Zoonotic diseases pose a greater health risk to humans. Viral zoonoses compound the risk since they spread fast and are hard to contain.
On the other hand, other zoonoses like those of parasitic origin may not show any clinical symptom in their immediate host. When people consume products from such hosts, they get infected.
One perfect example is taeniasis, which does not show any clinical symptom in cattle. However, when they get into the human host, the worm multiplies rapidly and reach an attacking threshold.
It can cause damaging effects on the host since the human victims feel ashamed to admit that they have worms.
We are going to look at some viral, rickettsial and parasitic zoonoses of economic importance in the food industry. We will also look at their symptoms, diagnosis, treatment, and control measures.
Viral zoonoses are acute and affect all warm-blooded animals and humans. The major characteristics of these diseases include hyper-excitability, paralysis, and death.
Aetiology of rabies
They are caused by an RNA virus that is very sensitive and will be inactivated by:
- Getting it out of the host
- Ordinary environmental conditions like heat and light
It is however resistant to freezing. Freezing it actually preserves it.
Epidemiology of rabies
When a viral zoonose occurs in humans or animals, it will cause acute symptoms.
Carnivores tend to be the natural hosts of viral diseases. Infected animals have very high concentration of the virus in their saliva before any clinical sign of infection occurs.
Viral zoonoses have a global presence.
Transmission of rabies
Viral zoonoses spread through bites from the natural host or contact with body fluids from an infected warm-blooded host.
The GIT may also be a route though there aren’t any documented cases.
Pathogenesis of rabies
The virus is introduced through a bite. It into the peripheral nerve and moves to the central nervous system through motor action.
Clinical signs of rabies
The signs are typically manifested in dogs.
Onset of the disease varies with the site of the bite. Incubation period takes long period (3 – 8 weeks on average though it can be as short as 10 days or as long as 6 months).
The symptoms of the disease takes two forms in dogs:
- Furious form
- Dumb form
This is the most common form of rabies in carnivores. It appears in three stages:
- Takes 2 – 3 days
- A slight increase in temperature
- Dilation of the pupils
- Lasts 3 – 7 days
- The animal is very alert and excited. It can move over very long distances while barking and biting until its voice becomes coarse.
- Starts from the head moving down to the limbs.
- Paralysis of the mouth leads to excessive salivation, dropped jaw, and the animal appear to choke whenever it tries to swallow anything.
- When paralysis reaches the limbs, the animal will exhibit uncoordinated movement and it flops. Death will follow in 3 – 4 days.
Dumb form of rabies
The dog starts with the prodromal phase but skips the excitable phase. It goes straight to paralysis phase.
Rabies in cattle
Rabid cattle are furious. They bellow a lot and are aggressive but they do not bite. Paralysis and death follows eventually.
Cattle are dead-end hosts of rabies because they do not transmit it to any other host.
Rabies in humans
People get the disease from a carnivore’s bite. Incubation period is between 30 – 60 days, which also depends on the site of the bite.
Initial symptoms are usually general, e.g. headache, general malaise, slight fever, nervousness, anxiety, and a tingling sensation at the bite site.
After these signs, the characteristic symptoms for humans will set in. They include:
- Hydrophobia (the victim fears water) due to the painful spasms in the pharyngeal muscles on attempt to swallow anything, including saliva.
- Convulsions will set in followed by paralysis and death.
Diagnosis of rabies
Confine animals suspected to have rabies. After their death, use their brain for diagnosis (check the negri bodies).
You can also do serological tests.
In humans, the patient’s history is very important in diagnosis.
Treatment of rabies
Once the disease has started in animals, it is untreatable. It will progress until the host dies.
In humans, give repeated vaccinations as soon as you realize the patient is suffering from rabies.
Control measures for rabies
- Prevent occurrence
- Vaccinate all carnivores
- Destroy all non-vaccinated wild and domestic carnivores when an outbreak notification is issued
- People at risk should receive regular vaccinations
- In case of an outbreak, issue a notification and pronounce quarantine then begin vaccination of all animals.
2) Rift Valley Fever
This disease was first diagnosed in Naivasha in 1931. It caused abortions in sheep and had high mortality rates of up to 95 percent.
