🐄 Herd Health One: The Tick-Borne Complex

A review of the constraints on African livestock productivity names disease as one of the major limits on output, alongside dry-season feed. Within that heading, one group of diseases dominates, and it is carried by an animal small enough to sit on your thumbnail.

Start with the scale, because it is easy to underestimate something you see every day. East Coast fever alone is credibly estimated to kill on the order of one million cattle a year across its endemic range in eastern, central and southern Africa. At least 40 million cattle in that region are estimated to be exposed to it, with losses put at over 300 million US dollars a year in one source, and a separate economics review estimating regional losses at roughly half a billion dollars a year. Those two estimates come from different studies, different years and probably different methods - treat them as two independent estimates of the same order of magnitude, not as one number to be averaged.

And East Coast fever is only one of four. The tick-borne complex that dominates African cattle health has four members, and every one of them is transmitted by a tick:

1. East Coast fever, caused by the protozoan parasite Theileria parva and carried by the brown ear tick, Rhipicephalus appendiculatus.
2. Anaplasmosis, known widely as gallsickness, caused by the rickettsial organism Anaplasma marginale.
3. Babesiosis, known as redwater or tick fever, caused by Babesia protozoa and carried principally by the blue tick, Rhipicephalus decoloratus, and related ticks.
4. Heartwater, caused by the rickettsial organism Ehrlichia ruminantium and carried by Amblyomma or bont ticks. It can cause mortality of up to 90 percent in susceptible domestic ruminants.

Four things follow from that list, and they shape the whole module.

First, they are carried by different tick species, with overlapping but not identical seasonal and habitat patterns. The tick that gives your cattle East Coast fever is not the tick that gives them redwater. So the tick population on your farm decides which diseases you face, and that population differs between one district and the next and between one rangeland type and another.

Second, they can occur together in the same animal. A sick cow is not a puzzle with one answer.

Third, they range enormously in behaviour. In a long-endemic area, indigenous cattle can show close to 100 percent morbidity - almost every animal infected - with comparatively low mortality, because generations of exposure have built a degree of tolerance. That is chronic and manageable, though not free, as the next lesson shows. At the other extreme, heartwater in susceptible stock is acutely lethal.

Fourth, and most important for what you actually do on Monday morning: there is no single vaccine and no single acaricide that controls all four. Effective control is built on tick control first, with vaccination as a second layer where a vaccine exists, is available and is appropriate to the specific disease. That ordering is not an opinion. It follows directly from the fact that reducing the number of ticks feeding on an animal reduces the number of chances for transmission - for every one of the four diseases at once, whether or not a vaccine for any of them exists or is within your reach.

There is a fifth point that this course must make even though it sits outside the tick complex. Across a band of more than nine million square kilometres - roughly a third of Africa's land area, across 37 countries - a fly-borne disease, trypanosomiasis, may be the dominant constraint on your herd instead. If you farm in or near a tsetse zone, tick-borne disease is still real but it is not necessarily your biggest problem. Ask locally which of the two dominates where you are.

Which brings us to the one instruction that matters most in this lesson. This course can teach you the diseases, the mechanism, the cost and the principles of control. It cannot tell you which of them are present on your land, because tick distribution is local. Only your veterinary authority, a district veterinarian or animal health technician, or the recorded experience of nearby farms can tell you that.

So before you buy anything or change anything, find out what you are actually fighting. A control plan built for the wrong disease is money spent for nothing.

East Coast fever is the best-documented tick-borne disease of African cattle and it deserves a lesson of its own.

The parasite is Theileria parva. The vector is the brown ear tick, Rhipicephalus appendiculatus. The incubation period - the time from the tick bite to the first clinical signs - is 8 to 12 days. That interval matters practically: the animal that falls sick today picked up the infection well over a week ago, so by the time you see one case, others in the herd may already be infected and not yet showing it.

Mortality, untreated, is severe and falls hardest on the young. Untreated calves can suffer up to 90 percent mortality. Untreated adult cattle, 10 to 30 percent. Read those two figures side by side, because they explain why this disease is so damaging to a breeding herd: the calf crop is your product, and the calf crop is what the disease takes.

