Communicable Diseases Module: 37. Other Vector-Borne Diseases of Public Health Importance

Study Session 37  Other Vector-Borne Diseases of Public Health Importance

Introduction

Three important vector-borne diseases have been discussed previously in this Module: malaria in Study Sessions 5–12 and relapsing fever and typhus in Study Session 36. In this study session, you will learn the causes, modes of transmission, clinical manifestations, prevention and control of four other vector-borne diseases of public health importance in Ethiopia. They are schistosomiasis, leishmaniasis, onchocerciasis and lymphatic filariasis. A better understanding of these diseases will help you to identify patients and refer them quickly to a health centre or hospital for specialist treatment.

You will also learn about the health education messages that you need to communicate to members of your community, so they can reduce their exposure to the vectors of these diseases and apply appropriate prevention measures. As you will see in this study session, prevention of all of these diseases includes controlling the vectors with chemicals and/or environmental management, using personal protective clothing or bed nets to reduce exposure to the vectors, and rapid case detection and referral for treatment. Early treatment prevents serious complications and can save lives, and it also reduces the reservoir of infectious agents in the human population.

Learning Outcomes for Study Session 37

When you have studied this session, you should be able to:

37.1  Define and use correctly all of the key words printed in bold. (SAQs 37.1 to 37.5)

37.2  Identify the vectors and modes of transmission of schistosomiasis, leishmaniasis, onchocerciasis and lymphatic filariasis. (SAQs 37.1, 37.2 and 37.3)

37.3  Describe the distribution and impact of schistosomiasis, leishmaniasis, onchocerciasis and lymphatic filariasis in Ethiopia. (SAQs 37.1, 37.3, 37.4 and 37.5)

37.4  Describe the symptoms of schistosomiasis, leishmaniasis, onchocerciasis and lymphatic filariasis, and how you would diagnose and refer cases to a higher level health facility. (SAQs 37.3 and 37.4)

37.5  Describe how you would apply prevention and control measures against schistosomiasis, leishmaniasis, onchocerciasis and lymphatic filariasis. (SAQs 37.1, 37.3 and 37.5)

37.1  Schistosomiasis

Schistosomiasis is a chronic communicable disease caused by parasitic flatworms (also known as trematodes, or blood flukes), which affect the blood vessels in the intestines or in the urinary tract of infected people. In some places, the disease is known by its alternative name – bilharzia. Two species of Schistosoma parasites are common in Ethiopia: Schistosoma mansoni (Figure 37.1) which causes disease mainly in the intestines, and Schistosoma haematobium, which causes disease mainly in the bladder and sometimes also in other parts of the urinary tract such as the kidneys.

Figure 37.1  A mating pair of Schistosoma mansoni flatworms, magnified and viewed through a microscope; the thin female worm is curled partly inside and below the much larger male worm. Adult worms measure 12 to 20 mm in length. (Photo: CDC Image Library, image number 11194, Dr Shirley Maddison)

The WHO estimates that more than 207 million people worldwide are infected with Schistosoma parasites – and 85% of them are in Africa. Approximately 200,000 people die every year in Africa as a result of the complications caused by these parasites. Rural communities living near water bodies such as rivers, lakes and dams may be highly affected by the disease, because the worms have a complex lifecycle in which they spend part of their development living in freshwater snails. You will learn more about their lifecycle later in this section. First, as a Health Extension Practitioner, you need to know where the disease is common in Ethiopia.

37.1.1  Where is schistosomiasis common in Ethiopia?

Schistosoma mansoni is widespread in several parts of Ethiopia, usually at an altitude of between 1,200 to 2,000 metres above sea level. Some of the common places include Ziway (Figure 37.2), Hawassa, Bishoftu, Wonji, Haromaya, Jimma, Bahir Dar and some places in Gojam, Dessie and Tigray. In many of these locations, more than 60% of schoolchildren are infected with Schistosoma mansoni. A high burden of the disease in children has severe adverse effects on their growth and performance at school.