In 1951, a similar syndrome occurred in South Africa in sheep. People who came into contact with the sick animals also got sick. One hundred people died and about 100 000 sheep and cattle were infected.
The disease then spread to other parts of Africa. No incident of this disease has ever been reported outside Africa.
Aetiology of rift valley fever
This disease is caused by the insect-borne arbovirus. This virus has high affinity for the liver hence it majorly affects the liver.
Transmission of rift valley fever
In animals, mosquitoes are majorly responsible for the transmission, though other insects are suspects as well.
People can be infected by handling aborted material from sick animals. Sick animals also shed the virus in milk, which becomes a route of transmission in humans. Human to human transmission is not documented.
How to recognize rift valley fever in animals
- Incubation period lasts 1 – 2 days
- High rates of abortion in sheep
- High mortality rates (90 – 100%) in lambs. Most of the deaths occur within 36 hours of the onset of the disease.
- Disease may also occur in mild form (no abortions, the animal just gets some diarrhea).
- Discharge from the nostrils.
Manifestation of rift valley fever in humans
- People are susceptible to this disease once exposed to the infected material / affected animals. The most common transmission routes include handling of aborted material, the sick animals themselves, and the lab samples.
- Incubation period is 4 – 6 days
- Influenza (flu) like symptoms
- Flushed face for the light-skinned people
- Epigastric pain occurs in the advanced stages of the disease
- The eyes will be affected and the victims may experience blurred vision, photophobia, and blindness if death does not occur.
- Death is a very common occurrence in humans
Diagnosis of the rift valley fever
- Clinical signs are very clear and provide a strong tentative diagnosis.
- Take post-mortem lesions in dead cases.
- Use necrotic hepatitis cells (dead cells) of the liver for diagnosis
- Confirm the virus through viral isolation
- You can also perform serological tests.
Control measures for the rift valley fever
- Prevent occurrence in animals by vaccination.
- Control insects, especially in breeding zones
- Carefully handle animals and animal products and byproducts
- Ensure minimal contact between animals and humans.
3) Haemorrhagic fevers (a group of diseases)
Majorly associated with monkeys. Cause haemorrhagic syndrome in humans.
1. Yellow fever
Common in Africa, South America, and several other Asian countries
Aetiology of yellow fever
Caused by yellow fever virus. Natural hosts are primates. The virus is transmitted by insects from the primates to humans.
Forest workers and hunters are more susceptible.
The disease is apparent in animals but humans get severe symptoms such as:
- Generalized haemorrhage affecting internal organs
- High fever
- Liver and kidney failure leading to severe jaundice and haemoglobinuria (haemoglobin in urine)
- Death is common
Control measures for yellow fever
- Control mosquitoes
- Take precaution when dealing with primates
- Vaccinate in face of exposure
2. Burbury fever
It is caused by a primate-associated virus. Lab workers are mostly affected and they contact the virus through aerial contamination.
Recognition of burbury fever
The disease is inapparent in animals but people experience acute fever, vomiting, and diarrhoea. Lymphadenopathy (swollen lymph nodes), haemorrhage, and death is quite common.
Control measures for burbury fever
Take a lot of care when handling patients
3. Lassa fever
Lassa virus is responsible for causing Lassa fever. The virus is common in rodents and people contact it from them via aerial contamination.
Symptoms of lassa fever in humans
- High fever
- Vomiting and diarrhoea
- Serious pneumonia, which starts as an inflammation of the upper respiratory tract
- Death due to circulatory failure
Control measures for lassa fever
- Control rodents
- Ensure safety while handling patients
4. Ebola fever
Ebola is a very severe and fatal disease in humans. It is associated with primates and is caused by the ebola virus, which has many strains including:
- Zaire sub-type (extremely severe)
- Cote de Ivoire
It was first confirmed in the Democratic Republic of Congo (DRC) but has since spread to other parts. In DRC, it occurs mainly as the Zaire sub-type.
Transmission of ebola fever
It is transmitted through contact with the body fluid of an infected patient.