Now look at what actually happens in the field, because it is not one number and pretending otherwise would mislead you. Reported field mortality in the sourced studies ranges enormously:

• Ranch herds in Uganda: 8.5 percent.
• Pastoral herds in Uganda: 8.2 percent.
• Yearling zebu in Kenya: 40 percent.
• A Tanzanian study: 19.4 percent per animal.

From single figures to 40 percent, within East Africa. That spread is itself one of the most important things to understand about this disease. Mortality is not fixed. It depends on the local tick challenge, on the breed and age of the animals exposed, and above all on whether any control - dipping or vaccination - is in place. Which means your own outcome is not decided for you by the disease's reputation. It is substantially decided by what you do.

Now the part that most farmers underestimate. The animals that survive are not fine.

The production losses documented in surviving, infected animals are these: milk loss of around 25 percent; draft or work capacity reduced by 28 to 64 percent; beef and growth loss of 5 to 10 percent; and a slaughter-value reduction of around 30 percent.

Put those against this course's core equation, that total kilograms weaned equals cows exposed, times calving percentage, times calf survival, times weaning weight. A calf that survives East Coast fever still carries a 5 to 10 percent growth loss into its weaning weight. A cow that survives loses around a quarter of her milk, which is what her calf grows on. An ox that survives loses up to two thirds of his working capacity, which on a mixed crop and livestock farm is your ploughing and your planting date and therefore your grain crop as well.

That is why the endemic-area picture from Lesson 1 - near total infection with low mortality in tolerant indigenous cattle - is not the good news it sounds like. Tolerance means the animals live. It does not mean the disease is free. A herd where almost every animal has been infected is a herd carrying a permanent tax on its growth, its milk and its work output, paid every year whether or not a single animal dies.

One more figure to hold on to, from the economics literature: the estimated annual cost per animal of East Coast fever ranges from about 2 US dollars to about 112 US dollars, depending heavily on the management and control approach used. That is a fiftyfold range across the same disease. It is not measurement error. It reflects how enormously the real cost depends on whether a herd is protected, and by which method. Those are historical study figures from particular countries and years, not prices you should expect today - but the message inside the range is the one that matters, and it is hopeful: this is a disease whose cost to you is largely determined by your own management.

What that means practically is covered in the next lessons: tick control first, and vaccination as a second layer where it is available to you. But the reason to bother is here, in this lesson. You are not only preventing deaths. You are preventing a quiet, permanent drag on the weight, the milk and the work of every animal that lives.

East Coast fever gets the attention. The other three members of the complex kill cattle too, and on many farms they are the ones you will actually meet.

Anaplasmosis, called gallsickness across much of southern Africa, is caused by the rickettsial organism Anaplasma marginale. It is transmitted by several tick species - and, importantly, also mechanically. That means by biting flies, and by contaminated instruments. Think about what that second route implies on a working farm: a needle reused across animals, a dehorning or castrating tool that is not cleaned between animals, an ear-tagging applicator moving down the line. Those instruments can carry infected blood from one animal to the next. This is a disease you can spread yourself, on a day when you thought you were doing herd health work.

Babesiosis, called redwater or tick fever, is caused by protozoan parasites of the Babesia group and is transmitted principally by the blue tick, Rhipicephalus decoloratus, and related ticks. The common name describes the sign farmers recognise: the destruction of red blood cells produces dark, red-stained urine.

Now the honest gap, and it is a real one. A specific African mortality or morbidity figure for anaplasmosis in cattle was not obtained for this course to a standard worth teaching as a number. Nor was one for babesiosis. An older South African survey that examined the incidence of heartwater, redwater and anaplasmosis together in endemic regions exists, but its figures could not be retrieved either. So this course will not tell you what percentage of cattle in your region get gallsickness, or how many of them die of redwater. Those numbers must come from your national veterinary service, your national veterinary research institute, or a district veterinarian who sees the cases. Ask them - and note that these are exactly the kind of figures a veterinary authority collects.

