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The influence that Parasites have on symptoms/diseases in the human body


Ascaris lumbricoides

This parasitic worm causes a disease known as ascariasis. This disease is most common in tropical and sub-tropical regions of the world where sanitation system is not adequate [1, 2]. This parasite is mainly transmitted from human to human primarily by its eggs present in the soils contaminated with human feces. Particularly children playing in these contaminated soils acquire the parasite egg when unwashed hands are used for eating and putting in the mouth.

In several regions of the world, wastewater depuration is used for reclaiming water. According to the World Health Organization, the reclaimed water should contain less than one Ascaris lumbricoides egg/liter, and molecular methodologies have been developed to ascertain for reuse of wastewater [3].

Dracunculus medinensis

The Dracunculus medinensis is a parasite causing devastating infection mainly in Africa and Asia. It is mostly in poor countries have inadequate sanitation system. The larvae of this parasite are mostly in the microscopic flea. The transmission of disease is primarily through the contaminated water having fleas bearing Dracunculus medinensis larvae. These larvae are released in the intestine and further reproduce to guinea worms. This parasitic disease is quite slow and upon acquiring the larvae manifested almost after a year. Major symptoms associated with this parasitic infection are fever like malaria, chills, nausea, and lethargy.

Among several other, the greater control for the guinea worm disease is to drink filtered water free of microscopic flea having larvae of this parasite. Over the past few decades, several programs were initiated for overcoming this parasitic infection [4, 5]. Global efforts are ongoing to eradicate this disease with a supply of filtered/purified water and the countries where this parasitic disease was prevalent are reporting encouraging data suggesting control over this parasitic disease [6].

Giardia lamblia

Giardiasis caused by a parasite Giardia lamblia is one of the most common parasitic gastrointestinal disease [7, 8]. This parasitic infection is also linked to poor sanitation and also travelers’ diarrhea that people acquire when they visit the countries having a prevalence of this parasite. Parasite transmission is through fecal-oral transmission and children are more prone to this parasitic infection.

The Giardia lamblia has two forms, the trophozoite an active form, and its inactive cyst. The active form, i.e. trophozoite is attached to the small intestine causing disease. Prevalence of giardiasis is not only in the countries with poor sanitation rather it can be transmitted by people to the regions where this parasite is not present [9].

Leishmania Species

There are almost twenty species of Leishmania causing parasitic Leishmaniasis among humans. There are three different types of parasitic infections caused by this protozoa, and these include visceral, cutaneous and mucocutaneous leishmaniasis. The transmission of the parasite is linked with a bite of sandflies [10]. The visceral leishmaniasis is manifested as fever, weight loss, enlarged spleen and anemia symptoms, cutaneous infection in the form of skin lesions and ulcers on various parts of the body and the mucocutaneous leishmaniasis mainly harm the mucous membranes of the nose, mouth, and throat.

The disease is strictly linked with its vector the sand fly population that fluctuates with the environment and several other factors. Efforts on ongoing to develop strategies for inhibiting Leishmania binding to its vector the fly thus controlling the disease [11].

Naegleria fowleri

The Naegleria fowleri caused a life threating brain infection known as naelgleriasis. Among the 130 cases reported over the past few decades in the United States of America, there were only three survivors, suggesting a better understanding of this serious parasitic infection and its proper control [12]. Due to its potential to severely damage the brain, it is also known as  brain eating ameba [13].

The transmission of this parasite among humans involve its inhalation through the nose followed by its passage into the brain. The passage of this parasite into the brain is an active area of investigation. This brain-damaging ameba is mainly present in ponds, lakes, and freshwaters. Higher temperature favors its multiplication rates.

Onchocerca volvulus

This parasite causes a disease known as river blindness (onchocerciasis. Besides trachoma, the river blindness is the second leading cause of blindness in the Word. The disease is mainly prevalent in tropical regions of the world and is transmitted to humans by the bite of black flies from the genus Simulium. The Onchocerca volvulus parasite and its vector the black fly both are found around streams, hydroelectric power plants and water supply systems.  

