SURRA

"El-debab - El-Gafar- Mal De Caderas-Murrina"

 


Nature of the disease

History
Etiology
Hosts
Transmission
Key signs
Lesions
Diagnosis
Immunity
Treatment
Control
References

 

Nature of the disease

  • Surra is essentially a disease of camels and horses, but all domestic animals are susceptible, caused by Trypanosoma evansi and the transmitted mechanically by biting flies. The disease may be acute, subacute or chronic, characterized clinically by fever, progressive emaciation, anemia, subcutaneous edema, nervous signs and death.

  • Surra is regarded as the most significant health problem in camels and horses. Surra is probably the most widespread and economically important diseases of camels in Africa and Asia. In endemic areas especially in Sudan, the disease causes significant losses due to reduced productivity, mortality, and costs of control and treatment.

  • OIE classification: list "B."

History and Occurrence

  • T. evansi was the first pathogenic trypanosome to be discovered in India in 1880, and it was detected in Egypt long ago.

  • Surra occurs within a wide range of climate and vegetation, It occurs in North Africa including Egypt( parts north to tsetse belt), the Middle East, Asia, the Far East, and Central and South America. The distribution of Trypanosoma evansi in Africa extends into the tsetse areas, where it is difficult to differentiate from T brucei.

  • In Africa and Asia, surra has a marked seasonal incidence with wet and humid climatic conditions that favor the vector development.

 

Etiology

  • T. evansi is a member of the subgenus Trypanozoon, which also comprises T. brucei and T. equiperdum, differing from these species by inability to develop cyclically in vector insects. It has many other synonyms, including T. cameli, T. equinum, and T. aegyptium.

  • The organism is an extracellular, flagellated, spindle-shaped, motile trypanosome with rapid twisting motion. Most forms are long and slender, although intermediate or short stumpy forms may occur sporadically. Morphologically, T. evansi is indistinguishable from the long slender forms of T. brucei.  The dyskinetoplastic state is also often observed. The length of blood forms ranges from 15-33 µm with a mean of 24 µm.  With Giemsa or leishman stain, it stains bluish with a red nucleus.

  • T. evansi can be cultivated and grows well in vitro using a modified RPMI 1640 medium.

             

Hosts

  • Surra is economically important in camels and horses, but dogs, cattle, buffaloes are susceptible. Wild animals' infection is rarely reported.

  • The disease can be fatal, particularly in camels, horses, and dogs. Cattle and buffaloes may harbor subclinical infections.

  • Indigenous cattle, buffalo, sheep and goats may act as reservoirs of infection for horses and camels, especially when they are closely stocked and during periods of high insect activity.

  • Laboratory animals of choice are rats and mice, which are highly susceptible.

 

Transmission

  • Surra is a non-contagious disease, transmitted only mechanically by several different genera of haematophagous flies. The most important genus is Tabanus spp.

  • The efficiency of vector transmission is dependent on high intensity of fly challenge, the presence of high numbers of the parasite in the blood of camels or horses, and the close herding of animals that maintains short intervals between successive feeds. The infectivity of a fly is highest within minutes of feeding and drops quickly thereafter, with the loss of ability to reinfect when feeding intervals exceed 8 hours.

  • Wild carnivores and dogs can be infected by ingestion of meat from parasitaemic animals.

  • In Central and South America, The vampire bat can also act as a vector.

  • The disease can be reproduced experimentally by blood inoculation.  

Key signs

In Camels "El-debab - El-Gafar"

  • The disease can be manifested in both acute and chronic forms, the IP varies from 7-15 days, the morbidity rate is up to 20 %, and the fatality rate may reach 100 % if untreated. Trypanosomes are present in the blood of acute cases but trypanosomes are often detected sporadically.

  • The acute form is usually fatal within a few months and few cases die in 2-3 weeks, spontaneous recovery is rare. The acute infection is characterized by fever lasting from a few days to a few weeks, oculonasal discharge, progressive emaciation and may develop anemia. Edema of dependant parts; under the belly, on the hind legs, sheath, scrotum and in the lungs may occur. Milk yield drops rapidly and infected animals become unable to feed their young's. Abortion at any stages of pregnancy and premature births may occur. The urine may be dark in color with a characteristic pungent odor.  Terminally, nervous signs including paraplegia, paralysis, and convulsions with cold sweats may develop just before death.

  • A protracted chronic course that persists for years is more frequent and characterized by anemia, progressive emaciation with disappearance of hump and atrophy of thigh muscles, weakness, and rough coat despite good appetite. The fever is recurrent with febrile paroxysms lasting from 5-7 days. Always, there is edema of the lower parts of the body and pronounced pale ecchymotic mucous membranes. The hair is often dull and rough, lost from the tail. Corneal opacity, diarrhea and sexual excitement may be seen also. The abortion rate is higher within infected herds.

