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72 0038-2809 Tydskr.S.Afr.vet.Ver. (2003) 74(3): 72–76
Article — Artikel
A survey of zoonotic diseases contracted by South African veterinarians
B Gummow
a
INTRODUCTION
Many of the human diseases that are
new, emerging and re-emerging at pres-
ent, are caused by pathogens that origi-
nate from animals or products of animal
origin
2
. These include transmissible
spongiform encephalopathies, entero
-
haemorrhagic E. coli, Hantavirus infec
-
tions, Napah virus infections, West Nile
viralencephalitisandInfluenzaAviruses.
The World Health Organisation (WHO)
defines zoonoses as ‘those diseases and
infections that are naturally transmitted
between vertebrate animals and man’.
It has long been known that zoonotic
diseases can rapidly cause extensive
human suffering and death. For example,
during an outbreak of Rift Valley fever in
Kenya in 1997/98
8
, 89 000 cases and 150–
250 deaths were reported.
On the other hand, zoonoses can mani
-
fest as non-dramatic erosive diseases,
such as taeniasis and dipylidiasis, placing
pressure on health systems and draining
the economy of a country. It has been
calculated that in the USA in 1985, human
salmonellosis alone caused financial loss
of some 3 billion dollars. This estimate did
not include expenses ensuing from the
sequelae of salmonellosis, or from the
legal action undertaken by victims of food
poisoning
1
.
In any given region or society, the
particular disease agents, the frequency
with which zoonotic transmission occurs
and the resulting public health impact
reflect the nature of the local human–
animal relationships as well as climatic
conditions and socioeconomic circum
-
stances.
Table 1 provides a list of what have pre
-
viously been considered the most impor
-
tant zoonotic conditions found in South
Africa
1,11
. It illustrates that many zoonotic
diseases are known to occur in South
Africaandshows that mostof the diseases
can be associated with farm animals or a
rural environment. The question there
-
fore arises: what are the risks to South
African veterinarians, and the general
public who routinely come into contact
with these animals?
Given that many emerging diseases
come from animals and that the human
population in South Africa is increasingly
immunocompromised as a result of ac
-
quired immune deficiency syndrome
(AIDS), it is concomitantly of importance
to consider the role of zoonotic diseases.
This survey aims at assessing the risks of
acquiring zoonotic diseases bySouth Afri
-
can veterinarians.
MATERIALS AND METHODS
The survey included all veterinarians
working at the Faculty of Veterinary
Science, University of Pretoria, Pretoria,
South Africa, in December 2001. They
comprised the single largest group of
employed veterinarians, from the various
disciplines in the profession, located at
one place in South Africa and could there-
fore be relatively easily interviewed.
During the interview-based, question-
naire survey, each veterinarian was per-
sonally interviewed and answers to
questions recorded on a data capture
sheet. The information was entered into
Microsoft Access (Office 2000, Microsoft
Corporation, Redmond, USA) for colla
-
tion and analysed using EpiInfo 2002
(Centers for Disease Control and Preven
-
tion, US Department of Human and
Health Sciences, USA).
The questionnaire required responses
to the following:
1.
Surname.
2. Initial.
3. Date of birth.
4. Sex.
5. Year of graduation as a veterinarian.
6. Species that you have most predominantly
worked with during your career – choose
one: small animal, large animal, mixed,
other (please specify).
a
Section of Epidemiology, Department of Production
Animal Studies,Faculty of Veterinary Science, University
of Pretoria, Private Bag X04, Onderstepoort, 0110 South
Africa. E-mail: bgummow@op.up.ac.za
Received: February 2003. Accepted: July 2003.
