Zoonotic diseases are diseases that can be transferred from animals to human beings or from humans to animals. Humans can act as carriers of the diseases and spread them as well as be affected and die in case of the more serious ones like Anthrax, Brucellosis, Rift Valley Fever, Tuberculosis etc.

Domestic animals present problems not only for their handlers, i.e., farmers, but also for consumers when animals are used for food. Food products made from animals include not only meat, but meat derivatives that are added to sweets and other foods, and therefore, are less obvious to consumers. An example of a disease believed to be transmitted to humans from an animal product is Creutzfeldt-Jakob disease-variant (vCJD), of Bovine Spongiform Encephalopathy (BSE), also known as "mad cow disease". Despite the extreme rarity of this illness, the effects are so devastating that public health officials around the world recommend their governments take strict prevention measures (CDC/Edwin P. Ewing, Jr.)

The following animal diseases are known to affect humans in one form or another:

Local names:
Luo: Aremo / Embu: thita / Kamba: ndulu / Gabbra: chimale, chirrmalle / Kikuyu: Muriru / Kipsigis: bursta / Nandi: purasta / Maasai: Emburwo, ol akirikir, ol ogereger, em bjangat, eng eanairogua / Maragoli:likenji / Samburu: lokuchum, nokulupo / Somali: kut, khut, kud, baargariirshe / Swahili: kimeta, imetha / Turkana: enomokere, lolewe, lookot, lotorob, lokuchum / Iteso: atular / Luidakho:lishenji / Luvugusu: muyaka /

Common names:
fievre charbonneuse, charbon (French) carbunco bacteridiano (Spanish)

Description:
Zoonotic disease

Anthrax is a soil-borne bacterial infection of domestic animals, wild animals, and man.

Anthrax is caused by the spore-forming organism Bacillus anthracis. It is most common in wild and domestic herbivores - cattle, sheep, goats, camels, antelopes - but it also occurs in humans exposed to tissue from infected animals, contaminated animal products, or directly to anthrax spores. It doesn't affect chickens but it is common in ostriches.

Anthrax occurs all over the world. It is more common in warm climates as spore formation only occurs when the temperature is between 20 degrees Celsius and 40 degrees Celsius, the humidity is over 60% and the pH is above 6.0. Under such conditions spore formation occurs rapidly, leading to the contamination of soil and water, where the spore may survive for years; up to 30 years in some cases. Spores are formed in the presence of oxygen. Within a carcass the organisms rapidly die. Only when they are exposed to air and oxygen do they form spores.

The disease is transmitted through pastures which are contaminated by the spores. The animals may be forced during drought to graze on short grass which may be contaminated by the infected soil. Anthrax spores can remain infective in soil for many years. During this time they are a potential source of infection to grazing livestock. Grazing animals may become infected when they ingest sufficient numbers of these spores from the soil.

Prevention and control requires a strict adherence to veterinary regulations to prevent and minimize the spread of the disease among livestock and humans. Anthrax can be a very severe food borne pathogen and must at all means be prevented from entering any food or feed.

Note:

Bacillus anthracis is susceptible to antibiotics such as penicillin, streptomycin and tetracyclines and these may be used by a qualified veterinarian either to treat infected animals in the unlikely event that they are seen alive, or to give protection to in-contact animals. This is then followed by vaccination about 7-10 days later.

Scientific name: Bovine nocardiosis

Read more under skin problems

This is a bacterial disease caused by Nocardia farcinica organisms. These organisms cause chronic, non-contagious diseases in animals and humans. They are commonly found in soil, decaying vegetation, compost and other environmental sources. They enter the body through contamination of wounds or by inhalation.

The disease in cattle is characterised by infection and swelling of the superficial lymphatic vessels and lymph nodes of the legs, neck and around the base of the ears.

Only cattle and humans are affected

It appears initially as small nodules under the skin, most often on the legs and on the neck, at the base of or near the ears. The nodules develop slowly, and some are grouped together in the form of a large mulberry. They are firm and painless. Swellings may persist for years with no apparent adverse effect on the health of the animal.

A veterinarian will confirm the diagnosis by smears of pus removed from an unopened abscess. The main concern is to distinguish the lesions of Bovine Farcy from those of Tuberculosis, which on occasion it can resemble, especially when there are internal lesions, such as those occurring within the chest cavity.