Heartwater is better documented, and it is the most acutely dangerous of the three. It is caused by the rickettsial organism Ehrlichia ruminantium, formerly called Cowdria ruminantium, and it is transmitted by Amblyomma, or bont, ticks. It can cause mortality of up to 90 percent in susceptible domestic ruminants. Two further points matter for your own decisions. Indigenous African breeds are documented as showing greater resistance than European taurine breeds - the same adaptation argument this course has made about breed choice from the start. And goats and sheep are generally more vulnerable than cattle, which matters on the many smallholdings that run both.

On vaccination against heartwater, be clear: no fully field-validated vaccine exists. Experimental vaccines are noted in the literature, but none had been validated under field conditions at the time of the source consulted. So for heartwater in particular, tick control is not the first layer of defence, it is very nearly the only one.

The most detailed single dataset this course has on these diseases is a 13-year retrospective study of heartwater in the Lephalale area of Limpopo, South Africa. Of 472 clinical cases investigated over the period, 161 were confirmed positive - an overall confirmed-positive rate of 34.11 percent. The annual confirmed rate ranged from 6.25 percent in 2019 to 72.22 percent in 2022.

The estimated total economic loss over that study period was ZAR 765,720, an average of ZAR 58,901 a year. Of that, mortality accounted for 81 percent, at ZAR 620,400; treatment costs 8 percent, at ZAR 62,600; and production losses 11 percent, at ZAR 82,720. Bovine losses specifically were the largest single species category, at ZAR 495,000.

Read those figures for their shape, not their size. They are one district, one period, one country, in rand, and the money values are historical rather than current. What travels is the structure: more than eight rand in every ten lost to this disease was lost to animals dying, not to treating them. The bill is written by the deaths, not the medicines.

And one more thing that does travel. In the same study, prevalence was highest in autumn and summer, at around 40 percent, and lowest in winter, at 25.5 percent. That is a clear seasonal pattern tied to tick activity. Your own district will have its own seasonal pattern, driven by its own ticks and its own rainfall - and finding out when your tick season peaks is one of the most useful things you can learn locally, because it tells you when your control effort has to be tightest and when a lapse costs most.

Acaricide application - by plunge dip, spray race, or pour-on and spot treatment - remains the primary practical tool for reducing tick-borne disease risk across every disease in this module. The logic is simple and it is worth stating in one sentence, because it is the sentence that justifies the whole expense: reducing the number of ticks feeding on an animal reduces the number of chances for disease transmission, whether or not a vaccine for that specific disease exists or is available to you.

That is why tick control is the first layer. It works on East Coast fever, gallsickness, redwater and heartwater at the same time, with one operation.

The three methods, and what each one asks of you.

A plunge dip is a deep tank of made-up acaricide wash that cattle swim through. It gives thorough, whole-body coverage including the ears, the tail switch, the udder and between the legs - which matters, because ticks attach in precisely those protected places. Its demands are a large permanent structure, a large volume of correctly made-up wash, and careful management of that wash as animals carry liquid out and dirt in. Many communal dips are government or community facilities on a fixed schedule rather than a private asset, which has consequences discussed in the next lesson.

A spray race is a set of nozzles that sprays animals as they walk through. Lower capital cost than a tank, less wash held at once, but coverage depends completely on the nozzles being unblocked, correctly aimed and at the right pressure, and on the animal walking through at the right speed. A spray race with three blocked nozzles is not a spray race, it is a shower.

Pour-on and spot treatments are applied along the animal's back and spread over the body. They need no structure beyond a crush that holds the animal still, they suit small herds, and they depend on the animal being restrained properly and the dose reaching the animal rather than the ground.

Whatever method you use, several things are true of all of them.

• Coverage is everything. A tick on a missed patch of skin is a tick that transmits.
• Every animal must go through, every time. The animal that stays behind in the kraal because it is difficult to handle becomes the reservoir that reinfests the rest.
• Ticks live on the ground and on the vegetation as well as on your cattle. A single treatment does not clear a farm; the interval between treatments is what keeps the population suppressed.
• This is a job that needs a crush or race that works. The handling module of this course explains why. An animal you cannot restrain safely is an animal that does not get treated properly, and a person who gets hurt doing it.

Now the part where this course stops and hands you over to someone else, and it stops completely.