ABSTRACT
A survey of 88 veterinarians employed at the Faculty of Veterinary Science, University of
Pretoria, South Africa, was carried out to investigate the occurrence of zoonotic diseases
among South African veterinarians. The survey found that 63.6 % of veterinarians inter
-
viewed had suffered from a zoonotic disease. Veterinarians predominantly involved in
farm animal practice were 3 times more likely to have contracted a zoonotic disease than
those working in other veterinary fields. Fifty-six percent of disease incidents were initially
diagnosed by the veterinarians themselves. Fifty-three percent of incidents required treat
-
ment by a medical practitioner, but the majority (61 %) of incidents did not require absence
from work. The incidence density rate for contracting a zoonotic disease was 0.06 per per
-
son year of exposure. Kaplan-Meier survival analysis estimated that the probability of hav
-
ing contracted a zoonotic disease was 50 % after 11 years in practice. The risk of contracting
azoonoticdisease appeared tobehigher early inpractice. The mostcommonmode of trans
-
mission was by direct contact. Approximately 46 % of South Africans still live in rural areas
andregularlycome into close contactwithfarmanimals. The implications ofthisin the light
of this survey’s results are discussed.
Key words: prevalence, South Africa, survey, veterinarians, zoonoses.
Gummow B A survey of zoonotic diseases contracted by South African veterinarians.
Journal of the South African Veterinary Association (2003) 73(3): 72–76 (En.). Section of Epidemi-
ology, Department of Production Animal Studies, Faculty of Veterinary Science, University
of Pretoria, Private Bag X04, Onderstepoort, 0110 South Africa.
Table 1: Zoonoses that have traditionally been regarded as important in South Africa.
Viral diseases Bacterial diseases Helminth infections Other
Rift Valley fever Anthrax Toxoplasmosis Psittacosis
Rabies Brucellosis Taeniasis S A tick bite fever
Congo haemorrhagic fever Leptospirosis Dipylidiasis Ringworm
Salmonellosis Hydatidosis Cat scratch fever
Campylobacteriosis Larval migrans
Erysipeloid
7. Has your career predominantly involved,
fieldwork, clinic/hospital work, both, other
(please specify)?
8. What zoonoses have you contracted during
your life? Please refer to attached document
for a list that may help you remember.
9. For EACH zoonosis please state:
a. Whether it was contracted by: direct con
-
tact (e.g. post mortem), vector (e.g. tick),
other means (specify).
b. Whether the diagnosis was made by:
yourself, a general practitioner or a spe
-
cialist (specify).
c. What year did you suffer from the zoo-
noses?
d.What province were you in when you
contracted the zoonoses?
e. How many days sick leave did you have
to take?
f. Did you require treatment from a medical
practitioner?
g. What was the treatment?
h.What type of work were you doing at the
time of contracting it: large animal, small
animal, mixed, research, recreation, other
(specify).
i. Any other facts that you may think will
help with the survey.
Question 8 referred to a list of 70 of the
more commonly found zoonotic diseases
as defined by the WHO. This was not an
all-inclusive list of zoonotic diseases and
was aimed at jogging an interviewee’s
memory as to what diseases he/she may
have contracted.
RESULTS
In total, 88 veterinarians were inter
-
viewed. Fifty-six (63.6 %) of the veterinar
-
ians had suffered from one or more
zoonoses. Amongst these veterinarians,
93 incidents of zoonotic disease (Table 2)
were reported, ranging from 1 to 6
incidents of disease per veterinarian, with
a mean of 1.66 incidents. Thirty-two
(36.4 %) veterinarians could not recall
ever having contracted a zoonotic disease
(Table 2). Recurrent infections of the same
disease were not considered.
Assuming the sample was representa
-
tive of the population of South African
veterinarians, then the true prevalence of
zoonotic disease can be simulated stochas
-
tically using a beta distribution function
and Latin hypercube sampling
12
. Fig. 1
shows the cumulative distribution curve
fortheestimatedtrue prevalence of South
African veterinarians that have experi
-
enced a zoonotic disease. Given the sam
-
ple size, the true prevalence could range
from a minimum of 45 % to a maximum of
82 %.
