East Coast fever – vaccination to combat the enemy in Africa’s cattle herds


By Nan Smith | 4 May 2018
Young cattle on the move are vulnerable to ticks and the diseases they carry. Calves have age-related immunity to ECF until they are six months as long as they have had colostrum after birth. Unfortunately many cows have extensive teat damage from ticks and one or more quarters may be out of action which means the calf does not get enough colostrum to ensure immunity. Exposed to ECF without protection they will die. Photo: Supplied

Driving its adapted mouthparts into the skin of its host the infected brown ear tick delivers a deadly injection as it starts to feed on bovine blood.

Catching a ride in the tick’s saliva, sporozoites (spores) of the protozoan parasite, Theileria parva, the agent of East Coast fever, make their way quickly to the lymph gland of the animal, a trip they can do in 4 hours.

Once there, the sporozoites start up a death machine from their position in the white blood cells. When the lymph system has been taken, the parasite turns its formidable fire-power on the red blood circulatory system.

The secret weapon of this parasite is stealth. The spores, rather than making a conventional penetration of the white blood cell membrane, trick cells into engulfing them – an unholy embrace which, once complete, allows the parasite to destroy and multiply from within the cell. Within a month, the host animal is dead.

More than a million cattle die in Africa every year as this microscopically tiny, single-celled parasite plunders the herds and livelihoods of African cattle farmers.

EAST COAST FEVER DEFINED

Theileriosis, East Coast fever, corridor disease, Zimbabwean theileriosis or January disease, are all names for the same disease, caused by the protozoan parasite Theileria parva.

The OIE, the world organisation for animal health, scrapped the previous classification of the parasite into 3 sub-species, T. parva parva, T. parva lawrencei and T. parva bovis in 1989. Since the protozoa are indistinguishable, have the same tick vectors and identical DNA, the current naming system recognises only Theileria parva with no sub species. For easy reference I will call it East Coast fever (ECF).

ECF maintains 2 reservoirs of infection: one in cattle populations and one in Buffalo herds. This is how it stays in circulation. If it is perhaps wiped out in one area, it will survive in another. The well is never dry.

At the appointed time, the bucket goes down and draws up a fresh supply of the parasite,which can then renew its assault on the cattle of Central, East and Southern Africa.

Buffalo are natural carriers of ECF and suffer no ill effects from infection. It is established that 100% of the buffalo in South Africa’s Kruger National Park and 100% of the buffalo in the country’s Hluhluwe – Umfolozi National Park are ECF carriers. Only there, officials call it corridor disease.

Vectored by the brown ear tick, ECF may be transmitted from buffalo to cow, adapt in mid-stride, transform, and continue from cow to cow. While this transformation may not have occurred in all regions, I wouldn’t put money on the chances of staying ECF-free if I was running a herd near a national park, or a game ranch, stocked with buffalo.

TICK SEASONALITY – ECF SEASONALITY

Warm spring, hot, rainy summer, cool autumn, dry, cold winter. Wherever the seasons are clearly separated ECF shows up in seasonal outbreaks.

These outbreaks are always associated with summer rain when adult ticks are most active and most abundant. It is the adult ticks that carry the highest parasite loads. Although they are efficient vectors, larvae and nymphs have significantly lower parasite loads than adult ticks.

So, while the seasonality of ECF and its vectors does not make the disease any less terrifying, it does give stockmen (and their cattle) some temporary relief from the ECF onslaught.

In the humid sub-tropics and tropics of the eastern and central parts of the sub-region the lines between seasons blur. With no strict seasonal population dynamic tick populations cycle year-round and there are always adult ticks on the cattle.

Tick and parasite control get a lot more difficult. There are areas in these zones of which it could be said that ECF is inevitable rather than probable.

Image: Theileria: Intracellular protozoan parasites of wild and domestic ruminants transmitted by ixodid ticks.

VACCINES AND VACCINATION

For about 100 years vets, cattle farmers and animal scientists have acted to reduce and eliminate ticks and tick-borne diseases.

Only in South Africa, where the state veterinary department ran a massively expensive 50-year programme which involved dipping every 5 days, and the quarantine and slaughter of positive animals, has ECF been eradicated.

Not entirely, of course… there are always those carrier buffalo in the national parks. Denialism, as a vet once told me, is not scientific.