This module gives you no product name, no acaricide class to choose, no concentration, no mixing instruction, no treatment interval and no withholding period. Not because they do not matter - they are the most important operational numbers in this entire subject - but because they are set by an authority and they differ by country and even by district within a country.

Which authority. Your national veterinary authority - the Directorate of Veterinary Services, the Chief Veterinary Officer, or whatever equivalent body your country has - together with your national animal-health product registration list, and the product label itself. In many places the dipping schedule is not even an individual decision: communal dip-tank schemes are frequently run as a community or government programme with a mandated schedule, and following that schedule may be a legal obligation rather than a choice.

Withholding periods deserve their own paragraph, because getting them wrong is both a food-safety failure and, in many countries, an offence. The withholding period is the time that must pass between the last acaricide or veterinary drug treatment and the slaughter of that animal or the sale of its milk. It exists so that chemical residues have cleared. It is set by the authority and stated on the label. No withholding period for any product appears anywhere in this course. Check the product label, and check with your national veterinary authority, for every product you use, every time the product changes.

So what should you actually do with this lesson? Two things. Learn the mechanism, which is now yours: coverage, every animal, every time, at an interval that suppresses the population. And then go and get the numbers from the only people entitled to give them to you, and write down the answers with the date and the name of who told you.

Every acaricide you use is a resource that can be used up. Not the bottle - the chemical's usefulness itself, on your farm, permanently.

Acaricide resistance in African tick populations is documented in the literature as a current and significant problem. Specific numeric resistance-prevalence figures - what percentage of farms or tick populations show resistance, by acaricide class - could not be obtained for this course, and that is a genuine gap given how directly it affects the advice a course must give. So no resistance percentage is quoted here. The existence and seriousness of the problem is not in doubt.

How resistance happens is worth understanding properly, because once you see the mechanism the management rules stop being arbitrary instructions and become obvious.

A tick population is not uniform. Among the many thousands of ticks on your farm, a few will, by natural variation, be slightly less affected by a given chemical. You kill the susceptible ones. The slightly tolerant ones survive and breed. Do that repeatedly with the same chemical, and each generation contains a higher proportion of survivors' descendants. Eventually the product still costs the same and no longer works.

Three things speed that process up, and they are exactly the three things a farmer under financial pressure is tempted to do:

1. Using the same acaricide class continuously, year after year. Constant pressure from one chemical selects hard for resistance to that one chemical.
2. Using the wrong concentration. An under-strength wash - because the tank was topped up with water and not replenished with product, or because a dose was stretched to cover more animals - kills the weakest ticks and lets the moderately tolerant ones through. That is the ideal condition for breeding resistance. You have paid for the chemical and bought resistance with it.
3. Applying on an irregular schedule, or skipping and stretching intervals to save money. Gaps let the population rebuild from survivors.

The same mechanism is documented numerically for deworming drugs, and the figures there are alarming enough to make the point concrete. A systematic review of 28 studies across 9 African countries found benzimidazole efficacy as low as zero percent in goats in Mozambique and 11 to 28.5 percent in Uganda; ivermectin-class efficacy as low as 24 percent in sheep in Algeria and 27 percent in South African goats; and levamisole efficacy as low as 7.9 percent in South African sheep - against a conventional threshold of 95 percent for a drug still considered effective. Those figures are predominantly sheep and goats, not cattle, and must not be quoted as cattle resistance figures. They are here because they show what the end of this road looks like: a drug that costs money, takes labour and does nothing.

So the resistance-management principles, which are standard and which you can apply without any product name:

• Rotate acaricide classes rather than relying on one. Note carefully: classes, not brand names. Two different-looking products from two different shops may contain the same active class, and rotating between them achieves nothing. Ask your veterinary authority or an animal health professional which class each product belongs to.
• Dip or spray at the concentration and frequency recommended by the product label and the national veterinary authority. Not the strength you can afford this month.
• Do not skip or stretch intervals to save money. Understand that stretching is not a partial control measure - it actively breeds the thing that will make the product useless.
• Keep the wash correctly made up and replenish it as the label directs, so the animals going through last receive the same strength as the first.

