Geographic Translocation of Bats: Known and Potential Problems

Post date: Jan 4, 2017 11:56:20 AM

Geographic Translocation of Bats:

Known and Potential Problems

Denny G. Constantine*

Natural, accidental, and intentional translocation of bats,

both intra- and intercontinentally, has been documented. Some

bats have been translocated while incubating infectious diseases,

including rabies or related lyssavirus infections; others

have escaped confinement en route to or at their destinations,

while others have been released deliberately. Known events

and potential consequences of bat translocation are reviewed,

including a proposed solution to the attendant problems.

Among the many potential consequences resulting from the

geographic translocation of life forms is the spread of

infectious disease organisms harbored by that life form. This

consequence was demonstrated long ago by the early devastation

of native American human populations caused by pathogens

inadvertently introduced by European explorers.

Similarly, wildlife rabies outbreaks occurred recently in the

United States after foxes, coyotes, and raccoons were translocated

to restock areas where these animals are hunted for

sport. Wild populations of introduced species can also become

common disease vectors where few or none existed before,

such as the current role of Indian mongooses (Herpestes javanicus)

in rabies transmission on Caribbean islands (1), or

they can become predators of native species, for example, the

wildlife destruction that occurred after ferrets and stoats were

introduced into New Zealand (2).

Bats have been translocated through natural, accidental,

and deliberate means. Pathogens associated with bats, such as

Rabies virus (RABV) and related lyssaviruses (3–6), can cause

disease after protracted incubation periods, ensuring the

extended survival of the host and parasite during periods of

translocation. Many bat species enter a hibernationlike state in

a cold environment, which further prolongs survival. In this

article, I describe some occurrences of bat translocation (published,

as well as previously unreported) and the potential consequences

of that translocation, as the basis for suggesting

preventive measures to alleviate the problems that accompany

the relocation of bats across the world.

Translocation of Bats

Natural Translocation

Some species of bats hibernate at the approach of cold

weather; other species migrate to warm areas instead. Bats that

migrate along coastlines take shortcuts over water and are

apparently blown far out to sea at times. Many North American

migrant bats have been found in Bermuda, 1,046 km east

of North Carolina, United States, during fall and spring migrations,

evidently having been blown there by wind along with

waves of migratory birds (7). These translocated bats include

Hoary Bats (Lasiurus cinereus), Red Bats (L. borealis), Seminole

Bats (L. seminolus), and Silver-haired Bats (Lasionycteris

noctivagans), all species from which RABV has been isolated

(8). Hoary Bats are also occasionally found in rabies-free Iceland,

also possibly blown there by the wind; one bat was captured

in the Orkney Islands, off rabies-free Scotland (9).

Similarly, Hoary Bats are sometimes found in the Galapagos

Islands, 966 km off the west coast of South America (10).

Translocation after Landing on Ships

Exhausted bats flying far at sea both individually and in

flocks have been reported to alight on ships and be transported

to unintended destinations. Most records are from the North

Atlantic Ocean and involve Red Bats and Silver-haired Bats

(11). A Southern Yellow Bat (Lasiurus ega) landed on a ship

over 322 km from the coast of Argentina (12). A “fruit-destroying

bat” was reported sleeping in the rigging of a ship upon

arrival in Hawaii from the Philippines (13), and a frugivorous

bat (Vampyressa pusilla) evidently boarded a vessel passing

through the Panama Canal and was later found aboard when the

ship was between Australia and Tasmania (14).

Translocation after Using Ships for Shelter

Bats sometimes roost in or on ships in port and may be

transported as a consequence. Silver-haired bats were discovered

hibernating in hulls of ships, and numbers of them found

various refuges on ships and yachts in New York (15). Little

Brown Bats (Myotis lucifugus) roosted aboard a ship that frequently

traveled from Canada to Europe, flying ashore after

arrival in the Netherlands and England (16). The presence of

individual Little Brown Bats in rabies-free Iceland (9) and

Kamchatka, Russia (17), has been attributed to travel by ship.

RABV, other viruses, and Histoplasma capsulatum have been

found in this species (3,8).