Common names
Contagious abortion, Bang's disease, In humans also called Undulant fever and often confused with malaria or influenza

For complete description please see: Reproductive Problems

Brucellosis is a bacterial infection, caused by organisms belonging to the genus . The disease is prevalent in most countries of the world. It primarily affects cattle, buffalo, pigs, sheep, goats, camels and dogs, and occasionally horses.

The disease in humans, sometimes called Undulant Fever, is a serious public health problem, especially when caused by Brucella Melitensis.

Brucellosis in cattle is caused almost exclusively by Brucella abortus, although occasionally Brucella melitensis or Brucella suis may be implicated. Melitensis occurs primarily in sheep and goats; suis in pigs. Brucella canis is confined to dogs.

Cattle of all ages and sex can be infected with B. abortus,but it is primarily a disease of sexually mature female cattle, with bulls and immature animals showing little or no clinical disease.

This is based on the history, serology and bacteriology. Abortions occurring after 6 months of pregnancy are suggestive. However, blood samples should be taken for detailed laboratory analysis to confirm the disease.

Diseases with similar symptoms Abortion: See Vibriosis, Leptospirosis, Rift Valley Fever

Brucella infections are known to be persistent, so treatment of animals with antibiotic is not recommended. It is therefore not practical and not useful to make any treatment attempt. Infected animals should be culled. Meat is safe for consumption if cooked well.

Hydatid cysts: Echinococcus granulosus

Hydatid cysts are unfortunately not uncommon in human beings. Mature cysts can reach up to half a meter in diameter if not attended to. A person may look very pregnant only to find out that what they have is a hydatid cyst, which will have to be removed surgically.

This is a very short dog tapeworm, whose main significance is that the larval stage forms large multiple hydatid cysts in the intermediate hosts, including humans. These cysts are located in the liver and lungs and can grow to a very large size indeed. People living in close association with dogs are especially at risk.

For full datasheet please link to Human Health/Insect transmitted diseases (under construction)

A skin disease of humans and in other parts of the world - dogs. In Africa it is mainly transmitted by sandflies, and dogs seem to be less affected.

Leishmaniasis is caused by protozoal parasites of the genus Leishmania, which were originally parasites of rodents, in which they cause a mild skin disease. They are transmitted by sandflies and have become adapted to dogs and to man in whom they cause three main clinical types of disease.

Lizards, rodents and rock hyraxes are intermediate hosts

Leptospirosis is a bacterial disease caused by members of a single species. Leptospira interrogans, which contains two major groups - those which are free-living and those which are strictly parasitic.

Domestic animals, wildlife and humans can all be infected.

Most infections are subclinical, but severe disease characterized by haemolytic anaemia leading to jaundice (pale yellow gums, underside of eyelids etc), blood in the urine, and sometimes death, or milder forms with fever, milk drop, atypical mastitis and abortion may occur.

The causal agent is a long, fine, wavy or spiral organism, which is bent into a hook at one or both ends. It moves actively, with a rotary action, but is fragile, readily losing its vitality on exposure to drying, excessive sunlight, acids or heat.

The disease is widespread throughout the world. The best environment for the organism is warm, wet conditions with a pH value close to neutral.

All domestic animals are susceptible.

The source of infection is usually an infected animal which contaminates pasture, drinking water and feed by infected urine, aborted fetuses and infected uterine discharges. Transmission is mainly via infected urine.

The largest reservoir of infection is in wild animals, and of these, rodents such as rats, voles and mice are the most important. Rats can excrete the organism for at least 220 days.

In cattle, leptospires can be excreted for a period which can last from a few weeks up to 18 months, or for the animal's lifetime.

Direct transmission can occur when animals are herded together. However infection usually arises from contact with an infected environment, with infected water playing an important part in the transmission cycle. The organism may survive for months in water-saturated soil.

The organism may enter a new host through the skin, especially damaged skin, or through the mucosa of the muzzle, mouth or conjunctiva. Other routes of infection are bites from rodents; venereal spread (leptospires have been isolated from bulls' semen); animals hunting and killing infected prey; and infection of the foetus through the placenta.

