Abstract

Many species of Megachiroptera are being kept in increasing numbers in zoos throughout North America and Europe. Megachiroptera have a number of medical problems associated with trauma and nutritional deficits. Traumatic injuries are usually seen during transportation or conditions of overcrowding as well as inappropriate social groupings (i.e., male groups). Dietary imbalances have resulted in dilated cardiomyopathy, fluorosis, and metabolic bone disease. Dental diseases mimic those seen in small animal medicine. Infectious diseases are uncommon and sporadic, but recent reports of zoonotic viral infections in Australasian bats warrant careful quarantine of wild-caught bats.

Introduction

After rodents, bats comprise the second largest group of mammals and are found across the entire globe except for Antarctica and north of the Arctic circle.⁸ The morphology of bats has been questioned in recent years, and it is estimated that there are some 900 species of living bats. All bats belong to the order Chiroptera, which consists of two suborders: Megachiroptera and Microchiroptera. Megachiroptera are the Old World fruit bats or flying foxes, which are found in subtropical regions of Africa, Asia, and Indo-Australia. These bats are all in one family, the Pteropodidae, and consume fruits, flowers, and/or flower products.⁶ The remaining bats are in the suborder Microchiroptera, which is composed of 17 families of bats. The Microchiroptera have greater diversity and consume insects, flesh, blood, nectar, flowers, and pollen.⁶ With bat persecution and environmental loss continuing worldwide, bat populations are becoming more endangered. Bats are now identified as major pollinators and distributors of seeds in tropical forests.⁹ Bat welfare plays an important role in the conservation of tropical forests. Recently bat conservation has taken a step forward, with work being completed both in the field and in captive situations.

Trauma

Abscesses and Swellings

Bite wounds are very common and are not usually noticed until a swelling or a draining wound develops. Bite wounds to the head may result in abscess formation on the snout and head; lacerations of the eyelid and third eyelid have also been documented. Streptococcus, Staphylococcus, Pasteurella, and various anaerobes have been cultured from these bite wounds.⁵ Treatment involves lancing the abscess and flushing with 2% chlorhexidine diacetate (Nolvasan®, Fort Dodge, Fort Dodge, IA) under anesthesia; oral antibiotics may decrease recurrence. Antibiotic treatments, such as trimethoprim-sulfamethoxazole (Septra®, Glaxo Wellcome, Research Triangle Park, NC; 20 mg/kg PO every 12 hours for seven days) or amoxicillin-clavulanate acid (Clavamox®, Beecham, Philadelphia, PA; 20 mg/kg PO every 12 hours for seven days), have been effective. The abscess may resolve in about one week; however, multiple debridements are often warranted. Damage to the eye may include lacerations of the eyelid and, possibly, cornea. Fluorescein staining followed by treatment with topical ophthalmic ointments is recommended.

Patagial Trauma

Trauma to the wing patagium may result in small holes or large lacerations. These wounds rarely become infected and will heal through constriction over a few weeks. Poor husbandry, such as malnutrition and chronic injury, may result in excess scar tissue formation along the healing edge, which may result in a permanent hole in the patagium. Palpable thickening of the wound edge may be noted, along with loss of pigmentation. Once husbandry conditions have been improved, excess scar tissue may be removed using electrocautery; suturing is not necessary. Trauma to greater than 75% of the wing patagium can result in constriction of the wing tissue and permanent loss of flight. This is rare and the wing should be given a number of weeks to heal before any drastic measures, such as amputation, are taken.

Iatrogenic thermal burns caused by artificial heating devices such as warm water bottles and heat lamps occur very easily. Wing tissue is very thin, and even warm water bottles that do not feel hot to the touch may result in large areas of necrosis within a few days after exposure. Circulating water blankets should be covered by a towel during prolonged anesthetic procedures. Wet bats can be dried using hair dryers set on low. Bats recovering from anesthesia are best placed in an avian or infant incubator to increase body temperatures.

