Poultry Diseases in Uganda: A Review of Major Viral, Bacterial, and Parasitic Conditions

Poultry production in Uganda is a vital component of the agricultural sector, providing protein, income, and employment for a large proportion of the rural population [1]. The sector comprises indigenous chickens, improved breeds, and commercial operations, each facing distinct disease challenges. Infectious diseases caused by viruses, bacteria, and parasites remain the primary constraints to productivity and flock survival [1, 2]. This review provides a comprehensive examination of the major poultry diseases in Uganda, focusing on clinical presentation, diagnostic methods, and control measures.

Viral Diseases of Poultry in Uganda

Newcastle Disease

Newcastle disease (ND) is caused by virulent strains of avian paramyxovirus serotype 1 (APMV-1), a single-stranded negative-sense RNA virus in the family Paramyxoviridae [2]. ND is enzootic in Uganda and remains the most frequently reported viral disease in village and commercial poultry [1]. Clinical signs vary with pathotype: viscerotropic velogenic strains cause severe depression, greenish diarrhea, tracheal rales, and high mortality. Neurotropic strains produce torticollis, paralysis, and opisthotonos, particularly in recovered birds [2].

Diagnosis relies on virus isolation in embryonated chicken eggs, followed by haemagglutination inhibition (HI) or reverse transcription polymerase chain reaction (RT-PCR) [2, 3]. Serological surveillance using ELISA or HI tests identifies flocks with inadequate vaccine immunity. Control is achieved through regular vaccination with live attenuated (lentogenic) or inactivated vaccines administered via drinking water, eye drop, or injection [1, 2].

Avian Influenza

Highly pathogenic avian influenza (HPAI) caused by H5 and H7 subtypes of influenza A virus (family Orthomyxoviridae) poses a constant threat to Ugandan poultry [1]. Outbreaks have been reported sporadically, often linked to wild waterfowl reservoirs. Clinical signs include sudden death, cyanotic combs and wattles, facial edema, hemorrhagic tracheitis, and respiratory distress [2, 3]. Subtype identification by RT-PCR and sequencing is essential for surveillance and reporting to the World Organisation for Animal Health (WOAH) [3]. Control involves stamping out, movement restrictions, and enhanced biosecurity. Vaccination is not routinely practiced in Uganda but may be considered in high-risk zones [1].

Infectious Bursal Disease (Gumboro)

Infectious bursal disease virus (IBDV), a birnavirus, causes immunosuppression and high mortality in young chickens [2]. Gumboro is endemic in Uganda, with outbreaks occurring throughout the year. Clinical signs include ruffled feathers, watery diarrhea, vent pecking, and trembling. Necropsy reveals swollen, hemorrhagic bursae of Fabricius and renal urate deposition [2]. Diagnosis is confirmed by histopathology, agar gel immunodiffusion, RT-PCR, or antigen capture ELISA [3]. Vaccination with intermediate or intermediate-plus live vaccines administered during the first two weeks of life provides protection [1, 2].

Marek's Disease

Marek's disease virus (MDV), a cell-associated alphaherpesvirus, causes lymphoproliferative lesions in nerves, viscera, and skin [2]. In Uganda, MD is common in unvaccinated backyard flocks. Clinical signs include asymmetric paralysis (one leg forward, one back), wing droop, dyspnea from thymic or bursal tumors, and visceral lymphomas [2]. Diagnosis is based on gross and histopathologic lesions, and PCR detection of MDV serotype 1 DNA in tumor tissues [3]. Vaccination with bivalent (HVT + SB-1) or recombinant vaccines is highly effective when administered in ovo or at day-old [2].

Fowl Pox

Fowl pox virus (FPV), an avipoxvirus, causes cutaneous and diphtheritic forms [2]. Cutaneous lesions appear as wart-like scabs on comb, wattles, and eyelids. The diphtheritic form produces necrotic plaques in the mouth, pharynx, and trachea, leading to suffocation [2]. FPV is transmitted by mosquitoes and persists in the environment. Diagnosis is by clinical appearance and histology (intracytoplasmic inclusion bodies) and can be confirmed by PCR [3]. Vaccination with live fowl pox vaccine (pigeon pox strain cross-reacts) is used in endemic areas [1, 2].

