Biomedical Engineering Reference
In-Depth Information
The limited interest for development of drugs against infectious diseases like malaria, African
trypanosomiasis, Chagas disease, schistosomiasis, leishmaniasis, and tuberculosis has led to the
use of the term neglected diseases, even though infectious diseases worldwide are responsible for a
heavier burden than cardiovascular or central nervous system (CNS) diseases.
Medicine for Malaria Venture is a nonproi t organization founded in 1999, which has set up a pub-
lic private partnership (PPP) in order to develop drugs according to the highest international standards
a g a i n s t d i s e a s e s of t h e d evelo p i n g c o u n t r ie s . T h e o r g a n i z a t io n i n clu d e s a c a d e m ic i n s t it u t io n s l i k e Ya l e
University, the University of Oxford, the University of California, San Francisco, private companies
like F. Hoffmann-La Roche, Novartis Pharma, Korea Shin Poong Pharm, Holleykin Pharmaceutical
Company (China), and international organizations like the World Health Organization (WHO).
In the past, the major inspiration for development of drugs against infectious diseases has come
from natural products (see Chapter 6).
21.2 INFECTIONS CAUSED BY HELMINTHIC PARASITES
A parasite is an organism that lives in or on and takes its nourishment from another organism. A para-
site cannot live independently. A helminth is a multicellular parasitic worm. In general, a helminth is
visible to the naked eye in its adult stages. Parasites might have more hosts. The smaller host is gener-
ally called the vector. Many neglected diseases are caused by parasites. In contrast to bacteria, which
are prokaryotes, parasites are eukaryotes.
21.2.1 S CHISTOSOMIASIS
Schistosomiasis (bilharziasis) is caused by infection with l atworms belonging to the genus
Schistosomas , S. mansoni is found in South America and Africa, S. haematopium found through-
out Africa, in particular in Egypt, and S. japonicum is coni ned to the Far East. Approximately
200 million people in more than 70 developing countries suffer from the diseases, 20 million suffer
severe consequences, such as colonic polyposis with bloody diarrhoea ( S. mansoni ), splenome-
gami, and portal haematemesis with vomiting of blood ( S. japonicum and S. mansoni ), cystitis, and
ureteritis, which might lead to bladder cancer ( S. haematopium ), and CNS lesions. The diseases
are estimated to cause 280,000 deaths each year. Three safe, effective drugs, praziquantel, oxam-
niquine, and metrifonate, are now available for schistosomiasis and are included in the WHO model
list of essential drugs. WHO has dei ned essential drugs as “those drugs that satisfy the health care
needs of the majority of the population; they should therefore be available at all times in adequate
amounts and in appropriate dosage forms, at a price the community can afford.”
21.2.2 F ILARIASIS
Filariasis is caused by parasites belonging to the order Filaroidea. Wuchereria bancrofti and Brugia
malayi both cause lymphatic i lariasis (elephantiasis), Loa loa causes fugitive swelling, in par ticular,
around the eyes, and Onchocerca volvulus causes onchocerciasis (river blindness). All the diseases
are caused by helminthic worms transmitted through bites of insects belonging to the order Diptera.
The symptoms pertaining to the diseases are caused by the presence of parasites restricting the l ow
of lymph l uid. Approximately, 120 million people are infected with the parasites and 40 millions
are severely disabled. Onchocerciasis is estimated to have infected 17.7 millions people, of which
500,000 have visual impairment and 270,000 are blinded. The disease is limited to the vicinity of
rivers where the vector, blackl ies of the genus Similium , is endemic. Unfortunately the burden of
the disease often forces the population to leave these areas uninhabited. The infection can be treated
with ivermectin ( 21.1 ) (Figure 21.1). Ivermectin, a dihydro derivative of avermectin B 1a , acts by
opening invertebrate specii c glutamate-gated chloride ion channels in the nerve end and muscles
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