Presenting problem: Respiratory Disease in Snakes

Understanding respiratory disease in snakes

Respiratory tract disease is common in captive snakes and often manifests as tracheitis and/or pneumonia. Disease is often unapparent to the owner until the problem is quite advanced and open-mouth breathing is observed (Fig 1). Respiratory disease is potentially life-threatening, and requires aggressive management.

Key points of urgent care

Disease is often quite advanced by the time of presentation therefore aggressive therapy is indicated.

• Begin antimicrobial therapy (see Table 1 belwo). Select a bacteriocidal antibiotic that may be administered for a minimum of 4-6 weeks. Until reptile veterinarians have a better understanding of oral drug pharmacokinetics between feedings, parenteral antibiotics are typically selected. The snake gastrointestinal tract is quiescent between meals (Jean-Hervé 2005; Starck 2005; Ott 2007), and it is unclear how well oral antibiotics are absorbed.

It is important that  antimicrobial therapy be based on culture and sensitivity testing in the snake since the susceptibility of Gram-negative organisms  is unpredictable. Popular empirical choices selected just until sensitivity results are available include ceftazidime (Fortaz^®, GlaxoSmithKline), cefotaxime (Claforan®, Aventis), and ceftiofur (Excenel^®, Pfizer) (Table ). Avoid repeated intramuscular administration of enrofloxacin (Baytril^®, Bayer Animal Health) since this medication is alkaline and known to be painful. Repeated intramuscular injection can also cause tissue necrosis and sterile abscess development.

• Ensure the snake is maintained at its preferred optimal temperature zone. It is pointless to administer antibiotics and other treatments if the patient is not housed appropriately
• Supplemental oxygen therapy may be contraindicated in most reptiles with pneumonia. Since one of the driving parameters for reptile respiration is the partial pressure of oxygen, significantly elevated oxygen levels may actually inhibit breathing in the reptile. Therefore oxygen supplementation actually runs the risk of compromising the breathing of an already ill reptile (Murray 2006). If supplemental oxygen is provided, administer no more than 30%-40%  humidified oxygen.

Case management

History

In addition to standard questions about signalment, clinical signs, as well as duration and progression of illness, question the owner about the snake’s origin and the cage set-up. Poor husbandry, particularly inappropriate cage temperature and relative humidity , often sets the stage for lower respiratory tract disease.

History of the sick snake should include:

• Cage temperature gradient?
• Cage humidity?
• How are temperature and humidity measured?
• How is the cage cleaned? What is used and how often?
• What is the origin of the animal?
• What, if any, quarantine procedures are used?
• Is there a history of anorexia or lethargy?

Visual examination

Observe the patient carefully for evidence of respiratory disease. Open-mouth breathing may be observed, particularly after exertion or the stress of manual restraint. Dyspnea is often inspiratory, and congested breathing may be audible.

Signs of lower respiratory tract disease in the snake:

• Open-mouth breathing
• Red, mucoid or foamy discharge from the glottis
• “Opisthotonus” in the snake involves postures that extends the head and trachea
• Increased respiratory rate and respiratory effort
• Cyanotic mucous membranes

There may also be signs of general ill thrift. The snake may appear lethargic or uninterested in its environment. It may lie listlessly in an uncoiled position, and there may also be loss of tongue flicking.

Physical examination

Complete physical examination should include careful evaluation of the oropharynx and coelomic palpation. Congested respiratory noise may be caused by loose skin around the nares–so be sure to check the patient for evidence of shedding or ecdysis (Murray 2006).

Box 1. Physical examination of the reptile with lower respiratory tract disease:
Oropharynx	Heavy oral discharge that is frothy and bubbling or mucoid Inflamed glottis Pale or cyanotic mucous membranes
Auscultation	Auscultation is a relatively insensitive test because of the presence of scales. Placing a moistened gauze over the stethoscope diaphragm may increase the examiner’s ability to auscult harsh breath sounds or rales.
Assess the snake’s body condition by palpating the ribs and epaxial musculature	Obesity can reduce tidal volume thereby exaggerating any signs of respiratory disease
Coelomic palpation	Other conditions that compromise tidal volume include ascites, mass lesions, and hepatic disease.

Also check the snake carefully for the presence of mites. Snake mites (Ophionyssus natricus) have been implicated as possible vectors of infectious disease including bacterial pneumonia (Murray 2006).

Differential diagnoses

The cause of respiratory disease in the snake is often multifactorial. Poor husbandry and substandard sanitation may be important underlying predisposing factors. Poor husbandry leads to opportunistic infections that are often caused by Gram-negative bacteria.

Box 2. Important causes of respiratory disease in snakes:
Aeromonas	Proteus
E. coli	Pseudomonas
Klebsiella	Salmonella

Atypical bacterial infections caused by Chlamydia spp., Mycoplasma spp., Mycobacterium spp. have also been reported as less common causes of pneumonia in the snake (Penner 1997, Jacobson  1989). Anaerobic bacteria isolated from the reptile lung include Bacteroides, Peptostreptococcus, Fusobacterium, and Clostridium spp. (Stewart 1990).