Man may be infected by domestic animals, wild animals, or by contact with surface water contaminated by urine from infected animals.

Apart from cattle BSE has been transmitted experimentally to several other species, including mice, pigs, sheep, goats, mink, monkeys and marmosets. During the British epidemic cases of BSE occurred in small numbers of captive ungulates - nyala, gemsbok, eland, oryx, kudu, Ankole cow and bison - and in five species of wild cat - puma, cheetah, ocelot, lion and tiger - either kept in, or originating from, British zoos. The ungulates were infected from the same food source as cattle and the cats, including a small number of domestic cats, were most likely infected by eating infected bovine tissue.

Cause

Transmission

Clinical Findings

Diagnosis




Zoonotic Risk

For complete datasheet please see here: Skin problems

Mange is a very itchy skin condition that comes when the skin is infected by small borrowing mites called sarcoptic mites. It may affect all warm blooded animals including humans. Humans may get it from any of the domesticated animals that have an infection.

Orf is an infectious viral skin disease of mainly sheep and goats. It mainly affects the lips of young animals. The disease is more severe in goats than in sheep. It can also affect wild sheep and goats. Humans are occasionally infected and the disease has been reported in dogs that have scavenged on infected carcases.

It is characterised by the development of pus-filled and scabby wounds on the muzzle and lips of lambs and kids, by the appearance of similar lesions on the teats of nursing ewes and nanny goats and it can also produce lesions on the teats of cows.

Epidemics tend to occur twice yearly - the first peak is associated with the disease in sucking lambs, the later one with susceptible stock lambs. But sporadic cases can occur at any time.

The disease is commonest in lambs and kids aged 3-6 months, although lambs aged 10-12 days and adults can be severely affected. Outbreaks can occur at any time but are most common in dry conditions. Recovered animals are solidly immune for 2-3 years but they do not transfer this immunity in their colostrum to their lambs, which are therefore susceptible to infection.

In humans typical wounds occur at the site of infection, usually an abrasion infected while handling diseased sheep, or milking infected cows or by accidental means when vaccinating sheep. The lesions are very itchy and respond poorly to treatment.

Infection only occurs if there is a break in the surface of the skin or the lips. The rapid spread during dry conditions may be due to scratches on the skin caused by dry feed, allowing a ready entry of infection. Spread in a flock is very rapid and occurs by contact with other infected animals or non-living objects. Ewes nursing affected lambs often develop crops of lesions on their teats which sometime lead to mastitis. As a result lambs are unable to suckle and may suffer from starvation.

Pseudo-Cow Pox is a common, mild infection of the udder and teats of cows and occurs worldwide. Other names for Pseudo-Cow Pox include Bovine Papular Stomatis (BPS) and Milkers' Nodules.

Pseudo-Cow Pox is visible as eroded patches (blisters) on the teats and udders of lactating cows, whereas BPS is acquired by calves suckling cows with active Pseudo-Cow Pox and is visible as circular patches around the nose and mouth and by a pimple-like inflammation on the margins of the nostrils, inner surfaces of the lips, and the edges of the tooth sockets.

Q Fever, Coxiella burnetti, is a disease passed to humans from sheep. People working around domestic sheep should consider getting vaccinated against this disease. The disease can be acquired from the inhalation of aerosolized barnyard dust should it contain infected dried urine, manure particles, or dried fluids from the birth of calves or lambs or through tick bites or by drinking raw milk.

Q-fever is found all over the world, in every country where it has been sought. Its main importance is its ability to infect man, and to cause abortions, metritis (inflammation of the lining of the uterus), and mastitis in infected ruminants.

Ventral view of a larval Ixodide, Dermacentor marginatus hard tick that has been cleared and mounted. This tick species is known to be a vector for Tick-borne encephalitis virus, caused by a member of the Tick-borne encephalitis virus complex, Flaviviridae, and Q fever, which is caused by the bacteria Coxiella burnetii.

Coxiella burnetii is an extremely difficult organism to eliminate. It is very tough, resisting most disinfectants, heat and drying, and surviving for years in dust

At-risk animals, and man, become infected by inhaling infected fluid discharges in the air or dust loaded with dried discharges.