  • Camels with chronic surra become more prone to infection with other diseases; it is usually associated with mange and pneumonia.

              

Horses     "Mal De Caderas- Murrina"

  • The IP varies from 1-2 weeks or more, with a morbidity rate up to 20 %, and a mortality rate up to 100 %. The acute syndrome may be as short as 2-3 weeks whereas the chronic syndrome may last up to 4 months.

  • The acute form is characterized by a sudden onset of fever, accompanied by dullness and lethargy. Infected animals show pronounced dependent edema, progressive emaciation despite a normal appetite, anemia with pale mucous membranes, and ocular discharge. Pinpoint hemorrhages of the mucous membranes and often around the eyelids, nostrils and anus may be present. Urticarial plaques on the skin with exudation that may give the skin a crusty appearance may be seen.

  • In the chronic form, progressive loss of weight and jaundice are pronounced. Superficial lymph node enlargement and keratitis may be seen. Central nervous system involvement leads to meningitis, progressive paralysis of the hindquarters causing difficulty in walking, recumbency and death. The terminal nervous signs are important feature for the disease in Central and South America.

Dogs and cats

  • Carnivores are highly susceptible to acute infection; the disease is characterized by well marked edema, particularly in the scrotum, ears, and neck. Opacity of the cornea is frequently present, emaciation is rapid and death can occur within 2 weeks. Dogs occasionally exhibit nervous signs suggestive of rabies.

Cattle and buffalo

  • Cattle and buffalo in enzootic situations usually have subclinical infections that may be exacerbated by stress factors developing overt disease with fever, emaciation and anemia. The disease may affect the quality of semen in bulls and cause irregular estrus, abortion and stillbirth in cows.

 Sheep, goats and pigs

  • In general, T. evansi is only slightly pathogenic for sheep, goats and pigs, although occasional outbreaks of disease may occur in pigs.

lesions

  • Necropsy findings vary and are not specific.

  • The carcass is emaciated, anemic, and may be icteric.

  • Edema is evident, ascites and hydrothorax may be present.

  • Petechial hemorrhages occur on serous membranes and viscera.

  • The lymph nodes and spleen are enlarged.

  • Trypanosomes are detected in all tissues and body fluids of fresh carcass.

  • Presence of blood in the cerebrospinal fluid (CSF) is evidence of CNS involvement.

Diagnosis    

  • In an endemic area, a presumptive diagnosis is usually based on finding an anemic animal in poor condition.

  • Specimens for laboratory use

  • Blood smears collected from ear vein.

  • Whole blood with heparin for animal inoculation and laboratory examination

  • Serum for serological and biochemical examinations.

  • The tentative diagnosis can be confirmed directly by demonstrating trypanosomes in Giemsa-stained thick or thin blood smears, or wet mounts.

  • The most sensitive rapid method is to examine a wet mount of the buffy coat area of a microhematocrite capillary tube after centrifugation with a dark-field or phase contrast microscope (Murray’s method) or examining the buffy coat directly at low power (Woo’s method).

  • Trypanosomes may readily seen in acute cases, but chronic infections are usually characterized by low parasitaemias so thick or thin blood smears from individual animals should be taken on consecutive days (or lymph node puncture smears).

  • Blood should be examined fresh and may refrigerated not more than 24 hour, beyond which trypanosomes will die and disappear from the sample.

  • Inoculation of blood from suspected animals into rodents such as mice and rats is a highly sensitive method for the detection of infection in animals with very low degree of parasitaemia.

  • Non-specific biochemical tests indicating increased serum protein levels as mercuric chloride test, formol gel test, and thymol turbidity test have been used.

  • Serologically, the IFAT, the capillary agglutination test "CAT", and the ELISA have all been used to demonstrate serological evidence of infection in sera or other body fluids. These tests have the disadvantage that does not distinguish between past and present infections and are not species specific. The ELISA technique using monoclonal antibodies is species specific and can detect circulating specific trypanosome antigens, so can detect only current recent infections but not provide reliable results and not in general field use.               

  • Hematological features of anemia may provide no more than a help in directing the diagnosis towards blood parasites.

  • Other infections that cause anemia and weight loss, such as babesiosis, anaplasmosis, theileriosis, and infections of other trypanosomes should be eliminated by examining a stained blood smear. Surra cannot be easily distinguished from T.brucei infection in areas where both coexist

          

  Immunity      

  • T. evasi has an antigenic variation leading to a relapsing parasitaemia in infected animals. The antigenic diversity in T. evasi is limited than that of tsetse-transmitted trypanosomes.