Figure 37.2  Lake Ziway, Ethiopia. Washing, swimming or standing in infected water exposes people to the risk of infection with Schistosoma parasites. Children are especially vulnerable. (Photo: Basiro Davey)

Schistosoma haematobium is limited to some lowland areas, including the swampy land and floodplains of the Awash and Wabe Shebele valleys and along the Ethiopian–Sudan border.

37.1.2  Mode of transmission of schistosomiasis

Let us now focus on the mode of transmission of schistosomiasis. The major reservoirs of Schistosoma parasites are infected humans (the primary hosts) and freshwater snails (the intermediate hosts).

Figure 37.3 shows how Schistosoma parasites are transmitted from infected people to new human hosts, via the intermediate hosts – freshwater snails. Figure 37.4 shows the lifecycle of the parasites in more detail, highlighting the immature forms that can be found in the water.

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Figure 37.3  How schistosomiasis is transmitted from infected humans to new human hosts, via freshwater snails. (Source: Adapted from http://www.who.int/schistosomiasis/epidemiology/en/)

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Figure 37.4  Lifecycle of Schistosoma parasites as they pass through human hosts and freshwater snails. (Source: The Open University, Environment: Journeys Through a Changing World, U116, Block 3, Figure 1.13)

The immature form of the parasite penetrates the skin of a new host when he or she is swimming, washing or standing in infected water. They pass to the liver, where they mature into adult worms. Male and female adult worms mate (look back at Figure 37.1) and deposit their eggs in the blood vessels of either the intestine (Schistosoma mansoni) or bladder (Schistosoma haematobium). The eggs pass out into the water in either the faeces or urine, to continue the infection cycle.

37.1.3  Clinical manifestations and diagnosis of schistosomiasis

The infected person’s immune system reacts against the parasites’ eggs in their blood vessels, which are recognised as ‘foreign bodies’. The immune reaction causes an acute inflammation around the eggs, which can lead to chronic symptoms (see Box 37.1). Note that the clinical manifestations of schistosomiasis are mainly related to the immune response against the eggs in the intestine or bladder – the symptoms are not due to the worms themselves. The adults can survive in the person’s body for up to 20 years, releasing around 300 eggs every day.

The clinical manifestations (described above) should lead you to suspect cases of schistosomiasis. Asking children if they have seen any blood in their urine is an important way of detecting whether Schistosoma haematobium is common in the area. The diagnosis of schistosomiasis is confirmed in a laboratory by direct observation of the parasite eggs in samples of faeces or urine examined under the microscope (Figure 37.5).

Figure 37.5  An egg from a Schistosoma parasite, magnified and viewed under a microscope, confirms the diagnosis of schistosomiasis. (Photo: CDC Image Library, image number 4841)

37.1.4  Prevention and control of schistosomiasis

Several prevention and control strategies should be integrated to reduce the burden of schistosomiasis. You have an important role as a Health Extension Practitioner to teach community members in affected areas how to apply the major prevention and control measures, which can be described in five general categories:

• Integrated vector control (IVC) measures, aimed at reducing the number of vectors; in areas affected by schistosomiasis, these measures involve using the chemical ‘Endod’ to kill the snails, and environmental management to destroy snail habitats by improving irrigation and farming practices; this could involve removing vegetation and draining and filling swampy areas or shallow pools wherever possible.
• Parasite control measures, aimed at reducing the number of parasites, e.g. treating water for washing with chlorine or iodine to kill the eggs and immature Schistosoma organisms.
• Personal protection against exposure to the parasites, e.g. farmers, fishermen and others who have to stand in infected water should wear rubber boots to protect their skin from penetration by the swimming forms of the Schistosoma parasites.
• Rapid case detection and referral to the nearest health centre for effective treatment; the drug used to treat schistosomiasis is called praziquantel, which is administered orally at a dosage of 40–60 mg per kg of body weight, given in two or three doses over a single day. You are not expected to prescribe praziquantel, which must be given at the health centre.
• Education in the community about the causes and modes of transmission of schistosomiasis.

