Managing diseases in non-ruminant animals is a critical responsibility for agricultural professionals in Kenya’s diverse farming systems. Non-ruminant species such as poultry, pigs, and rabbits contribute significantly to food security, income generation, and livelihoods. Effective disease management enhances productivity, reduces economic losses, and safeguards public health by preventing zoonotic transmissions. Understanding the nature and classifications of non-ruminant diseases equips extension officers and farmers with the knowledge to implement timely interventions and biosecurity measures.

4.1 Non-ruminant diseases

Diseases affecting non-ruminant animals pose unique challenges due to the variety of species and production systems involved. In Kenya, poultry farming is widespread both at smallholder and commercial levels, while pig and rabbit farming are growing sectors. Disease outbreaks can rapidly decimate flocks or herds, disrupting supply chains and causing financial hardship. This section clarifies key terminology and explores the principal types of diseases encountered in non-ruminants, forming a foundation for effective disease control strategies.

4.1.1 Definition of terms

Clarity in terminology related to animal diseases is essential for accurate diagnosis, reporting, and management. In the Kenyan agricultural context, extension agents and farmers must communicate precisely to ensure appropriate responses.

Definition of disease

Disease refers to any condition that impairs normal physiological functions of an animal, manifested by clinical signs or pathological changes. It results from infections, nutritional deficiencies, toxins, or genetic factors. For instance, Newcastle disease in chickens causes respiratory distress and high mortality, illustrating a disease caused by viral infection.

Infection and infectious disease

Infection is the invasion and multiplication of microorganisms such as bacteria, viruses, fungi, or parasites within an animal's body. Infectious diseases are those caused by these pathogens and can spread directly or indirectly among animals. An example is African swine fever in pigs, a highly contagious viral disease transmitted through contact or contaminated materials.

Pathogen

A pathogen is any microorganism or agent that causes disease. Pathogens include viruses, bacteria, fungi, protozoa, and helminths. Understanding the pathogen type is critical since it influences treatment and control measures. For example, coccidiosis in poultry is caused by protozoan parasites that damage the intestinal lining.

Zoonosis

Zoonosis describes diseases transmissible between animals and humans. Many non-ruminant diseases have zoonotic potential, posing public health risks. For example, salmonellosis from contaminated poultry products can cause foodborne illness in humans.

Vector and carrier

A vector is a living organism, such as a tick, louse, flea or biting fly, that carries a pathogen from one animal to another. A carrier is an animal that harbours a pathogen without showing signs of illness but can still infect others. Example: a hen that has recovered from fowl typhoid may keep shedding the bacteria and infect new chicks brought into the same house.

Morbidity and mortality

Morbidity refers to the incidence of disease or illness in a population, while mortality indicates the number of deaths caused by disease. High morbidity and mortality rates in poultry farms can severely impact production and farmer incomes.

4.1.2 Types of non-ruminant diseases

Non-ruminant animals suffer from a broad spectrum of diseases. For the purposes of this unit they are grouped by the type of causative agent or cause: bacteria, fungi, protozoa, rickettsiae and nutritional imbalances. Knowing the group a disease belongs to helps a farmer or extension agent decide whether antibiotics, antifungal measures, anticoccidial drugs, vector control or a corrected ration is needed.

4.1.2.1 Bacterial diseases

Bacterial diseases are caused by single-celled organisms that multiply in the blood, gut, respiratory tract or other tissues of the animal. They are often spread through contaminated feed, water, litter, bedding and equipment, and by carrier animals. Treatment normally uses antibiotics prescribed by a veterinarian, supported by good sanitation and observation of drug withdrawal periods.

Common bacterial diseases include:

• Fowl cholera: Caused by Pasteurella multocida in chickens, turkeys and ducks. It causes sudden deaths, swollen wattles, greenish diarrhoea and breathing difficulty, and spreads through contaminated water and wild birds or rodents.
• Fowl typhoid and pullorum disease: Caused by Salmonella Gallinarum and Salmonella Pullorum. Pullorum is passed through the egg to chicks, causing white diarrhoea and heavy chick mortality, while fowl typhoid mainly affects growing and adult birds.
• Colibacillosis: Caused by Escherichia coli, which often attacks birds already weakened by poor ventilation, dusty houses or other infections. It causes air sac infection, inflamed membranes around the heart and liver, and reduced growth.
• Infectious coryza: Caused by Avibacterium paragallinarum. Affected birds show nasal discharge, swollen faces and sneezing, and egg production falls in layers.
• Salmonellosis: Caused by other Salmonella species in poultry and pigs. Infected animals may show diarrhoea or no signs at all, and eggs and meat from carriers can cause food poisoning in humans.
• Swine erysipelas: Caused by Erysipelothrix rhusiopathiae in pigs. It produces high fever, diamond-shaped skin lesions and sudden death, and the bacteria can infect handlers through skin wounds.
• Swine dysentery: Caused by Brachyspira hyodysenteriae. It leads to bloody, mucus-filled diarrhoea, loss of condition and poor growth in weaners and growers.
• Pasteurellosis (snuffles) in rabbits: Caused by Pasteurella multocida. Rabbits show nasal discharge, sneezing and matted forelegs from wiping the nose, and the infection spreads quickly in poorly ventilated hutches.