The disease is highly infectious. Animal handlers are particularly at risk from infection, especially at lambing or calving, from inhalation, ingestion or direct contact with birth fluids or afterbirth.

However the main route of most human infections is by inhalation of contaminated air droplets or dust originating in infected ruminants or other animals e.g. cats.

Spread can occur up to 10 kilometres from the source of infection by wind dispersal of dried reproductive products, such as afterbirth, genital discharges, etc from infected sheep, cattle and goats, depending on wind condition.

Local names:
Luo: Tuo swao, Rabudi, swawo / Swahili: Kichaa cha mbwa / Turkana: long'okwo, arthim, nkerep, nkwang' / Somali: ramis, nyanyo, waalan, walan / Samburu: nkuang, nkwang / Maasai: Olloitirwa LolLdien, enkeyian orki, enkeya oldian / Meru: nthu cia kuuru / Maragoli: bulalu vwa tsimbwa / Gabbra: nyanye, aidurr / Kamba: mun'gethya, nduuka ya ngiti / Kipsigis: miotap ngokto /

Common names:
hydrophobia, lyssa, rage (French), rabia (Spanish) Tollwut (German)

Rabies is is a fatal viral inflammation of the central nervous system caused by Rhabdovirus. It occurs world wide and affects all warm blooded animals including man and other domestic and wild animals except birds.

Rabies is common in both rural and urban areas. Many people are unaware of the mortal dangers associated with this terrible disease. Many people in rural areas keep dogs both as pets and for security. Because most rural people are not aware of the hazards of the disease, they have not had their dogs vaccinated. As a result lives are put at risk for the lack of simple information and a few shillings.

Furious stage of Rabies in cattle: Salivation, dropped lower jaw and squinting can be seen on this highly exited rabid cow. Whilst pressing its head onto the fence it was producing a highly abnormal bellowing sound

Rabies is transmitted via the saliva of an infected animal, usually through its bite. Once clinical signs appear it is almost invariably fatal.

Rabid animals usually excrete the virus in their saliva 2 days before they show clinical signs and then throughout the course of the disease which is normally less than 10 days. On rare occasions dogs in Africa have been known to survive Rabies and to excrete the virus in their saliva for months.

Transmission usually occurs when infected saliva is deposited in a bite wound. Less common routes of transmission include inhalation of infected droplets in bat infested caves and by the ingestion of an infected carrier.

The rabies virus spreads when it is deposited in a bite wound and penetrates muscle cells where it either multiplies or becomes confined as a subviral particle. Within a few hours newly formed viral particles enter the peripheral nervous system and travel along the nerve trunks to the spinal cord and brain. From the brain the virus travels along peripheral nerves to the salivary glands.

In Kenya the dog is the main transmitter of Rabies though cats and wild animals, such as jackals, can also play a part in transmission. Ruminants such as cattle, sheep and goats play little part in direct transmission but their role as indirest transmitters can be important. The disease is of serious concern as the majority of dogs in the country are unvaccinated.

The incubation period is both prolonged and variable. Bites close to the head result in symptoms appearing sooner than in an animal bitten, for example, on a lower hind limb. Sequestration of the virus in the area of the bite is believed to explain the occasional very long incubation periods recorded. Bites in areas with a rich blood supply are especially dangerous. In most clinical cases of Rabies the incubation period is of the order of 3 to 12 weeks, with occasional cases of periods of up to a year.

The course of the clinical disease ranges from 2 to 10 days.

There are three clinical phases: pre-symptomatic, excitative and paralytic.

1. Before symptoms occur (pre-symptomatic phase) there is a change in behaviour; friendly dogs become aggressive, fierce dogs become friendly. Affected cattle stray away from the herd. In dogs this phase may last for 2-3 days; in cattle a few hours.

2. The excitative phase is refered to as "Furious" Rabies. In the excitative phase:

• Animals appear to be hypersensitive, restless, and agressive and may bite or attack without warning
• Voice changes occur. Depending on the species of the infected animal, the voice changes may include howling, roaring and bleating. Infected people may bark like dogs
• Dogs often have a peculiar staring expression and often drool saliva
• The conjunctiva often is red and inflamed
• They may attack any moving object and break their teeth and eat stones and sticks
• Cattle may stare intently at people before charging them. They may break their way through fences.
• Donkeys may mutilate themselves biting and chewing their bodies to such an extent they occasionally even disembowel themselves
• Cats become very aggressive, attacking without provocation.

