Preface

Diseases caused by parasitic helminths (helminthiasis) are infectious and they pose serious health problems, especially in underdeveloped and developing countries of the world. This is a reflection of poor socio-economic conditions, which impacts on the social life of victims and the economic development of affected regions. Helminthiasis is caused by helminths such as flukes, tapeworms, filarial worms, pinworms, thread worms, and soil-transmitted nematodes. Infectious helminths live in a large variety of habitats in humans and other vertebrate hosts.

Helminths are far more widespread than we think. Gastrointestinal helminths (GIHs) are the largest group of helminths that affect man, which results in major threats particularly in underdeveloped and developing countries where they are incorrectly classified as 'Neglected tropical diseases' (NTDS). However, it is a myth to assume that helminths do not exist in temperate countries. GIHs are usually soiltransmitted helminths (STHs) or geohelminths, affecting one third of the world population directly through fecal-oral routes.

The World Health Organization (WHO) reported that about 2.9 million people are infected with gastrointestinal nematodes yearly. A more recent estimate indicates 3.5 billion cases worldwide. About 125,000 deaths are estimated to occur yearly mainly due to STHs. The prevalence of STHs has remained unchanged in over 50 years with 39 million disability adjusted life years (DALYS) lost to these parasites.

Globally, filariasis, which is vector-transmitted, is the second leading cause of a permanent and long-term disabling and disfiguring disease in the world causing chronic suffering but rarely mortality. According to WHO, in 2002, the DALYS from filariasis was 6 million. In 2013, 1.3 billion people in 72 countries were within areas of endemic filariasis and are continually threatened while an estimated 120 million are already infected.

Control efforts in some communities in underdeveloped and developing countries are impaired by poor sanitation, poverty, and ignorance leading to a high rate of infections and eventually to grave public health challenges. This is why such areas suffer serious consequences due to helminthiasis compared to developed areas. Large scale control programs are essential in less developed countries.

This book provides insights into antihelminthic resistance in livestock, STHs with a focus on pregnant women and children, and what should be done to prevent and control helminth infections for which proper and adequate diagnosis is crucial.

Large scale targeted chemotherapy that focuses on the distribution of safe and effective drugs is an important component of helminthiasis control. This must be complemented with sustainable environmental sanitation and health education to produce a significant reduction in the transmission of helminth infections, especially in the tropics. Hand washing is a major way to prevent parasitic helminth contamination and transmission. This book has helped to close the information gap on helminthiasis, which has otherwise been overlooked as a serious cause of morbidity and mortality of man and animals.

> **Omolade Olayinka Okwa (Ph.d, CWF)** Associate Professor, Department of Zoology and Environmental Biology, Faculty of Science, Lagos State University, Nigeria

> > **1**

Section 1

Introductory Chapter

Section 1 Introductory Chapter

**3**

**Chapter 1**

**1. Introduction**

tropical diseases" [1].

*Omolade Olayinka Okwa*

these infections to humans by zoonoses [1, 2].

**2. Nematodes (the roundworms)**

**2.1 The ubiquity of nematodes**

Introductory Chapter: Helminthes

Parasitic helminthes are worms of great medical and veterinary importance. They include the Nematodes (Roundworms) and the Platyhelminthes (Flatworms) which consist of the Trematodes (Flukes) and Cestodes (Tapeworms). These invertebrates are agents of debilitating, deforming and fatal diseases of humans and their agricultural animals and so responsible for great morbidity and mortality. Domestic and wild animals affected by a barrage of helminthes infections may also transmit

Helminthes infections may be vectored, food or water borne. Infections due to parasitic helminthes are no doubt widespread in tropical as well as temperate regions with both regions having their own share of peculiar and distinctive infections. In fact, in Tropical Africa, helminthiasis is regarded as part of the "Neglected

The platyhelminthes (flatworms) are acoelomates that possess the beginning of some advanced features of the animal kingdom such as cephalization, bilateral symmetry and triploblastic body organization. The trematodes or flukes are endoparasitic platyhelminthes with complex life cycles. The Digeneans are a peculiar group of trematodes in having mollusca (snails) as their intermediate hosts in a life cycle involving one or two hosts; for example: *Schistosoma haematobium* and *Schistosoma mansoni* (blood flukes of man), *Fasciola hepatica* and *Fasciola gigantica* (sheep and