  • In areas where few serodems occur and the incidence of the disease is low, immunity may have a role in regulating natural infections.

Treatment

  • There are a few drugs which can be used to treat surra, most have a narrow therapeutic index, which makes administration of the correct dose essential. Drug resistance is known to occur amongst T. evansi isolates in several different countries in Africa and Asia and this should be considered in refractory cases. The most important drugs are Naganol and Antrycide. Hematopoiesis-stimulating drugs must be applied to avoid the deleterious effects of severe anemia.

  • Quinapyramine dimethylsulfate (Antricide) at a dose of 3-5 mg/kg s/c is effective curative drug against T. evansi, T. brucei, T. equiperdum in camels, pigs, and buffalo.

  • Quinapyramine prosalt (Antricide prosalt- Trypacide) at a dose of 3 mg/kg s/c is effective curative and preventive drug against T. evansi, T. brucei, T. equiperdum in horses, camels, and cattle. (In horses, the dose should be divided - The dose in cattle; 3-5 mg/kg s/c).

  • Suramine (Naganol) 10% solution at a dose of 10 mg/kg i.v is effective curative drug in camels, 6-10 mg/kg i.v in horses, and 30-50 mg/kg i.v in dogs.

  • Melarsomine (Cymelarsan) at a dose of 0.25 mg/kg i.m is effective curative drug in camels and horses. It is reported to be save even in pregnant camels.

  • Homidium bromide or chloride are effective curative drug in horses and cattle, but not effective in camels.

  • Diminazene aceturate (Berenil- babesin) a dose of 8-10 mg/kg i.m is effective curative drug in horses, cattle, and dogs but it is potentially toxic to camels.

    Drugs available for treatment of infections caused by trypanosomes of veterinary importance

    Drug

    Trade name

    Susceptible trypanosomes

     

    Species

    Dosage

    Remarks

    Quinapyramine dimethylsulfate

     

    Antricide

    T. evansi, T. brucei, T. equiperdum.

    Camels, pigs, buffalo

    3-5 mg/kg s/c

     

    Quinapyramine prosalt

     

    Trypacide Noroquin

    Quintrycide

    T. evansi, T. brucei, T. equiperdum.

    Camels, cattle, horses.

    3-5 mg/kg s/c

     

    3 mg/kg s/c

     

     

    the dose should be divided

    Suramine

    "Now, it is no longer widely available"

    Naganol

    T. evansi, T. brucei, T. equiperdum

    Camels,

    cattle, buffalo,

    horses,

    dogs.

    3.5-10 mg/kg i.v

     

     

    6-10 mg/kg i.v

    30-50  mg/kg i.v

    1-4 months prophylaxies

    , local painful réaction

     

    Therapy

    Therapy

    Diminazene aceturate

     

    Berenil, babesin

    T.vivax, T. congolense, (T.evansi,T.

     brucei) 

    Cattle, sheep, horses, dogs, camels.

     8-10  mg/kg i.m

     

     

     

    3.5mg/kg i.m

    C

     

     

    Low tolerance in dogs

    Potentially toxic to camels

    Isometamidium chloride

     

    Samorin

    Trypamidium

    T.vivax, T. congolense, (T.evansi,T. brucei) 

    Equidae

    dogs

    camels

    0.25mg/kg i.m

    0.5-1 mg/kg i.m

    C

    P

    Not recommended

    Melarsenoxide cysteamine

     

    Cymelarsan

    T. evansi and T. brucei

    camels, horses

    0.30-1.25 mg/kg i.m

    C

     

    Homidium chloride

    Novidiumb

    T. vivax, T. congolense

    cattle, sheep, camels 

    1 mg/kg

    C

 

Prevention and control measure  

  • There is no vaccine against trypanosomiasis. Therefore, conventional disease control measures are based on the use of curative and preventive drugs to combat the parasite and interventions to control fly populations. Control and eradication of surra from an area is usually depends upon:         

    Detection and treatment of infected animals.

  • Prophylactic treatment of susceptible animals, by injection of quinapyramine prosalt (Antricide prosalt) at a dose of 5 mg/kg s/c, 3-4 weeks after the start of rainy season when the risk of infection is greatest.

  • Seasonal movements of camels away from fly areas thickets and river basins.

  • Regular movements of camels to avoid flies hatching from the dung in which the maggots live.

  • Protection of susceptible animals from biting flies by smoking and using flies repellants.

  • Water animals in small groups so that they do not stay long at wells.

  • Watering animals in the hottest time of the day or at night, when fly activity is low.

References

1.   El Sawalhy, A. A. (1999) : "Veterinary Infectious Diseases" 2 nd Edit. Ahram Distribution Agency , Egypt .