Example: in a layer unit where drinking water is not changed daily and dead birds are left in the house, fowl cholera can move from a few birds to the whole flock within days.

4.1.2.2 Fungal diseases

Fungal diseases are caused by moulds and yeasts that grow on feed, litter, skin and mucous membranes. They are less frequent than bacterial diseases but cause serious losses where feed is stored damp or houses are poorly ventilated. Treatment is difficult, so attention to hygiene, dry feed and clean bedding is central.

Important fungal conditions include:

• Aspergillosis (brooder pneumonia): Caused by Aspergillus fumigatus, whose spores are inhaled from mouldy litter, grain or damp hatchery and brooder conditions. Chicks gasp, breathe with open beaks and die in large numbers.
• Candidiasis (thrush or sour crop): Caused by the yeast Candida albicans. The crop and mouth lining develop thick whitish patches, the crop becomes sour and slow to empty, and birds lose weight.
• Mycotoxicosis: Not an infection but poisoning by toxins from moulds such as Aspergillus flavus (aflatoxin). Mouldy maize or groundnut cake in poultry and pig feed reduces growth, damages the liver and lowers egg production and immunity.
• Ringworm (dermatophytosis): Caused by skin fungi such as Trichophyton and Microsporum, mainly in rabbits and pigs. It produces circular, scaly, hairless patches and can pass to the handlers.
• Favus: A skin fungal disease of poultry that forms whitish crusts on the comb and wattles. It is uncommon but spreads where birds are crowded and houses are dirty.

Example: a farmer who stores maize in a damp store and mixes it into pig meal may see slow growth and liver damage in the herd, caused by mould toxins rather than by an infection.

4.1.2.3 Protozoan diseases

Protozoan diseases are caused by single-celled animal parasites. Some live inside the cells of the gut or liver, others in the blood. They multiply quickly in warm, damp conditions, so wet litter, overcrowding and dirty drinkers favour their spread.

Common protozoan diseases include:

• Coccidiosis in poultry: Caused by Eimeria species that destroy the lining of the intestine. Birds pass bloody or watery droppings, huddle with ruffled feathers and grow poorly, and chicks on wet litter are the most at risk.
• Coccidiosis in rabbits: Caused by other Eimeria species. The intestinal form causes diarrhoea and weight loss, while the liver form (Eimeria stiedae) causes a swollen abdomen and poor growth in young rabbits kept on dirty hutch floors.
• Coccidiosis in piglets: Caused by Isospora suis. It produces yellowish, pasty diarrhoea in piglets around one to three weeks of age, even when the sow looks healthy.
• Histomoniasis (blackhead): Caused by Histomonas meleagridis, mainly in turkeys but also in chickens. It damages the caecum and liver, causing sulphur-yellow droppings and dark, drooping heads, and it is carried between birds by caecal worm eggs.
• Toxoplasmosis: Caused by Toxoplasma gondii, which infects pigs, among other animals, when they eat contaminated feed or carcasses. Infected pigs may show fever and breathing problems or abortion, and undercooked pork can infect humans.
• Trypanosomiasis: Caused by blood parasites (Trypanosoma species) spread by tsetse flies. Pigs, dogs, donkeys and horses in tsetse areas may show fever, anaemia and loss of condition.

Example: a broiler house with leaking drinkers produces wet litter, and coccidiosis then appears when the chicks are about three weeks old.

4.1.2.4 Rickettsial diseases

Rickettsiae are very small, bacteria-like organisms that can only multiply inside living cells. They are usually carried between animals by blood-feeding arthropods such as ticks, lice and fleas. They respond to antibiotics of the tetracycline group, given under veterinary advice, but control relies mainly on controlling the vectors that spread them.