Nail Avulsion

Besides the feet, the thumb (digit number 1 on each wing) is the main grasping claw and is necessary for ambulation. These nails are easily damaged, especially while moving around in wire caging. The trauma is similar to that of a dog or cat who has torn off a nail and may be painful for a few days. Thumbnail avulsion can be treated by application of Soft Nails® (SmartPractice, Inc., Phoenix, AZ), a plastic cap designed to glue over cat nails as an alternative to declawing. In this procedure, a small amount of surgical glue is applied to the nail bed and the appropriately sized cap is applied. This cap will protect the nail bed and will fall off once nail starts growing. In most cases, the cap will stay on for several weeks, but reapplication may be necessary if the cap falls off prematurely. These caps have worked very well, and speed recovery and the use of the thumb.

Frostbite

Megachiropterans housed in outdoor enclosures are susceptible to frostbite. Injuries seen at the Lubee Foundation have been limited to the nail beds of the toes and the wing tips. This injury presents similarly to the thumbnail avulsion, with nail bed necrosis and subsequent sloughing of the nail. The toe injuries are problematic, as the bats cannot roost in the normal hanging position. This problem can be solved by placing the bats in a smaller indoor enclosure equipped with plastic hammocks for the bats to lie in. Hammocks made of plastic fencing material are easy to install and clean. The hammocks were placed about 60 cm from the top of the cage, allowing the bats to lie down without using their feet. Soft Claws® can be used to cover the nail beds until the toenails regrow. Antibiotic treatment may be warranted for the first few weeks. As the nails heal, the bats perch by placing most of their foot through the wire cage and grip with the toes. Regrown nails may be straight, not curved, which does not allow for normal roosting behavior. Repeated grooming of the new nails over several months with a Dremel tool to place a curve on the plantar surface of the nail may facilitate return to normal roosting.

Fractures

Fractures of long bones such as the femur and radius, may be repaired using techniques similar to those used in avian medicine.¹ Metacarpal fractures of the finger bones are very common and may result from fighting or trauma. If the fracture is closed and is not in the distal 1/3 of the metacarpal bone it may heal without external fixation. Confine the bat for one month to stop flying and facilitate healing. Fractures near the distal end of the metacarpals may result in open fractures or malunions. Due to the small size of these bones, external fixation or coaptation are difficult to apply successfully. Alternatively, the chronic non-healing fracture or exposed bone fragment may be removed using electrocautery to dissect out the bone and loose wing skin. Fortunately, these fractures usually occur in the second phalanx (Megachiroptera do not have a third phalanx) and do not affect flight. Once the loose fragment is removed, shorten the exposed bone with a pair of Mayo scissors after pulling the skin proximally, allowing the skin to cover the end of the bone. A drop of tissue glue on the end will facilitate healing. The wound is subject to being damaged and reopened. Fortunately, progressive osteomyelitic lesions that ascend up the bone appear to be rare. Treatment with oral antibiotic may be warranted.

Nutrition

Dilated Cardiomyopathy

Dilated cardiomyopathy has been documented in wild-caught Pteropus sp.^3,4,9 These bats may show cranial edema, lethargy, muscle wasting, and blue mucous membranes. Enlarged hearts can be visualized on thoracic radiographs, while ultrasonography may reveal ventricular and atrial dilation, myocardial wall thinning, and poor contractility. All bats reported with this condition had undetectable blood levels of vitamin E (<56 IU/kg). Supplementation of vitamin E in the diet to 240 IU/kg (dry matter basis) has almost eliminated this problem in megachiropterans. Treatment of affected animals has been successful with medical management.⁴

Fluorosis

Excess fluoride ingestion causes multicentric hyperostosis of bone surfaces with resultant proliferation of bone in the carpus. Lesions seen at the Lubee foundation appeared as enlarged thumb joints in lactating Pteropus vampyrus. These lesions have also been described in Pteropus giganteus, Pteropus poliocephalus, and Rousettus aegyptiacus at the Toronto and Calgary Zoos.² These proliferations result in large, firm, raised areas which cause the overlying skin to become taut and subject to abrasion, laceration, and secondary infection. Fluoride levels of affected bats measured at necropsy were 2200–4700 ppm; unaffected bats at another collection had levels of 290–320 ppm.² Dicalcium phosphate from shrimp meal which contained ∼1900 ppm of fluoride was the main source of toxicosis. A change to monocalcium phosphate has resolved the problem.