Cestodes differ in a number of ways from other flatworms. Their bodies are elongated, ribbon-like and flattened, made up of many segments called proglottids. Most cestodes require at least two hosts of which vertebrates are usually the intermediate host [2]. All these features are adaptations to their exclusively parasitic mode of existence; for example, *Taenia solium* and *Taenia saginata* (pork and beef tapeworms of man), *Echinococcus granulosus* and *Echinococcus multilocularis* (dog

Nematodes are cosmopolitan and ubiquitous. They are one of the most numerous metazoans in the animal kingdom with broad ranges of environment having successfully adapted to every ecosystem both aquatic and terrestrial. They are a large group of bilaterally symmetrical, elongated, pseudocoelomate helminthes in the animal kingdom. They are elongated, non-metamerically segmented, and cylindrical or round so referred to as the round worms. *Nema* from the word Nematode

cattle liver flukes) and *Paragonimus westermani* (human lung fluke).

tapeworms) and *Diphyllobothrium latum* (broad fish tapeworm of man).

Diversity - Focus on Nematodes

## **Chapter 1**

## Introductory Chapter: Helminthes Diversity - Focus on Nematodes

*Omolade Olayinka Okwa*

## **1. Introduction**

Parasitic helminthes are worms of great medical and veterinary importance. They include the Nematodes (Roundworms) and the Platyhelminthes (Flatworms) which consist of the Trematodes (Flukes) and Cestodes (Tapeworms). These invertebrates are agents of debilitating, deforming and fatal diseases of humans and their agricultural animals and so responsible for great morbidity and mortality. Domestic and wild animals affected by a barrage of helminthes infections may also transmit these infections to humans by zoonoses [1, 2].

Helminthes infections may be vectored, food or water borne. Infections due to parasitic helminthes are no doubt widespread in tropical as well as temperate regions with both regions having their own share of peculiar and distinctive infections. In fact, in Tropical Africa, helminthiasis is regarded as part of the "Neglected tropical diseases" [1].

The platyhelminthes (flatworms) are acoelomates that possess the beginning of some advanced features of the animal kingdom such as cephalization, bilateral symmetry and triploblastic body organization. The trematodes or flukes are endoparasitic platyhelminthes with complex life cycles. The Digeneans are a peculiar group of trematodes in having mollusca (snails) as their intermediate hosts in a life cycle involving one or two hosts; for example: *Schistosoma haematobium* and *Schistosoma mansoni* (blood flukes of man), *Fasciola hepatica* and *Fasciola gigantica* (sheep and cattle liver flukes) and *Paragonimus westermani* (human lung fluke).

Cestodes differ in a number of ways from other flatworms. Their bodies are elongated, ribbon-like and flattened, made up of many segments called proglottids. Most cestodes require at least two hosts of which vertebrates are usually the intermediate host [2]. All these features are adaptations to their exclusively parasitic mode of existence; for example, *Taenia solium* and *Taenia saginata* (pork and beef tapeworms of man), *Echinococcus granulosus* and *Echinococcus multilocularis* (dog tapeworms) and *Diphyllobothrium latum* (broad fish tapeworm of man).

#### **2. Nematodes (the roundworms)**

#### **2.1 The ubiquity of nematodes**

Nematodes are cosmopolitan and ubiquitous. They are one of the most numerous metazoans in the animal kingdom with broad ranges of environment having successfully adapted to every ecosystem both aquatic and terrestrial. They are a large group of bilaterally symmetrical, elongated, pseudocoelomate helminthes in the animal kingdom. They are elongated, non-metamerically segmented, and cylindrical or round so referred to as the round worms. *Nema* from the word Nematode

means thread because they are threadlike, vermiform and slender worms [1]. They are the largest and the most successful pseudocoelomate phylum and very remarkable organisms. It has been estimated that the total number of nematode species might be approximately 1,000,000 in about 20 orders within two classes [3]. It is believed that 90% of animals on the ocean floor and 80% of animals on earth may be nematodes. It is believed that a handful of soil contains hundreds of nematodes and that soil habitats may contain undescribed free-living nematodes [4].

## **2.2 Parasitic nematodes**

Most nematodes are free-living but over 16,000 are parasitic and cause infections leading to great morbidity and mortality to humans, animals and plants [2].

