Introduction
East Coast fever Cause and distribution
East Coast fever (ECF) is a form of theileriosis caused by the parasite
Theileria parva transmitted by the tick
Rhipicephalus appendiculatus
(Norval et al, 1992). It is a major disease of cattle in 11 countries
in eastern, central and southern Africa. The affected countries are
Burundi, Kenya, Malawi, Mozambique, Rwanda, Sudan, Tanzania, Uganda,
Zaire, Zambia and Zimbabwe. The estimated land area and cattle
population affected by ECF in the region are provided in Table 1.
Table 1. Land area and cattle population affected by East Coast lever in 11 African countries, 1988.
Item
|
11 ECF countries
|
% of Africa
|
| Human population (million) |
175
|
29
|
| Total land area (million ha) |
835
|
28
|
| Land under theileriosis (million ha) |
158
|
|
| Land under theileriosis of total (%) |
19
|
5
|
| Total cattle population (million) |
83
|
35
|
| Cattle under theileriosis (million) |
24
|
|
| Cattle under theileriosis of total (%) |
38
|
13
|
Control costs
Tick control
East Coast fever is conventionally checked by the control of the
vector ticks through the application of acaricides to the surface of an
animal by dipping, spraying or hand-washing to kill the tick. In areas
of heavy tick infestation, cattle are treated with acaricides as often
as twice a week.
In many smallholder areas, the dipping service is provided by the
government through public dip tanks, either free of charge or at a
highly subsidised cost. Dipping is usually compulsory at stated
intervals to achieve more effective and widespread control. Even though
the majority of farmers have access to this assistance, there is a
significant private sector of commercial farmers, both small-and
large-scale, who bear the full cost of the fight to prevent the disease.
Depending on the frequency of applications, annual costs of
acaricide to farmers who are financially responsible for the purchase of
these drugs ranges from US$ 2 to US$ 20 per animal (Lawrence and
McCosker, 1981; de Leeuw and Pasha, 1988; Young et al, 1988; Young et
al, 1990; Perry et al, 1990). To the farmers who use public dip tanks,
the real cost of tick control includes loss of animal traction time and
human labour for the period spent in trekking animals to and from the
dip tanks, often several kilometres away from the farm.
Losses are also incurred whilst driving animals through dip tanks from stress-induced abortions, drowning and physical injury.
In addition, the constant trekking of animals to dip tanks often
creates gullies and the frequent concentration of animals around the
tanks leads to overgrazing, both of which cause erosion and
environmental degradation.
There are further indirect economic losses which can be
attributed to tick control. The application of acaricides on vector
ticks through dipping, spraying or hand-washing animals contributes to
the pollution of the environment and may endanger human health. This
arises from direct contact, spilled or misused acaricides and also from
consumption of products derived from animals treated with acaricides
(Keating, 1987; Young et al, 1988). In addition, the occurrence of ticks
and their control cause worry and anxiety to the farmers who have to
deal with the problem on a daily basis.
Treatment
.Pulmonary oedema is a common sign of East Coast fever (ECF, Theileria
parva infection) of cattle. A trial was conducted on farms in Uganda to
compare a product containing both the antitheilerial compound parvaquone
and the diuretic compound frusemide with one containing only
parvaquone, in the treatment of ECF.
The trial involved 40 clinical
cases of ECF, some of them complicated by other infections, in cattle of
all ages and on several farms. Confirmed cases were treated with either
parvaquone+frusemide (P+F) or parvaquone alone (P). Survival after
treatment with P+F was 77% compared with 71% with P. Five of the 10
fatalities were complicated cases. The cure rate for severe but
uncomplicated ECF was 89% with P+F and 40% with P. Pulmonary signs were
resolved within 24-48 h after treatment with P+F and clinical recovery
was noticeably more rapid than with P. The antiparasitic effect of the
two treatments was similar. P+F could be particularly useful when
reporting, diagnosis or laboratory confirmation of ECF is delayed,
because advanced cases are more likely to be encountered under these
circumstances.
Government expenditures on ECF control
This is how other countries do By providing curative and tick control services to farmers free or at
highly subsidised charges, governments spend substantial sums of money
annually, especially in foreign exchange, for the importation of drugs
and acaricides. For instance, Kenya spent about US$ 10 million in 1987
(Young et al, 1988) and Zimbabwe spent an estimated US$ 9 million during
the 1988/89 financial year (Perry et al, 1990). Even though these cost
estimates include costs of tick control against all tick-borne diseases,
ECF is the major disease prompting the use of acaricidal applications
in much of the region (Cunningham, 1977).
Governments also spend considerable funds on research, training
and extension services related to the control of ECF. In addition
private firms and international organisations invest large sums of money
on research aimed at developing new acaricides, treatment drugs,
vaccines and other improved control methods.
Other indirect losses
There are other indirect losses which can be attributed to ECF. For
instance, the depletion of scarce foreign exchange arising from
expenditure for importing livestock products in short supply. In
addition, losses in beef, milk and hides due to disease which reduces
the supply of these products as raw materials and thereby retards the
development of the livestock product processing industry. Furthermore,
the 1088 of beef and milk diminishes the supply of food protein and
consequently impoverishes household nutrition.
