Parasitic Diseases

A parasitic disease is an infectious disease caused or transmitted by a parasite. It can affect almost all living things, including plants and mammals. Many parasites do not cause diseases because they can eventually lead to the death of the organism and its host. Parasites that infect humans are called human parasites.

Signs and Symptoms

The effects of parasitic diseases range from mild discomfort to death. Some of the symptoms caused by worm infection include itching, abdominal pain, weight loss, increased appetite, intestinal obstruction, diarrhea, and vomiting eventually resulting in dehydration, sleeping problems, worms present in the vomit or stools, anemia, muscle or joint pain, overall discomfort, allergy, fatigue, and tension.

Fig.1 Parasitic diseases of travelers according to syndromic presentation. (Showler, 2014)

Causes of Diseases

Parasites usually enter the body through the skin or the mouth. Mammals can contract the parasite through contaminated food or water, insect bites, or sexual contact. Because dogs and cats are hosts to many parasites, close contact with pets can also lead to parasitic infections.

Treatment for Diseases

Parasitic infections can usually be treated with antiparasitic drugs. Because the treatment must repeatedly be administered, and drug resistance may occur. In severe cases, drugs designed to kill the parasite are used, while in other cases, measures to relieve the symptoms are used. Recent studies have also suggested the use of viruses to treat protozoan infections.

Diagnostic Approaches for Parasitic Diseases

• Microscopy

For years, microscopy has been the only tool to detect parasites by examining blood smears, tissue samples, feces, lymph node aspirates, bone marrow, and even cerebrospinal fluid. All major intestinal helminth infections are still diagnosed entirely by microscopy. As for other parasite infections, many have been confirmed using microscopy and other diagnostic methods, including serology-based assays, and more recently molecular-based assays.

Fig.2 Microscopy. Comparison of Trypanosoma cruzi trypomastigote (a) with Plasmodium malariae schizont (b) and with microfilaria (c: Mansonella perstans) in squirrel monkey blood smear. (Ndao, 2009)

• Serology-based Assays

In cases where biological or tissue samples are unavailable, serology is the gold standard for diagnosis. Although the ease of use and turnaround time of serological analysis is similar to that of a microscope, serology-based assays are more sensitive and specific. Serology-based diagnostic tools can be divided into two categories: antigen detection and antibody detection.

Fig.3 Serology-based assays: ELISA. (Ndao, 2009)

• Molecular-Based Approaches
• Nucleic acid-based approaches

These approaches offer greater sensitivity and specificity over the existing diagnostic tests. They permit the detection of infections from very low parasitized samples including those from asymptomatic patient samples.

• Real-time polymerase chain reaction (RT-PCR)

Using multiplexed RT-PCR, scientists were able to identify the four human Plasmodium species in a single reaction tube even in very low parasitized samples.

• Loop-mediated isothermal amplification (LAMP)

LAMP is a unique amplification method with extremely high specificity and sensitivity able to discriminate between a single nucleotide difference. Recently, parasitologists have adapted the LAMP approach for the detection of several parasitic diseases and even for the identification of vector mosquitoes carrying Plasmodium and Dirofilariimmitis parasites. Most of these studies have brought to light the many advantages of this method over the common PCR technique.

• Luminex xMAP technology

Luminex technology is a bead-based flow-cytometric assay that allows the detection of various targets simultaneously. Adapted to the study of parasites, the Luminex assay could identify multiple organisms or different genotypes of one organism during the same reaction utilizing very low volume. The approach was useful in the study of antigenic diversity and drug resistance alleles and for the diagnosis of parasitic diseases.

• Proteomics

Since proteins are the main catalysts, structural elements, signaling messengers, and molecular machines of biological tissues, proteomic studies can have substantial clinical relevance. Proteins can be utilized as biomarkers for tissues, cell types, developmental stages, and disease states as well as potential targets for drug discovery and interventional approaches.

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References

1. Showler, A.J.; et al. Parasitic diseases in travelers: a focus on therapy. Expert Rev Anti Infect Ther. 2014 Apr; 12(4): 497-521.
2. Ndao, M. Diagnosis of parasitic diseases: old and new approaches. Interdiscip Perspect Infect Dis. 2009; 2009: 278246.