Table 3 shows the percentage of inci-
dents of disease according to the occupa-
tion category of veterinarians at the time
when they contracted the zoonoses.
The category ‘Farm animal practice’
included mainly incidents of disease
while working with bovines (31 inci-
dents) and single incidents while pre-
dominantly working with equines,
porcines and poultry. Specialist veterinar-
ians that contracted zoonoses were exclu
-
sively pathologists. Other specialist
categories considered were anatomy,
anaesthesiology, dentistry, helminthol
-
ogy, exotic animals, surgery and pharma
-
cology, but none of these veterinarians
had contracted zoonoses. The odds ratio
of a veterinarian involved in farm animal
practice of contracting a zoonotic disease
was 3.11 (1.04 < OR < 11.23) compared
with all other categories and 3.58 (0.93 <
OR <15.13) compared only with small
animal practitioners.
In 55 % of the93 incidents of disease,the
initial diagnoses were made by the veteri
-
narian themselves. Thirty-two percent
were diagnosed by a general medical
practitioner and 10 % were diagnosed by
a specialist physician. The remainder
were 3 rabies exposure cases.
Fifty-three percent of incidents (n = 49)
required treatment by a medical practitio
-
ner.
Table 4 shows the number of days
sick leave required for each incident of
disease, grouped into intervals.
The majority of incidents (61 %) did not
require an absence from work. Forty-four
percent (n = 24) of these incidents were
cases of ringworm. Of those diseases
requiring up to 7 days sick leave, tick bite
fever made up the bulk of cases. Diseases
that consistently required a long absence
from work were notably Rift Valley fever
(RVF) and brucellosis. The days sick leave
for 4 incidents are not shown because of
uncertainty by the interviewee about the
time spent on sick leave or because there
were several bouts of the disease.
Table 5 shows the percentage of veteri
-
narians, grouped by year of graduation,
that reported having contracted zoono
-
ses. With the exception of the 1960–1969
period, the table confirms what is ex
-
pected, that the longer a veterinarian has
been in practice the greater are his/her
chancesofcontractingazoonoticdisease.
From the records of 47 of the 56 veteri
-
narians that had had zoonoses, it was
possible to calculate the number of years
from graduation until contracting their
1st zoonotic disease. The modal number
0038-2809 Jl S.Afr.vet.Ass. (2003) 74(3): 72–76 73
Table 2: Zoonotic diseases contracted by
the veterinarians interviewed and the num
-
ber of incidents reported for each disease.
Zoonoses Number
None 32
Ringworm 24
Tick bite fever 21
Rift Valley fever 8
Brucellosis 7
Cutaneous larval migrans 4
Sarcoptes
4
Malaria 3
Q-fever (
Coxiella burnetti
)3
Rabies exposure 3
Psittacosis 2
Shistosoma
2
Taeniasis 2
Candida
1
Corynebacteria 1
Erysipelothrix
1
Orf 1
Pseudocowpox 1
Rabies 1
Salmonella
1
Shigella
1
Toxoplasma
1
West Nile fever 1
Fig. 1: Cumulative distribution curve showing the expected true prevalence of South
African veterinarians that have contracted a zoonotic disease.
Table 3: Percentage of incidents of disease
per occupation category at the time of
contracting the disease.
Occupation category % of incidents
Farm animal practice 37
Small animal practice 20
Mixed animal practice 14
Specialist veterinarian 7.5
Research veterinarian 6.5
Other 15
of years to contracting the 1st zoonotic
disease was 1 year with an average of 6.5
years (SD = 7.5). It was also possible to
calculate an incidence density rate using
person years in practice as the
denominator
10
. There were 47 veterinari-
ans that contracted a zoonotic disease
over 833 person years at risk, thus giving
an incident density rate of 0.06 per person
year of exposure (i.e. a South African
veterinarian has on average a 6 % chance
of contracting a zoonoses for every year
of exposure). Another method used to
estimate risk to veterinarians was by
means of a Kaplan-Meier survival analy
-
sis. Survival analysis is the study of the
distribution of lifetimes. That is, the study
of the elapsed time between initiating an
event (in this case when the veterinarian
graduated) and a terminal event (in this
case when a veterinarian 1st contracted a
zoonotic disease). Table 6 shows the re
-
sults of a linear (Greenwood) Kaplan-
Meier survival analysis expressed in
quantiles of survival time, where survival
refers to the chances of not contracting a
zoonotic disease and failure refers to the
chances of contracting at least 1 zoonotic
disease.