37.2  Leishmaniasis

Leishmaniasis is a chronic parasitic disease, which exists in two forms: visceral leishmaniasis (also known as kala-azar), which affects the internal organs such as the liver and spleen, and cutaneous leishmaniasis, which affects the skin. The infectious agents are protozoa (single-celled organisms, Figure 37.6). There are four major species of Leishmania protozoa in Ethiopia:

• Leishmania donovani, which causes visceral leishmaniasis
• Leishmania aethiopica, Leishmania major and Leishmania tropica, all of which cause cutaneous leishmaniasis.

Figure 37.6  Leishmania protozoa, stained blue and magnified by viewing under a microscope. (Photo: CDC Image Library, image 11068)

Around 12 million people in 88 countries around the world are currently thought to be infected with Leishmania parasites and the WHO estimates that one to two million new cases occur each year. The vectors (and intermediate hosts) for these parasites are sandflies. The lifecycle will be described later in this section.

37.2.1  Where is leishmaniasis common in Ethiopia?

During your work in the community, you should know the common places where leishmaniasis is present. Visceral leishmaniasis affecting the internal abdominal organs such as the liver and spleen is widely distributed in the lowlands of Ethiopia. Important endemic locations include Konso woredas (Lake Abaya and Segen Valleys), the Lower Omo plains, the Metama and Humera plains and Adiss Zemen. Cutaneous leishmaniasis occurs in Meta-Abo, Sebeta, Kutaber in Wello, and in some places in South West Ethiopia such as Jimma Zone.

37.2.2  Mode of transmission of leishmaniasis

Leishmaniasis is transmitted through the bite of female phlebotomine sandflies (Figure 37.7), which bite humans and some animals, and take blood meals to feed the development of their eggs. Phlebotomine means ‘blood-sucking’ and is pronounced ‘fleb-otto-meen’. There are about 30 species of sandflies that can transmit Leishmania parasites to humans found throughout the tropical and temperate regions of the world. The females lay their eggs in many locations, including the burrows of rodents, old tree bark, cracks in buildings and rubbish heaps – anywhere that is warm and humid enough for their eggs to develop into flies.

Figure 37.7  A female phlebotomine sandfly taking a blood meal from a person’s arm. Note the human blood in its transparent abdomen. (Photo: CDC Image Library, image 10276/James Gathany)

When sandflies take blood meals from an infected person, they also become infected with the protozoa that cause leishmaniasis. The protozoa develop inside the sandfly and are passed on when the sandfly takes a blood meal from a healthy person. The Leishmania protozoa multiply inside the white blood cells of the healthy person and cause disease (Figure 37.8).

Figure 37.8  Transmission of Leishmania parasites from a sick person to a healthy person by a sandfly. The enlarged abdomen of the sick person on the left indicates visceral leishmaniasis affecting the internal organs.

37.2.3  Clinical manifestation and diagnosis of leishmaniasis

The clinical presentation of the two forms of leishmaniasis are very different. Cutaneous leishmaniasis normally produces skin ulcers on the exposed parts of the body such as the face, arms and legs (Figure 37.9). The disease can produce a large number of ulcers – sometimes up to 200 – which may result in physical disability (e.g. in using the hands). The visible ulcers are a source of social stigma, which can leave the patient suffering mental distress and rejection in their community.

Figure 37.9  Ulceration due to cutaneous leishmaniasis (a) on the face, (b) on the hand. (Photos: (a) WHO TDR Image Library, image 03061531/Crump; (b) CDC Image Library, image 352)

Visceral leishmaniasis (also known as kala azar, which means black fever in Hindu) is a life-threatening disease characterised by irregular episodes of fever, rapid and extensive weight loss, huge swelling of the spleen and liver (Figure 37.10), and anaemia. If left untreated, up to 100% of patients die within two years of infection. For this reason, visceral leishmaniasis is said to have a high case-fatality rate.