The World Health Organization current report suggests that 187 million individuals in Africa, America, and Eastern Mediterranean region are at the risk of acquiring river blindness [14]. The disease is preventable, and an effective anti-parasitic medication Ivermectin proper use can save people from getting blind.

Schistosoma mansoni

Schistosoma mansoni and several other closely resembling species of this parasite causes schistosomiasis. Fresh water snails are the major host for this parasite and people acquire disease when the larval form of the parasite attached to the human skin and penetrate into the tissues. People infected with this parasite are also responsible for releasing this parasite into the water during bath and water utilization for different activities.

The disease is associated with the activation of human body immune system against the parasite eggs trapped in tissues. This parasite is responsible for severe mortality and according to an estimate 200, 000 deaths are associated with schistosomiasis. According to very conservative estimates, 120 million people carry this parasite and among this 20 million are primary sufferers [15].

Trypanosoma brucei

Trypanosoma brucei causes a disease known as sleeping sickness [16, 17]. A fly known as tsetse mainly found in rural areas of Africa is responsible for the transmission of disease among humans. The sleeping sickness can be treated with appropriate medications, however, if left untreated leads to significant morbidity and mortality.

The sleeping sickness remained a major problem in the past, and even in current times, almost 10,000 new cases are reported annually. This parasite in the course of its pathogenesis crosses the blood-brain barrier a protective sheathing of the brain and infects the central nervous system for causing sleeping sickness. Primary symptoms are the patient becomes comatose and if not treated death is the ultimate result.

Toxoplasma gondii

Toxoplasmosis is the disease caused by this parasite, and its contamination in food items leads to severe illnesses [18, 19]. Mainly uncooked meat is the primary source of this parasite transmission. It has been reported that even in the developed nations like United States of American 30 million people are the carrier for this parasite kept under control by the immune system [20].

However, immunocompromised get the infections right away. Typical symptoms associated with this parasitic infection are fever, headache, seizure, nausea and bodily imbalance. Besides foodborne transmission toxoplasma can be transmitted congenitally and animals to human also. Person-to-person transmission only from mother to child.

Wuchereria bancrofti

Wuchereria bancrofti is a parasite that damage the human lymphatic system causing a disease known as lymphatic filariasis [21, 22]. The disease is also manifested in the form of lymphoedema due to a collection of fluid in the body. As the lymphatic system is involved in fighting germs and as such people infected have weakened potential to fight against the various disease. A set of complications are associated with the lymphatic filariasis.

Besides Wuchereria bancrofti there are two other species of this parasite causing the disease. Person-to-person transmission of the parasite is mediated through mosquito bites. Lymphatic filariasis is a widely spread all across the world and according to the Center for Disease Control (CDC) of the USA 120 million have this parasitic infection in 73 countries of the world prominently in sub-tropical region of Asia, Africa, South America and the Caribbean [23]. 

Professor Dr. Muhammad Mukhtar


1. Asaolu, S.O., et al., Effect of water supply and sanitation on the prevalence and intensity of Ascaris lumbricoides among pre-school-age children in Ajebandele and Ifewara, Osun State, Nigeria. Trans R Soc Trop Med Hyg, 2002. 96(6): p. 600-4.

2. Nishiura, H., et al., Ascaris lumbricoides among children in rural communities in the Northern Area, Pakistan: prevalence, intensity, and associated socio-cultural and behavioral risk factors. Acta Trop, 2002. 83(3): p. 223-31.

3. Acosta Soto, L., et al., Quantitative PCR and Digital PCR for Detection of Ascaris lumbricoides Eggs in Reclaimed Water. Biomed Res Int, 2017. 2017: p. 7515409.

4. Awofeso, N., Towards global Guinea worm eradication in 2015: the experience of South Sudan. Int J Infect Dis, 2013. 17(8): p. e577-82.

5. Edungbola, L.D., et al., Mobilization strategy for guinea worm eradication in Nigeria. Am J Trop Med Hyg, 1992. 47(5): p. 529-38.

