs to be individualized. NCC is potentially eradicable; proper sanitation, hygiene and animal husbandry are warranted.