Communicable Diseases Module: 38. Common Zoonotic Diseases in Ethiopia: Rabies and Taeniasis

Study Session 38  Common Zoonotic Diseases in Ethiopia: Rabies and Taeniasis

Introduction

In the last two study sessions in this Module, you learned about vector-borne diseases in which the infectious agent is transmitted to new human hosts by body lice, flying insects or snails. In this study session, we turn to two communicable diseases found in Ethiopia in which a non-human warm-blooded animal transmits the infectious agent to humans. These diseases are rabies transmitted to humans by dogs, and taeniasis (or tapeworm disease) transmitted by cows. Diseases in which a warm-blooded animal transmits the infectious agents to humans are known as zoonotic diseases (or zoonoses).

Zoonotic diseases are difficult to control because the non-human animal acts as a reservoir of infection that can be passed on to humans. Dogs and cows are domestic species, living in large numbers in human settlements (Figure 38.1), where it is very easy for the infection to be transmitted to people. In this study session, you will learn about the causes, modes of transmission, clinical manifestations, and the prevention and control measures against these two zoonotic diseases – rabies and taeniasis.

Figure 38.1  Cows are a reservoir of infection by intestinal tapeworms, which can be passed on to humans. (Photo: Basiro Davey)

Learning Outcomes for Study Session 38

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

38.1  Define and use correctly all of the key words printed in bold. (SAQs 38.1, 38.2 and 38.3)

38.2  Describe the mode of transmission of rabies and taeniasis to humans by their animal hosts. (SAQs 38.1, 38.2 and 38.3)

38.3  Describe the symptoms and diagnosis of rabies and taeniasis and state how you would treat or refer cases to a higher level health facility. (SAQs 38.1, 38.2 and 38.3)

38.4  Describe how you would apply prevention and control measures against rabies and taeniasis. (SAQs 38.2 and 38.3)

38.1  Rabies

Rabies is a severe life-threatening viral disease, transmitted to humans in saliva in the bite of infected animals, particularly those in the dog family (canines). Foxes, wolves, hyenas, bats, raccoons and skunks are also a reservoir of rabies virus, but in most countries they rarely transmit the disease. Bats are the main cause of rabies transmission in the USA and Canada.

The infectious agent of rabies is a virus in the rhabdovirus family, which attacks the nervous system. If an infected person is not treated very quickly, death is almost inevitable (i.e. rabies has a very high case-fatality rate). The WHO estimates that around 55,000 people die from rabies every year, and 24,000 of them are in Africa; 99% of these deaths are the result of a bite from a dog (Figure 38.2).

Figure 38.2  A bite from a dog infected with rabies virus is the source of 99% of human deaths from rabies. (Photo: CDC Image Library, image 8319)

38.1.1  The transmission of rabies in Ethiopia

Rabies is one of the most severe communicable diseases in Ethiopia, with many cases of the disease diagnosed in many parts of the country. For example, a study in Addis Ababa showed that about 73% of street dogs are infected with rabies virus and more than 2,000 people annually received treatment for rabies after a dog bite. Children are particularly vulnerable to being bitten by dogs, and about 40% of all cases are children under 15 years.

The rabies virus exists in the saliva of the infected animal (as well as in its nervous system) and is transmitted to a person through a bite. Transmission can also be if an infected animal licks a fresh break in the person’s skin or mucus membranes, e.g. in the mouth (see Table 38.1 later, for different exposure categories). The virus travels in the nerves to the brain, where it causes inflammation. Person-to-person transmission is theoretically possible if someone with advanced rabies bites another human, but this is not known to have occurred.

38.1.2  Clinical manifestations and diagnosis of rabies

From the site of the bite, the virus goes to the central nervous system (Figure 38.3) and causes the clinical manifestations which, if untreated, eventually lead to death. Rabies has the highest case-fatality rate of any communicable disease. After an incubation period usually lasting one to three months, but sometimes even up to one year after the bite, the patient develops symptoms that are similar to many other illnesses – fever, headache and general weakness. The speed of progression is faster if the original site of infection was in an area of the body that is close to the spinal cord or brain, e.g. a bite on the face or hands. As the disease gets worse, the patient experiences anxiety, confusion, difficulty sleeping, hallucination (seeing things that aren’t there), spreading paralysis (inability to move the muscles), difficulty swallowing and convulsions (uncontrollable shaking). A characteristic sign of late-stage rabies in some patients is hydrophobia (fear of water), which manifests in the patient reacting in terror if a bowl of water is brought near. This form of the disease (known as ‘furious’ rabies) prevents the patient from drinking and speeds the arrival of death within a few days. Other patients become increasingly paralysed and lose consciousness before death.

Figure 38.3  A rabid dog biting a man; the rabies virus from the dog’s saliva travels along the nerves to the person’s brain.