Figure 37.10  A child with severe weight loss and an enlarged abdomen with a huge liver and spleen due to visceral leishmanisis. (Photo: WHO at http://www.who.int/leishmaniasis/visceral_leishmaniasis/en/index.html)

You can identify patients with leishmaniasis by the clinical manifestations of the disease. For confirmation of the diagnosis, laboratory investigations should be done in health centres or hospitals, where the protozoan parasites can be detected in blood smears viewed with a microscope (look back at Figure 37.6).

37.2.4  Prevention and control of leishmaniasis

Several prevention and control measures are available for leishmaniasis. The general principles will already be familiar to you from the earlier discussion of schistosomiasis.

• Integrated vector control (IVC) measures, aimed at reducing the numbers of sandflies by indoor residual spraying of the inside and outside walls of houses, doorways, animal houses, and possible breeding sites of the sandflies (Figure 37.11); use of insecticide treated bed nets (ITNs) for sleeping under at night; and environmental management to reduce the breeding sites of sandflies.
• Rapid case detection and referral to the nearest health centre or hospital prevents the transmission of the parasite to others. Cases of leishmaniasis will be treated using intravenous or intramuscular drugs such as pentostam or amphotericin B. You cannot prescribe these drugs, which must be given under medical supervision.
• Investigate and control epidemics in epidemic-prone areas: early identification and management of epidemics of leishmaniasis helps to control the disease from spreading to the wider population.
• Education in the community about the causes and modes of transmission of leishmaniasis.

Figure 37.11  Spraying breeding sites of sandflies with insecticides.

37.3  Onchocerciasis

Onchocerciasis is a parasitic vector-borne disease caused by a worm that affects the skin, lymph nodes and the eyes of infected people. It is also called river blindness. The WHO estimates that worldwide there are about 500,000 people who are blind due to onchocerciasis. The disease is caused by a tiny worm called Onchocerca volvulus (Figure 37.12), which is transmitted from person to person in the bite of blackflies.

Figure 37.12  An Onchocerca volvulus worm, stained blue and magnified by viewing with a microscope. (Photo: CDC Image Library, image 1147)

37.3.1  Where is onchocerciasis common in Ethiopia?

Onchocerciasis is found in the western part of Ethiopia, where there are many rapidly flowing rivers and streams, with vegetation along the banks that provide good habitats for the blackflies that transmit the parasite. The most affected areas include Keffa, Illubabor, Gambella and Wollega. Cases of onchocerciasis have been also reported from Pawe, Humera and Metema.

37.3.2  Mode of transmission of onchocerciasis

The parasites that cause onchocerciasis are transmitted from human to human through the bites of blackflies, which belong to Simulum species (Figure 37.13). Blackflies breed in fast-flowing rivers and streams, with good vegetation nearby. Unlike mosquitoes and sandflies, they bite during the day when people are active in the area.

Figure 37.13  A blackfly feeding on the skin of a human host. (Photo: WHO at www.who.int/onchocerciasis )

The adult worms mate in the infected person, and the eggs hatch into microscopic worms called microfilaria, which burrow through the body tissues. The person’s immune system attacks the microfilaria, causing inflammation and damage in the surrounding tissues. Sight defects and eventually blindness develops when the microfilaria are embedded in the person’s eye. When a female blackfly bites an infected person during a blood meal, the microfilaria are transferred from the person to the fly (Figure 37.14a). Over the course of one to three weeks, the microfilaria develop inside the blackfly to form infective larvae (Figure 37.14b). These are then passed on to other people when the blackfly takes another blood meal (Figure 37.14c). The microfilaria migrate to the skin, lymph nodes and eyes of the infected person, causing inflammation and tissue damage.