For example, some nematodes are directly transmitted through the soil which harbors their eggs and larvae stages and hence called the soil transmitted helminthes. Such nematodes are *Ascaris lumbricoides* (common roundworm of man), *Trichuris trichiura* (whipworm), *Necator americanus* and *Ancylostoma duodenalis* (hookworms of man) and *Strongyloides stercoralis* (thread worm of man) [5, 6].

Some nematodes are indirectly transmitted as they require vectors usually arthropods for them to be transmitted from one host to another as in the filarial worms such as *Loa loa* (African eye worm), *Onchocerca volvulus, Wuchereria bancrofti* and *Brugia* species.

Some nematodes are parasitic in animals, for example, *Ascaris suum* (pig), *Ascaridia galli* (chicken), *Toxocara canis*, *Trichuris vulpis* and *Strongyloides canis* (dogs), *Ancylostoma tubaeforme* and *A. brazilense* (cat hookworms) [7].

### **2.3 Types of parasitic nematodes**

Nematode parasites can reside in every tissue in their vertebrate host. Therefore, they can be categorized according to their residence in their host [8, 9]:


**5**

**4. Conclusion**

*Introductory Chapter: Helminthes Diversity - Focus on Nematodes*

**3. General transmission and reproduction patterns of nematodes**

Nematodes have diverse modes of transmission strategies and great variation in life cycles which are complex. Nematodes are gonochoristic with distinct separate sexes. They have larger females than males, which possess copulatory spicules for internal fertilization. They have tubular gonads and amoeboid sperm cells. Only

Some nematodes are parthenogenetic such as threadworms. Most are oviparous such as *Ascaris lumbricoides* (common roundworm), *Trichuris trichiura* (whipworm) and *Enterobius vermicularis* (pinworm)*.* Ovoviviparous nematodes include threadworms and hookworms because they lay eggs with larvae. Viviparous nematodes are *Trichinella spiralis*, filarial worms and *Dracunculus medinensis* (Guinea worm)

Nematodes are long lived worms with highly resistant eggs and great fecundity (large egg outputs) which is adaptive to juvenile survival. Their eggs exhibit remarkable uniformity in size ranging from 50 to 90 μm long. However, the egg shells are highly variable but basically have three to five layers and are highly resistant to environmental conditions. Nematodes have life cycles with larval stages that resemble the adults. The larval stages have four molts and one adult basically (egg-L1-L2-L3-adult) [1, 2].

These are features that make their parasitic existence a success and they include the:

• **Body wall and pseudocoel**: this protects the worm in the host environment which is the small intestine. The epidermis is a syncytium consisting of a single layer of cells, covered by a thick collagenous cuticle. The complex and metabolically active cuticle often have two or three distinct layers. Underneath the epidermis, lies a layer of longitudinal muscle cells. The pseudocoel acts as

• **Digestive system:** the digestive systems are highly efficient for parasitic mode of life. The oral cavity opens into a muscular sucking pharynx, also lined with cuticle. They have complete digestive system, referring to the alimentary canal which extends from the anterior mouth to the anus located near the tail. The

• **Reproductive system**: this is adaptive to the survival of the parasites. Sexes in nematodes are separate and they have complex life cycles. They have prodigious fecundity and eggs are often highly resistant to desiccation. The eggs are protected by an outer shell, secreted by the uterus. The larval stages resemble the adults and undergo 4 molts (first to third stage larvae). The third stage larva is usually infective and can respond to a wide range of stimuli before it molts to adult in the host [1, 2].

Helminthiasis, no doubt consists of a group of diseases of important public health and socio-economic significance so it is a paradox to be described as "Neglected tropical diseases." The cosmopolitan, ubiquitous and adaptive nature of nematodes and other helminthes are far more than we often think. This gives reasons to suggest that helminthiasis should not be underestimated as a serious cause of morbidity and mortality.

*DOI: http://dx.doi.org/10.5772/intechopen.90473*

very few nematodes are monoecious [5, 6].

because they give rise directly to larvae [5–7].

**3.1 Adaptations of parasitic nematodes**

hydrostatic skeleton [6, 7].

mouth has lips in some cases.

*Helminthiasis*

**2.2 Parasitic nematodes**

*crofti* and *Brugia* species.

