Chapter 259 For most clinical problems or syndromes recognized in small animal practice, there are several infectious agents that may be the cause. Bacterial, fungal, parasitic, rickettsial, and viral agents frequently are encountered in small animal practice. Common infectious agents and the clinical problems with which they are associated are summarized in Tables 259-1 to 259-4. Recognizing the infectious agents that are most commonly associated with medical problems or syndromes allows the veterinary clinician first to rank the list of differential diagnoses using the signalment, history, and clinical examination findings. Diagnostic assays to aid in the diagnosis of small animal infectious diseases are plentiful and relatively inexpensive. However, starting with a syndromic approach allows the differential list to be narrowed and subsequently aids in selection of the optimal diagnostic assays for further evaluation of the case or choice of the most logical empiric therapeutic trials. In this chapter, the bacterial, fungal, parasitic, rickettsial, and viral agents associated with common medical problems are discussed briefly. TABLE 259-1 Common Bacterial Agents Infecting Small Animals and Associated Primary Clinical Findings TABLE 259-2 Common Fungal and Rickettsial Agents Infecting Small Animals and Associated Primary Clinical Findings TABLE 259-3 Common Parasitic Agents Infecting Small Animals and Associated Primary Clinical Findings TABLE 259-4 Common Viral Agents Infecting Small Animals and Associated Primary Clinical Findings
Infectious Agent Differentials for Medical Problems
Agent
Common Problems and Syndromes
Anaerobes (including Actinomyces and Nocardia)
Abscesses, stomatitis, rarely pneumonia
Bacterial endocarditis (multiple bacteria)
Fever, cardiac murmur
Bartonella henselae
Fever, uveitis, hyperglobulinemia, lymphadenopathy, myocarditis, endocarditis
Bartonella vinsonii subsp. berkhoffii (dogs)
Fever, epistaxis (vasculitis), endocarditis, thrombocytopenia, hemolytic anemia, polyarthritis, pyogranulomatous inflammation
Borrelia burgdorferi (dogs)
Lameness (polyarthritis), proteinuria with azotemia
Bordetella bronchiseptica
Sneezing or coughing
Brucella canis (dogs)
Reproductive failure, orchitis, uveitis, hyperglobulinemia; zoonotic
Campylobacter spp.
Mixed bowel diarrhea with or without vomiting
Chlamydia felis (cats)
Conjunctivitis; potentially sneezing and nasal discharge
Clostridium perfringens
Large bowel diarrhea, polycythemia, occasionally vomiting
Discospondylitis (multiple bacteria)
Fever, lameness, pain at the site of infection
Helicobacter spp.
Vomiting, nausea, weight loss, no diarrhea
Leptospira spp.
Fever, vomiting (nephritis, hepatitis), thrombocytopenia
Mycoplasma spp.
Sneezing or coughing (upper respiratory tract disease in cats and canine infectious respiratory disease complex in dogs), lameness (polyarthritis), reproductive failure
Mycoplasma haemominutum (cats)
Pale mucous membranes from hemolytic anemia
Mycoplasma haemofelis (cats)
Pale mucous membranes from hemolytic anemia
Mycoplasma turicensis (cats)
Pale mucous membranes from hemolytic anemia
Mycoplasma haemocanis (dogs)
Subclinical infection except in immunosuppressed dogs and then pale mucous membranes from hemolytic anemia may occur
Mycoplasma hematoparvum (dogs)
Subclinical infections except in immunosuppressed dogs, which can develop pale mucous membranes from hemolytic anemia
Salmonella spp.
Mixed bowel diarrhea with or without vomiting
Streptococcus equi var. zooepidemicus (dogs)
Cough
Staphylococcus pseudintermedius
Pyoderma
Yersinia pestis
Fever, lymphadenopathy, rarely cough or dyspnea
Agent
Type
Common Problems and Syndromes
Aelurostrongylus abstrusus (cats)
Lungworm
Coughing or dyspnea from bronchitis
Ancylostoma caninum (dogs)
Hookworm
Diarrhea with blood, pale mucous membranes
Ancylostoma tubaeforme (cats)
Hookworm
Diarrhea with blood, pale mucous membranes
Babesia vogeli (dogs)
Piroplasm
Pale mucous membranes and weakness from hemolytic anemia in dogs
Babesia gibsoni (dogs)
Piroplasm
Pale mucous membranes and weakness from hemolytic anemia in dogs
Babesia conradae (dogs)
Piroplasm
Pale mucous membranes and weakness from hemolytic anemia in dogs
Baylisascaris procyonis (dogs)
Roundworm
Subclinical in dogs; zoonotic
Cryptosporidium spp.
