Effective Control Methods for Haemophilus parasuis Disease

In recent years, with immunosuppressive diseases such as porcine reproductive and respiratory syndrome (PRRS) and porcine circovirus disease invading pig herds to varying degrees, and with another immunosuppressive disease in most pig farms, mycoplasma pneumonia, "adding fuel to the fire," the immunity and resistance of pig herds have been severely reduced, and mixed infections of diseases have become very common. In technical services, we have found that Haemophilus parasuis disease often appears as a secondary or concurrent infection in the nursery and growing barns of some pig farms, greatly increasing the mortality and culling rate of pig herds and causing huge losses to pig farms. Below is a discussion of the understanding and control methods for this disease, for the reference of colleagues.

1 Some Main Characteristics of Haemophilus parasuis Disease

1.1 Haemophilus parasuis disease is also called multiple fibrinous serositis and arthritis, and is also known as Glasser's disease. Haemophilus parasuis is a Gram-negative short bacillus with variable morphology and more than 15 serotypes, among which serotypes 5, 4, and 13 are the most common (accounting for more than 70%).

1.2 The growth of this bacterium strictly requires nicotinamide adenine dinucleotide, and it is difficult to isolate and culture under general conditions, especially from samples from pigs that have been treated with antibiotics, thus making diagnosis of the disease difficult. According to reports, the true incidence of Haemophilus parasuis disease may be as much as 10 times the number actually diagnosed.

1.3 This bacterium is a conditional bacterium, and the disease occurs frequently when the rearing environment is poor. Weaning, moving groups, mixing groups, or transportation are also common triggers.

2 Some Current Manifestations of Haemophilus parasuis Disease

2.1 Haemophilus parasuis infects only pigs and can affect young pigs from 2 weeks to 4 months of age, mainly causing disease around weaning and during the nursery stage. It is usually seen in pigs 5 to 8 weeks of age. The incidence rate is generally 10% to 15%, and in severe cases the mortality rate can reach 50%.

2.2 In acute cases, the disease often first occurs in pigs in good body condition. Affected pigs have fever (40.5°C to 42.0°C), depression, decreased appetite, difficulty breathing, abdominal breathing, red or pale skin, purple ear tips, subcutaneous edema of the eyelids, slow walking or unwillingness to stand, swelling of the carpal and tarsal joints, ataxia, and before death lying on their side or paddling with the limbs. Sometimes they die suddenly without obvious symptoms.

2.3 Chronic cases are mostly seen in nursery pigs, mainly with decreased appetite, coughing, difficulty breathing, rough hair coat, weakness or lameness of the limbs, poor growth, and eventually death from exhaustion.

2.4 If other respiratory diseases exist in the herd, such as mycoplasma pneumonia, porcine reproductive and respiratory syndrome, porcine circovirus disease, swine influenza, pseudorabies, and porcine respiratory coronavirus infection, the harm of Haemophilus parasuis disease will increase and will aggravate the clinical manifestations of PMWS (postweaning multisystemic wasting syndrome) in nursery barns in production.

3 Analysis of the Causes of Disease Prevalence

In pneumonia, Haemophilus parasuis is assumed to be a randomly invading secondary pathogen, a typical "opportunistic" pathogen that causes disease only when acting together with other viruses or bacteria. In recent years, the rate of isolation of Haemophilus parasuis from pigs with pneumonia has become higher and higher, which is related to the increasing prevalence of mycoplasma pneumonia and also to the increasing prevalence of viral pneumonia. These viruses mainly include porcine reproductive and respiratory syndrome virus, circovirus, swine influenza virus, and porcine respiratory coronavirus. When Haemophilus parasuis is combined with mycoplasma, the detection rate in the lungs of pigs with PRRS (porcine reproductive and respiratory syndrome) is 51.2%.

4 Prevention and Control Measures for Haemophilus parasuis Disease

4.1 There are few domestic reports on drug sensitivity tests for drugs to which Haemophilus parasuis is sensitive, but from the responses in practical application, florfenicol, cephalosporins, amoxicillin, ampicillin, quinolones, gentamicin, and potentiated sulfonamides have certain therapeutic effects. Most strains are resistant to erythromycin, aminoglycosides, and lincomycin.

4.2 Key Points for Prevention and Control of Haemophilus parasuis Disease

4.2.1 Antibiotic treatment of severe Haemophilus parasuis disease is not ideal. Once clinical symptoms have appeared, non-oral administration should immediately be adopted, using large doses of the above sensitive antibiotics for injection treatment of affected pigs, once every 6 to 8 hours, while at the same time preventing the disease in the rest of the herd.

4.2.2 The therapeutic effect of this disease is poor. In the production practice of pig farms, preventing outbreaks of this disease is the best policy. Because this disease usually occurs as a secondary or concurrent infection and is often accompanied by mixed mycoplasma infection, adding a scientific drug combination to the feed is an important means of preventing the disease. For example, after piglets are weaned, add tiamulin 100 mg/kg + chlortetracycline 300 mg/kg + amoxicillin 250 mg/kg to the feed; or tiamulin 100 mg/kg + florfenicol 80 mg/kg.

4.2.3 Immunization: In pig farms with severe Haemophilus parasuis disease, the herd may be immunized when necessary. Because there are many serotypes of this disease, the effect of commercial vaccines is uncertain, and autogenous vaccines have a certain preventive effect; if conditions do not permit, multivalent inactivated Haemophilus parasuis vaccine may also be used for immunization. For first-time immunized sows, the first vaccination is 40 days before farrowing and the second is 20 days before farrowing. For previously immunized sows, one vaccination 30 days before farrowing is sufficient. In pig farms seriously threatened by this disease, piglets should also be immunized. The timing of immunization should be inferred according to the age at which the disease occurs on the farm. Piglet immunization is generally arranged between 7 days and 30 days of age, 1 mL each time, and it is best to repeat the immunization once 15 days after the first vaccination, with an interval of more than 10 days between the second vaccination and the time of disease occurrence.

4.2.4 Eliminate triggers, strengthen feeding management and environmental disinfection, and reduce various stresses. During the epidemic period, pig farms with the conditions may temporarily avoid mixing piglets into groups at weaning; for those that are mixed into groups, strict control must be exercised, affected pigs must be isolated together in the same pig house, and "graded rearing" should be carried out for postweaning nursery pigs. This can also reduce the spread of porcine reproductive and respiratory syndrome and porcine circovirus disease in the herd. Pay attention to keeping warm and to changes in temperature difference. Before and after weaning, moving groups, mixing groups, or transportation, some anti-stress drugs such as vitamin C can be added to drinking water, and at the same time the above recommended drug combination can be added to the feed to effectively prevent the occurrence of this disease. Effective prevention and control of Haemophilus parasuis disease, like the prevention and control of any other disease on a pig farm, is a systematic project that requires us to strengthen immunization against major viral diseases, select effective drug combinations for routine preventive health care of the herd, improve herd feeding management, and redesign pig houses.