On January 21, 1997, a stevedore working in the hold of a

ship being unloaded in Long Beach, California, after its arrival

from Korea, was bitten on the back of his neck by a bat. A fluorescent

rabies antibody test was negative for RABV infection.

On February 1, I received the bat for evaluation and determined

it to be a Serotine bat (Eptesicus serotinus), which is similar to

the Big Brown Bat (E. fuscus) but with a slightly more massive

skull. The Serotine has been reported in North Africa and

England and across Europe and Asia to Korea. Hundreds of ill

or dead Serotines have been found infected with the

RABV-related European bat lyssavirus 1 (EBLV-1) in Europe,

where one or two persons have died of the infection after bat

bites (5). The rabies conjugate used in the rabies test on the

Serotine bat’s brain reportedly reacts with this virus as well.

Translocation in Shipping Containers

Translocation of bats by ship also occurs when bats are

closed inside shipping containers. Free-tailed bats from the

tropics are occasionally transported long distances in fruit

shipments (18). A Pallid Bat (Antrozous pallidus) was discovered

in Victoria, British Columbia, in a shipment of lettuce

from California (19), where RABV-infected Pallid Bats have

been identified. A Big Brown Bat was found hibernating in a

timber container from Canada when it was unloaded in the

Netherlands (16). An Asiatic Pipistrelle bat (Pipistrellus javanicus)

was discovered in a container transported by ship from

Japan to New Zealand (20). Sasaki et al. (21) reported the

arrival in rabies-free Hawaii of a RABV-infected Big Brown

Bat found flying in an automobile container from California.

Subsequent study indicated that previously the bat had been

transported to California either from Florida in the shipping

container or from Michigan in an automobile.

In October 1995, a group of live bats was observed hanging

in a dark corner within a large shipping container that had

just arrived at a Los Angeles port from Puerto Rico, but the

bats escaped as capture was attempted and no further reports

of these bats were made. Histoplasmosis, apparently absent in

California except for imported human infections, has been

diagnosed in some Puerto Rican bats.

Translocation by Aircraft

Bat translocation by aircraft has been reported several

times. A Little Brown Bat was found clinging to a seat in an

airplane at the end of a flight in Canada (22). An Eastern Pipistrelle

bat (Pipistrellus subflavus) was recovered from a plane

that had just arrived in Texas from Mexico (23); RABVinfected

bats of this species have been identified in the United

States and Canada. The carcass of a Little Brown Bat, presumably

from Tacoma, Washington, was found on a runway at an

Air Force base on rabies-free Guam (24). Stebbings reported

the arrival in England of a Silver-haired Bat aboard a U.S. Air

Force cargo plane from Delaware (25). Observed flying in the

plane en route, the bat was captured later while sleeping in a

crew member’s bed in the aircraft.

An Asiatic Pipistrelle bat was captured May 25, 1993,

aboard an airliner en route from Tokyo to San Francisco. This

bat was negative for RABV. The next month a Yuma Myotis

bat (Myotis yumanensis) was discovered flying aboard a U.S.

Air Force cargo plane en route from California to Hawaii. This

bat was also negative for RABV, although rabies has been

diagnosed in the species in California. Evidently the bat was

loaded into the aircraft within a shipment of fruit.

In early March 1995, a traveler who had just arrived in Los

Angeles by aircraft from South Africa opened his suitcase and

observed a bat fly out. The suitcase had been closed three days

earlier during darkness in a hut within Kruger National Park.

The bat was negative for RABV, and the frozen carcass was

sent to me 2 months later with the history of origin in a Los

Angeles County community. At first glance, the bat appeared

to be a common local free-tailed bat (Tadarida brasiliensis),

but closer inspection indicated differences, although the bat

belonged to a family with similar representatives in warm

areas worldwide. After extensive study, I determined the specimen

to be a Wrinkle-lipped bat (Chaerephon pumila), known

throughout sub-Saharan Africa, Madagascar, and southern

Arabia. Further research disclosed the transported bat’s African

origin. This species supports experimental replication of

Ebola virus without showing disease signs (26); the remainder

of the carcass was immediately sent to a federal laboratory for

Ebola virus tests, which proved negative. Several other viruses

have also been isolated from the salivary glands of this species

in Africa (3).

