Home › Animalia › Animal health › Animal diseases › Rift Valley Fever

viral disease Sheep, Goat Vaccine available Transmissible to humans

Rift Valley Fever

Find a veterinarian All sheep diseases

Definition Signs Causes Transmission Diagnosis Treatment Prevention Vaccination Complications When to see a vet Zoonosis Prognosis FAQ Sources Affected species

What is it?

Rift Valley Fever is a viral disease transmitted by mosquitoes, which affects ruminants and humans. In sheep, it manifests itself in two very marked ways: a wave of abortions which affects almost all pregnant females in a herd at the same time, and a massive mortality of newborn lambs. Adults often do better. This double signature, serial abortions and lambs which die within a few days, is what should make us think of the disease and trigger an immediate call to the veterinarian. The disease develops in outbreaks, usually after unusually heavy rains or floods, which cause mosquito populations to explode. Between two episodes, the virus remains discreet. It is present in sub-Saharan Africa, the Horn of Africa, Egypt, Madagascar and the Arabian Peninsula, with geographic progression closely monitored by international health authorities. Its presence is not established in the same way everywhere: this is precisely why any episode of grouped abortions must be reported, and not because the disease is established in each country. It is a disease requiring notification to veterinary services, and a serious zoonosis for breeders, shepherds, butchers and veterinarians.

Key point

A wave of abortions accompanied by mortality of newborn lambs should be reported immediately to the veterinarian and veterinary services, and aborts should never be handled with bare hands. Several diseases capable of producing this picture, including this one, seriously contaminate humans during birthing assistance or slaughter.

Commonly observed signs

These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.

Related signs — each one links to its page:

Abortion Fever Reduction Loss of appetite Jaundice Runny nose Diarrhea Nosebleed Vulvar discharge Lying animal that does not get up

In newborn lambs, the form is devastating: high fever, refusal to suck, profound depression, lambs that can no longer stand up, and death within one to two days. Mortality is very high in this age group.

In older and young lambs: fever, depression, refusal to feed, rapid breathing, runny nose sometimes tinged with blood, diarrhea which may contain blood, jaundice. Some die, the others recover slowly.

In pregnant ewes: abortions, at any stage of gestation, affecting a very large proportion of females in the flock, sometimes almost all. This is the most characteristic sign at the herd level.

In non-pregnant adults: fever, depression, loss of appetite, runny nose, sometimes jaundice and bloody discharge. Many recover.

Prolonged vulvar discharge after abortion, with retained placentas.

Fall in milk production.

In outbreaks, the farmer first sees dead lambs and serial abortions, before even noticing sick adults.

When to consult without delay

This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.

Causes and risk factors

The disease is caused by a virus transmitted mainly by the bite of infected mosquitoes.

The eggs of some mosquitoes can carry the virus and survive for a long time in the soil of flood-prone areas. When exceptional rains fill these depressions, a mass of infected mosquitoes hatch at the same time: this is the starting point of outbreaks.

Other mosquitoes then take over and amplify the circulation by biting viremic animals and then healthy animals.

The virus can also be transmitted directly by contact with the blood, abortions, placentas and birthing fluids of infected animals: it is this route which mainly contaminates humans.

Animal movement and trade between areas can introduce the virus into an unaffected territory.

Periods following exceptionally heavy rains, floods or floods, which trigger massive mosquito outbreaks.

Proximity to wetlands, floodplains, rice fields, dams, irrigation canals and temporary ponds.

Sheep flocks with many pregnant females and newborn lambs at the time of outbreak.

Introduction of animals from areas where the disease is circulating, without quarantine or control.

Animal gatherings: markets, fairs, holiday periods, transhumance.

Absence of vaccination in areas where the disease is known to be circulating.

Lack of protection against mosquitoes around the sheepfolds.

Transmission

The main transmission between animals is by mosquitoes.

Direct transmission also plays a role, through contact with blood, tissues, abortions and birthing fluids.

For humans, the most common route is not the mosquito bite but direct contact with infected animals or their products: helping a sheep to give birth, handling an abortion or placenta, slaughtering, skinning, cutting. Breeders, shepherds, butchers, renderers and veterinarians are therefore most exposed.

Consumption of raw milk from infected animals is also considered a possible route of contamination.

The disease is not transmitted from one person to another.

Movements of live animals are the main factor in geographic spread, explaining the importance of border controls and transport restrictions during outbreaks.

Diagnosis and care

Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.

Faced with a wave of abortions and mortality of newborn lambs, call the veterinarian without delay and do not handle the aborts with your bare hands.

The veterinarian assesses the situation at the herd level: number of abortions, age of affected animals, rain schedule, presence of mosquitoes.

The diagnosis cannot be made on signs alone: it is based on laboratory analyses, carried out on the blood of sick animals, on aborts and on placentas, with all the required precautions.

The veterinarian rules out other causes of cluster abortions in small ruminants, which are numerous and for the most part also transmissible to humans: brucellosis, Q fever, chlamydiosis, toxoplasmosis. This distinction is essential and can only be made in the laboratory.

The samples are handled by equipped professionals, because field and laboratory personnel are directly exposed.

The suspicion must be declared to the veterinary services: this is an obligation, and it is also what triggers aid and collective protection measures.

Treatment

There is no specific treatment for the virus.

