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Chimpanzee respiratory disease and visitation rules at Mahale and Gombe National Parks in Tanzania.

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American Journal of Primatology 70:734–737 (2008)
Chimpanzee Respiratory Disease and Visitation Rules at Mahale and Gombe
National Parks in Tanzania
Mountain Gorilla Veterinary, Musanze, Rwanda
Multiple outbreaks of often fatal respiratory
disease have occurred in Tanzania’s habituated
Eastern chimpanzees, Pan troglodytes schweinfurthii, since long-term research studies began there
in the 1960s. Disease events similar to those recently
reported among the Taı̈ Forest chimps have been
described at the Gombe Stream Research Center and
Mahale Mountain National Park [Goodall, 1986;
Hanamura et al., 2007; Kamenya, 2002; Lonsdorf
et al., 2006; Nishida, 1990]. The mortality rate
during some of these outbreaks has ranged as high
as 30% at Gombe and 20% at Mahale. The Taı̈ Forest
findings provide the first evidence that chimp
respiratory disease can be caused by introduced viral
pathogens. These findings help us better understand
the disease outbreaks at Gombe and Mahale. They
also emphasize the importance of veterinary involvement during all stages of an outbreak, from daily
clinical observations to post mortem exams and
sample collection.
Since many years veterinarians suspected a
possibility of human disease transmission to free
ranging Great Apes in Africa (Leendertz et al., 2006;
The Mountain Gorilla Veterinary Project, 2002).
Though viral pathogens introduced by people have
not yet been proven to cause respiratory disease at
Mahale (see article by Kaur et al., 2008) or Gombe,
the clinical signs and post mortem findings among
the chimps there closely resemble those described by
Köndgen et al. [2008] for the chimps of the Taı̈
Forest. Numerous outbreaks of respiratory disease
have been recorded at Gombe over the years
[Kamenya, 2002; Lonsdorf et al., 2006]. Gombe
chimp population has declined for various reasons,
including habitat loss and mortality from disease.
The impact of disease on the Mahale chimps, which
live in the well-protected piece of forest, is even more
evident. In 1965, the total population of chimps
under habituation was estimated to be at least 140
r 2008 Wiley-Liss, Inc.
individuals living in two communities. In 1984, there
were 101 chimps in just one community. By 2006,
that number had declined to a low of 52 animals,
with 12 deaths from one outbreak during that same
year. Because of the high mortality rates at Mahale,
researchers responsible for naming the new born
animals waited until infants reached the age of 2
years. Some of these individuals were the victims of
natural causes, but many have died during the
recorded outbreaks of disease.
Officials with the Tanzanian National Parks
(TANAPA) recommended that all visitors, including
tourists and researchers, follow standard visitation
rules at Gombe in 2000 and Mahale in 2006. It took
some time for the rules to be implemented and even
now they are not always entirely followed. However,
there have been no serious outbreaks—and no
deaths from respiratory disease—at Gombe since
the end 2002 (S. Kamenya, E. Lonsdorf, personal
communication) and at Mahale since August 2006
(Lukasik-Braum, unpublished data).
Veterinary Management of Respiratory
Disease Outbreaks: Mahale
Historically, veterinary clinicians have not been
involved in the management of respiratory disease
outbreaks at Mahale. Interventions were not allowed, clinical data were not collected, and no
veterinary equipment was available before 2006.
During the June 2006 outbreak when chimps started
dying, TANAPA officials, Frankfurt Zoological Society scientists, and Kyoto University researchers
invited me to participate in the daily veterinary
assessment of sick animals and to conduct post
mortem examinations when possible.
Sample collection and analysis from sick chimps
at Mahale were limited because researchers felt
that the disease outbreaks were natural and
Correspondence to: Magdalena Lukasik-Braum, Regional Field
Veterinarian, Mountain Gorilla Veterinary Project BP 115
Musanze, Rwanda. E-mail:
DOI 10.1002/ajp.20568
Published online 20 May 2008 in Wiley InterScience (www.
therefore should run their natural course. No clinical
exams were performed and no invasive samples
were obtained from individuals with clinical signs
of respiratory disease apart from few fecal,
urine, and wadge samples. Results of analysis are
pending at Kyoto University (see Kaur et al. in this
Clinically, chimps affected during the June
2006 outbreak at Mahale showed signs of moderate
to severe upper and lower respiratory tract
disease. Sneezing, rhinitis, wet and dry coughs,
lethargy, and tachypnea were observed. Some
animals seemed to develop signs of illness acutely,
from one day to the next. Severely affected animals
showed signs consistent with pneumonia including
increased respiratory effort, malaise, and anorexia.