3. The paralytic phase is refered to as "Dumb" Rabies. In the paralytic phase:

• Cattle may walk unsteadily and strain unproductively as though trying to pass dung, due to decreased sensation of the hindquarters
• They bellow hoarsely, continuously, sometimes for hours on end
• They drool saliva
• They are unable to eat or drink
• Dogs often have paralysis of the lower jaw, with a dry, darkened tongue
• Finally the animal becomes progressively paralysed,cannot eat or drink and dies.

The period from the onset of symptoms to death is generally short, usually 3 to 4 days. Occasionally a rabid animal may show no obvious clinical symptoms and may die after a short undramatic illness.

There is no treatment for rabies and it is not advisable to try to treat an animal infected with rabies because of the dangers in handling such an animal.

Rift Valley Fever (RVF) is a mosquito-borne viral disease affecting domestic ruminants (cattle, sheep, goats, camels, domestic buffaloes) and humans. It occurs mainly in East and Southern Africa and in year 2000 in Saudi Arabia and Yemen. During epidemics the occurrence of numerous abortions, deaths in young animals and influenza like diseases in humans tends to be characteristic. During recent epidemics in Kenya several deaths of humans were reported.

Formerly, apart from abortion, most cases in adult animals were subacute, but in recent times a haemorrhagic form of the disease has emerged with rapid death in mature animals, including cattle.

There is a remarkable age-related innate resistance to RVF virus; mortality rate in lambs less than 1 week old exceeds 90% whereas the rate in lambs over 1 week drops to 20%.

The virus is widely distributed in Africa, but major epidemic episodes in animals and humans are relatively rare, occurring in 5 to 20 year cycles. Between epidemics, the virus survives in mosquito eggs laid on vegetation in dambos-which are shallow depressions in forest edges. Only when these are flooded do the eggs hatch. This only occurs when the water table rises following prolonged heavy rain. The eggs then hatch and a new population of infected mosquitoes emerges.

Heavy rains and flooding cause mosquito eggs to hatch and Rift valley fever to become epidemic.

Vaccination of all domestic animals at the onset of heavy rains is a good precaution which will also protect humans from catching this serious disease.

Ringworm is a fungal skin infection - not a worm at all. Children are often observed with ringworm infestation. They can get ringworm infections from any domestic animal or from other children. Ringworm in children can be cured by using special medicated soaps. In animals use of iodine or chlorhexidine (Savlon) can be effective cures along with cleaning out their pens and living areas.

Animals slowly recover even without treatment. The hair grows back in about three months

This is a tapeworm of humans, in which it can cause abdominal discomfort. It is a very long tapeworm, growing up to 15 metres long. It can cause loss of weight and general weakness in humans

Adult Taenia saginata tapeworm. Humans become infected by eating raw or undercooked infected meat. In the human intestine the cysts (larval stage) develop over 2 months into adult tapeworms which can survive for years. They attach to and feed from the small intestine.

Tetanus is a poisoning, caused by the neurotoxin of the spore-forming bacterial organism, Clostridium tetani, characterized by muscular spasms.

The disease occurs worldwide, but is more common on well-manured land, in closely settled areas under intensive cultivation, or associated with surgical procedures. Cases are usually sporadic, although occasionally outbreaks involving several animals may occur, as in lambs or colts as a result of infection through operation wounds or via the naval cord.

Almost all mammals are susceptible to Tetanus, including humans, who are very susceptible. Among mammals horses are the most susceptible, followed by sheep and goats. Cattle are fairly resistant, as are dogs. Cats seem to the most resistant of all domestic animals.

Clostridium tetani is an anaerobe - it lives without oxygen. It is found in soil and in intestinal tracts and in faeces. The spores may persist in the ground for many years, and are very resistant to heat and to standard disinfectants. In most cases they are introduced into the tissues through wounds, particularly deep puncture wounds, which provide a suitable anaerobic environment. Horses' hooves are particularly susceptible. Cows after calving may also contract tetanus. In lambs, however, it often follows docking or castration. Sometimes the point of entry cannot be found because the wound itself may be minor or have healed.