Bacterial Diseases of Poultry in Uganda

Salmonellosis

Salmonellosis in poultry is caused by serovars of Salmonella enterica subspecies enterica. Pullorum disease caused by S. Gallinarum biovar Pullorum and fowl typhoid caused by S. Gallinarum biovar Gallinarum are host-specific, causing systemic infections and high mortality in chicks and growers [1, 2]. In Uganda, these diseases remain common in scavenging and semi-intensive flocks due to poor biosecurity and lack of routine testing [1, 4]. Clinical signs include white diarrhea, huddling, pasted vents, and acute death. Adult carriers show reduced egg production and ovarian regressive changes. Diagnosis relies on bacterial isolation from liver, spleen, and yolk sac using selective media, followed by serotyping [3, 4]. Serological screening with whole blood plate agglutination tests is used for monitoring infected flocks [4]. Control involves test-and-slaughter programs, biosecurity, and avoiding vertical transmission through hatching egg sanitation [1, 2]. Paratyphoid infections (non-host-specific serovars) are of food safety concern but cause subclinical disease in poultry unless birds are immunocompromised [4].

Colibacillosis

Avian pathogenic Escherichia coli (APEC) causes colibacillosis, a multisystemic disease primarily affecting respiratory, reproductive, and gastrointestinal tracts [2]. APEC strains typically possess virulence factors such as F1 and P fimbriae, aerobactin, and colicin V plasmids [2, 4]. In Uganda, colibacillosis is a leading cause of morbidity and mortality in broiler and layer flocks, often secondary to immunosuppressive viral infections (e.g., IBD, MD) or poor environmental hygiene [1]. Clinical signs include respiratory distress, pericarditis, airsacculitis, peritonitis, and septicemia [2, 4]. Diagnosis is confirmed by bacterial culture of internal organs with pure growth of E. coli, combined with serotyping or PCR detection of virulence genes [3, 4]. Antimicrobial resistance is widespread; thus, culture and sensitivity testing is recommended before treatment. Control emphasizes biosecurity, ventilation, litter management, and vaccination with inactivated APEC vaccines where available [1, 2].

Fowl Cholera

Fowl cholera is caused by Pasteurella multocida, a Gram-negative coccobacillus [2]. The disease occurs in acute and chronic forms. In Uganda, outbreaks are sporadic in rural flocks and more common in wet seasons [1]. Acute cases present with sudden death, fever, cyanosis, and mucoid discharge from the mouth. Chronic disease is characterized by caseous material in wattles, sinuses, joints, and air sacs [2]. Postmortem findings include petechiae on heart and liver, necrotic hepatic foci, and consolidation of lungs [2, 4]. Diagnosis is made by smear cytology (bipolar staining with Wright or Giemsa), culture on blood agar, and PCR [3]. Control includes vaccination with killed bacterins or live attenuated vaccines, rodent control, and removal of carrier birds [1, 2].

Mycoplasmosis

Mycoplasma gallisepticum (MG) and Mycoplasma synoviae (MS) are major respiratory and synovial pathogens in Ugandan poultry [1, 5]. MG causes chronic respiratory disease (CRD) in chickens and infectious sinusitis in turkeys, characterized by coughing, rales, nasal discharge, and air sac lesions [5]. MS primarily causes tenosynovitis and respiratory signs [5]. Transmission is both horizontal (aerosol, direct contact) and vertical (transovarian) [2]. Diagnosis uses serology (serum plate agglutination, ELISA) and PCR for species identification from tracheal swabs [3, 5]. Control strategies include establishing MG-free breeder flocks, antimicrobial therapy, and vaccination with live or inactivated MG vaccines [1, 5]. Biosecurity and eradication of infected flocks are recommended for commercial breeders.

Infectious Coryza

Caused by Avibacterium paragallinarum, a Gram-negative pleomorphic rod, infectious coryza produces catarrhal inflammation of the upper respiratory tract [2]. In Uganda, the disease is common in older pullets and layers in floor-housed flocks [1]. Clinical signs include serous to mucoid nasal discharge, facial edema, conjunctivitis, and decreased egg production [2]. Diagnosis is confirmed by bacterial isolation (chocolate agar in 5-10% CO2) and PCR [3]. Control involves vaccination with inactivated bacterins and management of ventilation and stocking density [1, 2].