**2.3 Types of parasitic nematodes**

means thread because they are threadlike, vermiform and slender worms [1]. They are the largest and the most successful pseudocoelomate phylum and very remarkable organisms. It has been estimated that the total number of nematode species might be approximately 1,000,000 in about 20 orders within two classes [3]. It is believed that 90% of animals on the ocean floor and 80% of animals on earth may be nematodes. It is believed that a handful of soil contains hundreds of nematodes

Most nematodes are free-living but over 16,000 are parasitic and cause infections leading to great morbidity and mortality to humans, animals and plants [2]. For example, some nematodes are directly transmitted through the soil which harbors their eggs and larvae stages and hence called the soil transmitted helminthes. Such nematodes are *Ascaris lumbricoides* (common roundworm of man), *Trichuris trichiura* (whipworm), *Necator americanus* and *Ancylostoma duodenalis* (hookworms of man) and *Strongyloides stercoralis* (thread worm of man) [5, 6]. Some nematodes are indirectly transmitted as they require vectors usually arthropods for them to be transmitted from one host to another as in the filarial worms such as *Loa loa* (African eye worm), *Onchocerca volvulus, Wuchereria ban-*

Some nematodes are parasitic in animals, for example, *Ascaris suum* (pig), *Ascaridia galli* (chicken), *Toxocara canis*, *Trichuris vulpis* and *Strongyloides canis*

Nematode parasites can reside in every tissue in their vertebrate host. Therefore,

• **Intestinal nematodes**: they are usually large nematodes transmitted directly to the host and dwelling in the gastrointestinal tract, e.g., *Ascaris lumbricoides, Trichuris trichiura, Hookworms, Strongyloides stercoralis,* and *Enterobius vermicu-*

• **Soil-transmitted nematodes** (geohelminths): these are nematodes whose eggs embryonate in the soil and larvae stages also undergo ecdysis in the soil and are transmitted directly to the host, e.g., *Ascaris lumbricoides, Trichuris trichiura*,

• **Filarial nematodes:** these are thread like nematodes that have a pre-larval stage call microfilaria and are transmitted indirectly via an insect vector to the host which are usually mammals, e.g., *Onchocerca volvulus*, *Loa loa, Wuchereria* 

*bancrofti, Brugia malayi, Brugia timori* and *Dipetalonema streptocerca*.

• **Tissue dwelling nematodes:** these are nematodes living in the tissues of the host such as in the lymphatics, e.g., *Wuchereria bancrofti, Brugia malayi* and

• **Subcutaneous nematodes**: these consist of nematode dwelling in the subcutaneous tissue of their host, e.g., *Onchocerca volvulus, Loa loa, Mansonella* 

*laris.* Polyparasitism of enteric nematodes has been documented [1].

(dogs), *Ancylostoma tubaeforme* and *A. brazilense* (cat hookworms) [7].

they can be categorized according to their residence in their host [8, 9]:

*Necator americanus* and *Ancylostoma duodenale* (hookworms).

*Dracunculus medinensis* (serous tissue).

and that soil habitats may contain undescribed free-living nematodes [4].

**4**

*perstans*.

## **3. General transmission and reproduction patterns of nematodes**

Nematodes have diverse modes of transmission strategies and great variation in life cycles which are complex. Nematodes are gonochoristic with distinct separate sexes. They have larger females than males, which possess copulatory spicules for internal fertilization. They have tubular gonads and amoeboid sperm cells. Only very few nematodes are monoecious [5, 6].

Some nematodes are parthenogenetic such as threadworms. Most are oviparous such as *Ascaris lumbricoides* (common roundworm), *Trichuris trichiura* (whipworm) and *Enterobius vermicularis* (pinworm)*.* Ovoviviparous nematodes include threadworms and hookworms because they lay eggs with larvae. Viviparous nematodes are *Trichinella spiralis*, filarial worms and *Dracunculus medinensis* (Guinea worm) because they give rise directly to larvae [5–7].

Nematodes are long lived worms with highly resistant eggs and great fecundity (large egg outputs) which is adaptive to juvenile survival. Their eggs exhibit remarkable uniformity in size ranging from 50 to 90 μm long. However, the egg shells are highly variable but basically have three to five layers and are highly resistant to environmental conditions. Nematodes have life cycles with larval stages that resemble the adults. The larval stages have four molts and one adult basically (egg-L1-L2-L3-adult) [1, 2].