The spores of C. tetani are unable to grow in normal tissue or even in wounds if the tissue remains at the oxidation-reduction potential of the circulating blood that is surface wounds. Suitable conditions for multiplication occur when a small amount of soil or a foreign object causes tissue damage and cell death such as deep puncture wounds. When this happens the bacteria remain localised in the destroyed tissue at the original site of infection and multiply. Sometimes the spores may lie dormant in the tissues for some time and only produce clinical illness when tissue conditions involving a drop in the oxygen level favours their proliferation.

As the bacterial cells themselves disintegrate the potent neurotoxin is released, being absorbed by the motor nerves in the area and passed up the nerve tracts to the spinal cord. The toxin causes spasmodic, tonic contractions of muscles by interfering with the release of neurotransmitters from the nerve endings. Even minor stimulation of the affected animal may trigger the characteristic muscular spasms, which may be so severe as to cause bone fractures. Respiratory failure may occur due to spasm of the larynx, diaphragm and muscles of the chest.

The incubation period varies from one to several weeks, but usually averages 10 - 14 days.

This is usually made from the characteristic clinical signs and history of a recent wound. It may be possible to demonstrate the organisms in smears taken from a wound or by culture, but this is rarely done.

Strychnine poisoning may be confused with Tetanus, but in poisoning the onset of symptoms is much more rapid, the muscular cramps are intermittent and not constant and death occurs in a much shorter period of time.

In humans is normally standard practice to administer tetanus vaccine immediately as part of treatment of any deep puncture wounds. Please ask your doctor for advice.

In animals proper treatment of all wounds is of primary importance. The persistence of pus, dead tissue, dirt or foreign bodies within the wound must be avoided and the proliferation of bacteria avoided. Careful drainage must be provided to prevent the accumulation of blood serum and excretions. Foreign bodies must be removed and the wound thoroughly opened to ensure careful cleaning. After any surgical procedure, such as docking or castration, animals must be turned out onto clean ground, preferably grass pastures. Remember that only oxidizing disinfectants, such as iodine or chlorine dependably kill the spores.

If symptoms have set in, place the animal in a quiet, comfortable place and do not disturb it in any way. It should receive soft, easily digestible food and, when eating becomes more difficult, gruels or milk. Plenty of fresh water should be placed within easy reach, but the administration of medicine by mouth is not advised.

Any wounds should be drained and cleaned to prevent further production of toxin, and antibiotic in the form of large doses of penicillin administered.

Tetanus anti-toxin (if available) may be administered but is of little use once symptoms have appeared. Valuable animals may be given tranquilizer or sedative drugs, such as Acetylpromazine or Chlorpromazine to act as muscle relaxants.

The outlook in any case of Tetanus is always poor, but with careful nursing and aggressive use of antibiotics and with particular attention to the cleansing of wounds, some animals may recover. But recovery is always slow and protracted and may take several weeks.

All surgical interventions such as docking lambs' tails, castrations, sheep shearing etc, should be carried in clean surroundings, paying especial care to the disinfection of skin and of any instruments used. Temporary pens for holding animals are preferable to permanent ones which are more likely to be contaminated and dirty.

Tetanus vaccine can be used to confer immunity in situations where animals may be at risk. One injection gives immunity in 10-14 days lasting for a year and revaccination in 12 months gives solid immunity for life. In areas where the disease is very common all animals should be vaccinated annually as a routine measure.

Prevention of tetanus in new-born lambs is best effected by vaccination of the ewe in the last 2-3 weeks of pregnancy, preferably by using a combined clostridial vaccine which will also confer immunity against other diseases such as Lamb Dysentery, and Pulpy Kidney Disease.

Toxoplasma gondii is an important zoonotic agent. In some parts of the world up to 60% of the population have serological evidence of persistent infection. Toxoplasmosis is of major concern for people who are immuno-compromised e.g. those infected with HIV. In these individuals toxoplasmosis usually presents as meningoencephalitis and results from the emergence of T.gondii from tissue cysts located in the brain as immunity wanes, rather than from primary infection.