Estimates of regional economic losses due to ECF
Estimates of farm level losses from tick control and treatment have
been discussed above. Country levels or regional estimates of ECF losses
are few. Miller et al (1977) estimated that ECF caused half a million
cattle deaths per year in Kenya, Tanzania and Uganda (Young et al,
1988).
Most recently, Mukhebi et al (1992) calculated annual economic
losses due to ECF in the 11 affected countries in the region. The
estimates indicate that the total direct 1088 (in beef, milk, traction
and manure, in treatment, acaricide, research and extension costs)
caused by the disease in the region is US$ 168 million a year (Table 2),
including an estimated mortality of 1.1 million cattle. The reduction
in milk production represented the greatest financial loss, followed by
the cost of acaricides, traction and beef in that order.
The diminished value of beef and milk from cattle morbidity was
estimated to be three times as high as that from mortality (Table 2).
Similarly, the value of beef and milk losses was three times the cost of
acaricide applications. Often it is the mortality and the acaricide
cost that appears to receive the greatest attention and concern from
those interested in controlling the disease. This may be due to the fact
that mortality is more discernible than morbidity, and acaricide
expense is a more direct cost than output reduction on beef and milk.
Table 2. Estimated regional losses in 1989 due to East Coast fever in 11 African countries affected by the disease.
Item
|
Quantity
|
Loss in US$ thousand
|
% of total loss
|
| Beef loss, total (t) |
19,428
|
20,607
|
12
|
| - mortality loss (t) |
16,246
|
17,232
|
-
|
| - morbidity loss (t) |
3,182
|
3.375
|
-
|
| Milk loss, total (t) |
97,482
|
78,697
|
47
|
| - mortality loss (t) |
9,284
|
7,495
|
-
|
| - morbidity loss (t) |
88,198
|
71,202
|
-
|
| Animal traction loss (ha) |
468,000
|
21,308
|
13
|
| Manure loss (t) |
701
|
88
|
0
|
| Treatment |
|
8,114
|
5
|
| Acaricide application |
|
3,008
|
20
|
| Research and extension |
|
8,550
|
4
|
| Total loss, US$ |
|
168,402
|
100
|
| ECF loss per cattle head |
|
US$ 7.00
|
|
| ECF loss per ha |
|
US$ 1.10
|
|
Source: Mukhebi et al I (1992).
Sparse and insufficient data exist on how ECF affects livestock
production. Therefore there is a need to improve estimates by conducting
a survey of economic losses country by country taking into account
differences in cattle types and production circumstances.
Limitations of current methods of ECF control
Although ECF is currently managed by the control of the vector ticks
with acaricides and the use of drugs to treat infections, the widespread
application of these methods in Africa has limitations. As discussed
above, governments incur huge expenses in the provision of curative and
tick control services.
In recent times, government budgets in most of the affected
African countries have shrunk and the scarcity of foreign exchange for
imports has grown more acute. As the competition for limited government
resources has heightened from other pressing national development needs,
the quantity and quality of animal health services and infrastructure
has declined considerably (Haan and Nissen, 1985). The ability of govern
meets to maintain dipping infrastructure, provide effective animal
health extension service and import drugs and acaricides has been
undermined.
The consequences of the control of ECF by currently available
methods are therefore grim; extension staff generally do not have
transport, most public dips are poorly managed and nonfunctional, the
few operational ones are often dilute in acaricides concentration, drugs
are not readily available to government veterinarians, and if they are
available in local markets, they are too expensive for most smallholder
farmers.
Other considerations which have rendered acaricide application a
less reliable method include shortages of water- for public dips, the
development of resistance to acaricide by tick populations, uncontrolled
cattle movements, civil unrest, contamination of the environment or
food with toxic residues of acaricides and the existence of alternative
hosts for ticks (mainly wild ungulates) in proximity to cattle (Young et
al, 1988; Dolan, 1989).
Even when drugs for chemotherapy are readily available, their
successful application requires diagnosis of the disease at its early
stage of development. This specialisation is beyond the capacity of many
smallholder farmers because of the poor state of the animal health
service infrastructure. This factor, coupled with the high cost of
drugs, implies that only a small proportion of animals which become
infected with the disease receive treatment.
There is evidence that production losses due to tick infestation
per se are
too small to justify intensive acaricide application on economic
grounds in zebu and Sanga cattle (Norval et al, 1988; Pegram et al,
1989). Furthermore, the existence of endemic stability in some areas
implies that control can be selective, strategic and focused only on
susceptible target cattle populations (Perry et al, 1990).
New methods of ECF control
The limitations associated with the current methods of ECF control
and the opportunities for reducing reliance on intensive acaricide use
in the region have prompted the search for new, safer, cheaper and more
sustainable control strategies through immunisation.