Review of the clinical notes recorded for the 65
animals in the community revealed high morbidity
as well as mortality. Six chimps were observed to be
severely ill and another 44 were affected with mild to
moderate signs.
Three infants died but were not recovered from
their mothers. Two other chimps died and post
mortem exams were conducted. One carcass was
decomposed; the other had severely decongested
lungs consistent with acute pneumonia. These
findings are similar to those found during post
mortem exams of the Taı̈ Forest chimps [Köndgen
et al., 2008, Leendertz personal communication], but
histopathology results are not available. The overall
morbidity was 50 of 65 chimps with a mortality of 12
of 65, or 20%, of which half were infants or juveniles.
However, 9 of the12 chimps noted as dead during
this outbreak were never observed sick. They were
presumed dead.
During the June 2006 outbreak at Mahale, the
first case was an adult male chimp, DW. As reported
in Hanamura et al. [2007] two males MA (Masudi)
and DW (Darwin) were suspected to be the likely
source of infection to the other chimps. Both of these
males were known to be the most habituated and
therefore regularly found in closer contact with
people compared to other chimpanzees. At the
beginning of June 2006 there also was an outbreak
of respiratory disease at one of the five Mahale
camps. Visitation rules were not yet in place and
people with respiratory symptoms did visit the
chimps. Because the outbreak of illness began among
the chimps at the same time, the disease transmission could have gone either way: from chimps to
humans or from humans to chimps.
There were two other, milder outbreaks of
respiratory disease after June 2006, both of which
occurred during the end of the rainy season, one in
November 2006 and another in late October 2007.
There was no mortality, only a few animals were
affected, their clinical signs were limited sneezing,
coughing, and nasal discharge and most were older
animals. There had also been a reportedly severe
outbreak of respiratory disease previous year in
2005, around June/July and another in October
2003, both with recorded mortalities among the
There is a common pattern to these outbreaks.
All six occurred during June/July, the end or the
beginning of rainy season at Mahale, which starts in
late October and ends at the end of May. The
weather is colder at the beginning and the end
compared to middle of the rains, and during these
periods preferred chimp foods are scarce. June/July
is also the beginning of the busy tourist season while
researchers study the chimps year round.
Ecotourism and chimp trekking are extremely
popular at Mahale Mountains National Park. Film
crews also visit regularly. There were days when the
habituated group was visited by up to five tourist
groups, two teams of researchers, and a film crew
(two film crews visited at the same time in mid2007). Gombe has never drawn anywhere near as
many tourists compared with Mahale, and the Taı¨
Forest chimps are mostly visited only by researchers.
It is possible that some outbreaks are ‘‘natural’’ or
endemic among chimps, rather than foreign or
introduced by people and, for whatever reason, the
time around the season change favors the transmission of diseases.
Veterinary Management of Respiratory
Disease Outbreaks: Gombe
Although veterinarians have worked closely
with researchers at Gombe for years, interventions
were rarely performed and diagnostic testing has
never been as complete as reported recently at the
Taı̈ Forest. Noninvasive samples, including fecal,
urine, wadge, and post mortem samples have been
regularly collected and stored frozen or fixed in
formalin/alcohol/RNA later. During my employment
as a resident veterinarian at Gombe between 2000
and 2003, these samples were analyzed to every
extent possible during a disease outbreak. We
regularly performed basic bacteriology examinations
in the local laboratory. We also developed a healthmonitoring sheet for the research assistants to
report daily on all the disease symptoms observed
during their chimp observation.
As at Mahale, we did not intervene to obtain
diagnostic samples for several reasons. Generally,
anesthesia of free-ranging chimps carries high risk.
In the case of respiratory tract infection, it may even
be contraindicated. Virus isolation and identification
require considerable expertise. Finally, antibiotic
therapy does appear to be life-saving in various
infections and in Gombe it can be administered
without anesthesia by the oral route with bananas.
On rare occasions, very sick chimps have been
treated for a presumptive illness at Gombe, including
respiratory disease.
Am. J. Primatol.