In June 1997, a woman was bitten by a bat hiding in clothing

she was packing before an airline flight from Costa Rica to

California. The live bat was restrained in a plastic bag during

the flight; it was dead on arrival. The bat was negative for

RABV and was identified as a Sinaloan Mastiff Bat (Molossus

sinaloae), an insectivorous species in which RABV has been

reported (5).

Translocation for Confinement

Bats have been transported varying distances, sometimes

worldwide, to be maintained in captivity as research animals,

as live specimens in zoos or other exhibits, and as pets. Transport

for research purposes is not noteworthy except in unusual

circumstances. A Big Brown Bat in the incubational stages of

rabies was among live bats sent from Canada to a laboratory in

Germany, where the bat developed clinical rabies (27). Similarly,

six Big Brown Bats that were incubating RABV were in

a group sent from the United States to a laboratory in Denmark

(28). However, recipient laboratories understood the risks and

had taken necessary precautions.

RABV-infected individual bats of the tropical American

common Vampire Bat (Desmodus rotundus) have been

reported throughout their geographic range, which extends

from northern Mexico south to Chile and Uruguay (8,29).

RABV has also developed in Vampire Bats after being transported

to laboratories. In addition, during the 1970s, a group of

these bats sent from Mexico to a laboratory in the United

States presumably escaped en route, because only the empty

shipping container arrived.

Increasing interest in bats has resulted in displaying of

more varieties of these mammals, including Vampire Bats, to

the public (5). One such display presented a problem I investigated

in 1988 after four of eight Vampire Bats escaped their

flight cage within a cavelike structure at a southern California

zoo 1 month after their arrival from Mexico through a Texas

Emerging Infectious Diseases • Vol. 9, No. 1, January 2003 19

supplier. Two escaped bats were found dead, possibly due to

starvation or unusually cold weather. One dead bat had nearly

escaped the building, and the other was outside. Neither bat

was infected with RABV. The apparent escape route to the outside

was through a fragile false cave ceiling, which could not

be inspected. This ceiling may have contained the carcasses of

the remaining two missing bats, possibly a male and a female.

I found no bat bites on zoo animals and no bats or bat feces in

likely hideaways in the zoo.

The large fruit-eating bats (genus Pteropus) live on land

masses, including islands, from Madagascar, India, Southeast

Asia, the East Indies, the Philippines, and Australia to the

Samoan and Cook Islands of the South Pacific Ocean. They

have been popular zoo attractions for many years. RABV was

reported in a Pteropus in India (8), and RABV-related lyssaviruses

were reported in four species of Pteropus and an insectivorous

species in Australia, where two persons died of these

infections (30).

Three additional viruses (Paramyxoviridae family)

ascribed to Pteropus origin have proven pathogenic or fatal to

people and domestic animals. Four species of Australian

Pteropus bats in Queensland carry Hendra virus without developing

symptoms. These bats disseminate virus in urine or placental

fluid during birthing, and the virus is later ingested by

pregnant horses that amplify the virus, which then spreads to

people and causes a fatal pneumonia (13/20 horses were

infected in a 1994 outbreak, which resulted in two human

deaths) (30). The second virus, Menangle virus, is considered

to be spread to pigs in Australia by the same four species of

Pteropus bats, producing stillbirths with deformities in 1998 in

27% of litters, as well as an influenzalike illness in humans

(30). The third virus, Nipah virus, identified in urine and saliva

of Pteropus bats in Malaysia, apparently spreads the virus to

pigs and destroyed that country’s swine industry in 1998. The

virus spread from pigs to hundreds of industry workers;

approximately 40% of these workers died of severe viral

encephalitis caused by the agent (31).