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Figure 37.14  Transmission of Onchocerca volvulus from person to person by blackflies. (Source: www.who.int/onchocerciasis)

In the human host, the larvae migrate into the skin, and nodules (swellings) form around them. They slowly mature into adult worms, which can live for 15 years in the human body. After mating, the female worm releases around 1,000 microfilaria a day into the surrounding tissue. Microfilaria live for one to two years, moving around the body. When they die, they cause an inflammatory response which leads to the clinical manifestations and complications such as blindness.

37.3.3  Clinical manifestations and diagnosis of onchocerciasis

The clinical manifestations of onchocerciasis are the result of inflammation against the dead microfilaria. The most common clinical manifestations include skin rashes, lesions, intense itching, loss of the colour of the skin, and nodule formation (Figure 37.15a). Microfilaria also migrate to the eye, and causes scarring of the cornea (the covering of the eyeball), which leads to sight defects and ultimately blindness (Figure 37.15b).

The itching and disfiguring nodules and blindness are sources of great distress to patients, who may be stigmatised and rejected by their communities.

Figure 37.15(a) Nodules on the legs and loss of pigmentation in the skin of a man with cutaneous onchocerciasis. (b) Blindness due to onchocerciasis. (Photos: (a) WHO at www.who.int/onchocerciasis; (b) WHO/TDR image 9703913/Crump)

Diagnosis of onchocerciasis is made by clinical examination. If you suspect that a patient may be infected, you should make a referral for laboratory confirmation and treatment. Microscopic investigation of a skin snip (taking samples from the skin) can identify the microfilaria and confirm the diagnosis.

37.3.4  Prevention and control of onchocerciasis

The WHO believes that onchocerciasis can be eliminated through the application of effective prevention and control methods, which are summarised below:

• Integrated vector control measures to reduce the population of blackflies, through application of insecticides in vegetation where vectors breed, and environmental management to reduce vegetation around fast-flowing rivers where people live.
• Personal protective clothing to avoid the bite of blackflies by covering exposed skin with clothing and wearing headgear in endemic areas.
• Community-directed mass drug administration (MDA) with ivermectin, i.e. mass drug treatment of everyone in communities where the diseases is endemic with the drug ivermectin, which kills the microfilaria, every 6 to 12 months (Figure 37.16). This is the most successful intervention at community level. Community members fully participate in the programme and the drugs are delivered by trained village drug distributors, supervised by Health Extension Workers and Practitioners like you. Community-directed MDA is being implemented in endemic areas of Ethiopia such as Pawe, Jimma, Illubabor and Keffa.
  

  Figure 37.16  Mass drug administration with ivermectin successfully prevents onchocerciasis in affected communities. (Photo: WHO TDR Image Library, image 9703979/Crump)
• Rapid case detection and referral, particularly for complicated cases involving sight loss
• Education in the community about the causes, mode of transmission and prevention measures against onchocerciasis (Figure 37.17). Encouraging acceptance of the mass drug administration programme is an important health education message that you can deliver in affected communities.

Figure 37.17  Women at a health education session on how to protect themselves and their children from onchocerciasis. (Photo: WHO/Crump/image 97031009)

37.4  Lymphatic filariasis

In this final section, you will learn about the definition, mode of transmission, clinical manifestations, and methods of prevention and control of lymphatic filariasis. It is also known as elephantiasis because of its effects on the legs of infected people. Lymphatic filariasis is a parasitic disease caused by a worm that invades the lymphatic system – the network of vessels that exists throughout the body, connecting the lymph nodes, spleen and other organs, and where white blood cells are primarily found (Figure 37.18).

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Figure 37.18  The human lymphatic system. (Diagram: The Open University, SXR376 Preparatory Reading, Figure 1.2)

The WHO estimates that over 120 million people worldwide are currently infected with the worm (species name Wuchereria bancrofti, Figure 37.19) which is responsible for 90% of all cases.