Characteristics of rickettsial agents:

• Obligate intracellular life: They live and multiply only inside host cells, often in red blood cells or white blood cells, so they cannot be grown on ordinary laboratory media.
• Arthropod transmission: Ticks, lice, fleas and biting flies pick up the organism while feeding on an infected animal and pass it on at the next feed.
• Blood-related damage: Many cause anaemia, fever and weakness by destroying or damaging blood cells.
• Carrier animals: Recovered animals can carry the organism for long periods and act as a source of infection for vectors.
• Link to vector numbers: Disease is most common where ticks, lice or fleas are abundant, such as in poorly maintained poultry houses, pig pens and kennels.

Important rickettsial and related diseases of non-ruminants:

• Aegyptianella (fowl) infection: Caused by Aegyptianella pullorum in poultry and spread by the fowl tick, Argas persicus. Infected birds are feverish, pale and anaemic, with ruffled feathers and diarrhoea, and mortality can be high.
• Eperythrozoonosis in pigs: Caused by Mycoplasma suis (formerly Eperythrozoon suis), a blood parasite traditionally grouped with the rickettsiae. It is spread by lice and biting flies, and by shared needles and castration or tail-docking instruments. Pigs become anaemic and pale and may be jaundiced, with poor growth.
• Canine ehrlichiosis: Caused by Ehrlichia canis in dogs and spread by the brown dog tick. Dogs show fever, bleeding tendencies, pale gums and weight loss.
• Equine granulocytic anaplasmosis: Caused by Anaplasma phagocytophilum in horses and donkeys and spread by ticks. Animals have fever, depression, swelling of the lower legs and reluctance to move.
• Murine typhus: Caused by Rickettsia typhi, carried by rats and spread by rat fleas. Rats show no illness, but humans handling feed stores infested with rats and fleas can become ill.

Example: in a deep-litter poultry house with cracks in the walls where fowl ticks hide, birds can become anaemic from Aegyptianella infection even though feed and water are adequate.

4.1.2.5 Nutritional diseases

Nutritional diseases arise when a ration lacks, or has too much of, energy, protein, vitamins or minerals. They are not caused by pathogens and do not spread from animal to animal, but they weaken the animal and make it more open to infectious disease. They are prevented by feeding balanced rations suited to the species and age, from feed that is fresh and properly stored.

Common nutritional diseases include:

• Vitamin A deficiency: Birds show watery eyes, sticky nasal discharge and pustules in the mouth and throat, sometimes called nutritional roup. Growth slows and egg production and hatchability fall.
• Vitamin E and selenium deficiency: In chicks it causes encephalomalacia, a brain disorder with unsteady walking, head tilting and paralysis. Piglets and rabbits may suffer muscle damage and sudden death.
• Riboflavin (vitamin B2) deficiency: Chicks develop curled-toe paralysis, walking on their hocks with toes curled inward. Growth is poor and hatchability of eggs falls.
• Calcium, phosphorus and vitamin D deficiency: Young animals develop rickets with soft, bent bones, while laying hens produce thin or soft-shelled eggs and may become weak in the legs. Calcium and phosphorus must be balanced and supported by vitamin D.
• Manganese deficiency (perosis): In chicks and poults the hock joint enlarges and the tendon slips from its groove, causing lameness. It is common where rations are poorly mixed or lack a trace-mineral premix.
• Iron deficiency anaemia in piglets: Sow's milk is low in iron, so piglets kept on concrete floors without an iron supply become pale, weak and slow growing. Scouring may follow.
• Fatty liver syndrome in laying hens: Caused by excessive energy intake with little exercise, often in hot weather. Hens become overweight, egg production drops and some die suddenly with pale, fat-filled livers.
• Salt poisoning: Excess salt in feed with limited water can cause thirst, wet droppings and nervous signs in poultry and pigs. It occurs when feed is wrongly mixed or water supply is interrupted.

Example: a farmer who mixes layer feed using home-grown maize and no mineral premix may find hens laying thin-shelled eggs and chicks developing slipped tendons.

Chapter Summary

This chapter provided a comprehensive overview of non-ruminant diseases, beginning with clear definitions and classifications, including bacterial, fungal, protozoan, rickettsial, and nutritional diseases. It highlighted common signs and symptoms such as loss of appetite, emaciation, staring coat, and dullness, which are critical for early detection. Various disease control measures were discussed, including deworming, spraying, dipping, quarantine, vector control, and vaccination to prevent and manage outbreaks effectively. The importance of maintaining accurate disease control records was emphasized to track interventions and outcomes. Proper management of disease control waste was covered to ensure environmental safety and reduce contamination risks. The chapter also detailed procedures for identifying diseases in non-ruminant animals and implementing appropriate control methods. Finally, best practices for the disposal and management of disease control waste were presented to support sustainable animal health management.