Symptoms of ebola fever
- Very high fever
- Severe weakness
- Back pain
- Blood may ooze from body orifices
- People get rash
- Liver and kidney failure followed by death
Control measures for ebola fever
- Take a lot of care while handling patients
- Reduce risk of sexual transmission
- Minimize contact with primates
- Practice outbreak containment e.g. proper burial (or cremation) of the dead
This is a food-borne disease as well as a zoonose. It is common in most parts of the world.
In animals, it causes abortions and in humans, it causes serious disease.
It is a professional hazard for people dealing with livestock and those handling raw animal products.
Ticks are the main carriers and the pathogen will be found in the aborted material. It is also found in the placenta of cattle, sheep, and goats as well as in milk of these animals.
Aetiology of Q-fever
It is caused by a rickettsia microorganism Coxiellae burnettii.
Manifestation of Q-fever in animals
- It is transmitted by tick bites. The sick animals exhibit the following symptoms:
- High rate of abortions at any stage of the pregnancy
- Inapparent / sub-clinical forms are also common in animals. The organism is shed in milk in this form posing danger to the human consumers.
Q-fever in humans
People get the disease as a professional hazard when they inhale or contact a sick animal and/or the aborted material.
Consuming contaminated milk and milk products is also a route of transmission.
Human to human transmission has not been recorded. However, the organism has been extracted from milks of mothers who have recovered from the disease.
Symptoms of Q-fever in humans
Incubation period lasts 2 – 4 weeks. Observable symptoms include:
- Sudden onset of influenza (flu) like syndrome (e.g. high fever, general malaise, weakness, depression, anorexia). This then progresses to,
- Dry cough
- Chest pain and dyspnoea due to pneumonia
- Jaundice since the liver is affected
- Fatality rates are very low. People recover after administration of drugs.
Diagnosis of Q-fever
Do serological tests for confirmation of the organism.
Isolate the microorganism from the aborted material.
Control measures for Q-fever
- Effective tick control
- Proper pasteurization of milk
- Wear personal protective gear while handling animals and animal products and byproducts
- Proper disposal of aborted material.
Other rickettsial zoonoses include:
- Epidemic typhis
- Murine typhis
- Rocky Murine typhis
- Spotted fever
Typhis fever affect both humans and animals, especially dogs. They are transmitted by ticks and fleas.
Dogs and monkeys do not get serious disease.
In humans, the patient may experience high fever, joint pains, muscle pain, swellings at the bite sites that may progress into ulcers.
Lymph nodes that are proximal to the bite site will swell.
Spontaneous recovery usually occur.
Summary of Ricketsial diseases and their vectors
|Antigenic group||Disease caused||Active species||Vector||Immediate host||Where found|
|Human anaplasmosis||Anaplasma phagocytophilum|
|Tick||Small mammals, rodents, deer|
|Primarily United States, worldwide|
|Human ehrlichosis||Ehrlichia chaffeensis|
|Tick||Deer, wild and domestic dogs, domestic ruminants, rodents|
|Common in United States, possibly worldwide|
|Neoehrlichia||Neoehrlichiosis||Neoehrlichia mikurensis||Tick||Rodents||Europe, Asia|
|Neorickettsia||Sennetsu fever, neorickettsiosis||Neorickettsia sennetsu||Trematode (ingestion)||Fish||Japan, Malaysia, possibly other parts of Asia|
|Scrub typhus||Orientia tsutsugamushi||Larval mite (chigger)||Rodents||Asia-Pacific region from maritime Russia and China to Indonesia and North Australia to Afghanistan|
|Tick||Unknown||South Africa, Morocco, Mediterranean littoral|
|African tick-bite fever||R. africae||Tick||Ruminants||Sub-Saharan Africa, West Indies|
|Rickettsialpox||R. akari||Mite||House mice, wild rodents||Countries of the former Soviet Union, South Africa, Korea, Turkey, Balkan countries, United States|
|Queensland tick typhus||R. australis||Tick||Rodents||Australia, Tasmania|
|Mediterranean spotted fever or Boutonneuse fever||R. conorii||Tick||Dogs, rodents||Southern Europe, southern and western Asia, Africa, India|