Coccidian
Small bowel diarrhea and weight loss
Cytauxzoon felis (cats)
Piroplasm
Pale mucous membranes and weakness from hemolytic anemia in cats
Dipylidium caninum
Cestode
Subclinical or unthrifty
Dirofilaria immitis
Heartworm
Coughing or dyspnea from bronchitis or emboli, proteinuria
Echinococcus granulosa (dogs)
Cestode
Subclinical or unthrifty; zoonotic
Echinococcus multilocularis
Cestode
Subclinical or unthrifty; zoonotic
Oslerus osleri (dogs)
Nematode
Coughing or dyspnea from worms in trachea
Giardia spp.
Flagellate
Small bowel diarrhea and weight loss
Hepatozoon americanum (dogs)
Coccidian
Lameness due to muscle inflammation and periosteal bone inflammation
Isospora spp.
Coccidian
Large bowel diarrhea or subclinical
Leishmania spp.
Flagellate
Skin disease, weight loss, multisystemic signs, Walker hounds
Ollulanus tricuspis (cats)
Nematode
Vomiting in cats
Neospora caninum (dogs)
Coccidian
Abortion, stillbirth, ascending neuromuscular disease
Paragonimus kellicotti
Fluke
Cough
Physaloptera canis
Nematode
Vomiting
Pneumonyssoides caninum (dogs)
Mite
Serous nasal discharge and sneezing
Strongyloides stercoralis
Nematode
Mixed bowel diarrhea
Toxocara canis (dogs)
Roundworm
Vomiting, abdominal distention, failure to thrive
Toxocara cati (cats)
Roundworm
Vomiting, abdominal distention, failure to thrive
Toxascaris leonina
Roundworm
Vomiting, abdominal distention, failure to thrive
Trichuris vulpis (dogs)
Whipworm
Large bowel diarrhea, occasional vomiting
Taenia spp.
Cestode
Subclinical or unthrifty
Toxoplasma gondii
Coccidian
Fever, uveitis, lameness (muscle pain)
Tritrichomonas foetus
Flagellate
Large bowel diarrhea
Trypanosoma cruzi (dogs)
Flagellate
Ventricular arrhythmias, myocarditis
Agent
Common Problems and Syndromes
Canine adenovirus 1
Vomiting, icterus, diarrhea (canine infectious hepatitis)
Canine adenovirus 2
Sneezing, nasal discharge, cough (part of CIRDC)
Canine coronavirus
Small bowel diarrhea in puppies
Canine distemper virus
Vomiting, diarrhea, sneezing, coughing, seizures, chorea, myoclonus, posterior uveitis
Canine herpesvirus
Vomiting, diarrhea, abdominal distention in fading puppies, possibly cough as part of CIRDC
Canine influenza virus
Cough, sneezing, nasal discharge (part of CIRDC)
Canine parvovirus
Vomiting, neutropenia, bloody diarrhea
Canine respiratory coronavirus
Cough, sneezing, nasal discharge (potentially part of CIRDC)
Feline calicivirus
Sneezing, stomatitis, vasculitis (virulent systemic strains)
Feline coronaviruses
Small bowel diarrhea, fever, uveitis, hyperglobulinemia, failure to thrive, central nervous system disease
Feline immunodeficiency virus
Fever, weight loss, multisystemic signs with involvement of most body systems
Feline herpesvirus 1
Sneezing, nasal discharge, keratitis, conjunctivitis, rarely stomatitis
Feline leukemia virus
Multisystemic signs due to immunodeficiency and secondary invaders, cytopenias, aplastic anemia, lymphoma
Feline panleukopenia virus
Vomiting, bloody diarrhea, neutropenia
Canine parainfluenza virus
Cough, sneezing, nasal discharge (part of CIRDC)
Rabies virus
Neurologic signs; zoonotic
