Selected infectious diseases in rabbits - what is feasible, what is important?

Diagnosis of infectious diseases in rabbits is not always easy. On the one hand, rabbits show clinical symptoms late and on the other hand, they are often presented to the veterinarian with a time delay. The workup of infectious diseases with nonspecific disease symptoms in particular presents a challenge to the practitioner. The first step is the detailed anamnesis. This should include questions about husbandry (individual or group), age, vaccination status, and special events. A comprehensive clinical examination and a general blood test are as essential as the laboratory diagnostic clarification of the infection itself. Sample material and detection method depend on the suspected infection.A few selected infectious diseases with nonspecific, respiratory, and/or predominantly gastrointestinal symptoms are discussed in more detail below. The most important facts are presented in tabular form for the sake of clarity.

Infections with non-specific symptoms

In patients with nonspecific symptoms such as apathy, lethargy, and anorexia or sudden deaths, it is often difficult to link them directly to a specific infectious agent. Typical lethal infectious diseases in this category are Rabbit Haemorrhagic Disease (RHD) and Tularaemia.

Tularemia

Even though is rare, recent cases in Germany and its zoonotic potential keep putting it in the spotlight. In the case of tularemia, also known as “rabbit plague“ is a notifiable bacterial zoonosis (caused by Francisella tularensis). Reservoir in Germany are v.a. Field hares. However, rabbits, rodents, squirrels and wild ruminants may also be infected.

Despite the low incidence in humans (17 – 72 cases per year in Germany [1]), tularemia is also reportable in humans (§7 Abs. 1 IfSG) and is considered an occupational disease of hunters and persons who trade in hares or process them into foodstuffs [1]. Because of the low infectious dose of 10 – 50 (!) pathogens, the sometimes severe course of the disease and the good chances of cure if therapy is started early in humans, detection should be carried out promptly in the event of suspicion. Human infection occurs oronasally, conjunctivally, or via skin or mucosal lesions. Sources include evisceration of the carcass, contaminated, inadequately heated food, contaminated water, aerosols, and bites/bites from arthropods (ticks, mosquitoes, horseflies). Typical clinical signs in humans include: nonspecific flu-like symptoms, skin ulceration, lymph node swelling and suppuration, fever, conjunctivitis, and pneumonia. Therapy with aminoglycosides, fluoroquinolones, tetracyclines, chloramphenicol, or rifampicin is recommended [2]. Prophylaxis for humans includes: avoidance of unprotected contact with wild animals, observance of occupational hygiene when handling sick or dead wild animals and game, eating game dishes only when well cooked.

Table 1: Profile of tularemia in rabbits and hares [1, 3 – 5]

Tularemia	Data and facts
Pathogen	Francisella tularensis, Fam. Francisellaceae (y-Proteobacteria) Gram-negative, immobile, pleomorphic rod-shaped bacterium Host range: v.a. Hares (reservoir: rodents u.a.); Zoonosis! Notifiable!
Infection	IKZ: 3 – 5 (14) days [2, 3] Biting insects, ticks
Excretion	Secretions and excretions Vektor: Zecken (Beherbergung über Monate, Pathogenvermehrung und transovarielle Übertragung [4]), Bremsen, Mücken
Clinic	mild – lethal acute course: Apathy, fever, tachypnea, fur ruffling, loss of shyness, lymph node swelling, diarrhea, vomiting, dyspnea, sepsis [1] chronic course: Emaciation, splenomegaly, liver abscesses [5]
Course	mild to severe (fatal), usually dying after 2 – 13 d due to sepsis
Diagnosis	Suspicion: clinic and preliminary report: contact with “wild animal“ direct pathogen detection by PCR: EDTA blood, smear, lymph nodes, spleen pathological examination
Therapy	none, killing !
Prophylaxis	high tenacity (0 – 10 °C: weeks, < 0 °C: months) easily killed with bactericidal disinfectants (RKI, VAH list) no vaccine is licensed in Europe

Infections with respiratory symptoms

Respiratory symptoms, such as sneezing, coughing, nasal and ocular discharge, and v.a. Dyspnea, resulting from upper and/or lower respiratory tract disorders and inflammatory changes in the non-respiratory tract that interfere with gas exchange. The causes are manifold. In addition to cardiological, traumatic, degenerative and/or neoplastic changes, infections are the most frequent causative factor.

Rabbit rhinitis (Rhinitis contagiosa cuniculi)

Rhinitis in rabbits is one of the most common reasons for presentation in practice. Under “rabbit cold“ is a worldwide spread, age-independent, predominantly bacterial mixed infection in the upper and partly lower respiratory tract. Many rabbits are asymptomatic carriers. In phases of immunosuppression, triggered by stress or other underlying diseases, clinical manifestation may occur. In addition to changes in husbandry and inadequate housing conditions, breed-related factors, such as short stature, can also lead to an increased incidence [6].

Pasteurella (P.) multocida and Bordetella (B.) bronchiseptica zum Beispiel gelten als Miterreger des Rabbitschnupfens, sind aber ebenso wie Mykoplasmen [7,8] v.a. also found in the upper respiratory tract of healthy rabbits [16]. Infections with P. multocida classically lead to rhinitis with mucopurulent nasal discharge, but may also manifest in otitis, conjunctivitis, pneumonia, abscesses, genital infections, and septicemia [9]. Due to the wide host range, both P. multocida as well as B. bronchiseptica is said to have a certain zoonotic potential and thus a certain risk for immunocompromised people or children [10, 11].