|Cat flea rickettsiosis||R. felis||Flea||Domestic cats, rodents, opossums||Europe, North and South America, Africa, Asia|
|Far Eastern spotted fever||R. heilong-|
|Tick||Rodents||Far East of Russia, Northern China, eastern Asia|
|Aneruptive fever||R. helvetica||Tick||Rodents||Central and northern Europe, Asia|
|Flinders Island spotted fever, Thai tick typhus||R. honei, including strain “marmionii”||Tick||Rodents, reptiles||Australia, Thailand|
|Japanese spotted fever||R. japonica||Tick||Rodents||Japan|
|Mediterranean spotted fever-like disease||R. massiliae||Tick||Unknown||France, Greece, Spain, Portugal, Switzerland, Siciliy, central Africa, Mali, and Argentina|
|Mediterranean spotted fever-like illness||R. monacensis||Tick||Lizards, possibly birds||Europe, North Africa|
|Maculatum infection; Tidewater spotted fever; American boutonneuse fever||R. parkeri||Tick||Rodents||North and South America|
|Tickborne lymphadenopathy, Dermcentor-borne necrosis and lymphadenopathy||R. raoultii||Tick||Unknown||Europe, Asia|
|Rocky Mountain spotted fever|
Brazilian spotted fever
|R. rickettsia||Tick||Rodents||North, Central, and South America|
|North Asian tick typhus, Siberian tick typhus||R. sibirica||Tick||Rodents||Russia, China, Mongolia|
|Lymphangitis-associated rickettsiosis||R. sibirica mongolotimonae||Tick||Rodents||Southern France, Portugal, China, Africa|
opathy (TIBOLA), Dermacentor-borne necrosis and lymphaden-
|R. slovaca||Tick||Lagomorphs, rodents||Southern and eastern Europe, Asia|
|Epidemic typhus, sylvatic typhus
Murine typhus, fleaborne typhus
|Human body louse, flying squirrel ecto-|
parasites, possibly some ticksFlea
|Humans, flying squirrels
|Central Africa; Asia; Central, North, and South America
Tropical and subtropical areas worldwide
1. Psittacosis / Ornithosis
Psittacosis is derived from the Greek word psittacus, which means parrot. Te disease is associated with parrots. Ornithosis means it is associated with birds.
The disease is simply referred to as psittacosis in humans regardless of the source. People get it by direct contact with sick birds.
The causative organism is Chlamydia psittaci.
Manifestation of ornithosis/ psittacosis in birds
The responsible chlamydia is a common flora in birds hence there only needs to be a change in the physiological conditions of the bird for the organism to attack.
Stressed birds will develop the disease. Stress can arise from different sources including transportation or noise. Affected birds will exhibit the following symptoms:
- Hurdling together
- Ruffled feathers
During the active stage of the disease, the microorganism is highly concentrated in the faeces, which becomes the major source of contamination.
Manifestation of ornithosis/ psittacosis in humans
People get the disease through contact with sick birds during the active stage of the disease.
Human to human transmission occurs, though not very common. The chlamydia can be air-borne.
Symptoms of ornithosis in humans
Incubation usually takes between 1 – 2 weeks after exposure. The symptoms then commence as a typical pneumonia. Observable symptoms include:
- High fever
- Dry cough
- Chest pains
- Severe headaches
- Hepatitis due to the effect on the liver
- When the chlamydia travels to the brain, it causes mental confusion that progresses into a coma
- Myocarditis (inflammation of the heart) leading to heart failure
Diagnosis of ornithosis
Conduct routine checks in animals. Isolate sick birds for confirmation.
In humans, perform lab tests at the hospital.
Treatment of ornithosis
In birds, do prophylactic treatment (give them oxytetracycline)
People should get prescription form the hospital. Usually, oxytetracycline is given.
Control measures for ornithosis
- In birds, conduct regular testing and treatment.
- Avoid predisposing factors (e.g. stressing the birds) as much as possible. Do prophylaxis before exposing the birds to stressful situations.
- Avoid faecal contamination of birds’ feed and water.
- In humans, ensure careful handling of birds whether they are sick or just normal.
1. Taeniasis / Cysticercosis
Parasitic zoonoses are associated with meat. Psychrozoonoses require more than one vertebrate host to cause a disease.