Necrotic Enteritis

Necrotic enteritis is caused by Clostridium perfringens type A (netB toxin) and less commonly type C [2]. Predisposing factors include dietary shifts, coccidiosis (particularly Eimeria acervulina and E. maxima), and immunosuppression [1, 2]. In Uganda, necrotic enteritis is increasingly reported in broiler flocks fed high-protein rations [1]. Clinical signs include depression, decreased feed intake, and bloody or brownish diarrhea. Necropsy reveals a thickened, necrotic small intestinal mucosa filled with particles and central necrosis with a friable brown pseudomembrane [2]. Diagnosis relies on gross lesions, histopathology, and intestinal content culture for C. perfringens [3]. Control involves anticlostridial medication (e.g., bacitracin, lincomycin), coccidia vaccination, and dietary management [1, 2].

Other Bacterial Pathogens

Bordetellosis caused by Bordetella avium is seen in turkeys but occasionally infects chickens [2]. Streptococcus zooepidemicus causes septicemia and pericarditis in sporadic outbreaks [2]. Ornithobacterium rhinotracheale (ORT) is an emerging respiratory pathogen in Ugandan layers and broilers, producing pneumonia and airsacculitis [1, 2]. Riemerella anatipestifer primarily infects ducks and geese but can affect chickens under stress [2]. Diagnosis for these less common agents requires culture on enriched media and PCR panels [3].

Parasitic Diseases of Poultry in Uganda

Coccidiosis

Coccidiosis, caused by several species of the protozoan genus Eimeria, is the most economically important parasitic disease in Ugandan poultry [1, 6]. The lifecycle is direct: oocysts shed in feces sporulate under warm, moist conditions within 48 hours and are ingested by new hosts. In the intestinal epithelium, the parasite undergoes asexual (schizogony) and sexual (gametogony) cycles, leading to cell lysis and clinical disease [6]. Common species in chickens include E. tenella (cecal coccidiosis, bloody droppings), E. acervulina (duodenal lesions, white plaques), E. maxima (intestinal distension, petechiae), and E. necatrix (midintestinal lesions, high mortality in grower birds) [6]. Clinical signs include depression, ruffled feathers, reduced weight gain, pasty vents, and diarrhea. Diagnosis is by fecal flotation for oocyst detection and species identification based on gross lesion distribution and oocyst morphology [3, 6]. Control includes anticoccidial feed additives (ionophores or chemical coccidiostats), live vaccination with attenuated or non-attenuated oocysts, and strict hygiene [1, 6]. In Uganda, many smallholder farmers rely on prophylactic use of sulfonamides or amprolium in drinking water [1].

Helminthiasis

Gastrointestinal nematodes, particularly Ascaridia galli, Heterakis gallinarum, and Capillaria species, are prevalent in free-range and deep-litter flocks in Uganda [1, 7]. A. galli is the largest roundworm, inhabiting the small intestine; heavy burdens cause intestinal impaction, reduced growth, and decreased egg production [7]. H. gallinarum inhabits the ceca and acts as a vector for Histomonas meleagridis, the causative agent of blackhead disease in turkeys and occasionally chickens [7]. Capillaria species embed in the intestinal mucosa and cause catarrhal enteritis and weight loss [7]. Diagnosis is by fecal flotation with saturated salt or sugar solutions and identification of characteristic eggs [3, 7]. Tapeworms (Raillietina, Davainea, and Choanotaenia species) are common in scavenging birds, transmitted by intermediate hosts such as ants and beetles [7]. They cause no specific clinical signs but interfere with nutrient absorption [7]. Control requires anthelmintic treatment (fenbendazole, flubendazole, or levamisole) combined with litter management and biosecurity to reduce environmental contamination [1, 7].

Ectoparasites

Ectoparasites including lice (Menacanthus stramineus, Goniocotes gallinae) and mites (Dermanyssus gallinae, the poultry red mite, and Knemidocoptes mutans, the scaly leg mite) are widespread in Ugandan poultry systems [1, 8]. Heavy louse infestations cause irritation, feather loss, decreased feed efficiency, and skin lesions [8]. D. gallinae is nocturnal, hides in crevices during the day, and feeds on blood at night, causing anemia, decreased egg production, and can transmit pathogens such as Salmonella and E. coli[8]. Scaly leg mites burrow under leg scales, causing thickening, crusting, and lameness [8]. Diagnosis is by visual inspection and microscopic examination of skin scrapings or crevice material [3, 8]. Control involves topical acaricides (e.g., permethrin, carbaryl), thorough cleaning and disinfection of housing, and dusting birds with insecticidal powders [1, 8].