Treatment is support for affected animals, decided by the veterinarian: hydration, protection against heat, care of females who have aborted, treatment of bacterial infections that set in after abortion, on prescription.

Affected newborn lambs most often die despite treatment.

The useful response is collective and not individual: reporting to veterinary services, protecting animals against mosquitoes, stopping animal movements, protecting people, and vaccination according to the decisions of the health authorities.

All handling of sick animals, abortions, placentas and carcasses is done with gloves and protection, without exception. This point concerns treatment as much as prevention: this is where people become contaminated.

Carcasses, aborts and placentas must be disposed of according to the instructions of the veterinary services, never left on site or given to dogs.

Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.

Prevention

Immediately report to the veterinarian and veterinary services any wave of abortions or any abnormal mortality of lambs: this is the first action, and it protects both the herd and the people.

In areas where the disease is circulating, vaccination of herds is the most effective means of prevention; it is decided and supervised by the health authorities and the veterinarian.

Fight against mosquitoes: eliminate stagnant water around buildings, maintain water troughs, gutters and containers, use protection on animals and buildings according to the advice of the veterinarian.

Bring animals in at night when possible, as the mosquitoes concerned are especially active at certain times.

Avoid introducing animals from risk areas and respect quarantines and movement restrictions.

Wear gloves and protection during any parturition intervention, any collection of runts and any slaughter.

Do not consume raw milk during periods of virus circulation, and always boil the milk.

Protect people from mosquito bites: mosquito nets, covering clothing, repellents.

Vaccination

Vaccines exist against Rift Valley Fever and constitute, in the areas concerned, the main tool for protecting herds. Their use is not free: it depends on official control programs and the decisions of veterinary services, depending on the epidemiological situation of the country and the period. The choice of the type of vaccine depends in particular on the condition of the animals, with certain formulations not being suitable for pregnant females. This decision is strictly up to the veterinarian. Vaccination is all the more effective if it is carried out before the risk period, that is to say before the rainy season, and not during the outbreak. Ask your veterinarian and veterinary services about the recommended behavior in your area: it may change from one year to the next depending on monitoring.

Possible complications

Loss of almost an entire season's lamb production during an outbreak.

Massive mortality of newborn lambs.

Retained placenta, uterine infections and infertility in aborted ewes.

Severe liver damage in the most affected animals.

Contamination of people on the farm, which is the most serious complication of all.

Restrictions on movement, closure of markets and blocking of exports during episodes, with serious economic consequences for an entire region.

When to see a veterinarian

Several ewes abort in a short time in your flock: call the veterinarian immediately and do not touch the aborts with your bare hands.

Newborn lambs die in series within the first days of life.

Animals present with fever, severe depression, jaundice or bloody discharge.

Abnormal mortality occurs in the herd after a period of heavy rain or flooding.

You have handled abortions or helped with a birth and you have a fever, headache or muscle pain: see a doctor and tell them that you are working with ruminants.

Cases are reported in your area: talk to the veterinarian before your herd is affected.

Transmission to humans

Rift Valley Fever is a serious zoonosis. In humans, contamination occurs mainly through direct contact with blood, tissues, abortions, placentas and carcasses of infected animals, and not through mosquito bites in most cases. The people most at risk are breeders, shepherds, people who assist with births, butchers, renderers and veterinarians. Periods of family slaughter and celebrations increase exposure. In most affected people, the disease manifests itself as a flu-like syndrome: sudden fever, headache, muscle and joint pain, weakness, which resolves within a few days. A minority of cases develop into serious forms: eye damage with sometimes lasting loss of vision, damage to the nervous system, or hemorrhagic form with jaundice and bleeding, which can be fatal. Any person presenting a fever after contact with ruminants in an area concerned must consult a doctor and inform him of this contact: it is this information which guides the diagnosis. The precautions are concrete: gloves and protection for any intervention at birth, for handling aborts, placentas and carcasses, hand washing, dedicated work clothing, and always boiled milk. Do not allow children near birthing areas or runts.

Prognosis

In newborn lambs, the individual prognosis is very poor: most die.

In older animals and adults, a majority recover, but pregnant females almost always lose their litter.

At the flock level, an outbreak costs an entire production season and leaves ewes in poor condition.

At the scale of a territory, the outcome depends on the speed of reporting, vaccination and control of animal movements: it is a disease where the collective response counts much more than individual care.

Frequently asked questions

All my ewes aborted within a few days, what should I do first?

Call the veterinarian immediately, isolate affected females, and do not touch abortions or placentas without gloves. Several diseases cause cluster abortions in sheep and most are transmitted to humans: only a laboratory analysis allows you to know which one, and this information protects your family.

Can I get this disease from helping a sheep give birth?

Yes, it is even the most frequent route of human contamination, before the mosquito bite. Contact with blood, birthing fluids, abortions and placentas is the most dangerous time. Gloves and hand washing really make a difference.

Are milk and meat dangerous?

Raw milk from an infected animal is considered a possible route of contamination: it must always be boiled. For meat, the risk mainly concerns slaughtering and cutting, that is to say contact with blood and organs, more than the consumption of well-cooked meat. Wear protection when felling.

Is this disease present in us?

Its distribution varies depending on the country and evolves over time; it is subject to international surveillance. Rather than assuming that it is or is not present in your home, report any episode of cluster abortions: this is exactly what surveillance expects, and this is what allows you to react in time.