Table 2: Profile rabbit rhinitis [6 – 7, 12 – 13]

Rabbit sniffles	Data and facts
Pathogen	diverse, depending on the stock and attitude: Hein et al. 2021: 32% Pasteurellaceae, 28% Enterobacteriaceae, 13% Pseudomonaceae, 12% Staphylococcaceae. [12] Villa et al. 2001: 43 % Mycoplasma spp., 39 % Bordetella bronchiseptica, 14 % Pasteurella multocida, 14 % Chlamydia spp., 10 % Staphylococcus aureus, 6 % Escherichia coli [7] Rougier et al. 2006: 55 % Pasteurella multocida, 52 % Bordetella bronchiseptica, 28 % Pseudomonas spp., 17 % Staphylococcus spp. [13]
Infection	oronasal, aerogenic
Excretion	respiratory secretions
Clinic	Unilateral or bilateral nasal stridor; sneezing; watery, later mucopurulent nasal discharge; agglutinated forelegs; more or less severe dyspnea Outflow disorders and ascending infections à Conjunctivitis, otitis media/interna z.T. mit Vestibularsyndrom [14]; Enzephalitis severe courses à pneumonia and sepsis
Course	Mild to severe, depending on the pathogen
Diagnosis	Nasal rinsing sample from the deep parts of the upper respiratory tract (to avoid contamination with intestinal/environmental bacteria) Clean the nasal speculum with alcohol-soaked swab Rinse sample collection with physiological saline solution using a 2- to 3-ml syringe and attached brown tube Lacrimal nasal duct irrigation specimen for dacryocystitis Bacteriological examination Rinse sample/swab in tubes with medium PCR (Mycoplasmen spp.) Rinse sample in sterile screw tube without medium
Therapy	according to pathogen/antibiogram, mucolysis, immune stimulation
Prophylaxis	Optimization of husbandry and housing conditions (too dry air due to heating heat in winter, drafts, lack of hygiene) [6]

Infections with gastrointestinal symptoms

Diarrhea is a common problem in the rabbit. Often, in addition to dietary causes, these are infections with endoparasites. In addition to anamnesis and clinical examination, fecal examination is essential to work up!

Coccidiosis

Coccidiosis is an infection caused by protozoa that v.a. in young animals is sometimes accompanied by high mortality rates.

Table 3: Profile coccidiosis [15, 16]

Coccidiosis	Data and facts
Pathogen	Genus Eimeria (E.), protozoa Intestinal coccidiosis: over 25 different Eimeria species, v.a. E. intestinalis, E. magna, E. media, E. perforans [15, 16] Hepatic/biliary duct coccidiosis: Eimeria stiedai host-specific and non-specific species
Infection	peroral ingestion of oocysts (contaminated water, food)
Excretion	enteral (intracellular proliferation in intestinal mucosa) Adults often permanent excretors for months
Clinic	Intestinal coccidiosis: v.a. Caecumtympany; watery, foul-smelling diarrhea; inappetence; apathy [15] Biliary coccidiosis: hepatopathy, lassitude, reduced feed intake, diarrhea or constipation, ascites, jaundice
Course	epidemic, high mortality (v.a. young animals), depending on infectious dose, pathogenicity and individual constitution
Diagnosis	Fecal examination: microscopic (native, flotation)
Therapy	Sulfonamides, toltrazuril (not approved for small mammals)
Prophylaxis	Oocysts remain infectious for months after sporulation in the outside world repeated thorough cleaning and disinfection of the environment [6]

Helminthosiss

Worm infestation sometimes occurs in rabbits. Of relevance for rabbits are mainly nematodes (round/threadworms). Rare in wild rabbits and even rarer in domestic rabbits are cestodes. Detection is done by microscopic fecal examination native and after flotation – if trematode larvae are suspected, also after sedimentation.

Table 4: Profile helminthoses of the rabbit [15]

Helminthosis	Data and facts
Nematodes	Passalurus ambiguus (“awl tails“, oxyuridosis) frequent, parasitize v.a. in caecum Larvae hatch while still in the rectum and can then be seen at the anus and/or on feces Symptome erst bei hgr. Infestation (mostly asymptomatic) Diagnosis: Tesa-Abklatsch vom Anus, Eier im Kot (nativ, Flotation) Graphidium strigosum (stomach worm),Trichostrongylus retortaeformisStrongyloides spp., Trichuris leporis rare, v.a. Young animals when fed contaminated green fodder Symptome: Apathie, Inappetenz, Enteritiden, schleimig-wässriger Durchfall, Kachexie, subakute bis chronische katarrhalische Darmentzündung bei massivem Infestation Diagnosis: Flotation
Cestodes	Anaplocephalidae rare in wild rabbits, very rare in domestic rabbits Intermediate host: moss mite, horn mite ingested with green fodder Symptoms Young animals: catarrhal enteritis with diarrhea, cachexia, developmental disorders, constipation in hgr. Infestation Diagnosis: Flotation
Trematodes	Fasciola hepatica (large liver fluke),Dicrocoelium dentriticum (lancet gel) Rarity, mostly without significance Infection through green fodder contaminated with metacercariae or infected ants Symptoms Large liver fluke: hepatitides, cholangitides, inappetence, cachexia, icterus, edema formation Symptoms lancet gel: unnoticeable, no clinical signs Diagnosis: combined sedimentation-flotation procedure, usually section findings

ConclusionInfectious diseases in rabbits play a role that should not be underestimated. With the knowledge of possible pathogens and corresponding evidence, the diagnosis can be made promptly and optimal therapy can be given.