Figure 37.19  A Wuchereria bancrofti worm, stained blue and magnified by a microscope. (Photo: CDC Image Library, image 3009)

37.4.1  Where is lymphatic filariasis common in Ethiopia?

Like onchocerciasis, lymphatic filariasis is common in western Ethiopia, such as Illubabor, Keffa, Jimma, Wollega, Gambella and Pawe. Though the disease is not fatal, it is responsible for considerable disability and distress, causing social stigma among men, women and children. You will learn more about the social consequences of lymphatic filariasis and a non-infectious cause of swelling in the legs (podoconiosis) in Study Session 39.

37.4.2  Mode of transmission of lymphatic filariasis

The parasites that cause lymphatic filariasis are transmitted from human to human through the bites of Culex and Anopheles mosquitoes. The female mosquitoes take the microscopic forms of the parasitic worm (microfilaria) from an infected person during a blood meal (Figure 37.20a). The microfilaria develop into larvae, and when the mosquito feeds on another person, the larvae enter the skin punctured by the mosquito bite (Figure 37.20b). The larvae travel via the lymphatic vessels, where they develop into adult worms all over the body (Figure 37.20c). After mating, the females lay millions of eggs which develop into microfilaria, completing the lifecycle.

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Figure 37.20  Life cycle of lymphatic filariasis. (Source: WHO at http://www.who.int/lymphatic_filariasis/en/)

37.4.3  Clinical manifestations of lymphatic filariasis

The clinical manifestations of the disease are as a result of the inflammation and damage to the lymphatic vessels caused by the person’s own immune response trying to reject the worms, and when vessels become blocked by clusters of worms. The overall effect is to disrupt the lymphatic system, which normally collects tissue fluids draining from the body’s cells and returns the fluid to the blood stream. If the lymphatic drainage is blocked, the lower limbs and sometimes also the genitals become hugely swollen with fluid – a condition called lymphoedema (pronounced ‘limf-ee-deem-ah’). Most infections do not produce symptoms, but in people where the lymphatic drainage is badly damaged the common symptoms include hydrocele (swelling of the scrotum, pronounced ‘hy-droh-seel’), swelling of the legs and feet, and thickening of the skin into folds (Figure 37.21). Infection of the swollen skin folds by bacteria is a frequent cause of very painful attacks. Patients suffer from episodes of fever and around 40% develop kidney damage.

Figure 37.21  Lymphatic filariasis causing swelling and tissue damage in (a) a leg; (b) the scrotum; (c) a breast. (Photos: WHO TDR Image Library, images (a) 94022625, (b) 9502756, (c) 9502760/Andy Crump)

37.4.4  Diagnosis of lymphatic filariasis

You can suspect lymphatic filariasis from the clinical manifestations, but the diagnosis can only be confirmed by laboratory tests to reveal the microfilaria in blood smears viewed with a microscope. Adult worms blocking the lymphatic vessels or nodes are difficult to reach. Therefore, if you live in an endemic area and you suspect a case of lymphatic filariasis, you should refer the patient to the nearest health centre for further testing and treatment.

37.4.5  Prevention and control of lymphatic filariasis

Lymphatic filariasis is one of the few communicable diseases that the WHO believes could be eradicated (totally removed from all populations in the world, never to return) with the currently available prevention and control measures. These are:

• Integrated vector control (IVC) measures to reduce the mosquito population, including indoor residual spraying, use of insecticide treated bed nets (ITNs), and environmental management such as drainage and filling of breeding sites for the mosquitoes.
• Community-directed mass drug administration (MDA). The WHO recommends a two-drug regimen of albendazole and diethylcarbamazine (or ivermectin in areas where onchocerciasis is also endemic), which is administered to the entire at-risk population once every year for four to six years. These drugs are prescribed by staff at health centres.
• Personal protective clothing to reduce exposure of skin to mosquito bites, and use of ITNs.
• Rapid case detection and referral to prevent cases from spreading.
• Education in the community about the causes and modes of transmission of lymphatic filariasis, and ways to protect themselves from mosquito bites. Encouraging acceptance of the mass drug administration programme is an important health education message that you can deliver if your community is affected. You also have a key role in educating patients about how to prevent and alleviate disabilities and pain due to lymphatic filariasis, as described in the final part of this study session.