The median point (0.5) is at 11 years, i.e.
half the veterinarians had contracted a
zoonotic disease within at least 11 years of
practice. Figure 2 shows the Kaplan-
Meier survival plot as well as the point
-
wise confidence intervals. In the plot,
time refers to years and survival to the
proportion of veterinarians not having
contracted a zoonotic disease. The shape
of the plot shows that a veterinarian has a
much higher chance of contracting a
zoonotic disease early in their time in
practice and that this risk levels off if they
have not yet contracted a zoonotic dis-
ease. It is important to note that the plot
74 0038-2809 Tydskr.S.Afr.vet.Ver. (2003) 74(3): 72–76
Table 4: Days absent from work per zoonoses.
Zoonoses No sick leave 1–7 days 6–14 days >14 days
Brucellosis 3 0 0 3
Candida
1000
Cutaneous larval migrans 4 0 0 0
Corynebacteria 1 0 0 0
Erysipelothrix 1 0 0 0
Malaria 0 1 0 1
Orf 0 1 0 0
Pseudocowpox 0 1 0 0
Psittacosis 1 0 1 0
Q-fever 0 2 1 0
Rabies 0 0 1 0
Rabies exposure 3 0 0 0
Ringworm 24 0 0 0
Rift Valley fever 1 3 3 1
Sarcoptes
3100
Shigella
0010
Schistosoma
1100
Taeniasis
2000
Tick bite fever 8 11 1 0
Toxoplasma
0001
West Nile fever 1 0 0 0
Total 54 21 6
Percentage 61 24 9 7
Table 5: Percentage of veterinarians according to graduation date that reported having contracted a zoonotic disease.
<1960 1960–1969 1970–979 1980–1989 1990–1999 >2000 Total
No zoonoses 1 5 3 10 12 1 32
Zoonoses 5 3 17 14 17 0 56
Total 6 8 20 24 29 1 88
% that contracted a zoonoses 83 37 85 58 59 0 64
Table 6: Kaplan-Meier survival analysis results expressed as quantiles.
Proportion surviving Proportion failing Survival time (years) Lower 95 % CL* Upper 95 % CL
survival time survival time
0.95 0.05 1 1
0.9 0.1 1 1
0.85 0.15 1 1 2
0.8 0.2 2 1 2
0.75 0.25 3 1 3
0.7 0.3 3 2 5
0.65 0.35 4 3 8
0.6 0.4 5 3 10
0.55 0.45 8 4 11
0.5 0.5 11 5 18
0.45 0.55 12 7 22
0.4 0.6 18 10 22
0.35 0.65 28 11 28
0.3 0.7 28 15 28
0.25 0.75 22 28
0.2 0.8 28 28
0.15 0.85 28 28
0.1 0.9 28
0.05 0.95 28
*CL = confidence limit
does not take into account multiple or re
-
peated infections.
Of the 88 veterinarians interviewed, 19
were female and 69 male. Twelve (63 %)
females and forty-four (63.8 %) males
contracted zoonoses. No difference could
therefore be shown between male and
female veterinarians in terms of the riskof
contracting a zoonotic disease.
Table 7 shows where each incident of
zoonotic disease was contracted. The
majorityof incidents occurredinGauteng
but this, in hindsight, may be due to
the biased nature of the survey, which
concentrated on veterinarians that proba
-
bly worked predominantly in Gauteng
while in practice.