Importation of fruit-eating bats has long been severely

restricted to protect the fruit industry in the United States. The

Egyptian Rousette bat (Rousettus egyptiacus) is a widespread

Old World fruit bat that readily reproduces in captivity; thus

colonies occur in some zoos. This species has been implicated

in several viral infections in Africa (3). An error occurred in

1994, when thousands of these and other bat species were permitted

entry into the United States for sale as pets or for exhibition

(28); this procedural mistake resulted in a policy change

to prevent recurrence. Antibodies to West Nile virus (WNV)

had been reported in the R. egyptiacus species in Uganda and

Israel (3), and the virus had been isolated in India from the

nearly indistinguishable R. leschenaulti, which overlaps geographically

with R. egyptiacus in Pakistan (32). The entry of

R. egyptiacus into the United States in 1994 suggests a remote

connection with the subsequent outbreak of WNV there, first

observed 5 years later among captive and wild birds at a zoo in

New York (33).

In 1997, two R. egyptiacus bats died with rabies-like

symptoms in a Denmark zoo; they were later found to be

infected with EBLV-1 subtype A, a RABV-related agent

known to have caused deaths in European insectivorous bats

and in humans. The two infected bats had arrived recently

from a Netherlands zoo, where the source captive bat population

subsequently was destroyed (34). A replacement colony

was similarly destroyed after a bat originating from a Belgian

zoo was also determined to be infected (35).

Persons concerned about sick and injured wildlife often try

to rehabilitate disabled bats, sometimes transporting the animals

a considerable distance from sites of discovery. Unfortunately,

an average of 10% of disabled bats tested in North

America are found to be infected with RABV, exposing those

trying to rehabilitate the bats to rabies. If they have received

preexposure rabies prophylaxis in advance, these persons are

advised to take booster shots of vaccine; otherwise, they are

advised to take both antirabies globulin as well as the full vaccine


Often, attempting to reverse the negative image of bats

usually held by the public, persons trying to rehabilitate sick

bats may suppress warnings of rabies hazards, doing both bats

and the public a disservice. Moreover, to avoid the embarrassment

of repeated exposures to rabid bats, some persons working

in bat rehabilitation are known to arrange submission of

rabies-suspect bats to a variety of different laboratories in different

geographic areas, thus disguising the true history of the

bat; this practice may protect the rehabilitator but prevent

other persons or pets exposed earlier from receiving adequate

antirabies management.

Translocation for Release

Bats have been translocated and released in attempts to

establish bat populations in new areas for reasons such as insect

control and experimental study. Such efforts are sometimes

supplemented by providing living quarters or shelters for bats

ranging from elevated boxlike structures to tunnels. Before the

knowledge that some insectivorous bats might be infected with

rabies or other pathogens, bats were sometimes transported

great distances over land or overseas and released in efforts to

establish populations at the new location. Tomich (13) assembled

historical records about the importation and release in

rabies-free Hawaii of Asiatic Pipistrelle bats from Japan and

free-tailed bats (Tadarida brasiliensis) from California during

the late 1800s to establish bat populations for insect control

purposes, but the attempts were evidently unsuccessful.

Observing that destruction of old-growth forests eliminated

the tree hollow homes of Polish bats, Krzanowski (36)

recommended the introduction into Poland of Red Bats and

Hoary Bats from the United States because these species take

shelter in tree foliage rather than hollows, and they migrate at

the approach of cold weather rather than hibernate in tree cavities.

However, rabies was discovered simultaneously in North

American insectivorous bats, including these two species, discouraging

further consideration of the proposal.


20 Emerging Infectious Diseases • Vol. 9, No. 1, January 2003

The homing abilities of bats have routinely been studied by

transporting and releasing marked bats up to 805 km from

their home roost, which is then monitored for the return of the

marked bats (37). RABV infection has now been identified in

11 of the 12 North American species studied, and histoplasmosis

is known in 6; RABV-related lyssavirus infections have

been reported in 5 of 12 European species studied (8).

During World War II, field trials were conducted in the

southwestern United States to determine the effectiveness of

disseminating thousands of free-tailed bats (T. brasiliensis) in

the air, each transporting a small time-activated fire bomb. The

objective was to start thousands of simultaneous fires in adversary

target areas, achieved after each bat had sought out a hideaway

in various available structures (38). As a participant in

the project, I observed that each bomb or dummy bomb,

attached by a short string and surgical clip to the bat’s abdominal

skin, was disengaged after the bat alighted in a refuge and

chewed through the string. Thousands of bats were transported

<1,609 km distant from source bat caves in Texas and New

Mexico to test areas in California, New Mexico, and Utah.