Adult parasite (tapeworm) causes taeniasis while the larval stage causes cysticercosis. The adult stage is usually hosted by humans while the larval stage is found in animals (especially the domesticated ones).
The intermediate host is domestic animals like cattle and shoats (sheep and goats).
There are two prominent species of the tapeworm:
- Taenia solium
- Taenia saginata
T. saginata majorly inhabits cattle but can also be found in other animals.
Cysticercosis in cattle is attributed to Cysticercus bovis (bovine) and Cysticercus cellulosae (pigs). Wild animals can also get Cysticercus bovis.
People can harbour both the larval and adult stages of Taenia solium. Humans are the immediate and permanent host of the worm. Human to human transmission does not occur.
Taenia solium eggs are transferred to other hosts through food.
Life cycle of Taenia spp. worm
The life cycle of these two worms can begin anywhere within the cycle.
Clinical signs and symptoms of taeniasis
- Taeniasis in an adult human being is asymptomatic except for pains and weight loss. High infection in children will cause other symptoms. Ulcer pains due to hooks in the intestines that cause bleeding.
- Diarrhoea with dysentery
- Nausea and vomiting in adults
- Psychological disturbance (adults do not want to admit that they have worms).
- The larval stage of Taenia solium will produce serious signs, especially when it gets into the brain.
- Some of the observable symptoms include:
- Severe headache
- Nausea and vomiting
- Blurred vision that may lead to blindness
- Feeling of numbness
- Cystircercosis in animals will be manifested as cysts in the masseter muscles and cardiac muscles.
- The disease in animals may be sub-clinical, only to be noted during post-mortem.
Diagnosis of taeniasis
Analyse the stool for the eggs in humans.
In animals, conduct post-mortem tests and evaluate the cyst count. If the cyst count is less than 10, the meat is not condemned but sold under instruction. If the cyst count is greater than 20, condemn the meat.
Treatment of taeniasis
In animals, the disease is not treated as they do not show clinical signs.
People should undergo regular deworming to eradicate the worm.
Control measures for taeniasis
- Inspect meat before consumption.
- Proper disposal of human waste
- Cook meat properly before consumption
- Regular deworming of people (3 months interval).
2. Hydatidosis / Echnococcosis
Hydatidosis is caused by hydatid cyst. The larval stage affects both humans and animals.
Echnococcosis is caused by two strains of echnococcus that inhabit dogs. The two strains are:
- Echnococcus granulosus
- Echnococcus multicularis
Humans are dead-end hosts for this parasite because dogs do not feed on human viscera.
Life cycle of the hydatid parasite
Symptoms of hydatidosis in dogs
- Severe enteritis under severe infestation
- Diarrhoea with blood
- Anaemia in young puppies
- Rough hair coat
Other domestic animals may have the cyst in the internal organs but do not show any clinical signs.
Clinical signs of hydatidosis in humans
- The cysts cause organ enlargement leading to an enlarged abdomen
- Organ failure may occur depending on the level of infestation
- When the severity reaches the CNS, nervous symptoms occur.
Diagnosis of hydatidosis
- Use faecal sample for analysis.
- It is not possible to diagnose domestic animals. The cysts will be seen in the organs when the animals die.
- In humans, suspect the disease from the symptoms, especially abdominal enlargement.
- Confirmation of infection by scanning the organs for cysts. Serological tests are also applicable.
Treatment of hydatidosis
- Deworm dogs using an anthelmintic
- Domestic animals do not show symptoms hence no treatment
- In humans, surgical procedures are applicable. The procedure should be very delicate because the worms contain a very toxic fluid.
Control measures for hydatidosis
- Proper meat inspection
- Regular deworming of dogs
- Minimize contact between humans and dogs
Summary table for the three worms
|Adult host||Definitive host||Organs affected||Larval stage||Intermediate host||Organs affected|
|T. saginata||Man||Intestines||C. bovis||Shoats & cattle||Active muscles (e.g. tongue, diaphragm|
|T. solium||Man||Intestines||C. cellulosae||Pigs||Muscles|
|Echnococcus||Dog||Intestines||Hydatid cyst||Humans & domestic animals||Soft organs like liver|
This is a protozoan disease that affect all domestic animals. The infection is critical when the infection enters the cat because the cat hosts the infective stage of the disease.