Table 8 shows the mode of transmission
of each disease incident. Included under
direct transmission were diseases con
-
tracted while conducting necropsies.
Direct contact was the most frequent
mode of transmission.
DISCUSSION
The survey carried out at the Faculty of
VeterinaryScience, University ofPretoria,
in 2001, showed that a high proportion of
veterinarians (45–82 %) had contracted
zoonotic diseases and that many of the
zoonotic diseases contracted by veteri-
narians had not immediately been diag
-
nosed by general practitioners and often
had to be diagnosed with the assistance of
the veterinarian. This highlights the fact
that many zoonotic conditions are diffi
-
cult to diagnose clinically and are proba
-
bly frequently misdiagnosed or missed.
For example, brucellosis, leptospirosis,
tick-bite fever, Q-fever and Rift Valley
fever can all present with similar clinical
signs in man in the early stages. In areas
where malaria is endemic, they can easily
be misdiagnosed as malaria cases if no
diagnostic confirmation tests are carried
out.
A study of medical curricula in South
Africa shows a deficiency of training at an
undergraduate level in recognising
zoonotic conditions. Another compound
-
ing factor is the inexperience of the junior
doctors working unsupervised in many
district hospitals in South Africa. Coupled
to this are limited laboratory facilities and
a lack of funds to carry out comprehensive
diagnostic procedures (D A Cameron,
Department of Family Medicine, Univer
-
sity of Pretoria, pers. comm., 2002). It is
thus conceivable that a large number of
zoonotic conditions are currently mis
-
diagnosed or go undiagnosed in South
Africa.
The survey showed that veterinarians
working with farm animals are at higher
risk of contracting zoonotic diseases than
those working with small animals. It also
showed that direct contact is still the most
prevalentmeans of contracting a zoonotic
disease. Personal hygiene and protective
clothing, therefore, are probably the most
important ways of preventing transmis
-
sion of zoonotic diseases.
The survey illustrated that the longer
veterinarians have been in practice, the
greater their chances are of contracting a
zoonotic disease. It also showed that a
veterinarian is more likely to contract a
zoonotic disease early on in his/her time
in practice. A similar trend is likely to
manifestintherural areas of South Africa.
South African demographic data show
that 46.3 % of the population still lives in
rural areas, and can be expected to regu
-
larly come into close contact with farm
animals and their parasites
9
. In many
cases, they share the same water sources
and habitat, making transmission of dis
-
eases between animals and man very
likely. Compounding this are the poor
socioeconomic conditions under which
many South Africans live. These result in
malnutrition and poor sanitation within
these communities, providing an ideal
environment for the transmission and
maintenance of infectious diseases.
In a recent study by the South African
Medical Research Council it was etimated
that 40 % of adult (15–49 years of age)
deaths that occurred in 2000 in South
Africa were due to HIV/AIDS
4
. Histori
-
cally, it has been this component of soci
-
ety that has been at lowest risk of con-
tracting zoonotic diseases because many
zoonotic conditions only manifest in
immunodeficient individuals, such as
children and the very old. Conditions
such as ringworm,Q-fever,tick-bite fever,
cutaneous-anthrax, cat scratch disease
and toxoplasmosis, to name but a few,
that many adults would shrug off, as
evidenced by the relatively few days
sick leave taken by veterinarians in this
study, take on a new meaning when indi
-
viduals become immunocompromised.
According to Grant and Olsen
6
, animal-
associated pathogens of concern to
immunocompromised persons in the
USA include Toxoplasma, Cryptosporidium,
Salmonella, Campylobacter, Giardia lamblia,
Rhodococcus equi, Bartonella, Mycobacte
-
rium, Bordetella bronchiseptica, Chlamydia
psittaci and zoophilic dermatophytes.
From the present survey it also became
apparent that in South Africa this list is
probably longer and the consequences
0038-2809 Jl S.Afr.vet.Ass. (2003) 74(3): 72–76 75
Fig. 2: Kaplan-Meier survival plot for the time (years) between graduation and contracting a
zoonotic disease.