## **3.1 Adaptations of parasitic nematodes**

These are features that make their parasitic existence a success and they include the:


## **4. Conclusion**

Helminthiasis, no doubt consists of a group of diseases of important public health and socio-economic significance so it is a paradox to be described as "Neglected tropical diseases." The cosmopolitan, ubiquitous and adaptive nature of nematodes and other helminthes are far more than we often think. This gives reasons to suggest that helminthiasis should not be underestimated as a serious cause of morbidity and mortality.

*Helminthiasis*

## **Author details**

Omolade Olayinka Okwa Department of Zoology, Lagos State University, Lagos, Nigeria

\*Address all correspondence to: okwaomolade@hotmail.com

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**7**

*Introductory Chapter: Helminthes Diversity - Focus on Nematodes*

*DOI: http://dx.doi.org/10.5772/intechopen.90473*

Parasitology in Tropical Africa. Ibadan, Nigeria: Text Flow Publishers; 1990.

[1] Ukoli FMA. Introduction to

[2] Okwa OO. The Biology of the Tropical Parasites. Germany: Lambert Academic Publishers; 2016. p. 145. ISBN:

[3] Otubanjo OA. Parasites of Man and Animals. Lagos, Nigeria: Concept Publications; 2013. p. 648. ISBN: 978-

[4] Anderson RC. Nematode Parasites of Vertebrates: Their Development and Transmission. 2nd ed. Oxford, UK: CABI Publishing; 2000. p. 650. ISBN:

[5] Hugot P, Banjard P, Morano S. Biodiversity in helminthes as a field of study: An overview. Nematology.

[6] Smyth JD. Introduction to Animal Parasitology. 3rd ed. Cambridge, UK: Cambridge University Press; 1994.

[7] World Health Organization. Global Burden of Diseases. Geneva: WHO Technical Report; 2008. p. 160. ISBN:

[8] Da Silva NR, Booker S, Hotex PJ, Montressor A, Eagles D, Savioli L. Soil transmitted helminthes. Updating the global picture. Trends in Parasitology.

[9] Larry RS, Janovy JJ. Foundations of Parasitology. 8th ed. New York, United States: McGraw-Hill; 2009. pp. 120-150

p. 549. ISBN: 0521-428114

p. 462. ISBN: 978-2783-005

978-3-330-00888-5

978-51446-04; 419-558

085198799-0

2001;**3**:199-208

978-924-1563710

2003;**19**:547-551

**References**

*Introductory Chapter: Helminthes Diversity - Focus on Nematodes DOI: http://dx.doi.org/10.5772/intechopen.90473*

## **References**

*Helminthiasis*

**6**

**Author details**

Omolade Olayinka Okwa

Department of Zoology, Lagos State University, Lagos, Nigeria

\*Address all correspondence to: okwaomolade@hotmail.com

provided the original work is properly cited.

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

[1] Ukoli FMA. Introduction to Parasitology in Tropical Africa. Ibadan, Nigeria: Text Flow Publishers; 1990. p. 462. ISBN: 978-2783-005

[2] Okwa OO. The Biology of the Tropical Parasites. Germany: Lambert Academic Publishers; 2016. p. 145. ISBN: 978-3-330-00888-5

[3] Otubanjo OA. Parasites of Man and Animals. Lagos, Nigeria: Concept Publications; 2013. p. 648. ISBN: 978- 978-51446-04; 419-558

[4] Anderson RC. Nematode Parasites of Vertebrates: Their Development and Transmission. 2nd ed. Oxford, UK: CABI Publishing; 2000. p. 650. ISBN: 085198799-0

[5] Hugot P, Banjard P, Morano S. Biodiversity in helminthes as a field of study: An overview. Nematology. 2001;**3**:199-208

[6] Smyth JD. Introduction to Animal Parasitology. 3rd ed. Cambridge, UK: Cambridge University Press; 1994. p. 549. ISBN: 0521-428114

[7] World Health Organization. Global Burden of Diseases. Geneva: WHO Technical Report; 2008. p. 160. ISBN: 978-924-1563710

[8] Da Silva NR, Booker S, Hotex PJ, Montressor A, Eagles D, Savioli L. Soil transmitted helminthes. Updating the global picture. Trends in Parasitology. 2003;**19**:547-551

[9] Larry RS, Janovy JJ. Foundations of Parasitology. 8th ed. New York, United States: McGraw-Hill; 2009. pp. 120-150

**9**

Section 2

Soil Transmitted

Helminthes

Section 2