Diagnosis is made on the basis of these clinical signs. There are no tests to confirm rabies with absolute certainty while the patient is still alive. Viruses can be detected by laboratory investigation of the patient’s brain after death, but this test is not usually carried out in countries with few resources.

38.1.3  First aid and post-exposure prophylaxis for rabies

Wound care and anti-rabies treatment after a dog bite can reduce the occurrence of rabies in a bitten person by up to 90%. This is what you should do if someone is bitten by a dog in your kebele.

Rabies vaccines

Two types of vaccines exist to protect people from rabies after a Category II or III exposure. The older type is made from nerve tissue infected with rabies virus and is given intramuscularly (IM). The newer type of vaccine is made from virus-infected cells grown (cultured) in the laboratory and is safer and more effective. The WHO recommends that the rabies cell-culture vaccine (rabies CCV) should be used in preference to the nerve tissue vaccine wherever possible. Rabies CCV can be given either by intramuscular injection, or intradermally (ID) into the upper arm (Figure 38.4). The intradermal route has been shown to be as safe and effective as the traditional intramuscular route, and is cheaper because it requires less vaccine.

Figure 38.4  Intradermal injection of rabies cell-culture vaccine into the upper arm. (Photo: WHO, 1996, Recommendations on Rabies Post-Exposure Treatment and the Correct Technique of Intradermal Immunization against Rabies)

Modern cell-culture vaccines should be given in four or five doses: the dosage for each injection depends on the vaccine type and the route of administration (intramuscular dosages are 0.5 ml or 1.0 ml, whereas the intradermal dosage is only 0.1 ml). If you are referring someone to a health centre for rabies post-exposure prophylaxis, you should tell the patient and their family that it is essential to return at fixed intervals for repeat vaccinations in order to prevent rabies if they have been infected by the bite.

The intramuscular regimen is given at days 0, 3, 7, 14 and 28 after the exposure. The intradermal regimen is given at days 0, 3, 7, 28 and 90 after exposure. There is also a rabies vaccine which is administered at days 0, 7 and 28 days (IM), and rabies duck embryo vaccine, which is administered at day 0, 7 and 21 days (IM or ID). For both these vaccines, a booster dose is given after two to three years.

38.1.4  Prevention of rabies

Since very few people survive after they develop symptoms of rabies, prevention is the best alternative. The main prevention measures against rabies are aimed at controlling the animals that transmit the virus, educating the community on how to protect themselves from dog bites, and what action to take if they are bitten. Your roles as a Health Extension Practitioner are to contribute to a comprehensive rabies control programme by carrying out the following activities:

• Educate the owners of dogs and the public on the importance of restricting the activity of their dogs.
• People should be educated that they must be careful handling or approaching strange-acting dogs and other canines. Warn parents that their children are particularly at risk.
• If a registration and immunization programme is available in your locality, register and immunize with anti-rabies vaccine any dog that owners want to keep.
• All unwanted dogs should be killed to reduce the population of animals living wild; maintain active searching for rabid dogs and take measures to ensure that they are killed.
• Detain and clinically observe for 10 days any healthy-appearing dog known to have bitten a person, if the owner wants to keep the animal. Unwanted dogs and dogs developing suspicious signs of rabies should be destroyed immediately.
• Give first aid for any dog bite and immediately refer the patient to the nearby health centre for post-exposure prophylaxis.

38.2  Taeniasis (tapeworm infestation)

In this section, you will learn about the definition, mode of transmission, clinical manifestations, and methods of prevention of taeniasis (tapeworm infestation). Taeniasis is a parasitic zoonotic disease caused by the adult stage of large tapeworms that live in the intestines of human hosts. The most common causative agent in Ethiopia is the beef tapeworm, Taenia saginata, which has the cow as its intermediate host. The other tapeworm that can cause taeniasis (Taenia solium) has pigs as its intermediate host, but they are not so common in Ethiopia. Taeniasis due to beef tapeworm is highly prevalent in Ethiopia due to the widespread habit of eating raw beef (kitfo in Amharic, Figure 38.5) and poor sanitary conditions. Defaecation in open fields in grazing lands, disposal of raw human sewage in rivers and its use as a fertiliser, facilitate the spread of taeniasis. The highest cases of taeniasis are found in the towns of Northern and Eastern Ethiopia.

Figure 38.5  The tradition of eating raw beef in Ethiopia exposes people to the risk of taeniasis through eating tapeworm eggs embedded in the meat. (Photo: Basiro Davey)

Other tapeworm diseases also exist in certain communities, e.g. people in fishing communities may be exposed to fish tapeworms (Diphyllobothrium species). Hydatid disease is also found in some parts of Ethiopia, caused by Ecchinococcus tapeworms transmitted mainly by dogs, which also infect people, cattle, sheep and horses. However, in this study session, we are focusing exclusively on the most prevalent form of tapeworm infestation in Ethiopia – taeniasis transmitted to humans by cows.