Table 7: Location where each incident of
zoonotic disease was contracted.
Country/region Frequency
Gauteng 42
Uncertain 10
KwaZulu-Natal 9
Mpumalanga 6
North West Province 6
Northern Province 5
Eastern Cape 3
Free State 3
Northern Cape 2
Western Cape 1
Mozambique 1
Nigeria 1
Ohio, USA 1
Swaziland 1
UK 1
Zimbabwe 1
Total 93
Table 8: Mode of transmission of each
disease incident.
Mode of transmission Number
Direct contact 58
Vector 24
Uncertain 7
Ingestion 4
76 0038-2809 Tydskr.S.Afr.vet.Ver. (2003) 74(3): 72–76
more life-threatening. Certainly, some of
the conditions found in the survey, such
as malaria, tick bite fever, brucellosis,
Q-fever and Rift Valley fever, need to be
included in a South African list.
While some work has been done on the
role of zoonotic diseases in immuno-com
-
promised persons, most, if not all,
emanated from first world countries.
Earlier studies concluded that the risk of
zoonotic transmission to HIV patients
was small and that the benefits of animal
companionship outweigh the risks to
HIV patients
5
. This perception appears to
be changing and, more recently, Grant
and Olsen
6
suggested that ‘with the ex
-
ception of Bartonella henselae and zoophi
-
lic dermatophytes, infections in humans
are more commonly acquired from
sources other than pets, and the infec
-
tious disease risk fromowning pets is con
-
sidered low. Nevertheless, HIV-infected
persons may still be advised not to own
pets’. While this may be so in developed
countries, the WHO in one of its latest
reports stated that ‘Infectious diseases
will remain the major causes of mortality
in most developing countries, with
HIV/AIDS and opportunistic infections
(including zoonoses) being especially
important’
13
. The high proportion of
veterinariansin this surveythathave con-
tracted zoonotic diseases supports this
statement.
Macpherson et al.
7
reported that ‘The
average prevalence of Cryptosporidiosis
parvum in patients with HIV has been re-
ported to be 27 % in developing countries
and 12 % in industrialised countries. The
life-threatening potential of C. parvum
infections in immunocompromised and
immunosuppressed individuals has
greatly enhanced the importance of
cryptosporidiosis asa global publichealth
problem’. Referring to toxoplasmosis
they go on to state that a risk group of
special interest has emerged, that of
‘non-immune HIV positive pregnant
women’. Toxoplasmosisin HIV patients is
reportedly of long-duration and may be
followed by death. Recent studies have
also shown that T. gondii is the most com
-
mon cerebral opportunistic infection of
patients with AIDS
3
. More than 90 % of
the estimated 36 million people with HIV/
AIDS live in developing countries
13
.In
Africa, the role of veterinarians in control
-
ling these diseases is thus becoming in
-
creasingly important. Coupled to this is
the responsibility of veterinarians to keep
abreast of new information on emerging
zoonotic conditions and to keep the
publiceducatedastotheirconsequences.
Given that a diversity of zoonotic condi
-
tions have been reproted in South Africa,
that a large segment of the population is
immunocompromised and that they are
likely to come into contact with animals
on a regular basis under poor socioecono
-
mic conditions, one can justifiably put
forward the hypothesisthat the incidence
and severity of certain zoonotic condi-
tions are likely to increase at a similar rate
to that of the HIV/AIDS epidemic, thus
compounding an already serious situa-
tion.
ACKNOWLEDGEMENTS
The author wishes to thank David Brad-
bury, a final-year student at the Faculty of
Veterinary Science at the time of the
survey, for assisting him in interviewing
veterinarians, and David Cameron, a
medical practitioner in the Department of
Family Medicine, University of Pretoria,
for providing insights into the AIDS situa
-
tion in South Africa.
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