The causative protozoan is Toxoplasma gondii.
The cat being the definitive host of the microorganism sheds the oocytes through the faeces. The oocytes sporulate once they come into contact with air.
Humans get the infection through the spores since they have a close association with cats. They can get into contact with the spores through:
- Consumption of contaminated foods
- Inhaling the spores in the air
- Congenital transmission (mother to child through the placenta)
Clinical signs of toxoplasmosis in animals
- Animals exhibit the inapparent form of the disease.
- Epidemics occur in rare cases when the disease occur in chickens, pigs, and rabbits
- In shoats (sheep and goats), the disease trigger abortions
Clinical signs of toxoplasmosis in humans
Symptoms usually vary with age.
- Adults get inapparent form of the disease
- Pregnancy in women activates the disease and the patient has pneumonia and swollen lymph nodes. The CNS may be affected and the pregnancy may end up in an abortion or a stillbirth.
- Babies born of infected mothers’ exhibit generalized infections immediately after birth. They developed enlarged liver and spleen and may experience convulsions. Babies who survive may be mentally retarded.
- Young children who acquire the infection from a cat may experience general malaise and mild infections.
Diagnosis of toxoplasmosis
In animals, examine the faecal sample for the oocytes.
In humans, perform serological tests.
Control measures for toxoplasmosis
- Pregnant women should ensure strict and paramount hygiene when handling cats
- Young children should avoid close contact with cats
- People should avoid raw and under-cooked meat
- Avoid feeding cats with raw meat
- Control vectors such as flies and cockroaches.
Trichinellosis is a parasitic zoonotic disease that is directly transmitted from animals to humans. The causative organism is a nematode called Trichinella spiralis.
Epidemiology of trichinellosis
The disease majorly occurs in the northern hemisphere. It is very prevalent in Alaska and places where people love wild boar and bear meat.
Horses also get the disease. Dogs, cats, and other carnivores also get the disease but they may not transmit it to humans.
Life cycle of the Trichinella spp. nematode
The disease undergoes a similar cycle in humans as in animals.
People get the cyst from boar/bear/horse meat. When the cyst gets into the stomach, it vegetates and grows into an adult. It then passes into the intestines where it lays eggs.
Immature larvae will get into the blood and then pass into the muscles.
Sources of trichinella infection
This disease is majorly transmitted through garbage and feeding. Some of the most common routes of transmission include:
- Consumption of raw / improperly cooked meat (from boar/bear/horse)
- People who feed garbage to pigs perpetrate the disease
- Birds eat garbage and spread the disease through their eggs and droppings
- Domestic animals may also get and transmit the disease when they scavenge through garbage.
Symptoms of trichinellosis in humans
When the nematode is still in larval stage, the patient may experience the following:
- Abdominal discomfort
- Facial oedema
- Itchy skin
- Myositis in the muscles (irritation and pain of the muscles)
- Pain and irritation of the tongue, masseter muscles, diaphragm, and the heart muscles
- If the disease reaches the lungs, the patient will experience dyspnoea and coughing.
- The patient may feel tired due to improper circulation when the disease affects the heart.
Symptoms of trichinellosis in animals
The adult parasite resides in the stomach. The sick animal will show the following signs:
- Abdominal discomfort
- General sickness
- Myositis in the muscles depending on the affected muscles
- Difficulty in breathing if the disease affects the diaphragm
- When the disease affects the masseter muscles, the animal will have difficulty in feeding
- The animal will tire if the heart is affected
Diagnosis of trichinellosis
Examine the faecal sample for the eggs of the parasite.
Treatment of trichinellosis
Regularly deworm the animals and people
Break the cycle of the nematode to discontinue infection cycle.
Control measures for trichinellosis
- Regular testing and treatment of sick patients. Treat any animal in whose faecal sample you find one egg
- Proper garbage disposal and management
- Avoid feeding pigs on garbage
- Proper cooking of meat
- Deep freezing can help eliminate the parasite.