37.4.6  Prevention and alleviation of disability due to lymphatic filariasis

Patients with lymphoedema and thickened skin folds (for example, as in Figure 37.21) can be empowered to manage their symptoms and reduce their discomfort and pain through simple, but rigorous, hygiene techniques. You should educate them to wash the affected parts carefully every day, especially between the folds of thickened skin, and gently dry the area with a clean cloth. They should elevate (raise) swollen legs as much as possible whatever they are doing during the day and raise the foot of the bed or sleeping mat at night (Figure 37.22). Advise the patient to exercise the limbs any time and anywhere, as often as possible, to help the fluid to exit from their swollen limbs.

Figure 37.22  Washing the affected limbs and elevating them while working or sleeping helps to alleviate the pain and swelling due to lymphatic filariasis. (Diagrams: WHO, 2003, Community Home-Based Prevention of Disability due to Lymphatic Filariasis)

In the next study session, you will learn about two more diseases of public health importance in Ethiopia – rabies and taeniasis (tapeworm disease) – which are spread to humans by warm-blooded animals (dogs and cattle).

Summary of Study Session 37

In Study Session 37, you have learned that:

1. Schistosomiasis is caused by parasitic flatworms transmitted from freshwater snails to humans. It is common in communities living near rivers, lakes and streams, where infected people shed Schistosoma eggs when they urinate or defaecate into the water.
2. Schistosoma mansoni affects blood vessels in the intestines and causes abdominal pain, bloody diarrhoea and anaemia. Schistosoma haematobium affects blood vessels in the bladder and causes pain during urination and bloody urine.
3. Leishmaniasis is caused by protozoan parasites transmitted to humans through the bite of sandflies, which breed in warm, humid places such as rubbish collections and rodent burrows.
4. Leishmania donovani causes the life-threatening condition called visceral leishmaniasis (or kalaazar), manifested by fever, weight loss and swelling of the liver and spleen. Three other Leishmania species cause cutaneous leishmaniasis, which manifests as ulcers in exposed areas of skin.
5. Onchocerciasis is caused by a nematode worm (Onchocerca volvulus) transmitted in the bite of blackflies, which breed near fast-flowing rivers with good vegetation. The microscopic microfilaria cause skin nodules and can migrate to the eye, causing blindness.
6. Lymphatic filariasis (or elephantiasis) is caused by a nematode worm (Wuchereria bancrofti) transmitted to humans in the bite of female mosquitoes. The worms block the lymphatic system, causing swelling of the limbs and sometimes the genitals, resulting in severe pain, disability and bacterial infection of thickened skin folds.
7. Integrated vector control measures such as indoor residual spraying, use of insecticide treated bed nets (ITNs), chemical treatment of water, use of personal protective clothing and environmental management to destroy vector breeding sites are key interventions to prevent these vector-borne diseases.
8. Mass drug administration of the entire at-risk population at regular intervals for several years is the recommended strategy to prevent onchocerciasis and lymphatic filariasis in endemic communities.
9. Educating the community on the modes of transmission of vector-borne diseases, effective prevention strategies, and early diagnosis and referral of patients are important activities for Health Extension Practitioners and Workers in affected areas.

Self-Assessment Questions (SAQs) for Study Session 37

Now that you have completed this study session, you can assess how well you have achieved its Learning Outcomes by answering the following questions. Write your answers in your Study Diary and discuss them with your Tutor at the next Study Support Meeting. You can check your answers with the Notes on the Self-Assessment Questions at the end of this Module.