736 / Lukasik-Braum and Spelman
The decision to treat the animal was based
on the age, clinical signs, and severity of illness,
and, if there had been a recent death, the results of
post mortem. It is important to note that food
provisioning, which made the treatment possible,
might also had contributed to disease transmission before the year 2000 when it was finally
Visitation rules for mountain gorillas were first
developed in 1985 and subsequently revised in
January 1999 in Gisakura (Rwanda). The initial set
of recommendations was based only on behavioral
concerns, including the risks of over-habituated
gorillas. Disease transmission between humans and
great apes was not a consideration at that time (Bill
Weber, personal communication).
The 1999 rules were produced by a team of
veterinarians, human doctors, and researchers concerned with the possibility of human pathogen
transmission to chimpanzees as well as gorillas. At
that time, visitation rules were proposed for all
African great apes alike, including chimps. These
rules were gradually established in most East
African countries. Officials with TANAPA recommended that all visitors, including tourists and
researchers, follow standard visitation rules at
Gombe in 2000 and Mahale in 2006. The rules
include the following: tourists are to remain 10 m
away from the chimpanzees and researchers 7.5 m.
People with disease symptoms are not allowed to
visit chimps and tourist visit cannot last longer than
1 hr. Many Mahale chimps are over-habituated and
will break the safe distance rule, sometimes coming
in contact with people. The Gombe researchers and
Mahale guides and trackers have been instructed to
discourage such contact by moving away as soon as
the chimpanzees approach.
Given that it will take time to change the
chimp’s behavior, the researchers from Kyoto University studying at Mahale decided to wear surgical
masks beginning in 2006. All visitors and researchers
now wear disposable surgical masks while visiting
chimps. Although there were concerns about the
reaction of tourists and chimps to the mask rule,
none have been observed. By explaining the reason
for the masks, tourists have become more aware of
the risks to chimps. The animals showed no change
in their behavior toward visitors wearing this new
piece of equipment. It should also be noted that these
are not the N95-type masks. The effectiveness of
such masks, especially when wet and used for any
length of time, is widely questioned, but together
with other rules they appear to have made a
significant difference.
Am. J. Primatol.
At Gombe there is rarely more than one group of
six tourists visiting chimps in a day, and often there
are no visitors apart from researchers. At Mahale,
the Frankfurt Zoological Society has recently recommended rules that would limit the number of tourists
visiting chimps to three groups of six people a day
and the number of researchers to two groups of two
people a day maximum. The rules for film crews have
not yet been revised.
It has taken some time for the visitation rules to
be implemented at Gombe and Mahale, the visitation
rate during the tourist season remains higher than
recommended at Mahale, and not all of the rules are
followed at either location all of the time. However,
there have been no serious outbreaks—and no
deaths from respiratory disease—at Gombe since
end 2002 (S. Kamenya, E. Lonsdorf, personal communication) and at Mahale since August 2006
(Lukasik-Braum unpublished data).
The trend of improved chimp health is encouraging. But whether or not the visitation rules
will continue to be enforced at Mahale and
Gombe remains a concern. The Taı̈ Forest example
underscores the fact that no one rule will protect
the chimps from respiratory disease. Distance,
number of visitors, preventing sick people from
visiting, and masks all contribute. Similar guidelines
would undoubtedly improve chimp health in
all settings where tourists or researchers visit
the animals.
Taı̈ Forest and now Mahale researchers have
shown us that we can identify the disease agent
responsible for respiratory disease among chimps,
and very likely for all great apes. It is our collective
responsibility to work together to improve our
data collection methods and pursue the diagnosis.
It is equally important that we work together on
the epidemiology of these outbreaks and prove
or disprove a correlation between visitation
rates, rules, or lack thereof, seasonality, and natural
vs. introduced diseases. It may take years before
clear patterns emerge that definitively show
the value of the visitation rules, but waiting
to implement rules puts the animals at risk. Disease
management may be the most important thing we
can do to ensure the future health of habituated
great apes in Africa.
Visitation rules will be accepted and successful
only if we work together to sensitize tourists,
researchers, and park staff about the risks. Given
the endangered status of the world’s great apes, it
seems prudent to be conservative as possible. We
need not assume that visitors to the great apes will
view the rules as a negative. On the contrary, they
can be positive for all those who are involved.
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Am. J. Primatol.
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gombo, parks, respiratory, chimpanzee, mahaleb, tanzania, national, disease, visitation, rules
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