Toxoplasmosis is also of major concern for the pregnant woman as tachyzoites can migrate across the placenta and cause birth defects in the foetus. Infection may occur after ingestion of undercooked meat or accidental ingestion of oocysts from cat faeces.

Toxoplasmosis is caused by a protozoal parasite, called Toxoplasma gondii, which infects humans and other warm-blooded animals, including birds, and occurs worldwide. It belongs to the same group of organisms which cause Coccidiosis.

It is an important zoonosis which means people can get it as well as animals.

Toxoplasmosis occurs worldwide.

Infection may be very common, but clinical Toxoplasmosis is relatively rare and its main importance is as a human disease and as a cause of abortion in sheep. In other species it can cause encephalitis, pneumonia and neonatal mortality.

The causative organism is a specific parasite of the definitive host, which is the Cat. There is a wide range of intermediate hosts, including rodents and wild birds, in which there is thus a reservoir of infection.

Mice are very important intermediate hosts in that vertical transmission from generation to generation without significant illness provides a long-lasting reservoir of infection for susceptible cats.

Young cats begin to catch and eat infected mice and thus acquire infection. Infected mice are more easily caught as they are less responsive to novel stimuli. Cats acquire infection by eating meat containing infective eggs od the parasite. They can also be infected by eating contaminated food.

In the small intestine of the cat the parasites go through a typical coccidian life cycle resulting in the shedding of unsporulated oocysts (eggs) in the faeces. Huge numbers of eggs may be excreted. 50 g of cat faeces may contain 10 million eggs while the dose needed to infect a sheep is less than 40 eggs. Therefore concentrate feed or hay contaminated with cat faeces may contain many infective doses. After several days the eggs hatch and are then infective, often in large numbers and may remain infective in the environment for long periods, exceeding a year. When eaten by the intermediate host the eggs invade tissues, multiply rapidly in a wide variety of tissues and then, a few weeks later, localize in certain tissues and become tissue cysts. This invasion can include the foetus in a pregnant female, the brain, the heart, the lung and the placenta. Young cats pose the greatest threat. Generally cats once infected when young only pass oocysts once in their lifetime although older immunosuppressed cats may exhibit a recrudescence of infection.

Human infections appear to be associated with the presence of cats, and the consumption of inadequately cooked meat.

The organism is readily destroyed by heating, drying and freezing and thawing and dies quickly in the carcases of infected animals. The tissue cysts formed in the tissues of chronically infected animals form the most effective means of perpetuating the disease.
Approximately 200 species of mammals and birds have been identified as being intermediate hosts of Toxoplasma gondii, including all domestic animals and man. But cats are the only known final host.

Cats, being the final host, shed oocysts in their faeces, which sporulate within 2-3 days to become infectious to other cats and all intermediate hosts. Eating of sporulated oocysts by cats results in a typical direct coccidial life-cycle in the intestine, resulting in further excretion of large numbers of oocyts

In the cat there is a sexual cycle. In other species the cycle is asexual. Oocysts shed by the cat develop into rapidly developing tachyzoites which in turn develop into tissue cyst bradyzoites which when ingested by the cat complete the cycle. (see life cycle above) The common method of spread in ruminants is by eating feed contaminated by cat faeces which contain infective oocysts. Carnivores get infected by eating uncooked meat containing tissue cysts.

Young and immuno-compromised animals may succumb to generalized toxoplasmosis. Older animals mount a powerful cell-mediated response and control infections, driving the tachyzoites or rapidly multiplying forms into the bradyzoite or tissue cyst forms. Individual cysts may enclose hundreds of bradyzoites in a thin, resilient cyst wall. These cysts in the host remain infective for many years, and possibly for the life of the host. These cysts are the main source of ongoing infections. They are commonly found in muscle and brain tissue, in which they persist for life. The organism has a preference for the central nervous system, and, in sheep and goats, for the placenta, with abortion as the result.

The only clinical syndrome recognized with any regularity is abortion and neonatal mortality in sheep, but goats are also susceptible with a similar scenario to that seen in sheep, with death of foetus and also probable transmission from dam to offspring.

Infection in most species appears to be common and widespread, but most cases are symptomless or mild. Clinical signs depend on the tissues infected and the stage of the parasite e.g. acute disease results from rapid multiplication of tachyzoites. Symptoms are very varied and may include pneumonia, endocarditis and neonatal mortality.