At present, the only practical method of immunisation is by the
infection and treatment method (Radley, 1981). This involves the
inoculation of cattle with a previously characterised and potentially
lethal dose of sporozoites of
T.
parva and simultaneous treatment with antibiotics. This confers life- long immunity to the animal.
The method has been shown to be technically efficacious in field
trials carried out in different countries of the region (e.g. Robson et
al, 1977; Morzaria et al, 1985; Musisi et al, 1989; Mutugi et al, 1989).
Immunisation through the infection and treatment method has been
estimated to cost US$ 1.50-US$ 20.00 (Radley, 1981; Kiltz, 1985; Mukhebi
et al, 1990), US$ 0.01-US$ 0.90 being the cost of producing one dose of
the vaccine and the balance being the cost of delivering the vaccine to
the animal in the field. The output will vary among countries depending
on their policies regarding the production or procurement, delivery and
pricing of the vaccine. Some countries conduct pilot immunisation
programmes to provide data for the planning and implementation of
widespread application of the infection and treatment method.
Assessing the economics of the infection and treatment method
There are few studies on the economic analysis of the infection and
treatment method. Mukhebi et al (1989) showed that immunisation of beef
cattle under farm conditions was extremely profitable. It yielded a
marginal rate of return of up to 562% and it allowed a reduction in
acaricide use from a frequency of twice a week to once every three weeks
and even to the mere use of prolonged release acaricide-impregnated ear
tags.
Perry et al (1990) used a cost-effective analysis to assess
alternative tick and tick-borne disease control strategies in communal
lands of Zimbabwe. The alternative control strategies, some of which the
Department of Veterinary Services had started implementing, e.g.
strategic dipping, would make less intensive use of expensive acaricides
and rely more on controlled immunisation and the phased development of
natural immunity to tick-borne diseases. The investigation revealed that
alternative strategies were more cost effective than the previous
intensive acaricide use practice and would reduce (save) the cost of
tick and tick-borne disease control by up to 68% from the estimated
amount of US$ 9 million annually.
Mukhebi et al (1992) assessed,
ex-ante, the economics of
immunisation by the infection and treatment method in the eastern,
central and southern African region affected by ECF. The analysis showed
high potential economic returns, with a benefit-cost ratio in the range
of 9 to 17 under various assumptions.
However, the costs of the method and the economics of its
application will obviously vary in time and space in each country
depending on the cattle type and prevailing level of disease risk, the
effect of immunisation on livestock productivity as well as the existing
structure of costs and prices.
Limitations of the infection and treatment method
The infection and treatment method of immunisation, however, has some
technical limitations. It does not eliminate the need for acaricide
application due to the potential existence of other tick-borne diseases,
although it allows considerable relaxation of acaricide use. In
addition, the use of live parasites in the vaccine poses some safety
drawbacks for large-scale immunisation purposes This is compounded by
uncertainty about the spectrum of different species, strains and
antigenic types of theileria parasites in different areas, variation in
the sensitivity of different parasite isolates to therapeutic drugs and
the development of a potentially infective carrier state in immunised
animals. Furthermore, the application of the infection and treatment
vaccine requires a liquid nitrogen system for cold storage and
transportation and during the pilot application stage, an extended
monitoring period post-immunisation to detect and treat any breakthrough
infections. Both these aspects currently constitute high cost items in
the delivery of the vaccine.
Research at the International Laboratory for Research on Animal
Diseases (ILRAD) based in Kenya is continuing to further improve the
safety and effectiveness of the infection and treatment vaccine and to
develop genetically engineered safer vaccines that will avoid most of
these drawbacks. In addition, ILRAD's socio-economics programme is
conducting studies in several countries in the region to assess the
epidemiological, economic, social and environmental impact of the
method. These studies are aimed at generating further information that
will be useful for the planning and implementation of widespread
application of the method.
Policy issues
The current methods of ECF control are clearly beset with numerous
limitations and are evidently inadequate and unsustainable. Prospects
for developing new, safer, cheaper and more effective methods based upon
immunisation are very promising. However, before a change in control
strategy is adopted, certain policy issues must also be addressed if the
new control strategies are to be sustainable. The decision for such
change in the control strategy is often political. Politicians and
government policy makers will therefore need to be convinced of not only
the technical and economic feasibility of immunisation but also of its
social, institutional and environmental soundness.
Policy issues regarding the production, delivery and financing of
immunisation by the infection and treatment method would have to be
addressed. For instance, how the production and delivery will be
organised.
Critical attention must be given to resource issues: what
facilities, equipment, materials and manpower will be needed; where,
when and how will they be procured and maintained; what institutions
(national, regional and international) will be involved; what
infrastructure (e.g. markets and extension) will need to be provided;
who will pay what cost; and what will be the role of the public and
private sectors. The control of other tick-borne diseases, other
infections and constraints that will confound the control of ECF also
needs to be considered. These and other questions require careful
analysis if the benefits of ECF control by immunisation are to be
maximised and their potential deleterious effects minimised.
Differences in livestock production systems and animal disease
control strategies mean that individual countries will need to assess
their own policy options to determine approaches compatible with optimal
and sustainable application of new control strategies.