Hypocalcemia and Metabolic Bone Disease

Swollen joints, curvature of long bones, and flattened faces were found on visual exam of Pteropus vampyrus pups. Serum calcium levels were low at 2.5 mg/dl (9.5±0.7 mg/dl) (ISIS physiological reference ranges, 1999). Discontinuation of the dicalcium phosphate supplement for a period of six months during the fluorosis problem resulted in metabolic bone disease in these rapidly growing pups of the largest megachiropteran. Affected pups were supplemented with oral calcium (calcionate syrup, Rugby, Norcross, GA; 23 mg/ml) 2 ml PO every 12 hours as a supplement to the diet. After two weeks of treatment, the serum calcium levels had normalized and the deformities in the long bones began correcting themselves.

Infectious Disease

Respiratory Disease

Respiratory disease is uncommon in the Megachiroptera. Sneezing and clear nasal discharge are common in healthy fruit bats. However, Wahlberg’s epauletted fruit bats (Epomorphus wahlbergi) with pneumonia frequently demonstrate anorexia and seclusion from the colony.⁵ Respiratory cultures have isolated a Pasturella-like bacteria as the pathologic agent.⁷ Treatment with enrofloxacin (Baytril, Bayer Corp., Shawnee Mission, KS;10 mg/kg IM or PO every 12 hours) may be indicated. Unfortunately, this species of bat is easily stressed and may die during treatment.

Gastrointestinal Disease

Acute death in three Rodrigues fruit bats (Pteropus rodricencis) was diagnosed as severe necrotizing enteritis caused by Yersinia enterocolitica. The primary enteric infection resulted in embolic spread of bacteria with hemorrhage, necrosis, and inflammation present within multiple organs. Fecal culture of 17 additional bats in the same enclosure was negative for Yersinia enterocolitica. Fecal culture for Yersinia is recommended for any “down” bats.

Dental Disease

Dental problems such as fractured teeth, dental abscesses, and staining are common in most species of Megachiroptera. Staining in wild-caught bats appears as dark brown to black areas of discoloration and may be related to enamel defects.⁵ The staining does not cause problems and should be considered an incidental finding. Tooth root or apical abscesses appear as swellings on the ventral mandible or dorsal maxilla. Treatment involves lancing the abscess and removing the tooth under general anesthesia. In smaller bats <500 g, an 18 ga needle can be used as an elevator to loosen the dental ligament, allowing removal of the tooth. Postoperative analgesia such as butorphanol (Torbugesic®, Fort Dodge, Fort Dodge, IA; 0.2 mg/kg IM) should be used in association with a course of antibiotics. These wounds heal quickly, and usually resolve within two weeks. Chronic abscesses involve bone and may appear as small, hard lumps under the ventral mandible. These lesions should be evaluated radiographically, and extended courses of bone-penetrating antibiotics such as amoxicillin-clavulanate acid at 20 mg/kg PO every 12 hours may be indicated.

Viral Diseases

A number of viral diseases of megachiropterans have been recently identified in the Australian/Southeast Asian region, including Hendra virus, bat lyssavirus (bat-like rabies), and Nipah virus. These viruses are zoonotic and have caused fatalities in humans, horses, and pigs. Newly imported bats should be quarantined appropriately, including serial titers for these diseases. For additional information, see the CDC Conference on Emerging Infectious Diseases at www.cdc.gov.

Conclusion

Nutritional deficiencies and trauma are the main causes of disease in captive megachiropterans. Infectious disease and neoplasia also occur. The use of volatile gas anesthesia (Isoflurane®, Abbott Labs, Chicago, IL) has made physical examination and treatment of common problems safe and easy. Megachiropterans respond well to treatment and learn to take medications without restraint using behavioral conditioning.

Acknowledgments

We would like to thank John Sayjaget, Dana LeBlanc, and all the keeper staff the Lubee foundation for their assistance and expertise.

Literature Cited

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