6. Greenwood, B., A. Greenwood, and A. Bradley, Guinea worm infection in northern Nigeria: reflections on a disease approaching eradication. Trop Med Int Health, 2017. 22(5): p. 558-566.

7. Einarsson, E., S. Ma'ayeh, and S.G. Svard, An up-date on Giardia and giardiasis. Curr Opin Microbiol, 2016. 34: p. 47-52.

8. Minetti, C., et al., Giardiasis. BMJ, 2016. 355: p. i5369.

9. Wensaas, K.A., N. Langeland, and G. Rortveit, Prevalence of recurring symptoms after infection with Giardia lamblia in a non-endemic area. Scand J Prim Health Care, 2009. 27(1): p. 12-7.

10. Steverding, D., The history of leishmaniasis. Parasit Vectors, 2017. 10(1): p. 82.

11. Soares, R.P., et al., In Vitro Inhibition of Leishmania Attachment to Sandfly Midguts and LL-5 Cells by Divalent Metal Chelators, Anti-gp63 and Phosphoglycans. Protist, 2017. 168(3): p. 326-334.

12. Pugh, J.J. and R.A. Levy, Naegleria fowleri: Diagnosis, Pathophysiology of Brain Inflammation, and Antimicrobial Treatments. ACS Chem Neurosci, 2016. 7(9): p. 1178-9.

13. Zaheer, R., Naegleria Fowleri--the brain-eating amoeba. J Pak Med Assoc, 2013. 63(11): p. 1456.

14. WHO, Progress towards eliminating onchocerciasis in the WHO Region of the Americas: verification of elimination of transmission in Guatemala - Progress report on the elimination of human onchocerciasis, 2015–2016., 2017.

15. WHO, Schistosomiasis- Epidemiological situation., 2017.

16. Hutchinson, O.C., et al., Lessons learned from the emergence of a new Trypanosoma brucei rhodesiense sleeping sickness focus in Uganda. Lancet Infect Dis, 2003. 3(1): p. 42-5.

17. Kato, C.D., et al., The role of cytokines in the pathogenesis and staging of Trypanosoma brucei rhodesiense sleeping sickness. Allergy Asthma Clin Immunol, 2016. 12: p. 4.

18. Hill, D.E. and J.P. Dubey, Toxoplasma gondii as a Parasite in Food: Analysis and Control. Microbiol Spectr, 2016. 4(4).

19. Hussain, M.A., et al., Toxoplasma gondii in the Food Supply. Pathogens, 2017. 6(2).

20. Guo, M., et al., A Systematic Meta-Analysis of Toxoplasma gondii Prevalence in Food Animals in the United States. Foodborne Pathog Dis, 2016. 13(3): p. 109-18.

21. Paniz Mondolfi, A.E. and E.M. Sordillo, Invited editorial: zoonotic lymphatic filariasis in the Americas: trends in epidemiology, diagnosis and treatment, with special emphasis on brugian filariasis. Recent Pat Antiinfect Drug Discov, 2014. 9(3): p. 161-3.

22. Rajan, T.V., Natural course of lymphatic filariasis: insights from epidemiology, experimental human infections, and clinical observations. Am J Trop Med Hyg, 2005. 73(6): p. 995-8.

23. CDC, Parasites - Lymphatic Filariasis., 2017.

Topics: Parasites

Professor Dr. Muhammad Mukhtar

Written by Professor Dr. Muhammad Mukhtar

Professor Dr. Muhammad Mukhtar has over 25 years teaching experience in biomedical sciences. Besides teaching, he has a very strong portfolio of academic administration and he is an accomplished researcher in the area of infectious diseases. Dr. Mukhtar received his Ph.D. in Biosciences from the Drexel University of Philadelphia, USA, and also completed a Graduate Certificate in Research Management from Thomas Jefferson University of Philadelphia, USA. He served in various academic/administrative positions in the USA on an outstanding scientist (O-1) visa.