Reports filter through of corridor disease (ECF by another name) showing up in the cattle of northern Zululand, South Africa, in areas adjoining the Hluhluwe – Umfolozi and Ndumu national parks, in parts of Mpumalanga, and in parts of Zululand to the south of Mozambique, where ECF is endemic.

Though dipping has been used to control ticks for the last century, brown ear tick populations are just as prolific as ever. Swimming cattle through a dip tank cannot be seen as a useful control when it comes to ECF.

Dipping every 5 days, as required for brown ear tick control, is horrendously expensive and will inevitably bring about tick resistance to the dip.

Strategic and careful use of dips is part of an integrated tick control plan and this is not a campaign for the banning of acaricides. Dipping just doesn’t work for ECF.

So, what’s to be done? At this stage vaccination is the only solution. Vaccine manufactured at the Centre for Ticks and Tickborne Diseases (CTTBD) in Lilongwe, Malawi has been available since 1967, but it is not without problems.

The parasite has, thus far, defied the scientific strategies of some seriously clever specialists to manipulate it into an easy-to-vaccinate formula. Fighting for solutions and overcoming production difficulties, scientists have developed a vaccine in a difficult-to-vaccinate formula, which is certainly better than no vaccine at all.

The vaccine comes in a 40-dose straw and must be shipped and stored in liquid nitrogen. Once the seals are broken, all the doses must be injected.

Using 40 doses at anything between US$6.00 and US$12.00 a dose presents a problem (although not an insurmountable problem) to cattle farmers who may only have 5, 10, 15 even 20 animals. Farmer groups seem the obvious solution as in – buy together, work together, vaccinate together.

INFECT AND TREAT

ECF vaccines are live and work on the infection and treatment method (ITM). Live sporozoites from crushed ticks and a liquid dilution agent make up the vaccine which is injected under the skin of the animal in a 2 ml dose. This is the infection part of the vaccine. For 2 simultaneous injections there must be 2 vaccinators.

At the same time oxytetracycline (an antibiotic) is injected into the muscle. This is the treatment. If treatment does not start at the same time as vaccine-induced infection the animal will die.

The technique with tick-borne diseases is to catch the infection early. Delay causes death, as every stockman knows.
The ECF parasite moves so fast that treatment will almost always be too late. The ITM vaccination makes it possible for farmers to control the timing of infection and therefore of treatment. Once an animal has been vaccinated she acquires immunity to the disease.

The oxytetracycline does not kill the parasite. It weakens the effect of the infection and elicits a mild response, or even a nil-response, from the vaccinated animal. But because the vaccine is live, the protozoa is locked in. After vaccination the parasite persists and the animal becomes a carrier.

CARRIERS, CROSS PROTECTION AND COCKTAILS

The carrier status of vaccinated cattle has made government ministries and veterinary departments wary of importing vaccines that will bring fresh stock into an area.

It is a wariness not without validity as was shown in Zambia where vaccinating with the Muguga cocktail introduced strains that did not occur there. This strain, or stock, difference between regions is common with tick-borne diseases.

Despite the difficulties of finding and isolating parasite stock, animal scientists have worked hard to make area-specific vaccines, and to combine isolate strains so that they have a reasonable degree of cross-protection.

The 3 strain Muguga cocktail, the primary vaccine used to control ECF in the sub-region, is manufactured at, and distributed from, the CTTBD in Malawi. The Muguga cocktail is a frontline fighter in the war against ECF and offers protection against the disease across a wide geographical area.

The CTTBD also makes the single stock Chitongo vaccine for southern Zambia and the Katete stock for eastern Zambia.

In Zimbabwe the single-strain Boleni vaccine, by a stroke of exceptionally good luck, protects against nearly all T.parva parasite stocks in the country. The naturally lower virulence of the Boleni stock does away with the need for oxytetracycline treatment – a double bonus.

This brings me back to my starting point – an article in the Zimbabwe Herald at the end of January reporting on 2 000 cattle deaths in the north-eastern sector caused by East Coast fever, or January disease as it is known in that country.

At that time dr. Josphat Nyika, director of livestock and veterinary services, urged farmers to step up dipping programmes and advocated farmer education on preventive measures.  The reality is that vaccination is the only preventive measure.

Also read:
Know you enemy – East Coast fever
East Coast fever and the brown ear tick
Dipping to control East Coast fever (part 1)
Dipping to control East Coast fever (part 2)