And the warning signs to watch for on your own farm. If you are finding live ticks on animals shortly after treatment; if the tick burden is climbing season on season despite unchanged routine; if disease cases are appearing in a herd that is being dipped on schedule - do not simply dip harder or more often. Take it to your veterinary authority or an animal health professional and say plainly what you use, at what strength, how often, and what you are seeing. Resistance can be tested for, and the answer changes what you should do next. Dipping harder with a failing product is the single most expensive mistake available in this subject: you pay full price, you get no protection, and you accelerate the resistance.

Last point, and it belongs here rather than in the costing lesson. Resistance is a shared problem. Ticks move between neighbouring herds on shared grazing and at shared dip tanks. Your neighbour's stretched intervals become your resistant ticks. That makes this one of the several areas in this course where the sensible unit of management is the community, not the individual farm.

Every farmer facing tick-borne disease is choosing between three things, whether or not they realise they are choosing: pay for tick control, pay for vaccination where one exists, or pay for the losses. Doing nothing is not a fourth option. It is the third one, chosen quietly.

This lesson teaches you to put those three side by side on paper.

Start with what a vaccine can and cannot do here. For East Coast fever, the main immunisation approach is the Infection and Treatment Method, sometimes known by the name of its most common formulation, the Muguga cocktail. It is unusual and worth understanding. Instead of a killed or weakened vaccine, ITM works by simultaneously injecting a live, virulent dose of the Theileria parva parasite together with a long-acting antibiotic, commonly a long-acting tetracycline. The antibiotic controls the infection enough that the animal survives, and in surviving it develops immunity.

Read that twice. You are deliberately infecting the animal with a live parasite while giving a drug to hold the infection in check. That is not a procedure to attempt from a course. Its availability, registration, price and administration all run through specific national or regional programmes and veterinary authorities. If you want it, the enquiry goes to your national veterinary service or the regional distribution programme they direct you to, and nobody else.

Remember also from Lesson 3 that there is no fully field-validated vaccine for heartwater, and that vaccination for the complex as a whole does not exist in one product. So for most farms most of the time, tick control is the practical layer and vaccination is a possibility to investigate for one specific disease.

Now the costing. The economics review this course draws on gives figures for each of the three routes. Treat every one of them as a historical study figure from a named country and year, not as a price you will pay - but use the structure they show.

• ITM vaccination: USD 1.08 to 27.70 per animal, with a cited net present value of USD 6,398 per farm annually in a Kenyan case.
• Acaricide-based control: USD 2.99 to 309.61 per animal annually depending on method, with the application-method cost alone ranging USD 16.17 to 40.44.
• Treating a clinical case with antibiotics: USD 7.66 to 45.65 per illness episode, with a broader annual range of USD 9.40 to 52.37 per animal depending on region and protocol.
• And from Lesson 2, the annual cost of the disease itself, unprotected or poorly protected: USD 2.13 to 111.94 per animal.

What those ranges show is not a price. It is a method. You compare the annual cost of vaccination, against the annual cost of acaricide-only control, against the expected loss from doing neither. That comparison is the actual decision, and you can only make it with your own local prices in your own currency.

So here is the arithmetic to do with your own numbers.

1. Cost your current control for a year: acaricide bought, dip fees paid, labour, transport, and the share of any facility cost.
2. Cost your losses last year: animals that died, valued at what they would have sold for; treatment bills; and the growth and milk lost in survivors, using the loss percentages from Lesson 2 as your guide.
3. Get a quoted cost for any vaccination available to you, from your veterinary authority.
4. Put all three on one page.

Almost always, step 2 is the number farmers have never written down, and almost always it is larger than they expected - because dead animals are remembered but the quiet losses in survivors are not.

Finally, records, because none of this works without them. Add to the herd record this course has already asked you to keep: the date of every dip or spray and which product was used; every animal treated for disease, with what and by whom; every death, with the suspected cause and whether anyone qualified examined it; and any animal that survived but grew poorly. That last category is the one nobody records and the one this module has spent five lessons proving matters.

With a year of those records you can answer the only question that finally counts: did what I spent on tick control cost me less than what the disease was taking? Without them, you will be answering it by feel, in a subject where the feel is reliably wrong - because the deaths are visible and the far larger, slower losses are not.