38.2.1  Mode of transmission of taeniasis

Adult beef tapeworms of the species Taenia saginata can grow very large – they can reach a length of five metres within a few months of infecting a person, but some have been recorded at up to 25 metres! The tapeworm attaches to the inside of the intestine by four strong suckers in its tiny head (Figure 38.6a). The long flat body of the tapeworm is formed from between 1,000 to 2,000 sections called proglottids (Figure 38.6b). The proglottids near the end of the tapeworm mature and become capable of surviving for a time after detaching from the main body of the worm. When a mature proglottid breaks away from the adult worm, it can contain up to 100,000 eggs. Approximately six mature proglottids are passed in the person’s stool every day – shedding up to 600,000 eggs into the environment daily!

Figure 38.6 The beef tapeworm, Taenia saginata (a) The magnified scolex (head) of the tapeworm, showing the four suckers where it attaches to the wall of the intestine; it is only 1–2 mm in diameter. (b) A proglottid shed in the faeces. (Photos: CDC Parasite Image Library, at http://www.dpd.cdc.gov/dpdx/HTML/ImageLibrary/Taeniasis_il.htm)

Proglottids of Taenia saginata passed in the faeces of an infected person onto grazing land, or used as fertiliser, are eaten by cows grazing on the same fields. The eggs hatch into larvae inside the cow’s intestine, and burrow out through the intestinal wall into the muscles, where they become trapped inside a wall of tissue that forms around them. This stage of the tapeworm’s lifecycle is called a cysticercus. Cysticercus (singular) is pronounced ‘siss-tee-surr-cuss’. The plural is cysticerci (‘siss-tee-surr-see’).Transmission to new human hosts occurs when the person eats raw or undercooked beef containing a cysticercus. The digestive enzymes in the person’s stomach and intestines digest the wall around the tiny immature tapeworm in the cysticercus, releasing it into the intestine, where it attaches to the intestinal wall by the four suckers shown in Figure 38.6(a). The tapeworm matures in the person’s intestine and begins to release proglottids, continuing the lifecycle.

38.2.2  Clinical manifestations, diagnosis and treatment of taeniasis

Generally, people live with relatively few symptoms even with a large tapeworm inside them. They may experience discomfort around the anus when proglottids are discharged, and diagnosis is made on the basis of seeing the flat white proglottids wriggling in the stools. Mild abdominal pain or discomfort, nausea, change in appetite, weakness, and weight loss can also occur with Taenia saginata infection.

Traditionally, people with tapeworm in Ethiopia self-treat with extracts of kosso – the Amharic name for a slender flowering tree (species name Hagenia abissinica, Figure 38.7), or enkoko – the scarlet fruits of the climbing shrub (Embelia schimperi), both of which have proven taenicidal properties.(Taenicidal refers to any treatment that kills tapeworms; it is pronounced ‘teen-ih-side-ull’). Medical treatment is to give a single dose of praziquantel (one 10 mg tablet for every kilogram of the patient’s body weight), which is highly effective at killing tapeworms. You are not expected to prescribe praziquantel, which is given at a health centre.

Figure 38.7  The flowers of Hagenia abissinica (or kosso) are a traditional treatment for tapeworms in Ethiopia. (Photo: Pam Furniss)

38.2.3  Prevention and control of taeniasis

The most important role for you as a Health Extension Practitioner in the prevention of taeniasis in your community is to educate community members about the mode of transmission of tapeworms from humans to cows and back to humans.

You also have a role in food hygiene inspection and community sanitation. Refrigeration or salting for long periods, or freezing at -10°C for at least nine days, also kills cysticerci in beef. You should also oversee the proper disposal of human faeces in your kebele.

Summary of Study Session 38

In Study Session 38, you have learned that:

1. Rabies is the most fatal of all communicable diseases; it is almost never cured once the patient shows symptoms.
2. The virus that causes rabies is transmitted in the bite of infected canines; 99% of cases in Africa are due to dog bites.
3. Immediate first aid for the wound and urgent referral for post-exposure prophylaxis with rabies vaccine and rabies immunoglobulin reduces the transmission of rabies after a dog bite and saves thousands of lives.
4. Prevention of rabies is mainly through elimination of unwanted dogs, vaccination where this can be afforded, and education of the population about avoiding dog bites and seeking immediate treatment if they are bitten.
5. Taeniasis due to beef tapeworm is a common disease in Ethiopia due to the culture of eating raw beef. Infected cows have tapeworms embedded in cysts in their muscles, which can be killed by thorough cooking.
6. Infected humans pass up to 600,000 eggs in their faeces every day. Open defaecation in fields and using raw human sewage as fertiliser contaminates grazing land, where cows eat the eggs attached to the grass. This perpetuates the lifecycle.
7. Environmental and food hygiene, proper sanitation, and cooking of beef thoroughly are the major prevention measures against taeniasis.

Self-Assessment Questions (SAQs) for Study Session 38

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.