Frequently, the tests were postponed, and the freshly captured

bats were released unencumbered at or near test sites.

Unknown at the time, RABV is now known to occur in 0.5%

of bats in the source caves (8), so the virus was almost certainly

translocated with the bats. H. capsulatum, the causative

fungus of histoplasmosis, also has been isolated from these

bats and their guano in the source caves, but neither bats nor

guano have yielded the agent in extensive surveys in California,

which is regarded as free of the fungus; no cases of indigenous

origin have been detected (8).


Bats and the pathogenic organisms they sometimes harbor

are being transported by humans within and between continents,

and sometimes these transported bats escape. Because

bats reproduce slowly (usually only one or two offspring are

produced annually by a female), the chances of successful

introduction of the species are minimized. Populations would

more likely develop should large numbers be freed in places

favorable to survival. Although a single escaped bat might not

survive long or reproduce, it would seek shelter in places frequented

by local bats to which it might transmit pathogens. As

has been observed, introduced pathogens include RABV, other

lyssaviruses, or various other agents.

Vampire Bats can be especially problematic in view of

their possible colonization in warm climates and their dependence

on a diet of blood, thus necessitating their biting vertebrates,

including man and domestic animals. As reported, in

addition to their known role as biologic vectors of rabies to

humans and domestic animals and surra (Trypanosoma evansi)

to horses and cattle, Vampire Bats can also be temporary biologic

as well as mechanical vectors of Venezuelan equine

encephalomyelitis virus and foot-and-mouth disease. They are

likely effective mechanical vectors if not biologic vectors of

any bloodborne pathogen, including the AIDS virus (29). Various

species of fruit-eating bats are infected at times with

pathogens destructive to other bats, humans, and domestic animals.

However, their entry to many areas is restricted due to

concern that their escape would lead to populations destructive

to fruit crops.

Accidental or planned translocations of bats between land

masses happens almost certainly with far greater frequency

than is reported. Such events can be embarrassing, and

although incidents that result in successful containment are

more likely to be reported, failed efforts can remain unpublicized.

Relevant reporting requirements do not exist. Personnel

involved in the various described incidents generally have performed

very well in efforts to resolve the problems, often with

immediately contrived solutions. Inspectors at entry centers

are usually exceptionally competent because they must cover a

broad array of subject areas, but their competency must be

taxed at times. For example, most bats are exceptionally adept

at avoiding capture, and even bat scientists with special equipment

frequently are outmaneuvered. Some inspectors contact

specialists for help in emergencies, but help is not always

available or is displaced by previous commitments and economic

necessities. Previous contractual arrangements with

institutions such as universities, natural history museums,

zoos, or specialized commercial services could dispel most relevant

problems, including funding, and maintain program continuity.

Unaffiliated specialized personnel would be expected

to maintain or acquire relevant competency, but incidents,

such as those cited here, show some lapses. Ideally, the services

of a bat expert are required. For example, if bats are to be

excluded from any vehicle of conveyance, the usual procedures

and equipment should be reviewed by responsible persons

very familiar with bats, their capabilities, their capture,

their confinement, and their exclusion in order to recognize

flaws that permit bats to be transported. Thus, experts can help

establish and maintain more effective programs.


Appreciation is extended to the counties and state of California

and to William E. Rainey, Elizabeth D. Pierson, Charles E. Rupprecht,

Jean S. Smith, Kevin F. Reilly, Thomas H. Kunz, and Amy Turmelle

whose help made relevant reports possible.

After the 1953 discovery of bat rabies in the United States, Dr.

Constantine established the Southwest Rabies Investigations Station

in New Mexico for the Centers for Disease Control and Prevention

and developed its program to investigate the problem and control bat

rabies. Now retired, he continues research in the field.


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Address for correspondence: Denny G. Constantine, 1899 Olmo Way, Walnut

Creek, California, 94598 USA