Diagnostic Workflow for Sick Poultry

A systematic approach is essential for diagnosing poultry diseases in Uganda. The following Mermaid diagram outlines a diagnostic decision tree for a sick bird.

flowchart TD
    A[Clinical signs observed], > B{System involvement?}
    B, > C[Respiratory signs: coughing, sneezing, nasal discharge]
    B, > D[Enteric signs: diarrhea, vent pasting]
    B, > E[Nervous signs: torticollis, paralysis]
    B, > F[Cutaneous or mucosal lesions: scabs, plaques]
    B, > G[Joint or leg signs: swelling, lameness]
    
    C, > H[Differential: ND, AI, IB, MG, ORT, infectious coryza, fowl cholera]
    H, > I[Collect tracheal/cloacal swabs, blood serum]
    I, > J[RT-PCR for NDV, AIV; ELISA/MG serology; culture for Avibacterium, ORT]
    
    D, > K[Differential: coccidiosis, necrotic enteritis, salmonellosis, Gumboro]
    K, > L[Fecal floatation for oocysts; intestinal tissue for histology; culture for Salmonella, Clostridium; bursa for IBDV RT-PCR]
    
    E, > M[Differential: ND, Marek's disease, vitamin E/selenium deficiency]
    M, > N[Collect brain, peripheral nerve, viscera]
    N, > O[Histology for perivascular cuffing (ND), lymphoproliferation (MD); RT-PCR for NDV/MDV]
    
    F, > P[Differential: fowl pox, mycotic dermatitis, favus]
    P, > Q[Scab homogenate for PCR (FPV); fungal culture for dermatophytes]
    
    G, > R[Differential: mycoplasmosis (MS), staphylococcal arthritis, reovirus, urate gout]
    R, > S[Joint synovia culture; serology for MS, reovirus; uric acid levels]
    
    J & L & O & Q & S, > T[Integrated diagnosis based on lab results, necropsy findings, and flock history]
    T, > U[Implement specific treatment and control measures]

Integrated Control and Prevention

Effective management of poultry diseases in Uganda requires a multifaceted approach. Vaccination programs are well established against ND, IBD, fowl pox, and MD but face challenges in logistics, cold chain maintenance, and coverage in rural areas [1, 2]. Biosecurity measures, including all-in-all-out management, foot baths, rodent control, and quarantine of new stock, reduce pathogen introduction [1]. Improved nutrition and housing conditions decrease host susceptibility. Producers should be trained in early recognition of disease signs and reporting to veterinary authorities [1, 2]. Antimicrobial use must be guided by sensitivity testing to slow the spread of resistance [4]. For parasitic diseases, regular deworming and coccidia control through vaccination or anticoccidials, combined with hygiene and pasture rotation, are recommended [6, 7]. Public health risks from zoonotic pathogens such as Salmonella, Campylobacter, and avian influenza require continued surveillance and food safety education [1, 4].

References

[1] FAO. Poultry sector country review: Uganda. FAO Animal Production and Health Division. Rome: Food and Agriculture Organization of the United Nations.

[2] Swayne DE, Boulianne M, Logue CM, et al. Diseases of Poultry. 14th ed. Hoboken, NJ: Wiley-Blackwell.

[3] OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals. 12th ed. Paris: World Organisation for Animal Health.

[4] Wray C, Davies RH, editors. Salmonella in Domestic Animals. 2nd ed. Wallingford: CABI.

[5] Ley DH. Mycoplasmosis. In: Swayne DE, et al., editors. Diseases of Poultry. 14th ed. Wiley-Blackwell.

[6] Chapman HD. Coccidiosis. In: Swayne DE, et al., editors. Diseases of Poultry. 14th ed. Wiley-Blackwell.

[7] Permin A, Hansen JW. Epidemiology, Diagnosis and Control of Poultry Parasites. FAO Animal Health Manual. Rome: Food and Agriculture Organization.

[8] Hinkle NC, Corrigan RM. External Parasites of Poultry. In: Swayne DE, et al., editors. Diseases of Poultry. 14th ed. Wiley-Blackwell. *** Disclaimer: This article is for educational and informational purposes only. It is not intended to substitute for professional veterinary advice, diagnosis, treatment, or regulatory guidance. Always consult a licensed veterinarian or qualified specialist regarding animal health, disease diagnosis, and therapeutic decisions.