Causes of viral pneumonia include the retrovirus that causes inclusion body disease (IBD) and paramyxovirus. Multiple epizootics of pneumonia in captive snakes have been attributed to ophidian paramyxovirus (Richter 1996; Jacobson 1997). Weight loss and chronic regurgitation predominate in boas with inclusion body disease of boids, however chronic pneumonia may also be seen.

Fungal pneumonia is rare (Timm 1988; Jacobson 2000), and parasitic disease typically causes only localized inflammation and irritation. Secondary bacterial pneumonia can develop with overwhelming loads of lungworms (Rhabdias spp.), ascarids, hookworms, or pentastomids (Murray 2006).

As in mammals, respiratory compromise may also be caused by cardiovascular disease (Schilliger 2010; Schroff 2010) or conditions that reduce tidal volume such as obesity, ascites, mass lesions, and hepatic disease.

Diagnostics

By the time of presentation, respiratory disease in the snake is often advanced and severe. Refer the patient to an experienced reptile veterinarian whenever possible.

Imaging is needed for definitive diagnosis of lower respiratory tract disease. Obtain two radiographic views (dorsoventral and lateral) to screen the patient for regions of increased pulmonary opacity, and to determine if disease is focal, unilateral, or bilateral. Serial radiographs are often required to include the entire lung field. Unless the patient is extremely debilitated, use sedation or a snake tube to achieve good positioning.

Computed tomography allows much more sensitive and precise identification of pulmonary lesions (Pees 2008), however the best way to evaluate the lungs is directly via endoscopy. Where available, tracheoscopy, pulmonoscopy, and endoscopic-guided lung samples provides the best opportunity to make a definitive diagnosis (Stahl 2008; Divers 2010).

Clinical pathology:

• Complete blood count (CBC): The degree of leukocytosis and azurophilia present on the CBC can aid in determining a prognosis. A baseline CBC may also help to determine when to discontinue antibiotic treatment.
• Biochemistry panel:  Evaluate kidney and liver function before administering systemic antibiotics to your reptile patient whenever possible, particularly since therapy must be long-term (Murray 2006).
• Use fecal parasite testing to look for evidence of endoparasitism.
• Collect sterile samples for cytology (Gram stain, modified Wright’s stain, and wet mount cytology) and culture (aerobic, anaerobic, fungal ). In select cases, cytologic evaluation can be instrumental in identifying the underlying etiologic agent, however non-specific granulomatous inflammation is often the only finding (Murray 2006). Interpret culture results cautiously since there may be contamination with oral flora. Organisms commonly isolated from healthy snakes include Providencia rettgeri and coagulase-negative Staphylococcus spp. (Hilf 1990).

If pulmonoscopy is not available, perform a tracheal wash to obtain samples for cytology and culture. Introduce a sterile red rubber catheter through the glottis, then infuse 0.5-1.0% of body weight (kg) of sterile saline into the lung. Immediately aspirate fluid back using gentle negative pressure. It may help to change the animal’s body position so that the head is directed downward.

Therapy

Disease is often quite advanced by the time of presentation therefore aggressive therapy is indicated.

• Administer fluids as needed. Maintenance fluids are often estimated at approximately 20-30 ml/kg/day in the snake.
• Begin aggressive antimicrobial therapy. Select a bacteriocidal antibiotic that may be administered for a minimum of 4-6 weeks.

Table 1. Popular empirical choices for pneumonia in snakes*:
IM: intramuscular; SC: subcutaneous; q: every; h: hour *Gram-negative bacteria have unpredictable susceptibilities and samples should be collected for culture/susceptibility before instituting therapy.
Medication	Dosage	Route	Frequency	Comments
Cefotaxime	20-40 mg/kg	IM	q24h	Carpenter formulary #84, 199
Ceftazidime	20 mg/kg	IM, SC	q72h	8, 122, 151
Ceftiofur	2.2 mg/kg	IM	q48h

• Nutritional support as needed
• If the patient has an ectoparasite or endoparasite load, administer anthelmintic(s) (Murray 2006).
• Nebulization with saline or antimicrobials for 15-30 minutes twice daily may also prove helpful (Mitchell 2006).
• It is also important to educate the owner on any husbandry related items that must be corrected. It is pointless to administer antibiotics and other treatments if the patient is not housed appropriately at its preferred optimal temperature zone.

Conclusion

Respiratory tract disease is common in captive snakes. Pneumonia and/or tracheitis are typically caused by opportunistic Gram-negative bacterial infections that are allowed to take hold due to poor husbandry practices. Unfortunately snakes with lower respiratory tract disease are often not presented until disease is quite advanced. Survey radiographs may be useful for detecting advanced lesions, however more sensitive diagnostic tests include computed tomography and/or pulmonoscopy and tracheoscopy. Culture/sensitivity testing of a sample collected via lung wash or endoscopy is essential for selecting the most effective antimicrobial. Ancillary testing that should be offered cytology, fecal parasite testing and CBC/biochemistry panel.

When should antimicrobial therapy be halted in the snake with pneumonia?  Certainly antibiotics must be continued until after clinical signs resolve , however most clinicians also rely upon diagnostic tests. Evaluate a CBC in conjunction with the result of serial radiographs, computed tomography, culture of a tracheal wash, or ideally endoscopic evaluation.

References