Toxoplasmosis is an important cause of abortion in sheep. The pattern of abortion depends on the stage of pregnancy when animals are infected. Infection early in pregnancy results in foetal death or abortion of a mummified foetus. Infection later in pregnancy causes inflammation of the placenta and abortion of a relatively fresh, well-developed foetus. Some lambs congenitally infected may be born alive but are weak and die within a few days. Infection outside of pregnancy is asymptomatic but results in immunity.

There is no sheep to sheep transmission. Sheep, once infected, remain so for life, but develop a solid immunity which is probably lifelong. There may be vertical transmission in sheep with lambs infected when they are born.

Diagnosis cannot, with confidence, be based on clinical findings alone.
Post mortem examination of aborted placenta reveals dark cotyledons with white speckles of necrosis visible to the naked eye, with normal intervening tissue.

Various serological and biological tests are in use in countries where the disease is recognized as being a potential threat to animal and human health. The Indirect Fluorescent Antibody Test is one. None is currently available in Kenya . Post mortem tachyzoites may be seen in tissue impression smears and microscopic examination of tissue sections may reveal the presence of tachyzoites and bradyzoites.

This is rarely applicable in animals. In humans drugs such as sulphadiazine and pyrimethamine are widely used, especially in the acute stage. Clindamycin is the treatment of choice in dogs and cats.

There is an effective tachyzoite vaccine (Toxovax) for use in sheep, which has lost the ability to form bradyzoites in tissue cysts. Duration of immunity is reported to be at least 18 months, although with natural infection boosting immunity in field conditions it is likely to be lifelong. It should be given to non-pregnant ewes at least 3 weeks before mating. It is not currently available in Kenya.

Animals may be immunized by exposure to controlled infection, such as having susceptible female sheep on known infected farms exposed to infection to Toxoplasma-contaminated areas several months before breeding in order to infect and immunize them before pregnancy. Monensin at 15 mg per ewe appears to prevent or lessen infection, as does Deccox given during the last two thirds of pregnancy.

Cats should not be allowed to mingle with farm animals and contamination of the food of farm animals with cat faeces must be prevented. Farm cats should be neutered to prevent straying and contracting and spreading infection. Cats should be kept healthy. Sick and immunosupressed cats may have a recurrence of infection.

Vermin such as mice and rodents should be controlled.

Cats themselves do not pose a threat in that handling is not a risk as oocysts are not infective until they have sporulated after being excreted by the cat. This takes one to five days. It is the environmental soil and water which poses the risk.

To prevent infection people handling meat should wash their hands thoroughly with soap and water after contact. This also applies to cutting boards, sink tops, knives and other materials. T. gondii is killed by exposure to extreme cold or heat. Tissue cysts in meat are killed by heating the meat throughout to 67 C or by cooling to -13 C. The meat of any animal should be cooked to 67 C before consumption. Tasting meat while cooking should be avoided.

Water should be boiled or filtered.

Pregnant women should avoid contact with cat litter, soil and raw meat. Pregnant women should also not assist at lambing time.

Pet cats should only be fed dry, canned or cooked food. The cat litter box should be emptied daily, preferably not by a pregnant woman. Gloves should be worn when gardening. Vegetables should be thoroughly washed before eating as they may have been contaminated with cat faeces. There is no human toxoplasma vaccine.

Tuberculosis is a bacterial infection that affects mainly cattle and human beings, as well as other domestic animals. Mycobacterium bovis is the usual cause of tuberculosis in cattle, while M.avium causes the disease in poultry and M. tuberculosis is responsible for the majority of cases in man. It occurs worldwide but prevalence is dependant on the type of husbandry and the efficacy of control measures. Its prevalence is low in cattle kept extensively and not housed at night.

Humans are more susceptible to tuberculosis if the immune system has other challenges such as HIV/AIDS. It is therefore often encountered as secondary infection to this disease.

1. William Ayako, KARI Naivasha. Aug - Dec 2009
2. Hugh Cran , Practicing Veterinarian Nakuru. Sept. 2011
3. Review workshop team. Nov 2 - 5, 2010